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Pneumococcal vaccination plays a crucial role in the prevention of bacterial respiratory infections caused by Streptococcus pneumoniae. Pneumococci are responsible for diseases such as pneumonia, sinusitis and acute otitis media and can cause serious invasive infections such as meningitis and bacteraemia. Pneumococcal pneumonia leads to increased morbidity and mortality, particularly in patients with chronic lung diseases such as chronic obstructive pulmonary disease (COPD). The introduction of 13-valent conjugate vaccines (pneumococcal conjugate vaccine 13 [PCV13]) has significantly reduced the burden of disease. However, infections caused by serotypes not covered by PCV13 continue to occur. Current vaccines such as the 20-valent conjugate vaccine (PCV20) provide extended serotype coverage and have shown a robust immune response in clinical trials. The recently updated recommendations of the German Standing Committee on Vaccination (Ständige Impfkommission, STIKO) include the use of PCV20 for all indication categories in adults, which represents a simplified and more effective vaccination strategy. Future developments include vaccines with even broader serotype coverage and improved immunological properties; these are expected to further reduce the burden of pneumococcal disease. Improving vaccination uptake and increasing vaccination rates, particularly among at-risk groups, remain key objectives to protect public health in the long term., (© 2024. The Author(s), under exclusive licence to Springer Medizin Verlag GmbH, ein Teil von Springer Nature.)

Streptococcus pneumoniae ( Sp ), a leading cause of community-acquired pneumonia, can spread from the lung into the bloodstream to cause septicemia and meningitis, with a concomitant threefold increase in mortality. Limitations in vaccine efficacy and a rise in antimicrobial resistance have spurred searches for host-directed therapies that target pathogenic immune processes. Polymorphonuclear leukocytes (PMNs) are essential for infection control but can also promote tissue damage and pathogen spread. The major Sp virulence factor, pneumolysin, triggers acute inflammation by stimulating the 12-lipoxygenase (12-LOX) eicosanoid synthesis pathway in epithelial cells. This pathway is required for systemic spread in a mouse pneumonia model and produces a number of bioactive lipids, including hepoxilin A3 (HXA 3 ), a hydroxy epoxide PMN chemoattractant that has been hypothesized to facilitate breach of mucosal barriers. To understand how 12-LOX-dependent inflammation promotes dissemination during Sp lung infection and dissemination, we utilized bronchial stem cell-derived air-liquid interface cultures that lack this enzyme to show that HXA 3 methyl ester (HXA 3 -ME) is sufficient to promote basolateral-to-apical PMN transmigration, monolayer disruption, and concomitant Sp barrier breach. In contrast, PMN transmigration in response to the non-eicosanoid chemoattractant N-formyl-L-methionyl-L-leucyl-phenylalanine (fMLP) did not lead to epithelial disruption or bacterial translocation. Correspondingly, HXA 3 -ME but not fMLP increased the release of neutrophil elastase (NE) from Sp -infected PMNs. Pharmacologic blockade of NE secretion or activity diminished epithelial barrier disruption and bacteremia after pulmonary challenge of mice. Thus, HXA 3 promotes barrier-disrupting PMN transmigration and NE release, pathological events that can be targeted to curtail systemic disease following pneumococcal pneumonia.IMPORTANCE Streptococcus pneumoniae ( Sp ), a leading cause of pneumonia, can spread from the lung into the bloodstream to cause systemic disease. Limitations in vaccine efficacy and a rise in antimicrobial resistance have spurred searches for host-directed therapies that limit pathologic host immune responses to Sp . Excessive polymorphonuclear leukocyte (PMN) infiltration into Sp -infected airways promotes systemic disease. Using stem cell-derived respiratory cultures that reflect bona fide lung epithelium, we identified eicosanoid hepoxilin A3 as a critical pulmonary PMN chemoattractant that is sufficient to drive PMN-mediated epithelial damage by inducing the release of neutrophil elastase. Inhibition of the release or activity of this protease in mice limited epithelial barrier disruption and bacterial dissemination, suggesting a new host-directed treatment for Sp lung infection., Competing Interests: The authors declare no conflict of interest.

Background: People with immune-mediated inflammatory disease are at increased risk of pneumococcal pneumonia. The effectiveness of pneumococcal vaccination in people with immune-mediated inflammatory diseases has not been evaluated. We investigated the effectiveness of pneumococcal vaccination in preventing morbidity and mortality associated with pneumonia in patients with immune-mediated inflammatory diseases., Methods: In this matched case-control study, we used primary-care electronic health record data from the Clinical Practice Research Datalink Gold database in the UK, with linked hospitalisation and mortality data. Adults with incident common immune-mediated inflammatory diseases diagnosed between April 1, 1997, and Dec 31, 2019, were followed up from the first diagnosis date to the occurrence of an outcome or date of last follow-up. Cases (ie, those with an outcome of interest) were age-matched and sex-matched to up to ten contemporaneous controls by use of incidence density sampling. Outcomes were hospitalisation due to pneumonia, death due to pneumonia, or primary-care consultation for lower respiratory tract infection requiring antibiotics. We defined hospital admission for pneumonia using hospital discharge diagnoses, death due to pneumonia using death certification data, and lower respiratory tract infection as present when primary-care consultation and antibiotic prescription occurred on the same date. We used multivariable, unconditional, logistical regression and constructed three models to examine the association between pneumococcal vaccination as an exposure and each of the three outcomes., Findings: The first nested case-control analysis included 12 360 patients (7326 [59·3%] women and 5034 [40·7%] men): 1884 (15·2%) who were hospitalised due to pneumonia and 10 476 (84·8%) who were not admitted to hospital due to pneumonia. The second analysis included 5321 patients (3112 [58·5%] women and 2209 [41·5%] men): 781 (14·7%) who died due to pneumonia and 4540 (85·3%) who were alive on the index date. The third analysis included 54 530 patients (33 605 [61·6%] women and 20 925 [38·4%] men): 10 549 (19·3%) with lower respiratory tract infection treated with antibiotics and 43 981 (80·7%) without infection. In the multivariable analysis, pneumococcal vaccination was negatively associated with hospitalisation due to pneumonia (adjusted odds ratio 0·70 [95% CI 0·60-0·81]), death due to pneumonia (0·60 [0·48-0·76]), and lower respiratory tract infection treated with antibiotics (0·76 [0·72-0·80])., Interpretation: Pneumococcal vaccination is associated with protection against hospitalisation and death due to pneumonia in patients with immune-mediated inflammatory diseases, without apparent residual confounding. However, residual unmeasured confounding cannot be fully excluded in observational research, which includes nested case-control studies. These findings should also be corroborated with data from other countries, given that this study used UK-based data., Funding: National Institute for Health and Care Research., Competing Interests: Declaration of interests AA reports personal fees from UpToDate (royalty), Cadilla Pharmaceuticals (lecture fees), and Limbic (consulting), unrelated to this work. CDM is Director of the National Institute for Health and Care Research (NIHR) School for Primary Care Research. Keele University has received research funding for CDM from the NIHR and the Medical Research Council. JSNV-T was seconded to the UK Department of Health and Social Care from October, 2017, to March, 2022. He performed a one-off consultancy for MSD, which manufactures PPV23, in May, 2023. All other authors declare no competing interests. The views expressed in this manuscript are those of its authors and not necessarily those of the NIHR, the Department of Health and Social Care, or any other entity mentioned above., (Copyright © 2024 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license. Published by Elsevier Ltd.. All rights reserved.)

Aim: Animal models of fatal pneumonia caused by Streptococcus pneumoniae ( Spn ) have not been reliably generated using many strains of less virulent serotypes. Materials & methods: Pulmonary infection of a less virulent Spn serotype1 strain in the immunocompetent mice was established via the intratracheal aerosolization (ITA) route. The survival, local and systemic bacterial spread, pathological changes and inflammatory responses of this model were compared with those of mice challenged via the intratracheal instillation, intranasal instillation and intraperitoneal injection routes. Results: ITA and intratracheal instillation both induced fatal pneumonia; however, ITA resulted in better lung bacterial deposition and distribution, pathological homogeneity and delivery efficiency. Conclusion: ITA is an optimal route for developing animal models of severe pulmonary infections.

Neutrophils are the first leukocytes to be recruited to sites of inflammation in response to chemotactic factors released by activated macrophages and pulmonary epithelial and endothelial cells in bacterial pneumonia, a common cause of acute respiratory distress syndrome (ARDS). Although neutrophilic inflammation facilitates the elimination of pathogens, neutrophils also may cause bystander tissue injury. Even though the presence of neutrophils in alveolar spaces is a key feature of acute lung injury and ARDS especially from pneumonia, their contribution to the pathogenesis of lung injury is uncertain. The goal of this study was to elucidate the role of neutrophils in a clinically relevant model of bacterial pneumonia. We investigated the effect of reducing neutrophils in a mouse model of pneumococcal pneumonia treated with antibiotics. Neutrophils were reduced with anti-lymphocyte antigen 6 complex locus G6D (Ly6G) monoclonal antibody 24 h before and immediately preceding infection. Mice were inoculated intranasally with Streptococcus pneumoniae and received ceftriaxone 12 h after bacterial inoculation. Neutrophil reduction in mice treated with ceftriaxone attenuated hypoxemia, alveolar permeability, epithelial injury, pulmonary edema, and inflammatory biomarker release induced by bacterial pneumonia, even though bacterial loads in the distal air spaces of the lung were modestly increased as compared with antibiotic treatment alone. Thus, when appropriate antibiotics are administered, lung injury in the early phase of bacterial pneumonia is mediated in part by neutrophils. In the early phase of bacterial pneumonia, neutrophils contribute to the severity of lung injury, although they also participate in host defense. NEW & NOTEWORTHY Neutrophil accumulation is a key feature of ARDS, but their contribution to the pathogenesis is still uncertain. We investigated the effect of reducing neutrophils in a clinically relevant mouse model of pneumococcal pneumonia treated with antibiotics. When appropriate antibiotics were administered, neutrophil reduction with Ly6G antibody markedly attenuated lung injury and improved oxygenation. In the early phase of bacterial pneumonia, neutrophils contribute to the severity of lung injury, although they also participate in host defense.

