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Because of the growing numbers of immunocompromised patients, the incidence of life-threatening fungal infections caused by Candida albicans and Aspergillus fumigatus is increasing. We have recently identified enolase 1 (Eno1) from A. fumigatus as an immune evasion protein. Eno1 is a fungal moonlighting protein that mediates adhesion and invasion of human cells and also immune evasion through complement inactivation. We now show that soluble Eno1 has immunostimulatory activity. We observed that Eno1 from both C. albicans and A. fumigatus directly binds to the surface of lymphocytes, preferentially human and mouse B cells. Functionally, Eno1 upregulated CD86 expression on B cells and induced proliferation. Although the receptor for fungal Eno1 on B lymphocytes is still unknown, the comparison of B cells from wild-type and MyD88-deficient mice showed that B cell activation by Eno1 required MyD88 signaling. With respect to infection biology, we noted that mouse B cells stimulated by Eno1 secreted IgM and IgG2b. These Igs bound C. albicans hyphae in vitro, suggesting that Eno1-induced Ab secretion might contribute to protection from invasive fungal disease in vivo. Eno1 also triggered the release of proinflammatory cytokines from monocytes, particularly IL-6, which is a potent activator of B cells. Together, our data shed new light on the role of secreted Eno1 in infections with C. albicans and A. fumigatus. Eno1 secretion by these pathogenic microbes appears to be a double-edged sword by supporting fungal pathogenicity while triggering (antifungal) immunity., (Copyright © 2023 by The American Association of Immunologists, Inc.)

Shigellosis is characterized as diarrheal disease that causes a high mortality rate especially in children, elderly and immunocompromised patients. More recently, the World Health Organization advised safe vaccine designing against shigellosis due to the emergence of Shigella dysenteriae resistant strains. Therefore, the aim of this study is to identify novel drug targets as well as the design of the potential vaccine candidates and chimeric vaccine models against Shigella dysenteriae. A computational based Reverse Vaccinology along with subtractive genomics analysis is one of the robust approaches used for the prioritization of drug targets and vaccine candidates through direct screening of genome sequence assemblies. Herein, a successfully designed peptide-based novel highly antigenic chimeric vaccine candidate against Shigella dysenteriae sd197 strain is proposed. The study resulted in six epitopes from outer membrane WP_000188255.1 (Fe (3+) dicitrate transport protein FecA) that ultimately leads to the construction of twelve vaccine models. Moreover, V9 construct was found to be highly immunogenic, non-toxic, non-allergenic, highly antigenic, and most stable in terms of molecular docking and simulation studies against six HLAs and TLRS/MD complex. So far, this protein and multiepitope have never been characterized as vaccine targets against Shigella dysenteriae. The current study proposed that V9 could be a significant vaccine candidate against shigellosis and to ascertain that further experiments may be applied by the scientific community focused on shigellosis., (© 2022. The Author(s).)

Non-human primate models of Tuberculosis (TB) are one of the most commonly used within the experimental TB field because they closely mimic the whole spectrum of disease progression of human TB. However, the early cellular interactions of the pulmonary granuloma are still not well understood. The use of this model allows investigation into the early interactions of cells within pulmonary granulomas which cannot be undertaken in human samples. Pulmonary granulomas from rhesus and cynomolgus macaques from two timepoints post infection were categorised into categories 1 - 6 (early to late stage granulomas) and immunohistochemistry was used to identify CD68+ macrophages, CD3+ T cells and CD20+ B cells. Multinucleated giant cells and acid-fast bacilli were also quantified. At week four post infection, cynomolgus macaques were found to have more CD68+ cells than rhesus in all but category 1 granulomas. Cynomolgus also had a significantly higher percentage of CD20+ B cells in category 1 granulomas. At week twelve post infection, CD68+ cells were most abundant in category 4 and 5 granulomas in both species; however, there were no significant differences between them. CD3+ T cells and CD20+ B cells were significantly higher in the majority of granuloma categories in cynomolgus compared to rhesus. Multinucleated giant cells and acid-fast bacilli were most abundant in categories 5 and 6 at week 12 post challenge in both species. This study has identified the basic cellular composition and spatial distribution of immune cells within pulmonary granulomas in both rhesus and cynomolgus macaques over time. The data from this study will add to the knowledge already gained in this field and may inform future research on vaccines and therapeutics for TB., 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 © 2022 Hunter, Hingley-Wilson, Stewart, Sharpe and Salguero.)

Background: Porphyromonas gingivalis (P. gingivalis) is a pathogenic bacterium widely present in subgingival plaques of patients with periodontitis. It induces periodontitis with bone loss as its main feature by changing the number and composition of symbiotic microorganisms, as well as inducing the natural immune response of the host. However, the mechanism of the latter remains unclear., Objective: This study aims to investigate the effect of P. gingivalis lipopolysaccharide (LPS) on regulatory B cells (Breg) in the occurrence and development of periodontitis., Methods: We detected the mRNA levels of IL-10 in B cells under the stimulation of P. gingivalis LPS and/or E. coli LPS, distinguished IL-10-producing cells from different B cell subgroups using flow cytometry. Through toll-like receptor (TLR) knockout mice, the role of TLR2 and TLR4 in this process was also evaluated., Results: Results showed that P. gingivalis stimulated B cells to produce IL-10 via TLR2/4. CD5+B1 subset is the main source of IL-10+Breg cell. Under P. gingivalis LPS stimulation, CD5+IgM+CD93-IL-10+B cell subset increased significantly, which was regulated through TLR2/ 4., Conclusion: The results of this study provides new insights into the immunopathogenic mechanism of P. gingivalis, preliminarily discussed the effect of P. gingivalis on the production of Breg, and present a theoretical foundation for subsequent investigations on the occurrence and development of periodontitis., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Fc receptor (FcR) is an important opsonin receptor on the surface of immune cells, playing an important role in antibody-dependent cell-mediated immunity. Our previous work found that the FcR of flounder showed a marked expression response in phagocytizing IgM + B cell, which suggested that FcR might participate in regulating Ig-opsonized phagocytosis. In this paper, in order to elucidate the potential role of FcR in mediating phagocytosis of IgM + B cell, flounder anti- E. tarda serum was prepared and complement-inactivated for the use of E. tarda opsonization, and the sera of healthy flounder were used as control. Flow cytometric analysis showed that the phagocytosis rates of antiserum-opsonized E. tarda in peripheral blood mIgM + B lymphocytes were significantly higher than the control group, and higher phagocytosis rates of mIgM + B lymphocyte could be detected with an increasing incubation time ranging from 1 to 5 h. The phagocytosis rates of antiserum-opsonized E. tarda by mIgM + B lymphocyte for an incubation time of 1, 3 or 5 h were 51.1, 63.0, and 77.5% respectively, which were significantly higher than the phagocytosis rates in the control groups with 40.2, 50.9, and 63.8%, respectively. While the Fc fragment of IgM on the surface of opsonized E. tarda was blocked by rabbit anti-flounder IgM polyclonal antibodies, phagocytosis rates of mIgM + B lymphocyte decreased significantly compared with the unblocked group. Moreover, the proportion of mIgM + B lymphocytes with higher intracellular reactive oxygen species (ROS) levels rose to 32.1% from the control level of 23.0% after phagocytosis of antiserum-opsonized E. tarda . FcγRII and Syk were found to be significantly upregulated, while FcγRIII was significantly downregulated in the mIgM + B lymphocytes post phagocytosis. Furthermore, when FcγRII of mIgM + B lymphocytes was blocked by the prepared antibodies, their phagocytosis rate of antiserum-opsonized E. tarda was 39.0%, which was significantly lower than the unblocked group of 54.0%. These results demonstrate that FcR plays a critical role in mediating phagocytosis and bactericidal activity of mIgM + B lymphocytes, which would facilitate an improved understanding of the regulatory roles of FcR in phagocytosis of teleost B lymphocytes., 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 Hao, Tang, Xing, Sheng, Chi and Zhan.)

