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Contains fulltext : 251784.pdf (Publisher’s version ) (Closed access) BACKGROUND: Concerns have been raised regarding the risks of SARS-CoV-2 breakthrough infections in vaccinated patients with immune-mediated inflammatory diseases treated with immunosuppressants, but clinical data on breakthrough infections are still scarce. The primary objective of this study was to compare the incidence and severity of SARS-CoV-2 breakthrough infections between patients with immune-mediated inflammatory diseases using immunosuppressants, and controls (patients with immune-mediated inflammatory diseases not taking immunosuppressants and healthy controls) who had received full COVID-19 vaccinations. The secondary objective was to explore determinants of breakthrough infections of the delta (B.1.617.2) variant of SARS-CoV-2, including humoral immune responses after vaccination. METHODS: In this substudy, we pooled data collected in two large ongoing prospective multicentre cohort studies conducted in the Netherlands (Target to-B! [T2B!] study and Amsterdam Rheumatology Center COVID [ARC-COVID] study). Both studies recruited adult patients (age ≥18 years) with immune-mediated inflammatory diseases and healthy controls. We sourced clinical data from standardised electronic case record forms, digital questionnaires, and medical files. We only included individuals who were vaccinated against SARS-CoV-2. For T2B!, participants were recruited between Feb 2 and Aug 1, 2021, and for ARC-COVID, participants were recruited between April 26, 2020, and March 1, 2021. In this study we assessed data on breakthrough infections collected between July 1 and Dec 15, 2021, a period in which the delta SARS-CoV-2 variant was the dominant variant in the Netherlands. We defined a SARS-CoV-2 breakthrough infection as a PCR-confirmed or antigen test-confirmed SARS-CoV-2 infection that occurred at least 14 days after vaccination. All breakthrough infections during this period were assumed to be due to the delta variant due to its dominance during the study period. We analysed post-vaccination serum samples for anti-receptor binding domain (RBD) antibodies to assess the humoral vaccination response (T2B! study only) and anti-nucleocapsid antibodies to identify asymptomatic breakthrough infections (ARC-COVID study only). We used multivariable logistic regression analyses to explore potential clinical and humoral determinants associated with the odds of breakthrough infections. The T2B! study is registered with the Dutch Trial Register, Trial ID NL8900, and the ARC-COVID study is registered with Dutch Trial Register, trial ID NL8513. FINDINGS: We included 3207 patients with immune-mediated inflammatory diseases who receive immunosuppressants, and 1807 controls (985 patients with immune-mediated inflammatory disease not on immunosuppressants and 822 healthy controls). Among patients receiving immunosuppressants, mean age was 53 years (SD 14), 2042 (64%) of 3207 were female and 1165 (36%) were male; among patients not receiving immunosuppressants, mean age was 54 years (SD 14), 598 (61%) of 985 were female and 387 (39%) were male; and among healthy controls, mean age was 57 years (SD 13), 549 (67%) of 822 were female and 273 (33%) were male. The cumulative incidence of PCR-test or antigen-test confirmed SARS-CoV-2 breakthrough infections was similar in patients on immunosuppressants (148 of 3207; 4·6% [95% CI 3·9-5·4]), patients not on immunosuppressants (52 of 985; 5·3% [95% CI 4·0-6·9]), and healthy controls (33 of 822; 4·0% [95% CI 2·8-5·6]). There was no difference in the odds of breakthrough infection for patients with immune-mediate inflammatory disease on immunosuppressants versus combined controls (ie, patients not on immunosuppressants and healthy controls; adjusted odds ratio 0·88 [95% CI 0·66-1·18]). Seroconversion after vaccination (odds ratio 0·58 [95% CI 0·34-0·98]; T2B! cohort only) and SARS-CoV-2 infection before vaccination (0·34 [0·18-0·56]) were associated with a lower odds of breakthrough infections. INTERPRETATION: The incidence and severity of SARS-CoV-2 breakthrough infections in patients with immune-mediated inflammatory diseases on immunosuppressants was similar to that in controls. However, caution might still be warranted for those on anti-CD20 therapy and those with traditional risk factors. FUNDING: ZonMw (the Netherlands Organization for Health Research and Development) and Reade foundation.