IL-22 plays a critical role in defending against mucosal infections, but how IL-22 production is regulated is incompletely understood. Here, we show that mice lacking IL-33 or its receptor ST2 (IL-1RL1) were more resistant to Streptococcus pneumoniae lung infection than wild-type animals and that single-nucleotide polymorphisms in IL33 and IL1RL1 were associated with pneumococcal pneumonia in humans. The effect of IL-33 on S. pneumoniae infection was mediated by negative regulation of IL-22 production in innate lymphoid cells (ILCs) but independent of ILC2s as well as IL-4 and IL-13 signaling. Moreover, IL-33's influence on IL-22-dependent antibacterial defense was dependent on housing conditions of the mice and mediated by IL-33's modulatory effect on the gut microbiota. Collectively, we provide insight into the bidirectional crosstalk between the innate immune system and the microbiota. We conclude that both genetic and environmental factors influence the gut microbiota, thereby impacting the efficacy of antibacterial immune defense and susceptibility to pneumonia., Competing Interests: Competing interests statement:The authors declare no competing interest.

Resolving inflammation is thought to return the affected tissue back to homoeostasis but recent evidence supports a non-linear model of resolution involving a phase of prolonged immune activity. Here we show that within days following resolution of Streptococcus pneumoniae-triggered lung inflammation, there is an influx of antigen specific lymphocytes with a memory and tissue-resident phenotype as well as macrophages bearing alveolar or interstitial phenotype. The transcriptome of these macrophages shows enrichment of genes associated with prostaglandin biosynthesis and genes that drive T cell chemotaxis and differentiation. Therapeutic depletion of post-resolution macrophages, inhibition of prostaglandin E2 (PGE 2 ) synthesis or treatment with an EP4 antagonist, MF498, reduce numbers of lung CD4 + /CD44 + /CD62L + and CD4 + /CD44 + /CD62L - /CD27 + T cells as well as their expression of the α-integrin, CD103. The T cells fail to reappear and reactivate upon secondary challenge for up to six weeks following primary infection. Concomitantly, EP4 antagonism through MF498 causes accumulation of lung macrophages and marked tissue fibrosis. Our study thus shows that PGE 2 signalling, predominantly via EP4, plays an important role during the second wave of immune activity following resolution of inflammation. This secondary immune activation drives local tissue-resident T cell development while limiting tissue injury., (© 2024. The Author(s).)

Sepsis is a leading cause of mortality worldwide, and pneumonia is the most common cause of sepsis in humans. Low levels of high-density lipoprotein cholesterol (HDL-C) levels are associated with an increased risk of death from sepsis, and increasing levels of HDL-C by inhibition of cholesteryl ester transfer protein (CETP) decreases mortality from intraabdominal polymicrobial sepsis in APOE*3-Leiden.CETP mice. Here, we show that treatment with the CETP inhibitor (CETPi) anacetrapib reduced mortality from Streptococcus pneumoniae-induced sepsis in APOE*3-Leiden.CETP and APOA1.CETP mice. Mechanistically, CETP inhibition reduced the host proinflammatory response via attenuation of proinflammatory cytokine transcription and release. This effect was dependent on the presence of HDL, leading to attenuation of immune-mediated organ damage. In addition, CETP inhibition promoted monocyte activation in the blood prior to the onset of sepsis, resulting in accelerated macrophage recruitment to the lung and liver. In vitro experiments demonstrated that CETP inhibition significantly promoted the activation of proinflammatory signaling in peripheral blood mononuclear cells and THP1 cells in the absence of HDL; this may represent a mechanism responsible for improved bacterial clearance during sepsis. These findings provide evidence that CETP inhibition represents a potential approach to reduce mortality from pneumosepsis.

We evaluated whether the quantification of IgG to pneumococcal capsular polysaccharides is an accurate diagnostic test for pneumococcal infection in children with pneumonia in Nepal. Children with pneumococcal pneumonia did not have higher convalescent, or higher fold change, IgG to pneumococcal polysaccharides than children with other causes of pneumonia. Caution is needed in interpreting antibody responses in pneumococcal infections., Competing Interests: Funded by a European Society for Paediatric Infectious Diseases Small Grant to M.J.C. With support from Wellcome (Clinical Research Training Fellowship to M.J.C., 104439/Z/14/Z) and the NIHR (Academic Clinical Lectureship). The wider study was supported by Gavi, the Vaccine Alliance through its support of the PneumoNepal Project (https://pneumonepal.org/). A.J.P. was chair of the UK Department of Health and Social Care’s Joint Committee on Vaccination and Immunisation (JCVI) during the study period and was a member for WHO’s Strategic Advisory Group of Experts on Immunization during this period. Detection of respiratory viruses was done by Micropathology Ltd, Warwick, UK and the authors are grateful for the support of Dr. Colin Fink and Dr. Marie Voice in particular. The views expressed in this report do not necessarily represent the views of the Joint Committee on Vaccination and Immunisation, NIHR, or WHO. This work received funding from the Wellcome Trust (now Wellcome). The other authors have no conflicts of interest to disclose., (Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc.)

Introduction: There was no 13-valent pneumococcal conjugate vaccine (PCV13) adult antibody concentration threshold regulatory criterion for licensure - unlike the pediatric indication; consequently, for the adult indication, PCV13 serotype-specific opsonophagocytic activity (OPA) geometric mean titer (GMT) values were immunobridged to the 23-valent plain polysaccharide vaccine (PPV23) to infer efficacy against invasive pneumococcal disease (IPD). Subsequently, a double-blind, randomized, controlled PCV13 efficacy trial (CAPiTA) was performed in community-living, older adults to confirm efficacy against vaccine-serotype IPD (VT-IPD) and establish efficacy against vaccine-serotype pneumococcal community-acquired pneumonia (VT-CAP)., Areas Covered: This article summarizes 31 publications from the PCV13 adult indication clinical development trials and other PCV13 clinical studies, organized by formulation, reactogenicity and safety, immunogenicity, coadministration, and clinical efficacy., Expert Opinion: PCV13 had a favorable safety profile with an OPA response generally greater than PPV23 irrespective of age and of previous pneumococcal vaccination. PCV13 primed for enhanced immune responses with subsequent PCV13 or PPV23 dosing. Conversely, PPV23 was shown to blunt the response to subsequent PCV13. CAPiTA demonstrated PCV13 efficacy for at least five years against both VT-IPD and VT-CAP. The PCV13 clinical development program provided fundamental insights into this vaccine's adult-specific immune responses and confirmed the advantages of conjugate over plain polysaccharide technology.

Previously, we demonstrated that post-immunobiotics derived from Lactobacillus gasseri TMT36, TMT39, and TMT40 strains (HK36, HK39 and HK40, respectively) differentially regulated Toll-like receptor 3 (TLR3)-mediated antiviral respiratory immunity in infant mice. In this work, we investigated whether the HK36, HK39 and HK40 nasal treatments were able to improve the resistance against primary respiratory syncytial virus (RSV) infection and secondary pneumococcal pneumonia. Our results demonstrated that the three treatments increased the resistance to primary viral infection by reducing variations in body weight, RSV titers and lung damage of infected infant mice. Post-immunobiotics significantly enhanced the expressions of interferon (IFN)-λ, IFN-β, IFN-γ, interleukin(IL) - 1β, IL-6, IL-27, Mx1, RNAseL and 2'-5'-oligoadenylate synthetase 1 (OAS1) genes and decreased tumour necrosis factor (TNF)-α in alveolar macrophages of RSV-challenged mice. In addition, the studies in the model of RSV-Streptococcus pneumoniae superinfection showed that the HK39 and HK40 treatments were capable of reducing lung damage, lung bacterial cell counts, and the dissemination of S. pneumoniae into the blood of infant mice. The protective effect was associated with increases in IFN-β, IFN-γ, IL-10, and IL-27 in the respiratory tract. This study demonstrates that the nasal application of the post-immunobiotics HK39 and HK40 stimulates innate respiratory immunity and enhances the defences against primary RSV infection and secondary pneumococcal pneumonia offering an alternative to combat respiratory superinfections in children, which can be fatal.

Importance: The association of 13-valent pneumococcal conjugate vaccine (PCV13) use with pneumonia hospitalization in older adults, especially those with underlying medical conditions, is not well described., Objective: To evaluate the association of PCV13 use with pneumonia, non-health care-associated (non-HA) pneumonia, and lobar pneumonia (LP) hospitalization among US Medicare beneficiaries 65 years or older., Design, Setting, and Participants: This cohort study with time-varying exposure assignment analyzed claims data from US Medicare beneficiaries 65 years or older enrolled in Parts A/B with a residence in the 50 US states or the District of Columbia by September 1, 2014. New Medicare Parts A/B beneficiaries within 6 months after their 65th birthday were continuously included in the cohort after September 1, 2014, and followed through December 31, 2017. Participants were censored if they died, changed enrollment status, or developed a study outcome. Most of the analyses were conducted from 2018 to 2019, and additional analyses were performed from 2021 to 2022., Exposures: Use of PCV13 vaccination 14 days or more before pneumonia hospitalization., Main Outcomes and Measures: Discrete-time survival models were used to estimate the incidence rate ratio (IRR) and number of pneumonia hospitalizations averted through PCV13 use. The adjusted IRR for the association of PCV13 vaccination with pneumonia hospitalization was used to estimate vaccine effectiveness (VE)., Results: At the end of follow-up (December 2017), 24 121 625 beneficiaries (13 593 975 women [56.4%]; 418 005 [1.7%] Asian, 1 750 807 [4.8%] Black, 338 044 [1.4%] Hispanic, 111 508 [0.5%] Native American, and 20 700 948 [85.8%] White individuals) were in the cohort; 4 936 185 (20.5%) had received PCV13 only, and 10 646 220 (79.5%) had not received any pneumococcal vaccines. More than half of the beneficiaries in the cohort were younger than 75 years, White, and had either immunocompromising or chronic medical conditions. Coverage with PCV13 increased from 0.8% (September 2014) to 41.5% (December 2017). The VE for PCV13 was estimated at 6.7% (95% CI, 5.9%-7.5%) for pneumonia, 4.7% (95% CI, 3.9%-5.6%) for non-HA pneumonia, and 5.8% (95% CI, 2.6%-8.9%) for LP. From September 2014 through December 2017, an estimated 35 127 pneumonia (95% CI, 33 011-37 270), 24 643 non-HA pneumonia (95% CI, 22 761-26 552), and 1294 LP (95% CI, 797-1819) hospitalizations were averted through PCV13 use., Conclusions and Relevance: The study results suggest that PCV13 use was associated with reduced pneumonia hospitalization among Medicare beneficiaries 65 years or older, many of whom had underlying medical conditions. Increased PCV13 coverage and use of recently approved higher-valent pneumococcal conjugate vaccines may avert additional pneumonia hospitalizations in adults.