Candida albicans is usually a benign member of the human gut microbiota, but can become pathogenic under certain circumstances, for example in an immunocompromised host. The innate immune system, in particular neutrophils and macrophages, constitutes a crucial first line of defense against fungal invasion, however adaptive immunity may provide long term protection and thus allow vaccination of at risk patients. While T H 1 and T H 17 cells are important for antifungal responses, the role of B cells and antibodies in protection from C. albicans infection is less well defined. In this study, we show that C. albicans hyphae but not yeast, as well as fungal cell wall components, directly activate B cells via MyD88 signaling triggered by Toll- like receptor 2, leading to increased IgG1 production. While Dectin-1 signals and specific recognition by the B cell receptor are dispensable for B cell activation in this system, TLR2/MyD88 signals cooperate with CD40 signals in promoting B cell activation. Importantly, recognition of C. albicans via MyD88 signaling is also essential for induction of IL-6 secretion by B cells, which promotes T H 17 polarization in T-B cell coculture experiments. B cells may thus be activated directly by C. albicans in its invasive form, leading to production of antibodies and T cell help for fungal clearance., 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 Ferreira-Gomes, Wich, Böde, Hube, Jacobsen and Jungnickel.)

The mucosal immune system is the first line of defense against pathogens. Germinal centers (GCs) in the Peyer's patches (PPs) of the small intestine are constantly generated through stimulation of the microbiota. In this study, we investigated the role of γδ T cells in the GC reactions in PPs. Most γδ T cells in PPs localized in the GCs and expressed a TCR composed of Vγ1 and Vδ6 chains. By using mice with partial and total γδ T cell deficiencies, we found that Vγ1 + /Vδ6 + T cells can produce high amounts of IL-4, which drives the proliferation of GC B cells as well as the switch of GC B cells towards IgA. Therefore, we conclude that γδ T cells play a role in sustaining gut homeostasis and symbiosis via supporting the GC reactions in PPs., 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 Ullrich, Lueder, Juergens, Wilharm, Barros-Martins, Bubke, Demera, Ikuta, Patzer, Janssen, Sandrock, Prinz and Rampoldi.)

Mucosal-associated invariant T (MAIT) cells are an innate-like population of T cells that display a TCR Vα7.2+ CD161+ phenotype and are restricted by the nonclassical MHC-related molecule 1 (MR1). Although B cells control MAIT cell development and function, little is known about the mechanisms underlying their interaction(s). Here, we report, for the first time, that during Salmonella enterica serovar Typhi ( S . Typhi) infection, HLA-G expression on B cells downregulates IFN-γ production by MAIT cells. In contrast, blocking HLA-G expression on S . Typhi-infected B cells increases IFN-γ production by MAIT cells. After interacting with MAIT cells, kinetic studies show that B cells upregulate HLA-G expression and downregulate the inhibitory HLA-G receptor CD85j on MAIT cells resulting in their loss. These results provide a new role for HLA-G as a negative feedback loop by which B cells control MAIT cell responses to antigens., 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 Salerno-Gonçalves, Rezwan, Luo, Tettelin and Sztein.)

Background and Aims: Crohn's disease and ulcerative colitis are characterized by dysregulated adaptive immune responses to the microbiota in genetically susceptible individuals, but the specificity of these responses remains largely undefined. Therefore, we developed a microbiota antigen microarray to characterize microbial antibody reactivity, particularly to human-derived microbiota flagellins, in inflammatory bowel disease., Methods: Sera from healthy volunteers (n = 87) at the University of Alabama at Birmingham and from patients recruited from the Kirklin Clinic of University of Alabama at Birmingham Hospital, including patients with Crohn's disease (n = 152) and ulcerative colitis (n = 170), were individually probed against microbiota bacterial flagellins of both mouse and human origin and analyzed for IgG and IgA antibody responses. Circulating flagellin-reactive T effector (CD4 + CD154 + ) and T regulatory (CD4 + CD137 + ) cells were isolated and evaluated in selected patients. Resulting adaptive immune responses were compared with corresponding clinical data to determine relevancy to disease behavior., Results: We show that patients with IBD express selective patterns of antibody reactivity to microbiota flagellins. Patients with Crohn's disease, but not patients with ulcerative colitis, display augmented serum IgG to human ileal-localized Lachnospiraceae flagellins, with a subset of patients having high responses to more than 10 flagellins. Elevated responses to CBir1, a mouse Lachnospiraceae flagellin used clinically to diagnose CD, correlated with multi-Lachnospiraceae flagellin reactivity. In this subset of patients with CD, multi-flagellin reactivity was associated with elevated flagellin-specific CD154 + CD45RA - T memory cells, a reduced ratio of flagellin-reactive CD4 + T regulatory to T effector cells, and a high frequency of disease complications., Conclusions: Patients with Crohn's disease display strong adaptive immune response to human-derived Lachnospiraceae flagellins, which may be targeted for prognosis and future personalized therapies., (Copyright © 2021 AGA Institute. Published by Elsevier Inc. All rights reserved.)

Recent advances in complement research have revolutionized our understanding of its role in immune responses. The immunomodulatory features of complement in infections by intracellular pathogens, e.g., viruses, are attracting increasing attention. Thereby, local production and activation of complement by myeloid-derived cells seem to be crucial. We could recently show that C3, a key player of the complement cascade, is required for effective defense against the intracellular bacterium Chlamydia psittaci . Avian zoonotic strains of this pathogen cause life-threatening pneumonia with systemic spread in humans; closely related non-avian strains are responsible for less severe diseases of domestic animals with economic loss. To clarify how far myeloid- and non-myeloid cell-derived complement contributes to immune response and resulting protection against C. psittaci , adoptive bone marrow transfer experiments focusing on C3 were combined with challenge experiments using a non-avian (BSL 2) strain of this intracellular bacterium. Surprisingly, our data prove that for C. psittaci -induced pneumonia in mice, non-myeloid-derived, circulating/systemic C3 has a leading role in protection, in particular on the development of pathogen-specific T- and B- cell responses. In contrast, myeloid-derived and most likely locally produced C3 plays only a minor, mainly fine-tuning role. The work we present here describes authentic, although less pronounced, antigen directed immune responses., 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 Kohn, Lanfermann, Laudeley, Glage, Rheinheimer and Klos.)

The emergence of drug-resistant Mycobacterium tuberculosis (Mtb) stains has escalated the need for developing more efficient drugs and therapeutic strategies against tuberculosis. Here we functionally annotate a secretory mycobacterial asparaginase Rv1538c (MtA) and describe its biochemical properties. MtA primarily existed as dimer along with a minor population of multimers. Circular dichroism and fluorescence spectroscopy demonstrated a compact structure in Tris HCl buffer at pH 8.0. Under these conditions it also displayed optimum activity. It retained ∼40% activity at pH 5.5, supporting its physiological relevance in acidic phagosomal environment. MtA contravened classical Michaelis-Menten kinetics and exhibited product inhibition profile, yielding a K cat of 869.4 s -1 and an apparent K m of 8.36 mM. We report the presence of several antigenic epitopes and a C-terminal YXXXD/E motif in MtA, hinting towards its potential to interact or influence host immune system. This was supported by our observation of morphological changes in MtA-treated human B lymphoblasts. We propose that MtA is a dual purpose enzyme used by Mtb to survive inside its host by; 1) ammonia-mediated neutralization of the phagosomal acidic pH and 2) inducing stress to primary immune cells and compromising the host immune response. Overall, this study contributes to our understanding of the biological role of mycobacterial asparaginase opening avenues for developing effective TB therapeutics., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2021 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.)

Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) was suggested as an entity separate from other types of Hodgkin lymphoma 40 years ago and recognized in the WHO classification in 2001. Based on its relatively benign course with late distant relapses, relation with lymph node hyperplasia with progressively transformed germinal centers, presence of clonal immunoglobulin gene rearrangements with somatic hypermutations and ongoing mutations, and relation with a number of inherited defects affecting the immune system, it has been suspected that NLPHL might be antigen-driven. Recent evidence has shown that cases of IgD-positive NLPHL are associated with infection by Moraxella catarrhalis, a common bacterium in the upper respiratory tract and in lymph nodes. This review summarizes the evidence for NLPHL as a B-cell lymphoma involving follicular T-lymphocytes normally found in germinal centers, its molecular features and relation to inherited immune defects, and its relation and differential diagnosis from similar entities. Finally, it discusses the evidence that in many cases a watch and wait policy might be a viable initial management strategy. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd., (© 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

Dendritic cells (DC) are the most important antigen-presenting cells, which guide T cell activation and function, and dysregulated DC function might be one of the crucial causes of inflammatory bowel disease (IBD). It has been well-known that microbiota and their metabolites play an essential role in regulating the biology and function of DC, thus contributing to the pathogenesis of IBD. However, the underlying mechanisms remain largely unknown. Amphiregulin (AREG), a molecule of the epidermal growth factor (EGF) family, is primarily described as an epithelial cell-derived cytokine and recognized as a critical regulator of cell proliferation and tissue repair. Here, we found that DC expression of AREG depended on butyrate (a microbiota-derived short chained fatty acid), which required the interaction between butyrate and G-protein-coupled receptor 43 (GPR43). Furthermore, we found that butyrate-GPR43 interaction failed to induce AREG expression in DC deficient in B lymphocyte induced maturation protein 1 (Blimp-1). Notably, DC-derived AREG was indispensable for the protection against experimental colitis in mice. Additionally, AREG expression was significantly decreased in DC from IBD patients. Our data provide novel evidences to interpret how AREG expression is regulated in DC, and shed new light on the mechanisms whereby microbiota regulate DC function., Competing Interests: Declaration of competing interest The authors have declared that no conflict of interest exists., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Mycoplasma genitalium is a sexually transmitted bacterial pathogen that infects men and women. Antigenic variation of MgpB and MgpC, the immunodominant adherence proteins of M. genitalium, is thought to contribute to immune evasion and chronic infection. We investigated the evolution of mgpB and mgpC sequences in men with non-gonococcal urethritis persistently infected with M. genitalium, including two men with anti-M. genitalium antibodies at enrollment and two that developed antibodies during follow-up. Each of the four patients was persistently infected with a different strain type and each patient produced antibodies targeting MgpB and MgpC. Amino acid sequence evolution in the variable regions of MgpB and MgpC occurred in all four patients with changes observed in single and multiple variable regions over time. Using the available crystal structure of MgpC of the G37 type strain we found that predicted conformational B cell epitopes localize predominantly to the variable region of MgpC, amino acids that changed during patient infection lie in these epitopes, and variant amino acids are in close proximity to the conserved sialic acid binding pocket. These findings support the hypothesis that sequence variation functions to avoid specific antibodies thereby contributing to persistence in the genital tract., Competing Interests: The authors have declared that no competing interests exist.

Emerging evidences indicated that the dysbiosis of microbiota was related to the onset of systemic lupus erythematosus (SLE). Bacteroides fragilis (B. fragilis) ATCC 25285, a human commensal, was discovered to improve inflammatory diseases. However, whether B. fragilis (ATCC 25285) has the beneficial effects on the treatment of lupus nephritis has still remained elusive. In the present study, oral treatment with B. fragilis (ATCC 25285) ameliorated the activity of MRL/lpr mice, including decreased levels of autoantibodies and symptoms of lupus nephritis. Furthermore, we demonstrated that treatment with B. fragilis (ATCC 25285) could promote CD1d expression in B cells by Est-1 pathway, while inhibit CD86 expression via SHP-2 signaling pathway to repair the immune response of B cells in MRL/lpr mice. In addition, our findings revealed a possible role of treatment with B. fragilis (ATCC 25285) in relieving intestinal inflammation in MRL/lpr mice. Meanwhile, it was uncovered that B. fragilis (ATCC 25285) restored the Th17/Treg balance in MRL/lpr mice that was consistent with the role of B. fragilis in other autoimmune diseases. Overall, the current study may highlight the potential application of B. fragilis (ATCC 25285) to treat manifestations of SLE in high-risk individuals., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Clostridioides difficile is a leading cause of nosocomial infection responsible for significant morbidity and mortality with limited options for therapy. Secreted C. difficile toxin B (TcdB) is a major contributor to disease pathology, and select TcdB-specific Abs may protect against disease recurrence. However, the high frequency of recurrence suggests that the memory B cell response, essential for new Ab production following C. difficile reexposure, is insufficient. We therefore isolated TcdB-specific memory B cells from individuals with a history of C. difficile infection and performed single-cell deep sequencing of their Ab genes. Herein, we report that TcdB-specific memory B cell-encoded antibodies showed somatic hypermutation but displayed limited isotype class switch. Memory B cell-encoded mAb generated from the gene sequences revealed low to moderate affinity for TcdB and a limited ability to neutralize TcdB. These findings indicate that memory B cells are an important factor in C. difficile disease recurrence.

Recent studies have demonstrated that induction of a diverse repertoire of memory T cells ("immune education") affects responses to murine cecal ligation and puncture (CLP), the most widely - used animal model of sepsis. Among the documented effects of immune education on CLP are changes in T cell, macrophage and neutrophil activity, more pronounced organ dysfunction and reduced survival. Little is known, however, about the effects of CLP on B cell responses, and how these responses might be altered by immune education. Importantly, effective B cell responses are modulated by IL21 produced by CD4 + /CXCR5 + /PD1 + T follicular helper (Tfh) cells. We examined the B cell population in control and immune educated mice 24 h and 60 days after CLP. Education alone increased Tfh cells. Twenty-four hours after CLP, Tfh cells were depleted. However, this reduction was less pronounced in immune educated mice than in controls and the percentage of CD4 T cells expressing a Tfh phenotype increased in the animals. CLP did not alter splenic architecture and decreased numbers of follicular, marginal, and germinal center B cells. CLP induced changes were not, however, noted following CLP in immune educated mice. At 60 days post - CLP, numbers of follicular, germinal center and marginal zone B cells were increased; this increase was more pronounced in immune educated mice. Finally, while CLP reduced the induction of antigen specific B cells in controls, this response was maintained following CLP in immune educated mice. Our data suggest that preexisting Tfh assists in rescuing the B cell response to CLP., (Copyright © 2020 Taylor, Brewer, Nedeljkovic-Kurepa, Yang, Reddy, Abraham, Barnes and Deutschman.)

Edwardsiella ictaluri causes enteric septicemia of catfish. Our group developed two E. ictaluri live attenuated vaccines (LAVs). However, their effects on the innate functions of catfish B cells are still unexplored. We evaluated phagocytosis and killing of wild-type (WT) E. ictaluri opsonized with sera from vaccinated fish and the survival of B cells exposed to E. ictaluri strains. We assessed phagocytosis of the opsonized WT at 30 °C and 4 °C. B cells killed the internalized E. ictaluri opsonized with sera from vaccinated fish with LAVs more efficiently than other groups at 30 °C. However, catfish B cells were unable to destroy E. ictaluri at 4 °C. Furthermore, E. ictaluri opsonized with serum from fish exposed to WT induce apoptosis and decreased live B cells numbers. Results indicate that opsonization of E. ictaluri with sera from vaccinated fish enhanced phagocytosis and killing activity in B cells and inhibited apoptotic changes in the infected B cells., Competing Interests: Declaration of competing interest The authors have declared no competing interests., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

We studied the expression of activation markers CD25 and CD69 by blood lymphocytes in white mice vaccinated with Brucella abortus 19 BA in antigen-specific tests in vitro. During incubation of blood lymphocytes with brucellosis polysaccharide-protein antigen, a statistically significant increase in the expression of CD25 by B cells and CD69 by T cells was observed; brucellin increased the expression of CD25 by B and T cells. Comparative analysis of the action of antigen preparations B. abortus showed that only brucellin has antigen-specific activity against CD19 + CD25 + cells. The used method can be considered as a promising test for evaluation of the effectiveness of brucellosis immunoprophylaxis, which substantiates the need for further research.