Summary Background People aged 60 years or older are at high risk for respiratory infections, one of the leading causes of mortality worldwide. Vaccination is the main way to protect against these infections; however, vaccination is less effective in older adults than in younger adults due to ageing of the immune system, so innovative strategies that improve vaccine responses could provide a major public health benefit. The gut microbiota regulates host immune homoeostasis and response against pathogens, but human studies showing the effects of the gut microbiota on respiratory infections in older adults are sparse. We aimed to investigate the composition of the microbiota in relation to respiratory infections and local and systemic immune markers in older adults during an influenza season. Methods In this observational study, participants were selected from an influenza-like illness (ILI) prospective surveillance cohort in which community-dwelling adults aged 60 years and older in the Netherlands were recruited through their general practitioner or the Civil Registry. Inclusion criteria have been described elsewhere. Participants completed questionnaires and self-reported symptoms. To measure microbiota composition, faecal samples were collected from participants registering an ILI event, with a follow-up (recovery) sample collected 7–9 weeks after the ILI event, and from asymptomatic participants not reporting any event throughout the season. We tested associations between microbiota profiles and a set of health-related variables, patient characteristics, and local and systemic immune markers. We cultured identified bacterial biomarkers for ILI with CaCo-2 cells in an in vitro intestinal epithelial model and measured the induced immune response. This study is registered with http://www.trialregister.nl , NL4666. Findings Between Oct 1, 2014, and April 30, 2015, 2425 older adults were recruited into the ILI surveillance cohort. From Oct 1, 2014, to June 15, 2015, faecal samples were collected from 397 participants, of whom 213 (54%) reported an ILI event once throughout the season and 184 (46%) did not. 192 ILI participants recovered and provided follow-up samples. Microbiota composition was altered during an ILI event. The Bacteroidetes (mean relative abundance 17·51% [SD 11·41] in the ILI group and 14·19% [10·02] in the control group; adjusted p=0·014) and the Proteobacteria (3·40% [8·10] in the ILI group and 1·57% [3·69] in the control group; adjusted p=0·015) were more abundant in the ILI group than in the control group. The abundance of Ruminococcus torques was positively associated with ILI and the abundance of Escherichia/Shigella, negatively correlated with alpha diversity, and negatively co-occurred with beneficial taxa, including butyrate producers. R torques was associated with pro-inflammatory profiles, both locally in faeces and systemically in blood. ILI-associated taxa (R torques and Escherichia coli) had symbiotic effects on the cellular immune response when cultured together in an in vitro model. Interpretation The abundances of specific bacteria could be used as potential biomarkers for susceptibility to respiratory infections and as targets for intervention in the ageing population. Funding The Dutch Ministry of Health, Welfare and Sport, and the Strategic Program of the National Institute for Public Health and the Environment.