Bacterial pneumonia induces the rapid recruitment and activation of neutrophils and macrophages into the lung, and these cells contribute to bacterial clearance and other defense functions. TBK1 (TANK-binding kinase 1) performs many functions, including activation of the type I IFN pathway and regulation of autophagy and mitophagy, but its contribution to antibacterial defenses in the lung is unclear. We previously showed that lung neutrophils upregulate mRNAs for TBK1 and its accessory proteins during Streptococcus pneumoniae pneumonia, despite low or absent expression of type I IFN in these cells. We hypothesized that TBK1 performs key antibacterial functions in pneumonia apart from type I IFN expression. Using TBK1 null mice, we show that TBK1 contributes to antibacterial defenses and promotes bacterial clearance and survival. TBK1 null mice express lower concentrations of many cytokines in the infected lung. Conditional deletion of TBK1 with LysMCre results in TBK1 deletion from macrophages but not neutrophils. LysMCre TBK1 mice have no defect in cytokine expression, implicating a nonmacrophage cell type as a key TBK1-dependent cell. TBK1 null neutrophils have no defect in recruitment to the infected lung but show impaired activation of p65/NF-κB and STAT1 and lower expression of reactive oxygen species, IFNγ, and IL12p40. TLR1/2 and 4 agonists each induce phosphorylation of TBK1 in neutrophils. Surprisingly, neutrophil TBK1 activation in vivo does not require the adaptor STING. Thus, TBK1 is a critical component of STING-independent antibacterial responses in the lung, and TBK1 is necessary for multiple neutrophil functions.

Background: Mechanical ventilation for pneumonia may contribute to lung injury due to factors that include mitochondrial dysfunction, and mesenchymal stem cells may attenuate injury. This study hypothesized that mechanical ventilation induces immune and mitochondrial dysfunction, with or without pneumococcal pneumonia, that could be mitigated by mesenchymal stem cells alone or combined with antibiotics., Methods: Male rabbits underwent protective mechanical ventilation (8 ml/kg tidal volume, 5 cm H2O end-expiratory pressure) or adverse mechanical ventilation (20 ml/kg tidal-volume, zero end-expiratory pressure) or were allowed to breathe spontaneously. The same settings were then repeated during pneumococcal pneumonia. Finally, infected animals during adverse mechanical ventilation received human umbilical cord-derived mesenchymal stem cells (3 × 106/kg, intravenous) and/or ceftaroline (20 mg/kg, intramuscular) or sodium chloride, 4 h after pneumococcal challenge. Twenty-four-hour survival (primary outcome), lung injury, bacterial burden, immune and mitochondrial dysfunction, and lung transcriptomes (secondary outcomes) were assessed., Results: High-pressure adverse mechanical ventilation reduced the survival of infected animals (0%; 0 of 7) compared with spontaneous breathing (100%; 7 of 7) and protective mechanical ventilation (86%; 6 of 7; both P < 0.001), with higher lung pathology scores (median [interquartile ranges], 5.5 [4.5 to 7.0] vs. 12.6 [12.0 to 14.0]; P = 0.046), interleukin-8 lung concentrations (106 [54 to 316] vs. 804 [753 to 868] pg/g of lung; P = 0.012), and alveolar mitochondrial DNA release (0.33 [0.28 to 0.36] vs. 0.98 [0.76 to 1.21] ng/μl; P < 0.001) compared with infected spontaneously breathing animals. Survival (0%; 0 of 7; control group) was improved by mesenchymal stem cells (57%; 4 of 7; P = 0.001) or ceftaroline alone (57%; 4 of 7; P < 0.001) and improved even more with a combination treatment (86%; 6 of 7; P < 0.001). Mesenchymal stem cells reduced lung pathology score (8.5 [7.0 to 10.5] vs. 12.6 [12.0 to 14.0]; P = 0.043) and alveolar mitochondrial DNA release (0.39 (0.34 to 0.65) vs. 0.98 (0.76 to 1.21) ng/μl; P = 0.025). Mesenchymal stem cells combined with ceftaroline reduced interleukin-8 lung concentrations (665 [595 to 795] vs. 804 [753 to 868] pg/g of lung; P = 0.007) compared to ceftaroline alone., Conclusions: In this preclinical study, mesenchymal stem cells improved the outcome of rabbits with pneumonia and high-pressure mechanical ventilation by correcting immune and mitochondrial dysfunction and when combined with the antibiotic ceftaroline was synergistic in mitigating lung inflammation., (Copyright © 2021, the American Society of Anesthesiologists. All Rights Reserved.)

The current pneumococcal capsular polysaccharide (PPS) conjugate vaccine (PCV13) is less effective against Streptococcus pneumoniae serotype 3 (ST3), which remains a major cause of pneumococcal disease and mortality. Therefore, dissecting structure-function relationships of human ST3 pneumococcal capsular polysaccharide (PPS3) antibodies may reveal characteristics of protective antibodies. Using flow cytometry, we isolated PPS3-binding memory B cells from pneumococcal vaccine recipients and generated seven PPS3-specific human monoclonal antibodies (humAbs). Five humAbs displayed ST3 opsonophagocytic activity, four induced ST3 agglutination in vitro , and four mediated both activities. Two humAbs, namely, C10 and C27, that used the same variable heavy (V H ) and light (V L ) chain domains (V H 3-9*01/V L 2-14*03) both altered ST3 gene expression in vitro ; however, C10 had fewer V L somatic mutations, higher PPS3 affinity, and promoted in vitro ST3 opsonophagocytic and agglutinating activity, whereas C27 did not. In C57BL/6 mice, both humAbs reduced nasopharyngeal colonization with ST3 A66 and a clinical strain, B2, and prolonged survival following lethal A66 intraperitoneal infection, but only C10 protected against lethal intranasal infection with the clinical strain. After performing V L swaps, C10V H /C27V L exhibited reduced ST3 binding and agglutination, but C27V H /C10V L binding was unchanged. However, both humAbs lost the ability to reduce colonization in vivo when their light chains were replaced. Our findings associate the ability of PPS3-specific humAbs to reduce colonization with ST3 agglutination and opsonophagocytic activity, and reveal an unexpected role for the V L in their functional activity in vitro and in vivo . These findings also provide insights that may inform antibody-based therapy and identification of surrogates of vaccine efficacy against ST3. IMPORTANCE Despite the global success of vaccination with pneumococcal conjugate vaccines, serotype 3 (ST3) pneumococcus remains a leading cause of morbidity and mortality. In comparison to other vaccine-included serotypes, the ST3 pneumococcal capsular polysaccharide (PPS3) induces a weaker opsonophagocytic response, which is considered a correlate of vaccine efficacy. Previous studies of mouse PPS3 monoclonal antibodies identified ST3 agglutination as a correlate of reduced ST3 nasopharyngeal colonization in mice; however, neither the agglutinating ability of human vaccine-elicited PPS3 antibodies nor their ability to prevent experimental murine nasopharyngeal colonization has been studied. We generated and analyzed the functional and in vivo efficacy of human vaccine-elicited PPS3 monoclonal antibodies and found that ST3 agglutination associated with antibody affinity, protection in vivo , and limited somatic mutations in the light chain variable region. These findings provide new insights that may inform the development of antibody-based therapies and next-generation vaccines for ST3.

Background: Our previous study showed that neonatal S. pneumoniae pneumonia promoted airway smooth muscle myosin heavy chain (SMMHC) expression and AHR development. Researches demonstrated HMGB1, TLR4 and ERK are involved in smooth muscle contractile protein expression, so we hypothesis that HMGB1/TLR4/ERK pathway participated in airway SMMHC overexpression in neonatal S. pneumoniae pneumonia model., Method: Neonatal (1-week-old) BALB/c mice were intranasal inoculated with D39 to establish non-lethal S. pneumoniae pneumonia model. TLR4 was inhibited 2 weeks after infection with TLR4 specific inhibitor (TAK-242). Five weeks after infection, the bronchoalveolar lavage fluid (BALF) and lungs of neonatal S. pneumoniae pneumonia and mock infection mice with or without TLR4 inhibition were collected to assess the expressions of HMGB1, TLR4 and p-ERK1/2. Airway Hyperresponsiveness (AHR) of the three groups was determined by whole-body plethysmograph., Results: Our results demonstrated that neonatal S. pneumoniae pneumonia promoted HMGB1/TLR4 production, SMMHC expression and AHR development significantly, with ERK1/2 phosphorylation decreased remarkably. TLR4 inhibition after pneumonia significantly increased ERK1/2 phosphorylation, reversed airway SMMHC overexpression and alleviated AHR., Conclusion: Neonatal S. pneumoniae pneumonia promotes airway SMMHC expression and AHR through HMGB1/TLR4/ERK., (Copyright © 2021 European Federation of Immunological Societies. Published by Elsevier B.V. All rights reserved.)