Chlamydia bacteria are obligate intracellular pathogens which can cause a variety of disease in humans and other vertebrate animals. To successfully complete its life cycle, Chlamydia must evade both intracellular innate immune responses and adaptive cytotoxic T cell responses. Here, we report on the role of the chlamydial lipooligosaccharide (LOS) in evading the immune response. Chlamydia infection is known to block the induction of apoptosis. However, when LOS synthesis was inhibited during Chlamydia trachomatis infection, HeLa cells regained susceptibility to apoptosis induction following staurosporine treatment. Additionally, the delivery of purified LOS to the cytosol of cells increased the levels of the antiapoptotic protein survivin. An increase in survivin levels was also detected following C. trachomatis infection, which was reversed by blocking LOS synthesis. Interestingly, while intracellular delivery of lipopolysaccharide (LPS) derived from Escherichia coli was toxic to cells, LOS from C. trachomatis did not induce any appreciable cell death, suggesting that it does not activate pyroptosis. Chlamydial LOS was also a poor stimulator of maturation of bone marrow-derived dendritic cells compared to E. coli LPS. Previous work from our group indicated that LOS synthesis during infection was necessary to alter host cell antigen presentation. However, direct delivery of LOS to cells in the absence of infection did not alter antigenic peptide presentation. Taken together, these data suggest that chlamydial LOS, which is remarkably conserved across the genus Chlamydia , may act both directly and indirectly to allow the pathogen to evade the innate and adaptive immune responses of the host., (Copyright © 2020 American Society for Microbiology.)

Background: CD19 + IL-10 + B cells are considered as a particular subset of immunosuppressive cells by producing interleukin 10 (IL-10), which plays an important role in infectious and autoimmune diseases. The aim of this study was to determine the number of CD19 + IL-10 + B cells in Helicobacter pylori (H. pylori) positive patients in comparison with H. pylori negative patients, and to determine the association with different clinical outcomes, such as gastritis and peptic ulcer disease (PUD), in infected patients., Methods and Materials: We studied 25 infected patients with gastritis, 25 infected patients with PUD, and 25 patients negative for H. pylori. The number of CD19 + IL-10 + B cells was determined by immunofluorescence., Results: The number of CD19 + IL-10 + B cells in patients infected with H. pylori was significantly 2.5-fold higher than uninfected patients (P < 0.0001). Also, the number of CD19 + IL-10 + B cells in infected patients with gastritis was significantly 1.45-fold elevated compared to infected patients with PUD (P = 0.001)., Conclusions: These results demonstrate that the increased number of CD19 + IL-10 + B cells in infected patients and its association with other cells may play an important role in the pathogenesis of H. pylori infection., (Copyright © 2020 Southern Society for Clinical Investigation. Published by Elsevier Inc. All rights reserved.)

The obligate intracellular bacterium Chlamydia trachomatis causes the most prevalent bacterial sexually transmitted infection worldwide. CD4 T cells play a central role in the protective immunity against Chlamydia female reproductive tract (FRT) infection, while B cells are thought to be dispensable for resolution of primary Chlamydia infection in mouse models. We recently reported an unexpected requirement of B cells in local Chlamydia-specific CD4 T-cell priming and bacterial containment within the FRT. Here, we sought to tackle the precise effector function of B cells during Chlamydia primary infection. Using mixed bone marrow chimeras that lack B-cell-dependent Ag presentation (MHCII B - / - ) or devoid of circulating antibodies (AID -/- × μS -/- ), we show that Chlamydia-specific CD4 T-cell expansion does not rely on Ag presentation by B cells. Importantly, we demonstrate that antibody, but not B-cell-dependent Ag presentation, is required for preventing systemic bacterial dissemination following Chlamydia FRT infection., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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.

An effective vaccine against Staphylococcus aureus infection is a major planetary heath priority, particularly with increasing antibiotic resistance worldwide. Previous efforts for a highly effective S. aureus vaccine were largely unsuccessful, in part, because the vaccine designs have tended to target mainly the B cell immunity and development of opsonic antibodies. In contrast, recent observations suggest that cell mediated immunity may be critical for protection against S. aureus . In addition, the S. aureus surface proteins are among the key immunodominant antigens because they are the first molecules to interact with the host organism cells and tissues. We report here an original vaccinomics study in which we used a reverse vaccinology and immunoinformatics in silico strategy integrated with genomics. After analyzing 2767 proteins, we defined 16 proteins of S. aureus as promising subunit vaccine candidates. Phosphatidylinositol phosphodiesterase (Plc) is secreted by extracellular pathogens such as S. aureus . We mapped the B and T cell epitopes for the Plc protein, tested the reactivity of the synthesized epitopes by Western blotting, and verified our findings in a pilot study of 10 patients with S. aureus infection. The peptides were then tested for their protective effect in groups of mice challenged with pathogenic S. aureus strain, which showed high protection level. These findings warrant further translational research for development of novel vaccines against S. aureus infection. Reverse vaccinology is an advanced approach that can be applied to identify new vaccine candidates against a host of microorganisms, including S. aureus .

Signalling lymphocyte activation molecule family member 9 (SLAMF9) is an orphan receptor of the CD2/SLAM family of leucocyte surface proteins. Examination of SLAMF9 expression and function indicates that SLAMF9 promotes inflammation by specialized subsets of antigen-presenting cells. Within healthy liver and circulating mouse peripheral blood mononuclear cells, SLAMF9 is expressed on CD11b + , Ly6C - , CD11c low , F4/80 low , MHC-II + , CX 3 CR1 + mononuclear phagocytes as well as plasmacytoid dendritic cells. In addition, SLAMF9 can be found on peritoneal B1 cells and small (F4/80 low ), but not large (F4/80 high ), peritoneal macrophages. Upon systemic challenge with Salmonella enterica Typhimurium, Slamf9 -/- mice were impaired in their ability to clear the infection from the liver. In humans, SLAMF9 is up-regulated upon differentiation of monocytes into macrophages, and lipopolysaccharide stimulation of PMA-differentiated, SLAMF9 knockdown THP-1 cells showed an essential role of SLAMF9 in production of granulocyte-macrophage colony-stimulating factor, tumour necrosis factor-α, and interleukin-1β. Taken together, these data implicate SLAMF9 in the initiation of inflammation and clearance of bacterial infection., (© 2019 The Authors. Immunology published by John Wiley & Sons Ltd.)

Although mouse infection models have been extensively used to study the host response to Mycobacterium tuberculosis, their validity in revealing determinants of human tuberculosis (TB) resistance and disease progression has been heavily debated. Here, we show that the modular transcriptional signature in the blood of susceptible mice infected with a clinical isolate of M. tuberculosis resembles that of active human TB disease, with dominance of a type I interferon response and neutrophil activation and recruitment, together with a loss in B lymphocyte, natural killer and T cell effector responses. In addition, resistant but not susceptible strains of mice show increased lung B cell, natural killer and T cell effector responses in the lung upon infection. Notably, the blood signature of active disease shared by mice and humans is also evident in latent TB progressors before diagnosis, suggesting that these responses both predict and contribute to the pathogenesis of progressive M. tuberculosis infection.