Background: Disease-specific studies have reported impaired humoral responses after SARS-CoV-2 vaccination in patients with immune-mediated inflammatory disorders treated with specific immunosuppressants. Disease-overarching studies, and data on recall responses and third vaccinations are scarce. Our primary objective was to investigate the effects of immunosuppressive monotherapies on the humoral immune response after SARS-CoV-2 vaccination in patients with prevalent immune-mediated inflammatory disorders.Methods: We did a cohort study in participants treated in outpatient clinics in seven university hospitals and one rheumatology treatment centre in the Netherlands as well as participants included in two national cohort studies on COVID-19-related disease severity. We included patients aged older than 18 years, diagnosed with any of the prespecified immune-mediated inflammatory disorders, who were able to understand and complete questionnaires in Dutch. Participants with immune-mediated inflammatory disorders who were not on systemic immunosuppressants and healthy participants were included as controls. Anti-receptor binding domain IgG responses and neutralisation capacity were monitored following standard vaccination regimens and a three-vaccination regimen in subgroups. Hybrid immune responses-ie, vaccination after previous SARS-CoV-2 infection-were studied as a proxy for recall responses.Findings: Between Feb 2 and Aug 1, 2021, we included 3222 participants in our cohort. Sera from 2339 participants, 1869 without and 470 participants with previous SARS-CoV-2 infection were analysed (mean age 49·9 years [SD 13·7]; 1470 [62·8%] females and 869 [37·2%] males). Humoral responses did not differ between disorders. Anti-CD20 therapy, sphingosine 1-phosphate receptor (S1P) modulators, and mycophenolate mofetil combined with corticosteroids were associated with lower relative risks for reaching seroconversion following standard vaccination (0·32 [95% CI 0·19-0·49] for anti-CD20 therapy, 0·35 [0·21-0·55] for S1P modulators, and 0·61 [0·40-0·90] for mycophenolate mofetil combined with corticosteroids). A third vaccination increased seroconversion for mycophenolate mofetil combination treatments (from 52·6% after the second vaccination to 89·5% after the third) but not significantly for anti-CD20 therapies (from 36·8% to 45·6%) and S1P modulators (from 35·5% to 48·4%). Most other immunosuppressant groups showed moderately reduced antibody titres after standard vaccination that did not increase after a third vaccination, although seroconversion rates and neutralisation capacity were unaffected. In participants with previous SARS-CoV-2 infection, SARS-CoV-2 antibodies were boosted after vaccination, regardless of immunosuppressive treatment.Interpretation: Humoral responses following vaccination are impaired by specific immunosuppressants. After standard vaccination regimens, patients with immune-mediated inflammatory disorders taking most immunosuppressants show similar seroconversion to controls, although antibody titres might be moderately reduced. As neutralisation capacity and recall responses are also preserved in these patients, this is not likely to translate to loss of (short-term) protection. In patients on immunosuppressants showing poor humoral responses after standard vaccination regimens, a third vaccination resulted in additional seroconversion in patients taking mycophenolate mofetil combination treatments, whereas the effect of a third vaccination in patients on anti-CD20 therapy and S1P modulators was limited.Funding: ZonMw (The Netherlands Organization for Health Research and Development).

To investigate B-cell differentiation and maturation occurring in the germinal center (GC) using

Aging leads to alterations in the immune system that result in ineffective responsiveness against pathogens. Features of this process, collectively known as immunosenescence, accumulate in CD8

BackgroundSevere acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has led to considerable morbidity/mortality worldwide, but most infections, especially among children, have a mild course. However, it remains largely unknown whether infected children develop cellular immune memory.MethodsTo determine whether a memory T cell response is being developed as an indicator for long-term immune protection, we performed a longitudinal assessment of the SARS-CoV-2-specific T cell response by IFN-γ ELISPOT and activation marker expression analyses of peripheral blood samples from children and adults with mild-to-moderate COVID-19.ResultsUpon stimulation of PBMCs with heat-inactivated SARS-CoV-2 or overlapping peptides of spike (S-SARS-CoV-2) and nucleocapsid proteins, we found S-SARS-CoV-2-specific IFN-γ T cell responses in most infected children (83%) and all adults (100%) that were absent in unexposed controls. Frequencies of SARS-CoV-2-specific T cells were higher in infected adults, especially in those with moderate symptoms, compared to infected children. The S-SARS-CoV-2 IFN-γ T cell response correlated with S1-SARS-CoV-2-specific serum IgM, IgG, and IgA antibody concentrations. Predominantly, effector memory CD4+ T cells of a Th1 phenotype were activated upon exposure to SARS-CoV-2 antigens, which persisted for 4-8 weeks after symptom onset. We detected very low frequencies of SARS-CoV-2-reactive CD8+ T cells in these individuals.ConclusionsOur data indicate that an antigen-specific memory CD4+ T cell response is induced in children and adults with mild SARS-CoV-2 infection. T cell immunity induced after mild COVID-19 could contribute to protection against re-infection.

Mumps is nowadays re-emerging despite vaccination. The contribution of T cell immunity to protection against mumps has not been clearly defined. Previously, we described a set of 41 peptides that were eluted from human leukocyte antigen (HLA) class I molecules of mumps virus (MuV)-infected cells. Here, we confirmed immunogenicity of five novel HLA-B*07:02- and HLA-A*01:01-restricted MuV T cell epitopes from this set of peptides. High frequencies of T cells against these five MuV epitopes could be detected ex vivo in all tested mumps patients. Moreover, these epitope-specific T cells derived from mumps patients displayed strong cytotoxic activity. In contrast, only marginal T cell responses against these novel MuV epitopes could be detected in recently vaccinated persons, corroborating earlier findings. Identifying which MuV epitopes are dominantly targeted in the mumps-specific CD8+ T- response is an important step towards better understanding in the discrepancies between natural infection or vaccination-induced cell-mediated immune protection