Seasonal Influenza A virus (IAV) infections can promote dissemination of upper respiratory tract commensals such as Streptococcus pneumoniae to the lower respiratory tract resulting in severe life-threatening pneumonia. Here, we aimed to compare innate immune responses in the lungs of healthy colonized and non-colonized mice after IAV challenge at the initial asymptomatic stage of infection. Responses during a severe bacterial pneumonia were profiled for comparison. Cytokine and innate immune cell imprints of the lungs were analyzed. Irrespective of the colonization status, mild H1N1 IAV infection was characterized by a bi-phasic disease progression resulting in full recovery of the animals. Already at the asymptomatic stage of viral infection, the pro-inflammatory cytokine response was as high as in pneumococcal pneumonia. Flow cytometry analyses revealed an early influx of inflammatory monocytes into the lungs. Neutrophil influx was mostly limited to bacterial infections. The majority of cells, except monocytes, displayed an activated phenotype characterized by elevated CCR2 and MHCII expression. In conclusion, we show that IAV challenge of colonized healthy mice does not automatically result in severe co-infection. However, a general local inflammatory response was noted at the asymptomatic stage of infection irrespective of the infection type., (© 2021. The Author(s).)

The transcription factor Krueppel-like factor (KLF) 4 fosters the pro-inflammatory immune response in macrophages and polymorphonuclear neutrophils (PMNs) when stimulated with Streptococcus pneumoniae , the main causative pathogen of community-acquired pneumonia (CAP). Here, we investigated the impact of KLF4 expression in myeloid cells such as macrophages and PMNs on inflammatory response and disease severity in a pneumococcal pneumonia mouse model and in patients admitted to hospital with CAP. We found that mice with a myeloid-specific knockout of KLF4 mount an insufficient early immune response with reduced levels of pro-inflammatory cytokines and increased levels of the anti-inflammatory cytokine interleukin (IL) 10 in bronchoalveolar lavage fluid and plasma and an impaired bacterial clearance from the lungs 24 hours after infection with S. pneumoniae . This results in higher rates of bacteremia, increased lung tissue damage, more severe symptoms of infection and reduced survival. Higher KLF4 gene expression levels in the peripheral blood of patients with CAP at hospital admission correlate with a favourable clinical presentation (lower sequential organ failure assessment (SOFA) score), lower serum levels of IL-10 at admission, shorter hospital stay and lower mortality or requirement of intensive care unit treatment within 28 days after admission. Thus, KLF4 in myeloid cells such as macrophages and PMNs is an important regulator of the early pro-inflammatory immune response and, therefore, a potentially interesting target for therapeutic interventions in pneumococcal pneumonia., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Herta, Bhattacharyya, Rosolowski, Conrad, Gurtner, Gruber, Ahnert, Gutbier, Frey, Suttorp, Hippenstiel and Zahlten.)

Bruton's tyrosine kinase (Btk) is a cytoplasmic kinase expressed in B cells and myeloid cells. It is essential for B cell development and natural antibody-mediated host defense against bacteria in humans and mice, but little is known about the role of Btk in innate host defense in vivo . Previous studies have indicated that lack of (natural) antibodies is paramount for impaired host defense against Streptococcus (S.) pneumoniae in patients and mice with a deficiency in functional Btk. In the present study, we re-examined the role of Btk in B cells and myeloid cells during pneumococcal pneumonia and sepsis in mice. The antibacterial defense of Btk -/- mice was severely impaired during pneumococcal pneumosepsis and restoration of natural antibody production in Btk -/- mice by transgenic expression of Btk specifically in B cells did not suffice to protect against infection. Btk -/- mice with reinforced Btk expression in MhcII + cells, including B cells, dendritic cells and macrophages, showed improved antibacterial defense as compared to Btk -/- mice. Bacterial outgrowth in Lysmcre-Btk fl /Y mice was unaltered despite a reduced capacity of Btk-deficient alveolar macrophages to respond to pneumococci. Mrp8cre-Btk fl /Y mice with a neutrophil specific paucity in Btk expression, however, demonstrated impaired antibacterial defense. Neutrophils of Mrp8cre-Btk fl /Y mice displayed reduced release of granule content after pulmonary installation of lipoteichoic acid, a gram-positive bacterial cell wall component relevant for pneumococci. Moreover, Btk deficient neutrophils showed impaired degranulation and phagocytosis upon incubation with pneumococci ex vivo . Taken together, the results of our study indicate that besides regulating B cell-mediated immunity, Btk is critical for regulation of myeloid cell-mediated, and particularly neutrophil-mediated, innate host defense against S. pneumoniae in vivo ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 de Porto, Liu, de Beer, Florquin, Roelofs, de Boer, den Haan, Hendriks, van ‘t Veer, van der Poll and de Vos.)

Streptococcus pneumoniae co-infection post-influenza is a major cause of mortality characterized by uncontrolled bacteria burden and excessive immune response during influenza pandemics. Interleukin (IL)-4 is a canonical type II immune cytokine known for its wide range of biological activities on different cell types. It displays protective roles in numerous infectious diseases and immune-related diseases, but its role in influenza and S. pneumoniae (influenza/S. pneumoniae) co-infected pneumonia has not been reported. In our study, we used C57BL/6 wild-type (WT) and IL-4-deficient (IL-4 -/- ) mice to establish co-infection model with S. pneumoniae after influenza virus infection. Co-infected IL-4 -/- mice showed increased mortality and weight loss compared with WT mice. IL-4 deficiency led to increased bacterial loads in lungs without altering influenza virus replication, suggesting a role of IL-4 in decreasing post-influenza susceptibility to S. pneumoniae co-infection. Loss of IL-4 also resulted in aggravated lung damage together with massive proinflammatory cytokine production and immune cell infiltration during co-infection. Administration of recombinant IL-4 rescued the survival and weight loss of IL-4 -/- mice in lethal co-infection. Additionally, IL-4 deficiency led to more immune cell death in co-infection. Gasdermin D (GSDMD) during co-infection was induced in IL-4 -/- mice that subsequently activated cell pyroptosis. Treatment of recombinant IL-4 or inhibition of GSDMD activity by disulfiram decreased immune cell death and bacterial loads in lungs of IL-4 -/- co-infected mice. These results suggest that IL-4 decreases post-influenza susceptibility to S. pneumoniae co-infection via suppressing GSDMD-induced pyroptosis. Collectively, this study demonstrates the protective role of IL-4 in influenza/S. pneumoniae co-infected pneumonia., (© 2021 British Society for Immunology.)

Zinc (Zn) is required for proper immune function and host defense. Zn homeostasis is tightly regulated by Zn transporters that coordinate biological processes through Zn mobilization. Zn deficiency is associated with increased susceptibility to bacterial infections, including Streptococcus pneumoniae , the most commonly identified cause of community-acquired pneumonia. Myeloid cells, including macrophages and dendritic cells (DCs), are at the front line of host defense against invading bacterial pathogens in the lung and play a critical role early on in shaping the immune response. Expression of the Zn transporter ZIP8 is rapidly induced following bacterial infection and regulates myeloid cell function in a Zn-dependent manner. To what extent ZIP8 is instrumental in myeloid cell function requires further study. Using a novel, myeloid-specific, Zip8 knockout model, we identified vital roles of ZIP8 in macrophage and DC function upon pneumococcal infection. Administration of S. pneumoniae into the lung resulted in increased inflammation, morbidity, and mortality in Zip8 knockout mice compared with wild-type counterparts. This was associated with increased numbers of myeloid cells, cytokine production, and cell death. In vitro analysis of macrophage and DC function revealed deficits in phagocytosis and increased cytokine production upon bacterial stimulation that was, in part, due to increased NF-κB signaling. Strikingly, alteration of myeloid cell function resulted in an imbalance of Th17/Th2 responses, which is potentially detrimental to host defense. These results (for the first time, to our knowledge) reveal a vital ZIP8- and Zn-mediated axis that alters the lung myeloid cell landscape and the host response against pneumococcus., (Copyright © 2021 by The American Association of Immunologists, Inc.)

Resolution of the acute respiratory distress syndrome (ARDS) from pneumonia requires repair of the injured lung endothelium and alveolar epithelium, removal of neutrophils from the distal airspaces of the lung, and clearance of the pathogen. Previous studies have demonstrated the importance of specialized proresolving mediators (SPMs) in the regulation of host responses during inflammation. Although ARDS is commonly caused by Streptococcus pneumoniae , the role of lipoxin A4 (LXA4) and resolvin D1 (RvD1) in pneumococcal pneumonia is not well understood. In the present experimental study, we tested the hypothesis that endogenous SPMs play a role in the resolution of lung injury in a clinically relevant model of bacterial pneumonia. Blockade of formyl peptide receptor 2 (ALX/FPR2), the receptor for LXA4 and RvD1, with the peptide WRW4 resulted in more pulmonary edema, greater protein accumulation in the air spaces, and increased bacteria accumulation in the air spaces and the blood. Inhibition of this receptor was also associated with decreased levels of proinflammatory cytokines. Even in the presence of antibiotic treatment, WRW4 inhibited the resolution of lung injury. In summary, these experiments demonstrated two novel findings: LXA4 and RvD1 contribute to the resolution of lung injury due to pneumococcal pneumonia, and the mechanism of their benefit likely includes augmenting bacterial clearance and reducing pulmonary edema via the restoration of lung alveolar-capillary barrier permeability.

Lung-resident memory B cells (BRM cells) are elicited after influenza infections of mice, but connections to other pathogens and hosts - as well as their functional significance - have yet to be determined. We postulate that BRM cells are core components of lung immunity. To test this, we examined whether lung BRM cells are elicited by the respiratory pathogen pneumococcus, are present in humans, and are important in pneumonia defense. Lungs of mice that had recovered from pneumococcal infections did not contain organized tertiary lymphoid organs, but did have plasma cells and noncirculating memory B cells. The latter expressed distinctive surface markers (including CD69, PD-L2, CD80, and CD73) and were poised to secrete antibodies upon stimulation. Human lungs also contained B cells with a resident memory phenotype. In mice recovered from pneumococcal pneumonia, depletion of PD-L2+ B cells, including lung BRM cells, diminished bacterial clearance and the level of pneumococcus-reactive antibodies in the lung. These data define lung BRM cells as a common feature of pathogen-experienced lungs and provide direct evidence of a role for these cells in pulmonary antibacterial immunity.