Background: Cytotoxic T lymphocyte-associated antigen-4-Ig (CTLA-4-Ig) competes with CD28 for binding CD80/CD86 on antigen-presenting cells (APCs) to limit T cell activation. B cells are believed to be important APCs in the pathogenesis of autoimmune diseases and express CD80/CD86 after activation; however, relatively little is known about the effect of CTLA-4-Ig on B cells. This study tested the impact of CTLA-4-Ig on human B cell responses., Methods: Human blood B cells were purified from healthy donors and activated in the presence of CTLA-4-Ig or the L6-Ig control protein in vitro. RT-q-PCR and immunofluorescence staining were performed to detect activation marker expression. ELISA was conducted to measure cytokine secretion. The CD80/CD86 levels on the surface of the memory B cells in the blood of 18 patients with rheumatoid arthritis (RA) were detected using immunofluorescence staining., Results: CTLA-4-Ig suppressed the expression of Staphylococcus aureus (SAC)-induced CD80, CD86, TNFA, and IL6 in human B cells at the transcriptional level. Furthermore, CTLA-4-Ig concomitantly decreased SAC-induced CD80/CD86 surface expression on and TNF-α and IL-6 secretion from B cells. On the other hand, T cell-dependent (TD) stimulation-induced B cell activation, proliferation, plasma cell differentiation, and antibody secretion were not affected by CTLA-4-Ig. As expected, TD stimulation-induced surface CD80 was hindered by CTLA-4-Ig. Notably, a blockade of CD80/CD86 on the surface of the memory B cells was observed in the patients with RA after abatacept (CTLA-4-Ig) treatment. In a portion of the RA patients, restoration of CD80/CD86 staining on the surface of the memory B was detected starting in the 3rd month of abatacept treatment. Interestingly, the surface levels of CD80/CD86 on the patients' memory B cells positively correlated with disease activity., Conclusions: We found that CTLA-4-Ig directly suppressed SAC-induced B cell activation in vitro. Obstruction of CD80 and CD86 on the surface of the memory B cells was detected in the RA patients after abatacept treatment. Blocking CD80/CD86 on B cells by CTLA-4-Ig may hinder T cell activation and associated with the disease activity of RA in vivo. Our findings indicate that CTLA-4-Ig may regulate humoral responses by modulating B cell activation and interfering T cell-B cell interaction.

Mycobacterium tuberculosis is the main etiological agent of tuberculosis. The Bacillus Calmette-Guérin (BCG) microbes that are primarily used as a vaccine against tuberculosis also constitute the dominant infection model for studying the interaction of mycobacteria with the host cell types. The majority of interaction experiments have been conducted using macrophages and monocytes as prototype phagocyte cell types. Here, we report that M. bovis BCG infects mouse primary B cells as well as human B cell line. The complement receptors, along with B cell receptors, are engaged in the process of bacterial entry into the host B cells. Once inside the B cells, the intracellular trafficking of BCG follows the complete endocytic pathway of the ingested particles, which is in contrast to the events taking place during ingestion of BCG by macrophages. In vivo infection of mice with M. bovis BCG activated peritoneal as well as splenic B cells to produce proinflammatory cytokines. This paper further supports the evidence that B cells are involved in a host's early interactions with intracellular bacterial pathogens and participate in the induction of innate defense responses., (Copyright © 2019. Published by Elsevier Ltd.)

Human immunodeficiency virus (HIV) infection is associated with greatly increased risk for development of non-Hodgkin lymphoma (NHL). Nearly all acquired immunodeficiency syndrome (AIDS)-associated NHL (AIDS-NHL) is of B-cell origin. Two major mechanisms are believed to contribute to the genesis of AIDS-NHL: (1) loss of immunoregulation of Epstein-Barr virus (EBV)+ B cells, resulting from impaired T-cell function late in the course of HIV disease and (2) chronic B-cell activation, leading to DNA-modifying events that contribute to oncogene mutations/ translocations. HIV infection has long been known to be associated with chronic inflammation and polyclonal B-cell activation, and more recently, microbial translocation. Microbial translocation is bacterial product leakage from gut lumen into the peripheral circulation, resulting in high levels of lipopolysaccharide (LPS) in the peripheral circulation, leading to chronic immune activation and inflammation. We review recent literature linking microbial translocation to lymphom-agenesis. This includes epidemiological studies of biomarkers of microbial translocation with risk of AIDS-NHL and emerging data on the mechanisms by which microbial translocation may lead to AIDS-NHL development.

B lymphocytes must respond to vast numbers of foreign antigens, including those of microbial pathogens. To do so, developing B cells use combinatorial joining of V-, D-, and J-gene segments to generate an extraordinarily diverse repertoire of B-cell antigen receptors (BCRs). Unsurprisingly, a large fraction of this initial BCR repertoire reacts to self-antigens, and these "forbidden" B cells are culled by immunological tolerance from mature B-cell populations. While culling of autoreactive BCRs mitigates the risk of autoimmunity, it also opens gaps in the BCR repertoire, which are exploited by pathogens that mimic the forbidden self-epitopes. Consequently, immunological tolerance, necessary for averting autoimmune disease, also acts to limit effective microbial immunity. In this brief review, we recount the evidence for the linkage of tolerance and impaired microbial immunity, consider the implications of this linkage for vaccine development, and discuss modulating tolerance as a potential strategy for strengthening humoral immune responses., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

In 1993, I reported that Coxiella burnetii transforms human B cells into hairy cells (cbHCs), the first hairy cell reported outside of hairy cell leukemia (HCL). Over last few decades, advances in molecular biology have provided evidence supporting that C. burnetii induces hairiness and inhibits the apoptosis of host cells. The present review summarizes new information in support of cbHC. C. burnetii was shown to induce reorganization of the cytoskeleton and to inhibit apoptosis in host cells. Peritoneal B1a cells were found to be permissive for virulent C. burnetii Nine Mile phase I (NMI) strains in mice. C. burnetii severely impaired E-cad expression in circulating cells of Q fever patients. B-cell non-Hodgkin lymphoma was linked to C. burnetii . Mutation of BRAF V600E was pronounced in HCL, but "hairiness" was not linked to the mutation. Risk factors shared among coxiellosis and HCL in humans and animals were reported in patients with Q-fever. Accordingly, I propose that C. burnetii induces reorganization of the cytoskeleton and inhibits apoptosis as cytopathic effects that are not target cell specific. The observed hairiness in cbHC appears to be a fixed image of dynamic nature, and hairy cells in HCL are distinct among lymphoid cells in circulation. As the cytoskeleton plays key roles in maintaining cell structural integrity in health and disease, the pathophysiology of similar cytopathic effects should be addressed in other diseases, such as myopathies, B-cell dyscrasias, and autoimmune syndromes., Competing Interests: The author has no potential conflicts of interest to disclose., (© Copyright: Yonsei University College of Medicine 2019.)