Severe respiratory viral infectious diseases such as influenza and COVID‐19 especially affect the older population. This is partly ascribed to diminished CD8+ T‐cell responses a result of aging. The phenotypical diversity of the CD8+ T‐cell population has made it difficult to identify the impact of aging on CD8+ T‐cell subsets associated with diminished CD8+ T‐cell responses. Here we identify a novel human CD8+ T‐cell subset characterized by expression of Killer‐cell Immunoglobulin‐like Receptors (KIR+) and CD45RA (RA+). These KIR+RA+ T cells accumulated with age in the blood of healthy individuals (20–82 years of age, n = 50), expressed high levels of aging‐related markers of T‐cell regulation, and were functionally capable of suppressing proliferation of other CD8+ T cells. Moreover, KIR+RA+ T cells were a major T‐cell subset becoming activated in older adults suffering from an acute respiratory viral infection (n = 36), including coronavirus and influenza virus infection. In addition, older adults with influenza A infection showed that higher activation status of their KIR+RA+ T cells associated with longer duration of respiratory symptoms. Together, our data indicate that KIR+RA+ T cells are a unique human T‐cell subset with regulatory properties that may explain susceptibility to viral respiratory disease at old age., Viral infectious diseases such as influenza especially affect the older population due to immunological dysfunctions. We describe a new aging‐related subset of CD8+ T cells that is identified by the co‐expression of KIR and CD45RA and expresses features of senescence/exhaustion and immune suppression. This T‐cell subset increases with age and comprises a major part of the T cells that become activated during influenza correlating with disease in older persons, indicating clinical relevance. ​

Background The re-emergence of mumps among vaccinated young adults has become a global issue. Besides waning of antibody responses, suboptimal induction of T-cell responses may reduce protection. In a recent study, we observed a dominant polyfunctional CD8+ T-cell response after natural mumps virus (MuV) infection that was not present after vaccination. Unraveling the MuV epitope repertoire can provide insight in the specificity, functionality, and breadth of the T-cell response against MuV. Methods Peptides were eluted from human leukocyte antigen (HLA) class I molecules of MuV-infected cells and characterized by advanced mass spectrometry. Selected identified MuV peptides were tested for in vitro and ex vivo immunogenicity. Results In this study, we identified a broad landscape of 83 CD8+ T-cell epitopes of MuV, 41 of which were confirmed based on synthetic peptide standards. For 6 epitopes, we showed induction of an HLA-A*02-restriced CD8+ T-cell response. Moreover, robust T-cell responses against 5 selected MuV epitopes could be detected in all tested mumps patients using peptide/HLA-A*02:01 dextramers. Conclusions The identified CD8+ T-cell epitopes will help to further characterize MuV-specific T-cell immunity after natural MuV infection or vaccination. These MuV epitopes may provide clues for a better understanding of, and possibly for preventing, mumps vaccine failure. We identified for the first time 41 mumps virus (MuV)-specific HLA-A*02 epitopes. For 6 epitopes, CD8+ T-cell responses were confirmed in T cells derived from several mumps cases, and MuV-specific CD8+ T cells could be identified by peptide/dextramer staining.

IL-7 is a key factor in T-cell immunity and IL7R polymorphisms are implicated in autoimmune pathogenesis. IL7R mRNA is induced in stimulated monocytes in a genetically determined manner, yet a role for IL7R in monocyte biology remains unexplored. Here we characterize genetic regulation of IL7R at the protein level across multiple cell subsets and conditions in healthy individuals. We find monocyte surface and soluble IL7R (sIL7R) protein are markedly expressed in response to lipopolysaccharide (LPS). We further demonstrate alleles of rs6897932, a non-synonymous IL7R polymorphism associated with susceptibility to Multiple Sclerosis, Ankylosing Spondylitis and Primary Biliary Cirrhosis, form the key determinant of both surface IL7R and sIL7R in the context of inflammation. No effect of this allele was observed in unstimulated monocytes or across lymphoid subsets. Production of sIL7R by monocytes greatly exceeded that of CD4+ T-cells, and was strongly associated with both rs6897932 genotype and expression of the splicing factor gene DDX39A. Stimulated monocytes were sensitive to exogenous IL-7, which elicits a defined transcriptional signature. Flow cytometry and single-cell sequencing of synovial fluid derived monocytes from patients with spondyloarthritis showed an enlarged subset of IL7R+ monocytes with a unique transcriptional profile that markedly overlaps that induced by IL-7 in-vitro and shows similarity to the previously described ‘Mono4’ subset. These data demonstrate disease-associated genetic variants at IL7R specifically impact monocyte surface IL7R and sIL7R following innate immune stimulation, suggesting a previously unappreciated key role for monocytes in IL-7 pathway biology and IL7R-associated diseases.