H9N2 avian influenza virus has been continuously circulating among poultry and can infect mammals, indicating that this virus is a potential pandemic strain. During influenza pandemics, secondary bacterial (particularly pneumococcal) pneumonia usually contributes to excessive mortality. In the present study, we observed the dynamic effect of H9N2 virus infection on host defense against secondary pneumococcal infection in mice. BALB/c mice were intranasally inoculated with 1.2 × 10 5 PFU of H9N2 virus followed by 1 × 10 6 CFU of Streptococcus pneumoniae at 7, 14, or 28 days post-H9N2 infection (dpi). The bacterial load, histopathology, body weight, and survival were assessed after pneumococcal infection. Our results showed that H9N2 virus infection had no significant impact on host resistance to secondary pneumococcal infection at 7 dpi. However, H9N2 virus infection increased pulmonary pneumococcal clearance and reduced pneumococcal pneumonia-induced morbidity after secondary pneumococcal infection at 14 or 28 dpi, as reflected by significantly decreased bacterial loads, markedly alleviated pulmonary histopathological changes, and significantly reduced weight loss in mice infected with H9N2 virus followed by S. pneumoniae compared with mice infected only with S. pneumoniae Further, the significantly decreased bacterial loads were observed when mice were previously infected with a high dose (1.2 × 10 6 PFU) of H9N2 virus. Also, similar to the results obtained in BALB/c mice, improvement in pulmonary pneumococcal clearance was observed in C57BL/6 mice. Overall, our results showed that pulmonary pneumococcal clearance is improved after resolution of H9N2 virus infection in mice., (Copyright © 2021 Li et al.)

Microvesicles (MVs) are cell-derived extracellular vesicles that have emerged as markers and mediators of acute lung injury (ALI). One of the most common pathogens in pneumonia-induced ALI is Streptococcus pneumoniae (Spn), but the role of MVs during Spn lung infection is largely unknown. In the first line of defense against Spn and its major virulence factor, pneumolysin (PLY), are the alveolar epithelial cells (AEC). In this study, we aim to characterize MVs shed from PLY-stimulated AEC and explore their contribution in mediating crosstalk with neutrophils. Using in vitro cell and ex vivo (human lung tissue) models, we demonstrated that Spn in a PLY-dependent manner stimulates AEC to release increased numbers of MVs. Spn infected mice also had higher levels of epithelial-derived MVs in their alveolar compartment compared to control. Furthermore, MVs released from PLY-stimulated AEC contain mitochondrial content and can be taken up by neutrophils. These MVs then suppress the ability of neutrophils to produce reactive oxygen species, a critical host-defense mechanism. Taken together, our results demonstrate that AEC in response to pneumococcal PLY release MVs that carry mitochondrial cargo and suggest that these MVs regulate innate immune responses during lung injury.

Community-acquired pneumonia is the most common type of pneumonia and remains a leading cause of morbidity and mortality worldwide. Although many different pathogens can contribute to pneumonia, Streptococcus pneumoniae is one of the common bacterial pathogens that underlie community-acquired pneumonia. RIPK3 (receptor-interacting protein kinase 3) is widely recognized as a key modulator of inflammation and cell death. To elucidate a potential role of RIPK3 in pneumonia, we examined plasma from healthy control subjects and patients positive for streptococcal pneumonia. In human studies, RIPK3 protein concentrations were significantly elevated and were identified as a potential plasma marker of pneumococcal pneumonia. To expand these findings, we used an in vivo murine model of pneumococcal pneumonia to demonstrate that RIPK3 deficiency leads to reduced bacterial clearance, severe pathological damage, and high mortality. Our results illustrated that RIPK3 forms a complex with RIPK1, MLKL (mixed-lineage kinase domain-like protein), and MCU (mitochondrial calcium uniporter) to induce mitochondrial calcium uptake and mitochondrial reactive oxygen species(mROS) production during S. pneumoniae infection. In macrophages, RIPK3 initiated necroptosis via the mROS-mediated mitochondrial permeability transition pore opening and NLRP3 inflammasome activation via the mROS-AKT pathway to protect against S. pneumoniae . In conclusion, our study demonstrated a mechanism by which RIPK3-initiated necroptosis is essential for host defense against S. pneumoniae .

Carbohydrate-binding antibodies play diverse and critical roles in human health. Endogenous carbohydrate-binding antibodies that recognize bacterial, fungal, and other microbial carbohydrates prevent systemic infections and help maintain microbiome homeostasis. Anti-glycan antibodies can have both beneficial and detrimental effects. For example, alloantibodies to ABO blood group carbohydrates can help reduce the spread of some infectious diseases, but they also impose limitations for blood transfusions. Antibodies that recognize self-glycans can contribute to autoimmune diseases, such as Guillain-Barre syndrome. In addition to endogenous antibodies that arise through natural processes, a variety of vaccines induce anti-glycan antibodies as a primary mechanism of protection. Some examples of approved carbohydrate-based vaccines that have had a major impact on human health are against pneumococcus, Haemophilus influeanza type b, and Neisseria meningitidis. Monoclonal antibodies specifically targeting pathogen associated or tumor associated carbohydrate antigens (TACAs) are used clinically for both diagnostic and therapeutic purposes. This review aims to highlight some of the well-studied and critically important applications of anti-carbohydrate antibodies., (© 2021 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society.)

Methotrexate (MTX) impairs antibody response after pneumococcal vaccination. We aimed to investigate differences in phenotypes of circulating B and T cells after pneumococcal conjugate vaccine (PCV) in rheumatoid arthritis (RA) patients on MTX (MTX group), RA without disease-modifying drugs (0DMARD), and controls (HC). MTX group (n = 11), 0DMARD (n = 12) and HC (n = 13) were studied. Blood samples were collected: before MTX, ≥ 4 weeks on stable MTX dose (prevaccination), and 7 days postvaccination (MTX group), and pre- and 7 days postvaccination (0DMARD and HC). Phenotypes of B- and T cell subsets were determined using flow cytometry. Serotype-specific IgG were quantified using multiplex bead assay, pre- and 4-6 weeks postvaccination. Concentrations of plasmablasts and switched memory B cells increased after PCV in HC (both p = 0.03) and the 0DMARD group (p = 0.01 and p = 0.02), but not in the MTX group. Postimmunization plasmablasts were lower in MTX group, compared to the 0DMARD group and HC (p = 0.002 and p < 0.001). Th17 cells decreased after MTX start (p = 0.02), and increased in HC after immunization (p = 0.01). Postimmunization plasmablasts correlated with mean antibody response ratio in all RA patients (R = 0.57, p = 0.035). Methotrexate reduced Th17 cells and blocked activation of plasmablasts and switched memory B cells following polysaccharide-protein conjugate antigen challenge in RA.

Bacterial co-infections represent a major clinical complication of influenza. Host-derived interferon (IFN) increases susceptibility to bacterial infections following influenza, but the relative roles of type-I versus type-II IFN remain poorly understood. We have used novel mouse models of co-infection in which colonizing pneumococci were inoculated into the upper respiratory tract; subsequent sublethal influenza virus infection caused the bacteria to enter the lungs and mediate lethal disease. Compared to wild-type mice or mice deficient in only one pathway, mice lacking both IFN pathways demonstrated the least amount of lung tissue damage and mortality following pneumococcal-influenza virus superinfection. Therapeutic neutralization of both type-I and type-II IFN pathways similarly provided optimal protection to co-infected wild-type mice. The most effective treatment regimen was staggered neutralization of the type-I IFN pathway early during co-infection combined with later neutralization of type-II IFN, which was consistent with the expression and reported activities of these IFNs during superinfection. These results are the first to directly compare the activities of type-I and type-II IFN during superinfection and provide new insights into potential host-directed targets for treatment of secondary bacterial infections during influenza., Competing Interests: The authors have declared that no competing interests exist.

Alpha-1 antitrypsin (AAT) is a major inhibitor of serine proteases in mammals. Therefore, its deficiency leads to protease-antiprotease imbalance and a risk for developing lung emphysema. Although therapy with human plasma-purified AAT attenuates AAT deficiency-related emphysema, its impact on lung antibacterial immunity is poorly defined. Here, we examined the effect of AAT therapy on lung protective immunity in AAT-deficient (KO) mice challenged with Streptococcus pneumoniae. AAT-KO mice were highly susceptible to S. pneumoniae, as determined by severe lobar pneumonia and early mortality. Mechanistically, we found that neutrophil-derived elastase (NE) degraded the opsonophagocytically important collectins, surfactant protein A (SP-A) and D (SP-D), which was accompanied by significantly impaired lung bacterial clearance in S. pneumoniae-infected AAT-KO mice. Treatment of S. pneumoniae-infected AAT-KO mice with human AAT protected SP-A and SP-D from NE-mediated degradation and corrected the pulmonary pathology observed in these mice. Likewise, treatment with Sivelestat, a specific inhibitor of NE, also protected collectins from degradation and significantly decreased bacterial loads in S. pneumoniae-infected AAT-KO mice. Our findings show that NE is responsible for the degradation of lung SP-A and SP-D in AAT-KO mice affecting lung protective immunity in AAT deficiency.

Current treatments for pneumonia (PNA) are focused on the pathogens. Mortality from PNA-induced acute lung injury (PNA-ALI) remains high, underscoring the need for additional therapeutic targets. Clinical and experimental evidence exists for potential sex differences in PNA survival, with males having higher mortality. In a model of severe pneumococcal PNA, when compared with male mice, age-matched female mice exhibited enhanced resolution characterized by decreased alveolar and lung inflammation and increased numbers of Tregs. Recognizing the critical role of Tregs in lung injury resolution, we evaluated whether improved outcomes in female mice were due to estradiol (E2) effects on Treg biology. E2 promoted a Treg-suppressive phenotype in vitro and resolution of PNA in vivo. Systemic rescue administration of E2 promoted resolution of PNA in male mice independent of lung bacterial clearance. E2 augmented Treg expression of Foxp3, CD25, and GATA3, an effect that required ERβ, and not ERα, signaling. Importantly, the in vivo therapeutic effects of E2 were lost in Treg-depleted mice (Foxp3DTR mice). Adoptive transfer of ex vivo E2-treated Tregs rescued Streptococcus pneumoniae-induce PNA-ALI, a salutary effect that required Treg ERβ expression. E2/ERβ was required for Tregs to control macrophage proinflammatory responses. Our findings support the therapeutic role for E2 in promoting resolution of lung inflammation after PNA via ERβ Tregs.