Commensal microbiota modulates the anti-tumor immune response and alters the tumor infiltration of T cells in numerous human malignancies. Moreover, the existence of commensals and microbial metabolites has been directly observed inside numerous epithelial tumors. Their effects on the host immune system, independent of the pre-existing malignancy, are not completely understood. To resolve this issue, we compared immune modulatory roles of the fecal bacteria from healthy individuals and the fecal bacteria from colorectal cancer (CRC) patients. Peripheral blood mononuclear cells that were provided by healthy donors were used as study systems. Overall, fecal bacteria could potently activate the degranulation and cytotoxicity of CD8 + T cells. Interestingly, fecal bacteria from CRC patients in general induced higher degranulation and higher cytotoxicity than fecal bacteria from healthy individuals. These effects were dependent on the presence of antigen-presenting cells, such as monocytes and B cells, as fecal bacteria added directly to isolated CD8 + T cells failed to induce high cytotoxicity. Additionally, fecal bacteria from CRC patients induced stronger upregulation of CD80 and NOS2 expression in monocytes than fecal bacteria from healthy individuals. On the other hand, the viability of CD8 + T cells was significantly reduced with increasing levels of bacterial stimulation. Overall, we demonstrated that fecal bacteria from CRC patients could upregulate degranulation and cytotoxicity of CD8 + T cells in a manner that was dependent on antigen-presenting cells, and was more proinflammatory than fecal bacteria from healthy individuals., (Copyright © 2019. Published by Elsevier Inc.)

The generation of robust systemic and mucosal antibody and cell-mediated immune (CMI) responses that are protective, long-lasting, and can quickly be recalled upon subsequent re-exposure to the cognate antigen is the key to the development of effective vaccine candidates. These responses, whether they represent mechanistic or non-mechanistic immunological correlates of protection, usually entail the activation of T cell memory and effector subsets (T-CMI) and induction of long-lasting memory B cells. However, for ETEC and Shigella, the precise role of these key immune cells in primary and secondary (anamnestic) immune responses remains ill-defined. A workshop to address immune correlates for ETEC and Shigella, in general, and to elucidate the mechanistic role of T-cell subsets and B-cells, both systemically and in the mucosal microenvironment, in the development of durable protective immunity against ETEC and Shigella was held at the recent 2nd Vaccines against Shigella and ETEC (VASE) conference in June 2018. This report is a summary of the presentations and the discussion that ensued at the workshop., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

It is well established that B cells play an important role during infections beyond antibody production. B cells produce cytokines and are APCs for T cells. Recently, it has become clear that several pathogenic bacterial genera, such as Salmonella, Brucella, Mycobacterium, Listeria, Francisella, Moraxella, and Helicobacter, have evolved mechanisms such as micropinocytosis induction, inflammasome down-regulation, inhibitory molecule expression, apoptosis induction, and anti-inflammatory cytokine secretion to manipulate B cell functions influencing immune responses. In this review, we summarize our current understanding of B cells as targets of bacterial infection and the mechanisms by which B cells become a niche for bacterial survival and replication away from extracellular immune responses such as complement and antibodies., (©2019 Society for Leukocyte Biology.)

Tetragenococcus halophilus is a halophilic lactic acid bacterium that exists in the traditional Japanese seasoning miso-a fermented soy paste. Considering the popularity of miso as a component of healthy diet, we attempted to evaluate the immunoregulatory functions of T. halophilus spices isolated from miso. We screened 56 strains that facilitated the upregulation of activation markers such as CD86 and CD69 on B cells and T cells in vitro. Of these, 7 strains (Nos. 1, 3, 13, 15, 19, 30, and 31) were found to preferentially induce the CD86 expression on B cells. Furthermore, DNA microarray analysis revealed that T. halophilus strain No. 1 significantly augmented the gene expressions of CD86, CD70, IL-10, INF-γ, and IL-22 in B cells. We confirmed these results at the protein level by flow cytometry. Mice feeding diet containing 1% T. halophilus No. 1 exhibited significantly greater IgA production in the serum. Furthermore, a diet containing 1% T. halophilus No. 1 augmented ovoalbumin (OVA)-specific IgG titer in mice upon OVA/alum immunization. Thus, we demonstrated that T. halophilus No. 1 is a strong immunomodulatory strain with potential as a probiotic., Competing Interests: This study was financially supported by Ichibiki CO., LTD. (http://www.ichibiki.co.jp/). T.K. A.N. and N.A. are employees of Ichibiki CO., LTD. The heat-killed LAB strains used for this study were provided by Ichibiki CO., LTD. We have applied for a patent on a modal halotolerance LAB and the cultivation (WO2018/047979), and in Japan, a patent was acquired (Japanese patent No. 6337262), and T. halophilus strain No.1 was commercialized under T. halophilus strain KURAHANA LTK-1 by Ichibiki CO., LTD. These does not alter our adherence to PLOS ONE policies on sharing data and materials.

Endogenous circular RNAs (circRNAs) have been reported in various diseases. However, their role in active TB remains unknown. The study was aimed to determine plasma circRNA expression profile to characterize potential biomarker and improve our understanding of active TB pathogenesis. CircRNA expression profiles were screened by circRNA microarrays in active TB plasma samples. Dysregulated circRNAs were then verified by qRT-PCR. CircRNA targets were predicted based on analysis of circRNA-miRNA-mRNA interaction. GO and KEGG pathway analyses were used to predict the function of circRNA. ROC curve was calculated to evaluate diagnostic value for active TB. A total of 75 circRNAs were significantly dysregulated in active TB plasma. By further validation, hsa&#95;circRNA&#95;103571 exhibited significant decrease in active TB patients and showed potential interaction with active TB-related miRNAs such as miR-29a and miR-16. Bioinformatics analysis revealed that hsa&#95;circRNA&#95;103571 was primarily involved in ras signalling pathway, regulation of actin cytoskeleton, T- and B-cell receptor signalling pathway. ROC curve analysis suggested that hsa&#95;circRNA&#95;103571 had significant value for active TB diagnosis. Circulating circRNA dysregulation may play a role in active TB pathogenesis. Hsa&#95;circRNA&#95;103571 may be served as a potential biomarker for active TB diagnosis, and hsa&#95;circRNA&#95;103571-miRNA-mRNA interaction may provide some novel mechanism for active TB., (© 2018 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.)

Host-microbiota mutualism has been established during long-term co-evolution. A diverse and rich gut microbiota plays an essential role in the development and maturation of the host immune system. Education of the adaptive immune compartment by gut microbiota antigens is important in establishing immune balance. In particular, a critical time frame immediately after birth provides a 'window of opportunity' for the development of lymphoid structures, differentiation and maturation of T and B cells and, most importantly, establishment of immune tolerance to gut commensals. Depending on the colonization niche, antigen type and metabolic property of different gut microbes, CD4 T-cell responses vary greatly, which results in differentiation into distinct subsets. As a consequence, certain bacteria elicit effector-like immune responses by promoting the production of pro-inflammatory cytokines such as interferon-γ and interleukin-17A, whereas other bacteria favour the generation of regulatory CD4 T cells and provide help with gut homeostasis. The microbiota have profound effects on B cells also. Gut microbial exposure leads to a continuous diversification of B-cell repertoire and the production of T-dependent and -independent antibodies, especially IgA. These combined effects of the gut microbes provide an elegant educational process to the adaptive immune network. Contrariwise, failure of this process results in a reduced homeostasis with the gut microbiota, and an increased susceptibility to various immune disorders, both inside and outside the gut. With more definitive microbial-immune relations waiting to be discovered, modulation of the host gut microbiota has a promising future for disease intervention., (© 2018 John Wiley & Sons Ltd.)