Background B cells mediate humoral immunity against pathogens but also direct CD4 + T-cell responses. Recent plasticity studies in mice have challenged the concept of strict fate commitment during CD4 + T-cell differentiation into distinct subsets. Objective We sought to elucidate the contribution of human antigen-primed B cells in CD4 + T-cell responses that support humoral immunity. Methods CD4 + T-cell differentiation by primary human B cells was investigated in in vitro cocultures by using tetanus toxoid and Salmonella species as antigen models. T-cell differentiation was assessed by using intracellular cytokines and subset-specific transcription factors and markers. IgM and IgG formation was analyzed by means of ELISA. Results Human B cells, but not dendritic cells, induce prominent and stable coexpression of T H 1 and follicular helper T (T FH ) cell characteristics during priming and on antigen recall. T H 1/T FH cells coexpress the T H 1 and T FH effector cytokines IFN-γ and IL-21 and the T FH marker CXCR5, demonstrating that the coexpressed T H 1 and T FH subset–specifying transcription factors T-box transcription factor (T-bet) and B cell lymphoma 6 are both functionally active. B cell–derived IL-6 and IL-12 controlled respective expression of IL-21 and IFN-γ, with IL-21 being key for humoral immunity. Conclusion Human B cells exploit CD4 + T-cell plasticity to create flexibility in the effector T-cell response. Induction of a T-cell subset coexpressing IL-21 and IFN-γ might combine IL-21–mediated T-cell aid for antibody production while maintaining T H 1 cytokine expression to support other cellular immune defenses.

Background Immunological, genetic and therapeutic studies have implicated T lymphocytes in the pathogenesis of Spondyloarthritis (SpA). GM-CSF is emerging as a cytokine that marks out pathogenic T lymphocytes. Inhibition of this cytokine pathway in the SKG mouse model of SpA leads to improvement of joint scores. Methods Matched blood (PBMC) and synovial fluid (SFMC) from patients with SpA was studied ex-vivo using a 40 colour surface and intracellular CyTOF panel. CyTOF findings were validated by flow cytometry in a cohort of patients with SpA, rheumatoid arthritis (RA) controls and healthy donors. CyTOF data was analysed by multi-dimensional viSNE mapping in order to understand the heterogeneity of the synovial fluid inflammatory response. Novel triple cytokine capture was used to purify GM-CSF producing lymphocytes to high purity and RNA sequencing used to interrogate their transcriptional profile. Results CyTOF revealed ex-vivo GM-CSF production from multiple lymphoid cell lineages, with CD4 and CD8 cells the main producers in PBMC and SFMC. GM-CSF production overlaps with multiple other cytokines including IL-17A, IFN- and TNF-. 43% (SEM 3.98) of all GM-CSF producing cells in SpA PBMC were CD4 cells. The percentage of CD4 cells producing GM-CSF was significantly increased in SpA PBMC ex-vivo compared to healthy controls (mean 7.73% vs 4.96% n=38, p Conclusions The synovial fluid of patients with SpA shows an expanded GM-CSF signature. This corresponds with an expansion of GM-CSF producing T lymphocytes in the peripheral blood of patients with SpA compared to controls. Human GM-CSF-positive CD4 cells have a unique ‘pathogenic’ transcriptional profile.