The anti-CD20 antibody Rituximab to deplete CD20+ B cells is an effective treatment for rheumatoid arthritis and B cell malignancies, but is associated with an increased incidence of respiratory infections. Using mouse models we have investigated the consequences of B cell depletion on natural and acquired humoral immunity to Streptococcus pneumoniae . B cell depletion of naïve C57Bl/6 mice reduced natural IgM recognition of S. pneumoniae , but did not increase susceptibility to S. pneumoniae pneumonia. ELISA and flow cytometry assays demonstrated significantly reduced IgG and IgM recognition of S. pneumoniae in sera from mice treated with B cell depletion prior to S. pneumoniae nasopharyngeal colonization compared to untreated mice. Colonization induced antibody responses to protein rather than capsular antigen, and when measured using a protein array B cell depletion prior to colonization reduced serum levels of IgG to several protein antigens. However, B cell depleted S. pneumoniae colonized mice were still partially protected against both lung infection and septicemia when challenged with S. pneumoniae after reconstitution of their B cells. These data indicate that although B cell depletion markedly impairs antibody recognition of S. pneumoniae in colonized mice, some protective immunity is maintained, perhaps mediated by cellular immunity., Competing Interests: GW was employed by the company Novartis Institute for BioMedical Research. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Ercoli, Ramos-Sevillano, Nakajima, de Assis, Jasinskas, Goldblatt, Felgner, Weckbecker and Brown.)

Nucleotides are important for RNA and DNA synthesis and, despite a de novo synthesis by bacteria, uptake systems are crucial. Streptococcus pneumoniae, a facultative human pathogen, produces a surface-exposed nucleoside-binding protein, PnrA, as part of an ABC transporter system. Here we demonstrate the binding affinity of PnrA to nucleosides adenosine, guanosine, cytidine, thymidine and uridine by microscale thermophoresis and indicate the consumption of adenosine and guanosine by 1 H NMR spectroscopy. In a series of five crystal structures we revealed the PnrA structure and provide insights into how PnrA can bind purine and pyrimidine ribonucleosides but with preference for purine ribonucleosides. Crystal structures of PnrA:nucleoside complexes unveil a clear pattern of interactions in which both the N- and C- domains of PnrA contribute. The ribose moiety is strongly recognized through a conserved network of H-bond interactions, while plasticity in loop 27-36 is essential to bind purine- or pyrimidine-based nucleosides. Further, we deciphered the role of PnrA in pneumococcal fitness in infection experiments. Phagocytosis experiments did not show a clear difference in phagocytosis between PnrA-deficient and wild-type pneumococci. In the acute pneumonia infection model the deficiency of PnrA attenuated moderately virulence of the mutant, which is indicated by a delay in the development of severe lung infections. Importantly, we confirmed the loss of fitness in co-infections, where the wild-type out-competed the pnrA-mutant. In conclusion, we present the PnrA structure in complex with individual nucleosides and show that the consumption of adenosine and guanosine under infection conditions is required for virulence., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Vitamin D is an essential component of immune function and childhood deficiency is associated with an increased risk of acute lower respiratory infections (ALRIs). Globally, the leading childhood respiratory pathogens are Streptococcus pneumoniae , respiratory syncytial virus and the influenza virus. There is a growing body of evidence describing the innate immunomodulatory properties of vitamin D during challenge with respiratory pathogens, but recent systematic and unbiased synthesis of data is lacking, and future research directions are unclear. We therefore conducted a systematic PubMed literature search using the terms "vitamin D" and " Streptococcus pneumoniae " or "Respiratory Syncytial Virus" or "Influenza". A priori inclusion criteria restricted the review to in vitro studies investigating the effect of vitamin D metabolites on human innate immune cells (primary, differentiated or immortalised) in response to stimulation with the specified respiratory pathogens. Eleven studies met our criteria. Despite some heterogeneity across pathogens and innate cell types, vitamin D modulated pathogen recognition receptor (PRRs: Toll-like receptor 2 (TLR2), TLR4, TLR7 and nucleotide-binding oligomerisation domain-containing protein 2 (NOD2)) expression; increased antimicrobial peptide expression (LL-37, human neutrophil peptide (HNP) 1-3 and β-defensin); modulated autophagosome production reducing apoptosis; and modulated production of inflammatory cytokines (Interleukin (IL) -1β, tumour necrosis factor-α (TNF-α), interferon-ɣ (IFN-ɣ), IL-12p70, IFN-β, Regulated on Activation, Normal T cell Expressed (RANTES), IL-10) and chemokines (IL-8 and C-X-C motif chemokine ligand 10 (CXCL10)). Differential modulation of PRRs and IL-1β was reported across immune cell types; however, this may be due to the experimental design. None of the studies specifically focused on immune responses in cells derived from children. In summary, vitamin D promotes a balanced immune response, potentially enhancing pathogen sensing and clearance and restricting pathogen induced inflammatory dysregulation. This is likely to be important in controlling both ALRIs and the immunopathology associated with poorer outcomes and progression to chronic lung diseases. Many unknowns remain and further investigation is required to clarify the nuances in vitamin D mediated immune responses by pathogen and immune cell type and to determine whether these in vitro findings translate into enhanced immunity and reduced ALRI in the paediatric clinical setting.

Colonization of the upper respiratory tract with Streptococcus pneumoniae is the precursor of pneumococcal pneumonia and invasive disease. Following exposure, however, it is unclear which human immune mechanisms determine whether a pathogen will colonize. We used a human challenge model to investigate host-pathogen interactions in the first hours and days following intranasal exposure to Streptococcus pneumoniae Using a novel home sampling method, we measured early immune responses and bacterial density dynamics in the nose and saliva after volunteers were experimentally exposed to pneumococcus. Here, we show that nasal colonization can take up to 24 h to become established. Also, the following two distinct bacterial clearance profiles were associated with protection: nasal clearers with immediate clearance of bacteria in the nose by the activity of pre-existent mucosal neutrophils and saliva clearers with detectable pneumococcus in saliva at 1 h post challenge and delayed clearance mediated by an inflammatory response and increased neutrophil activity 24 h post bacterial encounter. This study describes, for the first time, how colonization with a bacterium is established in humans, signifying that the correlates of protection against pneumococcal colonization, which can be used to inform design and testing of novel vaccine candidates, could be valid for subsets of protected individuals. IMPORTANCE Occurrence of lower respiratory tract infections requires prior colonization of the upper respiratory tract with a pathogen. Most bacterial infection and colonization studies have been performed in murine and in vitro models due to the current invasive sampling methodology of the upper respiratory tract, both of which poorly reflect the complexity of host-pathogen interactions in the human nose. Self-collecting saliva and nasal lining fluid at home is a fast, low-cost, noninvasive, high-frequency sampling platform for continuous monitoring of bacterial encounter at defined time points relative to exposure. Our study demonstrates for the first time that, in humans, there are distinct profiles of pneumococcal colonization kinetics, distinguished by speed of appearance in saliva, local phagocytic function, and acute mucosal inflammatory responses, which may either recruit or activate neutrophils. These data are important for the design and testing of novel vaccine candidates., (Copyright © 2021 Nikolaou et al.)

Macrophage-inducible C-type lectin (Mincle)-dependent sensing of pathogens triggers proinflammatory immune responses in professional phagocytes that contribute to protecting the host against pathogen invasion. In this study, we examined whether overexpression of Mincle that is designed to improve early pathogen sensing by professional phagocytes would improve lung-protective immunity against Streptococcus pneumoniae in mice. Proteomic profiling of alveolar macrophages of Mincle transgenic (tg) mice stimulated with the Mincle-specific pneumococcal ligand glucosyl-diacylglycerol (Glc-DAG) revealed increased Nlrp3 inflammasome activation and downstream IL-1β cytokine release that was not observed in Glc-DAG-stimulated Mincle knockout or Nlrp3 knockout macrophages. Along this line, Mincle tg mice also responded with a stronger Nlrp3 expression and early proinflammatory cytokine release after challenge with S. pneumoniae , ultimately leading to fatal pneumonia in the Mincle tg mice. Importantly, Nlrp3 inhibitor treatment of Mincle tg mice significantly mitigated the observed hyperinflammatory response to pneumococcal challenge. Together, we show that overexpression of the pattern recognition receptor Mincle triggers increased Glc-DAG-dependent Nlrp3 inflammasome activation in professional phagocytes leading to fatal pneumococcal pneumonia in mice that is amenable to Nlrp3 inhibitor treatment. These data show that ectopic expression of the Mincle receptor confers increased susceptibility rather than resistance to S. pneumoniae in mice, thus highlighting the importance of an inducible Mincle receptor expression in response to microbial challenge., (Copyright © 2020 by The American Association of Immunologists, Inc.)

Pneumonia is one of the leading causes of death worldwide. The course of the disease is often highly dynamic with unforeseen critical deterioration within hours in a relevant proportion of patients. Besides antibiotic treatment, novel adjunctive therapies are under development. Their additive value needs to be explored in preclinical and clinical studies and corresponding therapy schedules require optimization prior to introduction into clinical practice. Biomathematical modeling of the underlying disease and therapy processes might be a useful aid to support these processes. We here propose a biomathematical model of murine immune response during infection with Streptococcus pneumoniae aiming at predicting the outcome of different treatment schedules. The model consists of a number of non-linear ordinary differential equations describing the dynamics and interactions of the pulmonal pneumococcal population and relevant cells of the innate immune response, namely alveolar- and inflammatory macrophages and neutrophils. The cytokines IL-6 and IL-10 and the chemokines CCL2, CXCL1 and CXCL5 are considered as major mediators of the immune response. We also model the invasion of peripheral blood monocytes, their differentiation into macrophages and bacterial penetration through the epithelial barrier causing blood stream infections. We impose therapy effects on this system by modelling antibiotic therapy and treatment with the novel C5a-inactivator NOX-D19. All equations are derived by translating known biological mechanisms into equations and assuming appropriate response kinetics. Unknown model parameters were determined by fitting the predictions of the model to time series data derived from mice experiments with close-meshed time series of state parameters. Parameter fittings resulted in a good agreement of model and data for the experimental scenarios. The model can be used to predict the performance of alternative schedules of combined antibiotic and NOX-D19 treatment. We conclude that we established a comprehensive biomathematical model of pneumococcal lung infection, immune response and barrier function in mice allowing simulations of new treatment schedules. We aim to validate the model on the basis of further experimental data. We also plan the inclusion of further novel therapy principles and the translation of the model to the human situation in the near future., Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: MS receives funding from Pfizer Inc. for epidemiologic modelling of pneumonia. This does not alter our adherence to PLOS ONE policies on sharing data and materials. The other authors have declared that no competing interests exist.