The immune system not only provides protection against infectious disease but also contributes to the etiology of neoplastic, atopic, and cardiovascular and metabolic diseases. Prenatal and postnatal nutritional and microbial environments have lasting effects on multiple aspects of immunity, indicating that immune processes may play important roles in the developmental origins of disease. The objective of this study is to evaluate the association between birth weight and the distribution of leukocyte (white blood cell) subsets in peripheral blood in young adulthood. Postnatal microbial exposures were also considered as predictors of leukocyte distribution. Participants (n=486; mean age=20.9 years) were drawn from a prospective birth cohort study in the Philippines, and analyses focused on the following cell types: CD4 T lymphocytes, CD8 T lymphocytes, B lymphocytes, natural killer cells, monocytes, granulocytes. Higher birth weight was a strong predictor of higher proportion of CD4 T lymphocytes (B=0.12, s.e.=0.041, P=0.003), lower proportion of CD8 T lymphocytes (B=-0.874, s.e.=0.364, P=0.016), higher CD4:CD8 ratio (B=1.964, s.e.=0.658, P=0.003), and higher B lymphocytes (B=0.062, s.e.=0.031, P=0.047). Measures of microbial exposure in infancy were negatively associated with proportions of B lymphocytes and granulocytes, and lower CD4:CD8 ratio. Leukocytes are the key regulators and effectors of innate and specific immunity, but the origins of variation in the distribution of cell type across individuals are not known. Our findings point toward nutritional and microbial exposures in infancy as potentially important determinants of immune-phenotypes in adulthood, and they suggest that leukocyte distribution is a plausible mechanism through which developmental environments have lasting effects on disease risk in adulthood.

A fundamental question in human susceptibility to bacterial infections is to what extent variability is a function of differences in the pathogen species or in individual humans. To focus on the pathogen species, we compared in the same individual the human adaptive T and B cell immune response to multiple strains of two major human pathogens, Staphylococcus aureus and Streptococcus pyogenes. We found wide variability in the acute adaptive immune response induced by various strains of a species, with a unique combination of activation within the two arms of the adaptive response. Further, this was also accompanied by a dramatic difference in the intensity of the specific protective T helper (Th) response. Importantly, the same immune response differences induced by the individual strains were maintained across multiple healthy human donors. A comparison of isogenic phage KO strains, demonstrated that of the pangenome, prophages were the major contributor to inter-strain immune heterogeneity, as the T cell response to the remaining "core genome" was noticeably blunted. Therefore, these findings extend and modify the notion of an adaptive response to a pathogenic bacterium, by implying that the adaptive immune response signature of a bacterial species should be defined either per strain or alternatively to the species' 'core genome', common to all of its strains. Further, our results demonstrate that the acquired immune response variation is as wide among different strains within a single pathogenic species as it is among different humans, and therefore may explain in part the clinical heterogeneity observed in patients infected with the same species.

Multiple sclerosis (MS) is the prototypic complex disease, in which both genes and the environment contribute to its pathogenesis. To date, > 200 independent loci across the genome have been associated with MS risk. However, these only explain a fraction of the total phenotypic variance, suggesting the possible presence of additional genetic factors, and, most likely, also environmental factors. New DNA sequencing technologies have enabled the sequencing of all kinds of microorganisms, including those living in and around humans (i.e., microbiomes). The study of bacterial populations inhabiting the gut is of particular interest in autoimmune diseases owing to their key role in shaping immune responses. In this review, we address the potential crosstalk between B cells and the gut microbiota, a relevant scenario in light of recently approved anti-B-cell therapies for MS. In addition, we review recent efforts to characterize the gut microbiome in patients with MS and discuss potential challenges and future opportunities. Finally, we describe the international MS microbiome study, a multicenter effort to study a large population of patients with MS and their healthy household partners to define the core MS microbiome, how it is shaped by disease-modifying therapies, and to explore potential therapeutic interventions.

B cells are a target of Salmonella infection, allowing bacteria survival without inducing pyroptosis. This event is due to downregulation of Nlrc4 expression and lack of inflammasome complex activation, which impairs the secretion of IL-1β. YAP phosphorylation is required for downregulation of Nlrc4 in B cells during Salmonella infection; however, the microorganism's mechanisms underlying the inhibition of the NLRC4 inflammasome in B cells are not fully understood. Our findings demonstrate that the Salmonella effector SopB triggers a signaling cascade involving PI3K, PDK1 and mTORC2 that activates Akt with consequent phosphorylation of YAP. When we deleted sopB in Salmonella, infected B cells that lack Rictor, or inhibited the signaling cascade using a pharmacological approach, we were able to restore the function of the NLRC4 inflammasome in B cells and the ability to control the infection. Furthermore, B cells from infected mice exhibited activation of Akt and YAP phosphorylation, suggesting that Salmonella also triggers this pathway in vivo. In summary, our data demonstrate that the Salmonella effector inositide phosphate phosphatase SopB triggers the PI3K-Akt-YAP pathway to inhibit the NLRC4 inflammasome in B cells. This study provides further evidence that Salmonella triggers cellular mechanisms in B lymphocytes to manipulate the host environment by turning it into a survival niche to establish a successful infection.

Human and animal pathogens are able to circumvent, at least temporarily, the sophisticated immune defenses of their hosts. Several serovars of the Gram-negative bacterium Salmonella enterica have been used as models for the study of pathogen-host interactions. In this review we discuss the strategies used by Salmonella to evade or manipulate three levels of host immune defenses: physical barriers, innate immunity and adaptive immunity. During its passage through the digestive system, Salmonella has to face the acidic pH of the stomach, bile and antimicrobial peptides in the intestine, as well as the competition with resident microbiota. After host cell invasion, Salmonella manipulates inflammatory pathways and the autophagy process. Finally, Salmonella evades the adaptive immune system by interacting with dendritic cells, and T and B lymphocytes. Mechanisms allowing the establishment of persistent infections are also discussed.

This study aimed to design a novel chimeric protein in silico to serve as a serotype-independent vaccine candidate against Shigella. The chimera contains amino acid residues 240-460 of Shigella invasion plasmid antigen B (IpaB) and the C-terminus of Clostridium perfringens enterotoxin (C-CPE). Amino acid sequences of 537 peptide linkers were obtained from two protein linker databases. 3D structures of IpaB-CPE 290-319 , IpaB-CPE 184-319 , IpaB-CPE 194-319 and 537 newly designed IpaB-linker-CPE 290-319 constructs with varying linker regions were predicted. These predicted 3D structures were merged with the 3D structures of native IpaB 240-460 , CPE 194-319 , CPE 184-319 and CPE 290-319 to select the structure most similar to native IpaB and C-CPE. Several in silico tools were used to determine the suitability of the selected IpaB-C-CPE structure as a vaccine candidate. None of the 537 linkers was capable of preserving the native structure of CPE 290-319 within the IpaB-linker-CPE 290-319 structure. In silico analysis determined that the IpaB-CPE 194-319 3D structure was the most similar to the 3D structure of the respective native CPE domain and that it was a stable chimeric protein exposing multiple B-cell epitopes. IpaB-CPE 194-319 was designed for its capability to bind to human intestinal epithelial and M cells and to accumulate on these cells. The predicted B-cell epitopes are likely to be capable of inducing a mucosal antibody response in the human intestine against Shigella IpaB. This study also showed that the higher binding affinities of CPE 184-319 and CPE 194-319 to claudin molecules than those of CPE 290-319 is the result of preserving the 3D structures of CPE 184-319 and CPE 194-319 when they are linked to the C-termini of other proteins.

Organ tissue damage is a key contributor to host morbidity and mortality following infection with microbial agents. Severe immune responses, excessive cellular recruitment and necrosis of cells all play a role in disease pathology. Understanding the pathogenesis of disease can aid in identifying potential new therapeutic targets or simply act as a diagnostic tool. Burkholderia pseudomallei is a Gram-negative bacterium that can cause acute and chronic diseases. The BALB/c mouse has been shown to be highly susceptible to aerosol challenge with B. pseudomallei and hence acts as a good model to study the acute and potentially lethal form of the disease melioidosis. In our study, BALB/c mice were challenged and culled at predetermined time points to generate a pathological time course of infection. Lung, liver and spleen were subjected to pathological and immunohistochemical analysis. The number and type of microscopic lesions within each organ, as well as the location and the mean percentage of neutrophils, B cells, T cells and Burkholderia capsule antigen within the lesions, were all characterized during the time course. Neutrophils were determined as the key player in tissue pathology and generation of lesions, with B cells playing an insignificant role. This detailed pathological assessment increases our understanding of B. pseudomallei disease., (© 2018 Crown copyright. International Journal of Experimental Pathology published by John Wiley & Sons Ltd on behalf of Company of the International Journal of Experimental Pathology (CIJEP). This article is published with the permission of the Controller of HMSO and the Queen’s Printer for Scotland.)