Natural killer (NK) cells are essential in the early immune response against viral infections, in particular through clearance of virus-infected cells. In return, viruses have evolved multiple mechanisms to evade NK cell-mediated viral clearance. Several unrelated viruses, including influenza virus, respiratory syncytial virus, and human immunodeficiency virus, can directly interfere with NK cell functioning through infection of these cells. Viral infection can lead to immune suppression, either by downregulation of the cytotoxic function or by triggering apoptosis, leading to depletion of NK cells. In contrast, some viruses induce proliferation or changes in the morphology of NK cells. In this review article, we provide a comprehensive overview of the viruses that have been reported to infect NK cells, we discuss their mechanisms of entry, and describe the interference with NK cell effector function and phenotype. Finally, we discuss the contribution of virus-infected NK cells to viral load. The development of specific therapeutics, such as viral entry inhibitors, could benefit from an enhanced understanding of viral infection of NK cells, opening up possibilities for the prevention of NK cell infection.

Increased frequencies of T-helper cells producing the proinflammatory cytokine IL-17A (TH17) have been reported in ankylosing spondylitis (AS), rheumatoid arthritis (RA), psoriatic arthritis (PsA), and inflammatory bowel disease (IBD).1 Genome-wide association studies have linked multiple TH17-associated genes, including IL23R, with AS, psoriasis, and IBD, further supporting a common pathogenic role for the IL-17/IL-23 axis in these diseases. 2 Neutralizing IL-17A with mAbs has shown efficacy in AS and PsA,3 and some benefit in RA,4 but has proved ineffective and possibly deleterious in patients with IBD.5 There is therefore a need for new therapies, including small-molecule inhibitors, that target type 17 immune responses.

The Editorial on the Research Topic Role of HLA and KIR in Viral Infections The immune system continuously protects its host against pathogens. During viral infections, both innate and adaptive immune cells contribute to an effective immune response. Natural killer (NK) cells can respond quickly to eliminate pathogens and infected cells and suppress dissemination to other tissues. Subsequently, activation of virus-specific CD8+ cytotoxic T cells results in specific killing of infected cells and activation of virus-specific CD4+ T cells further supports the immune response. Human leukocyte antigens (HLA) play an essential role in activation of both NK cells and T cells. This research topic contains eight articles highlighting the latest insights into the various effects of HLA molecules on both NK cell and T-cell reactivity upon viral infection. Natural Killer cell activation is regulated by a variety of activating and inhibitory receptors, including killer-cell immunoglobulin-like receptors (KIRs). KIRs bind to HLA class I molecules, which are expressed on all nucleated cells. As HLA and KIR molecules are highly polymorphic, each individual expresses a unique set of these molecules. The wide range of combinations of HLA and KIR expression results in differences in binding strengths and variation in NK cell activation (1). In this research topic, a review by Walter and Ansari illuminates the associations of HLA and KIR polymorphisms with the outcome of experimental simian immunodeficiency virus infection in rhesus macaques, a model used to study human immunodeficiency virus (HIV) infection. Not only do these associations show which interactions contribute to disease resistance, they also pinpoint combinations that increase susceptibility to disease. Such associations of HLA and KIR with disease progression have also been found in hepatitis C virus (HCV) infection. In her review, Gardiner summarizes current insights into these associations, and further illustrates how NK cells modulate disease outcome in HCV infection. Furthermore, this review highlights the ongoing search for the NK cell subsets required for protective host responses. In addition to KIRs, NK cells express C-type lectin receptors, including NKG2C, which regulate activation via ligation to non-classical HLA-E molecules. Della Chiesa et al. summarize the role of activating KIRs and NKG2C in several virus infections, including human cytomegalovirus (HCMV) and HIV. In addition, they discuss the induction of memory-like NK cells, which show enhanced responses upon reinfection and may play a role in controlling recurrent or chronic infections. Expression of NKG2C has also been associated with expansion of NK cells during viral infection. This expansion of NKG2C+ NK cells with expression of self-HLA class I-specific KIRs has been observed in HCMV infection (2). The force driving these NK cell expansions is largely unclear. In this collection, Beziat et al. investigate the importance of HLA class I expression levels in host defense using data derived from transporter associated with antigen processing (TAP)-deficient individuals who express less than 10% of normal HLA class I levels. They demonstrate that self-HLA class I molecules shape the KIR repertoire of NKG2C+ NK cells, but are not a requirement for expansion. Besides influencing innate NK responses via ligation to KIRs, HLA induces adaptive immune responses by presenting pathogen-derived peptides to T cells. Recognition of HLA:peptide complexes by a peptide-specific T-cell receptor leads to activation of specific CD8+ cytotoxic T cells or CD4+ T helper cells. In HCMV infection, effective CD8+ T-cell responses have been shown to be dominated by peptides derived from immediate-early 1 (IE-1) protein (3–5). Whether IE-1 is also the dominant peptide source for CMV-specific CD4+ T cell responses is unclear. Using cells derived from healthy HCMV-positive donors, Ameres et al. generated multiple IE-1-specific CD4+ T cell clones with a highly diverse repertoire and found that IE-1-specific CD4+ T cells participate in the antiviral response. Since both CD4+ and CD8+ T cells respond to IE-1-derived peptides, it might be an interesting target for immunotherapeutic approaches. Infection with measles virus is known to induce a strong T cell response (6, 7), but information regarding the specific measles virus antigens that are responsible for activation of these cells is limited. Schellens et al. investigated which measles peptides are presented by HLA class I molecules by eluting naturally presented peptides from virus-infected cells. They show that a broad spectrum of the measles peptidome is presented by different HLA class I molecules. Furthermore, they found that while HLA-B molecules present the most diverse set of peptides, the abundant epitopes were eluted from HLA-A and HLA-C molecules, suggesting that the HLA loci also influence peptide presentation. Due to the polymorphic nature of HLA molecules, a great diversity of peptides are typically presented, resulting in T-cell activation of variable strengths. In HCV infections, some HLA molecules (e.g., HLA-B27 and HLA-B57) are significantly associated with viral clearance (8, 9). However, it is not yet known why such HLA molecules provide an advantage during HCV infections. Using known HCV epitopes combined with in silico predictions, Rao et al. demonstrate that HLA-B27 preferentially presents epitopes from the HCV protein NS5B, which is highly conserved and, therefore, might be one of the underlying mechanisms behind the protective effect of this molecule during HCV infection. Preferential presentation of peptides derived from conserved regions was also found for HIV (10–12). However, the induction of effective immune responses also puts pressure on the virus to adapt toward escape variants. The generation of escape variants often comes with significant costs, such as reduced viral replicative capacity. In the final paper of this issue, a review by KlOverpris et al. illustrates the effects of viral escape variants within the HIV-infected patient as well as the consequences of transmission of these variants at the population level. Together, the research and reviews in this research topic provide an up-to-date overview of the importance of HLA and KIR molecules in host responses to viral infection. Given the central role of HLA in modulating both innate and adaptive immune responses, it is important to expand our knowledge on the role of different HLA molecules in various diseases. A better understanding of the differences between the individual immune responses, especially when it fails to protect against pathogens, should ultimately help to develop better – and possibly more individualized – treatment options.