BACKGROUND A lethal synergism between the influenza virus and Streptococcus pneumoniae has been identified. However, bacterial coinfection is considered relatively infrequent in hospitalized patients with COVID-19, and the co-prevalence of Streptococcus pneumoniae is low. MATERIAL AND METHODS We retrospectively analyzed the clinical characteristics and outcomes of patients subsequently admitted to AMITA Health Saint Francis Hospital between March 1 and June 30, 2020, with documented SARS-CoV-2 and S. pneumoniae coinfection. RESULTS We identified 11 patients with S. pneumoniae coinfection. The median age was 77 years (interquartile range [IQR], 74-82 years), 45.5% (5/11) were males, 54.5% (6/11) were white, and 90.9% (10/11) were long-term care facility (LTCF) residents. The median length of stay was 7 days (IQR, 6-8 days). Among 11 patients, 4 were discharged in stable condition and 7 had died, resulting in an inpatient mortality rate of 64%. CONCLUSIONS At our center, 11 patients with COVID-19 pneumonia who had confirmed infection with SARS-CoV-2 were diagnosed with Streptococcus pneumoniae infection while in hospital. All patients had pneumonia confirmed on imaging and a nonspecific increase in markers of inflammation. The in-hospital mortality rate of 64% (7 patients) was higher in this group than in previous reports. This study highlights the importance of monitoring bacterial coinfection in patients with viral lung infection due to SARS-CoV-2.

Bacterial pneumonia is one of the most prevalent infectious diseases and has high mortality in sensitive patients (children, elderly and immunocompromised). Although an infection, the disease alters the alveolar epithelium homeostasis and hinders normal breathing, often with fatal consequences. A special case is hospitalized aged patients, which present a high risk of infection and death because of the community acquired version of the Streptococcus pneumoniae pneumonia. There is evidence that early antibiotics treatment decreases the inflammatory response during pneumonia. Here, we investigate mechanistically this strategy using a multi-level mathematical model, which describes the 24 first hours after infection of a single alveolus from the key signaling networks behind activation of the epithelium to the dynamics of the local immune response. With the model, we simulated pneumonia in aged and young patients subjected to different antibiotics timing. The results show that providing antibiotics to elderly patients 8 h in advance compared to young patients restores in aged individuals the effective response seen in young ones. This result suggests the use of early, probably prophylactic, antibiotics treatment in aged hospitalized people with high risk of pneumonia.

Background: Vaccination with the 23-valent pneumococcal polysaccharide vaccine (PPV23) is available in the United Kingdom to adults aged 65 years or older and those in defined clinical risk groups. We evaluated the vaccine effectiveness (VE) of PPV23 against vaccine-type pneumococcal pneumonia in a cohort of adults hospitalised with community-acquired pneumonia (CAP)., Methods and Findings: Using a case-control test-negative design, a secondary analysis of data was conducted from a prospective cohort study of adults (aged ≥16 years) with CAP hospitalised at 2 university teaching hospitals in Nottingham, England, from September 2013 to August 2018. The exposure of interest was PPV23 vaccination at any time point prior to the index admission. A case was defined as PPV23 serotype-specific pneumococcal pneumonia and a control as non-PPV23 serotype pneumococcal pneumonia or nonpneumococcal pneumonia. Pneumococcal serotypes were identified from urine samples using a multiplex immunoassay or from positive blood cultures. Multivariable logistic regression was used to derive adjusted odds of case status between vaccinated and unvaccinated individuals; VE estimates were calculated as (1 - odds ratio) × 100%. Of 2,357 patients, there were 717 PPV23 cases (48% vaccinated) and 1,640 controls (54.5% vaccinated). The adjusted VE (aVE) estimate against PPV23 serotype disease was 24% (95% CI 5%-40%, p = 0.02). Estimates were similar in analyses restricted to vaccine-eligible patients (n = 1,768, aVE 23%, 95% CI 1%-40%) and patients aged ≥65 years (n = 1,407, aVE 20%, 95% CI -5% to 40%), but not in patients aged ≥75 years (n = 905, aVE 5%, 95% CI -37% to 35%). The aVE estimate in relation to PPV23/non-13-valent pneumococcal conjugate vaccine (PCV13) serotype pneumonia (n = 417 cases, 43.7% vaccinated) was 29% (95% CI 6%-46%). Key limitations of this study are that, due to high vaccination rates, there was a lack of power to reject the null hypothesis of no vaccine effect, and that the study was not large enough to allow robust subgroup analysis in the older age groups., Conclusions: In the setting of an established national childhood PCV13 vaccination programme, PPV23 vaccination of clinical at-risk patient groups and adults aged ≥65 years provided moderate long-term protection against hospitalisation with PPV23 serotype pneumonia. These findings suggest that PPV23 vaccination may continue to have an important role in adult pneumococcal vaccine policy, including the possibility of revaccination of older adults., Competing Interests: The authors of this manuscript have read the journal's policy and have the following competing interests: WSL's institution has received unrestricted investigator-initiated research funding from Pfizer for a multicentre cohort study in which WSL is the Chief Investigator. WSL is a member of the UK Joint Committee on Vaccination and Immunisation. NKF declares: The Public Health England - National Infection Service, Immunisation and Countermeasures Division provides vaccine manufacturers with post-marketing surveillance reports, which Marketing Authorisation Holders are required to submit to the UK Licensing authority in compliance with their Risk Management Strategy. A cost recovery charge is made for these reports. SDE is an employee of Public Health England's National Infection Service in the Vaccine Preventable Bacteria Section (VPBS). The VPBS conduct contract research for pharmaceutical industries on behalf of Public Health England. No personal remuneration is received. The Public Health England National Infection Service Immunisation and Countermeasures Division has provided vaccine manufacturers with post-marketing surveillance reports, which Marketing Authorisation Holders are required to submit to the UK Licensing authority in compliance with their Risk Management Strategy. A cost recovery charge is made for these reports. No other conflicts of interest are declared.

Community-acquired pneumonia (CAP) remains an important cause of morbidity and mortality throughout the world with much recent and ongoing research focused on the occurrence of cardiovascular events (CVEs) during the infection, which are associated with adverse short-term and long-term survival. Much of the research directed at unraveling the pathogenesis of these events has been undertaken in the settings of experimental and clinical CAP caused by the dangerous, bacterial respiratory pathogen, Streptococcus pneumoniae (pneumococcus), which remains the most common bacterial cause of CAP. Studies of this type have revealed that although platelets play an important role in host defense against infection, there is also increasing recognition that hyperactivation of these cells contributes to a pro-inflammatory, prothrombotic systemic milieu that contributes to the etiology of CVEs. In the case of the pneumococcus, platelet-driven myocardial damage and dysfunction is exacerbated by the direct cardiotoxic actions of pneumolysin, a major pore-forming toxin of this pathogen, which also acts as potent activator of platelets. This review is focused on the role of platelets in host defense against infection, including pneumococcal infection in particular, and reviews the current literature describing the potential mechanisms by which platelet activation contributes to cardiovascular complications in CAP. This is preceded by an evaluation of the burden of pneumococcal infection in CAP, the clinical features and putative pathogenic mechanisms of the CVE, and concludes with an evaluation of the potential utility of the anti-platelet activity of macrolides and various adjunctive therapies., (Copyright © 2020 Feldman and Anderson.)

Streptococcus pneumoniae is the main cause of bacterial pneumonia, a condition that currently produces significant global morbidity and mortality. The initial immune response to this bacterium occurs when the innate system recognizes common motifs expressed by many pathogens, events driven by pattern recognition receptors like the Toll-like family receptors (TLRs). In this study, lung myeloid-cell populations responsible for the innate immune response (IIR) against S. pneumoniae , and their dependence on the TLR4-signaling axis, were analyzed in TLR4 -/- and Myeloid-Differentiation factor-88 deficient (MyD88 -/- ) mice. Neutrophils and monocyte-derived cells were recruited in infected mice 3-days post-infection. Compared to wild-type mice, there was an increased bacterial load in both these deficient mouse strains and an altered IIR, although TLR4 -/- mice were more susceptible to bacterial infection. These mice also developed fewer alveolar macrophages, weaker neutrophil infiltration, less Ly6C high monocyte differentiation and a disrupted classical and non-classical monocyte profile. The pro-inflammatory cytokine profile (CXCL1, TNF-α, IL-6, and IL-1β) was also severely affected by the lack of TLR4 and no induction of Th1 was observed in these mice. The respiratory burst (ROS production) after infection was profoundly dampened in TLR4 -/- and MyD88 -/- mice. These data demonstrate the complex dynamics of myeloid populations and a key role of the TLR4-signaling axis in the IIR to S. pneumoniae , which involves both the MyD88 and TRIF (Toll/IL-1R domain-containing adaptor-inducing IFN-β) dependent pathways., (Copyright © 2020 Sánchez-Tarjuelo, Cortegano, Manosalva, Rodríguez, Ruíz, Alía, Prado, Cano, Ferrándiz, de la Campa, Gaspar and de Andrés.)