Many studies have demonstrated that the inflamed mucosa of Crohn's disease (CD) patients presented a disturbed gut commensal community, and the shift in microbial composition and species variety is associated with disease severity. To establish a link between changes in the intestinal bacterial composition and the alteration of inflammation, we obtained fecal bacteria from CD patients and non-CD controls. The bacteria were then used to stimulate the peripheral blood mononuclear cells (PBMCs) from one non-CD individual. We found that the frequency of IFN-γ- and IL-17-expressing CD4 T cells was significantly higher after stimulation with CD bacteria than with non-CD bacteria, while the frequency of IL-4- and IL-10-expressing CD4 T cells was significantly decreased after stimulation with CD bacteria. A similar trend was observed in the level of cytokine expression and transcription expression. However, this difference was not clear-cut, as overlapping regions were observed between the two groups. With longer stimulation using CD bacteria, the skewing toward Th1/Th17 responses were further increased. This increase depended on the presence of monocytes/macrophages. Interestingly, we also found that B cells presented an inhibitory effect in CD bacteria-mediated skewing toward Th1/Th17 cells and promoted IL-10 secretion in CD bacteria-stimulated PBMCs. Together, our results demonstrated that CD bacteria could promote Th1/Th17 inflammation in a host factor-independent fashion., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The Campylobacter jejuni -host interaction may be affected by the host's gut microbiota through competitive exclusion, metabolites, or modification of the immune response. To understand this interaction, C. jejuni colonization and local immune responses were compared in chickens with different gut microbiota compositions. Birds were treated with an antibiotic cocktail (AT) (experiments 1 and 2) or raised under germfree (GF) conditions (experiment 3). At 18 days posthatch (dph), they were orally inoculated either with 10 4 CFU of C. jejuni or with diluent. Cecal as well as systemic C. jejuni colonization, T- and B-cell numbers in the gut, and gut-associated tissue were compared between the different groups. Significantly higher numbers of CFU of C. jejuni were detected in the cecal contents of AT and GF birds, with higher colonization rates in spleen, liver, and ileum, than in birds with a conventional gut microbiota ( P < 0.05). Significant upregulation of T and B lymphocyte numbers was detected in cecum, cecal tonsils, and bursa of Fabricius of AT or GF birds after C. jejuni inoculation compared to the respective controls ( P < 0.05). This difference was less clear in birds with a conventional gut microbiota. Histopathological gut lesions were observed only in C. jejuni -inoculated AT and GF birds but not in microbiota-colonized C. jejuni -inoculated hatchmates. These results demonstrate that the gut microbiota may contribute to the control of C. jejuni colonization and prevent lesion development. Further studies are needed to identify key players of the gut microbiota and the mechanisms behind their protective role., (Copyright © 2017 Han et al.)

The spleen is known as an important filter for blood-borne pathogens that are trapped by specialized macrophages in the marginal zone (MZ): the CD209 + MZ macrophages (MZMs) and the CD169 + marginal metallophilic macrophages (MMMs). Acute systemic infection strongly impacts MZ populations and the location of T and B lymphocytes. This phenomenon has been linked to reduced chemokine secretion by stromal cells. Brucella spp. are the causative agent of brucellosis, a widespread zoonotic disease. Here, we used Brucella melitensis infection as a model to investigate the impact of chronic stealth infection on splenic MZ macrophage populations. During the late phase of Brucella infection, we observed a loss of both MZMs and MMMs, with a durable disappearance of MZMs, leading to a reduction of the ability of the spleen to take up soluble antigens, beads, and unrelated bacteria. This effect appears to be selective as every other lymphoid and myeloid population analyzed increased during infection, which was also observed following Brucella abortus and Brucella suis infection. Comparison of wild-type and deficient mice suggested that MZ macrophage population loss is dependent on interferon gamma (IFN-γ) receptor but independent of T cells or tumor necrosis factor alpha receptor 1 (TNF-αR1) signaling pathways and is not correlated to an alteration of CCL19, CCL21, and CXCL13 chemokine mRNA expression. Our results suggest that MZ macrophage populations are particularly sensitive to persistent low-level IFN-γ-mediated inflammation and that Brucella infection could reduce the ability of the spleen to perform certain MZM- and MMM-dependent tasks, such as antigen delivery to lymphocytes and control of systemic infection., (Copyright © 2017 American Society for Microbiology.)

Mucosal-associated invariant T (MAIT) cells are conserved T cells that express a semi-invariant T-cell receptor (Vα7.2 in humans and Vα19 in mice). The development of MAIT cells requires the antigen-presenting MHC-related protein 1 (MR1), as well as commensal bacteria. The mechanisms that regulate the functional expression of MR1 molecules and their loading with bacterial antigen in antigen-presenting cells are largely unknown. We have found that treating B cells with the Toll-like receptor 9 (TLR9) agonist CpG increases MR1 surface expression. Interestingly, activation of TLR9 by CpG-A (but not CpG-B) enhances MR1 surface expression. This is limited to B cells and not other types of cells such as monocytes, T or natural killer cells. Knocking-down TLR9 expression by short hairpin RNA reduces MR1 surface expression and MR1-mediated bacterial antigen presentation. CpG-A triggers early endosomal TLR9 activation, whereas CpG-B is responsible for late endosomal/lysosomal activation of TLR9. Consistently, blocking endoplasmic reticulum to Golgi protein transport, rather than lysosomal acidification, suppressed MR1 antigen presentation. Overall, our results indicate that early endosomal TLR9 activation is important for MR1-mediated bacterial antigen presentation., (© 2017 John Wiley & Sons Ltd.)

An underdeveloped or impaired immune response in young children is associated with increased susceptibility to Streptococcus pneumonia (Spn) infections. We determined serum antibody titers against 3 Spn vaccine candidate proteins and vaccine serotype polysaccharide antigens in a group of Spn infection prone 9-18months old and found lower IgG antibody titers to all tested antigens compared to age-matched non-infection-prone children. We also found the children had significantly reduced percentages of total memory B-cells, switched memory B-cells and plasma cells. We sought a mechanistic explanation for that result by examination of TNF family receptors (TNFRs) TACI, BCMA, and BAFFR receptor expression on B-cells and found significantly lower BAFFR and TACI expression; significantly lower proliferation of B-cells stimulated with exogenous BAFF; and diminished expression of co-stimulatory receptors B7-1 and B7-2 among infection prone vs. non-prone children. We conclude that lower expression of TNFRs, lower proliferation of B-cells in response to BAFF and lower expression of B7-1 and B7-2 by B-cells may contribute to reduced antibody responses to Spn and consequent infection proneness in young children., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Lipophilic copper (Cu)-containing complexes have shown promising antibacterial activity against a range of bacterial pathogens. To examine the susceptibility of the intracellular human pathogen Chlamydia trachomatis to copper complexes containing bis(thiosemicarbazone) ligands [Cu(btsc)], we tested the in vitro effect of CuII-diacetyl- and CuII-glyoxal-bis[N(4)-methylthiosemicarbazonato] (Cu(atsm) and Cu(gtsm), respectively) on C. trachomatis. Cu(atsm) and to a greater extent, Cu(gtsm), prevented the formation of infectious chlamydial progeny. Impacts on host cell viability and respiration were also observed in addition to the Chlamydia impacts. This work suggests that copper-based complexes may represent a new lead approach for future development of new therapeutics against chlamydial infections, although host cell impacts need to be fully explored., (© FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)