Secondary Streptococcus pneumoniae infection is a significant cause of morbidity and mortality during influenza epidemics and pandemics. Multiple pathogenic mechanisms, such as lung epithelial damage and dysregulation of neutrophils and alveolar macrophages (AMs), have been suggested to contribute to the severity of disease. However, the fundamental reasons for influenza-induced susceptibility to secondary bacterial pneumonia remain unclear. In this study, we revisited these controversies over key pathogenic mechanisms in a lethal model of secondary bacterial pneumonia with an S. pneumoniae strain that is innocuous to mice in the absence of influenza infection. Using a series of in vivo models, we demonstrate that rather than a systemic suppression of immune responses or neutrophil function, influenza infection activates IFN-γR signaling and abrogates AM-dependent bacteria clearance and thereby causes extreme susceptibility to pneumococcal infection. Importantly, using mice carrying conditional knockout of Ifngr1 gene in different myeloid cell subsets, we demonstrate that influenza-induced IFN-γR signaling in AMs impairs their antibacterial function, thereby enabling otherwise noninvasive S. pneumoniae to cause deadly pneumonia., (Copyright © 2020 by The American Association of Immunologists, Inc.)

Pneumococcal conjugate vaccination (PCV) may prevent influenza-related pneumonia, including Streptococcus pneumoniae pneumonia. To investigate PCV efficacy against secondary pneumococcal pneumonia following influenza, PCV was administered intramuscularly 2 and 5 weeks before S. pneumoniae serotype-3 colonization of murine nasopharynges followed by intranasal challenge with a sublethal dose of influenza A virus. Bacterial and viral loads, including innate immune responses were compared across conditions. PCV vaccination improved the survival of mice with secondary pneumococcal pneumonia and significantly reduced the pulmonary bacterial burden. Increased monocyte/macrophage influx into the lungs, alleviated loss of alveolar macrophages and decreased neutrophil influx into the lungs occurred in PCV-treated mice irrespective of pneumococcal colonization. Higher monocyte chemoattractant protein 1 levels and lower levels of CXCL1, interferon-γ, interleukin-17A, and IL-10, were detected in PCV-treated mice. Additionally, PCV treatment activated the macrophage intracellular killing of S. pneumoniae. Collectively, PCV potentially modulates the host's innate immunity and specific antibodies induction. Macrophage-related innate immunity should be further explored to elucidate the efficacy and mechanisms of PCV versus influenza-related life-threatening diseases., Competing Interests: Declaration of Competing Interest The authors declare no competing interests., (Copyright © 2020 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)

Polymorphonuclear leukocytes (PMNs) are crucial for initial control of Streptococcus pneumoniae (pneumococcus) lung infection; however, as the infection progresses their persistence in the lungs becomes detrimental. Here we explored why the antimicrobial efficacy of PMNs declines over the course of infection. We found that the progressive inability of PMNs to control infection correlated with phenotypic differences characterized by a decrease in CD73 expression, an enzyme required for production of extracellular adenosine (EAD). EAD production by CD73 was crucial for the ability of both murine and human PMNs to kill S. pneumoniae. In exploring the mechanisms by which CD73 controlled PMN function, we found that CD73 mediated its antimicrobial activity by inhibiting IL-10 production. PMNs from wild-type mice did not increase IL-10 production in response to S. pneumoniae; however, CD73 -/- PMNs up-regulated IL-10 production upon pneumococcal infection in vitro and during lung challenge. IL-10 inhibited the ability of WT PMNs to kill pneumococci. Conversely, blocking IL-10 boosted the bactericidal activity of CD73 -/- PMNs as well as host resistance of CD73 -/- mice to pneumococcal pneumonia. CD73/IL-10 did not affect apoptosis, bacterial uptake, and intracellular killing or production of antimicrobial neutrophil elastase and myeloperoxidase. Rather, inhibition of IL-10 production by CD73 was important for optimal reactive oxygen species (ROS) production by PMNs. ROS contributed to PMN antimicrobial function as their removal or detoxification impaired the ability of PMNs to efficiently kill S. pneumoniae. This study demonstrates that CD73 controls PMN antimicrobial phenotype during S. pneumoniae infection., (©2020 Society for Leukocyte Biology.)

Objectives: Streptococcus pneumoniae (S. pneumoniae) is an important commensal and pathogenic bacterium responsible for pneumonia, meningitis and other invasive diseases. Pneumolysin (PLY) is the major virulence factor that contributes significantly to the interaction between S. pneumoniae and the host., Key Findings: In this study, the results of antibacterial analysis, the haemolysis test and the Western blotting assay showed that acacetin inhibited PLY-mediated pore-forming activity caused by S. pneumoniae culture precipitates and purified PLY without anti-S. pneumoniae activity. In addition, acacetin treatment inhibited PLY oligomerization without affecting the expression of PLY in S. pneumoniae culture supernatants. Live/dead cells and cytotoxicity assays suggested that acacetin significantly enhanced the survival rate of injured cells by inhibiting the biological toxicity of PLY without cytotoxicity in the coculture system. The in vivo mouse model of S. pneumoniae infection further demonstrated that acacetin treatment could significantly reduce the levels of inflammatory factors (INF-γ and IL-β) in bronchoalveolar lavage fluid (BALF) and alleviate the pathological damage of lung injury., Conclusions: Taken together, the results presented in this study indicated that acacetin inhibited the pore-forming activity of PLY and reduced the virulence of S. pneumoniae in vivo and in vitro, which may provide a leading compound for the treatment of S. pneumoniae infection., (© 2020 Royal Pharmaceutical Society.)

Allergic asthma (AA) is characterized as a Th2-biased airway inflammation that can develop lung inflammation and remodeling of the respiratory tract. Streptococcus pneumoniae is a major respiratory pathogen, causing noninvasive (otitis media and pneumonia) and invasive diseases (sepsis) in humans. We sought to determine the role of IL-6 in the regulation of lung inflammation in murine AA caused by Aspergillus fumigatus as well as its consequence on the regulation of airway barrier integrity and S. pneumoniae disease. In an AA model, IL-6 deficiency led to increased lung inflammation, eosinophil recruitment, tissue pathology, and collagen deposition. Additionally, IL-6-deficient asthmatic mice exhibited reduced goblet cell hyperplasia and increased TGF-β production. These key changes in the lungs of IL-6-deficient asthmatic mice resulted in dysregulated tight junction proteins and increased lung permeability. Whereas the host response to AA protected against S. pneumoniae lung disease, the IL-6 deficiency abrogated the protective effect of allergic inflammation against S. pneumoniae pathogenesis. Consistent with in vivo data, IL-6 knockdown by small interfering RNA or the blockade of IL-6R signaling exacerbated the TGF-β-induced dysregulation of tight junction proteins, E-cadherin and N-cadherin expression, and STAT3 phosphorylation in MLE-12 epithelial cells. Our findings demonstrate a previously unrecognized role of host IL-6 response in the regulation of lung inflammation during AA and the control of S. pneumoniae bacterial disease. A better understanding of the interactions between lung inflammation and barrier framework could lead to the development of therapies to control asthma inflammation and preserve barrier integrity., (Copyright © 2020 by The American Association of Immunologists, Inc.)

Patients with respiratory syncytial virus (RSV) infection exhibit enhanced susceptibility to subsequent pneumococcal infections. However, the underlying mechanisms involved in this increased susceptibility remain unclear. Here, we identified potentially novel cellular and molecular cascades triggered by RSV infection to exacerbate secondary pneumococcal pneumonia. RSV infection stimulated the local production of growth arrest-specific 6 (Gas6). The Gas6 receptor Axl was crucial for attenuating pneumococcal immunity in that the Gas6/Axl blockade fully restored antibacterial immunity. Mechanistically, Gas6/Axl interaction regulated the conversion of alveolar macrophages from an antibacterial phenotype to an M2-like phenotype that did not exhibit antibacterial activity, and the attenuation of caspase-1 activation and IL-18 production in response to pneumococcal infection. The attenuated IL-18 production failed to drive both NK cell-mediated IFN-γ production and local NO and TNF-α production, which impair the control of bacterial infection. Hence, the RSV-mediated Gas6/Axl activity attenuates the macrophage-mediated protection against pneumococcal infection. The Gas6/Axl axis could be a potentially novel therapeutic target for RSV-associated secondary bacterial infection.

The available pneumococcal conjugate vaccines provide protection against only those serotypes that are included in the vaccine, which leads to a selective pressure and serotype replacement in the population. An alternative low-cost, safe and serotype-independent vaccine was developed based on a nonencapsulated pneumococcus strain. This study evaluates process intensification to improve biomass production and shows for the first time the use of perfusion-batch with cell recycling for bacterial vaccine production. Batch, fed-batch, and perfusion-batch were performed at 10 L scale using a complex animal component-free culture medium. Cells were harvested at the highest optical density, concentrated and washed using microfiltration or centrifugation to compare cell separation methods. Higher biomass was achieved using perfusion-batch, which removes lactate while retaining cells. The biomass produced in perfusion-batch would represent at least a fourfold greater number of doses per cultivation than in the previously described batch process. Each strategy yielded similar vaccines in terms of quality as evaluated by western blot and animal immunization assays, indicating that so far, perfusion-batch is the best strategy for the intensification of pneumococcal whole-cell vaccine production, as it can be integrated to the cell separation process keeping the same vaccine quality., (© 2020 Wiley Periodicals, Inc.)

Streptococcus pneumoniae is a major human pathogen, causing pneumonia and sepsis. Genetic components strongly influence host responses to pneumococcal infections, but the responsible loci are unknown. We have previously identified a locus on mouse chromosome 7 from a susceptible mouse strain, CBA/Ca, to be crucial for pneumococcal infection. Here we identify a responsible gene, Cd22, which carries a point mutation in the CBA/Ca strain, leading to loss of CD22 on B cells. CBA/Ca mice and gene-targeted CD22-deficient mice on a C57BL/6 background are both similarly susceptible to pneumococcal infection, as shown by bacterial replication in the lungs, high bacteremia and early death. After bacterial infections, CD22-deficient mice had strongly reduced B cell populations in the lung, including GM-CSF producing, IgM secreting innate response activator B cells, which are crucial for protection. This study provides striking evidence that CD22 is crucial for protection during invasive pneumococcal disease., Competing Interests: The authors have declared that no competing interests exist.