IL-17–producing CD4+ T helper (Th17) cells are important for immunity against extracellular pathogens and in autoimmune diseases. The factors that drive Th17 development in human remain a matter of debate. Here we show that, compared with classic CD28 costimulation, alternative costimulation via the CD5 or CD6 lymphocyte receptors forms a superior pathway for human Th17-priming. In the presence of the Th17-promoting cytokines IL-1β, IL-6, IL-23, and transforming growth factor-β (TGF-β), CD5 costimulation induces more Th17 cells that produce higher amounts of IL-17, which is preceded by prolonged activation of signal transducer and activator of transcription 3 (STAT3), a key regulator in Th17 differentiation, and enhanced levels of the IL-17–associated transcription factor retinoid-related orphan receptor-γt (ROR-γt). Strikingly, these Th17-promoting signals critically depend on CD5-induced elevation of IL-23 receptor (IL-23R) expression. The present data favor the novel concept that alternative costimulation via CD5, rather than classic costimulation via CD28, primes naive T cells for stable Th17 development through promoting the expression of IL-23R.

The present paradigm is that primary B cells are nonphagocytosing cells. In this study, we demonstrate that human primary B cells are able to internalize bacteria when the bacteria are recognized by the BCR. BCR-mediated internalization of Salmonella typhimurium results in B cell differentiation and secretion of anti-Salmonella Ab by the Salmonella-specific B cells. In addition, BCR-mediated internalization leads to efficient Ag delivery to the MHC class II Ag-loading compartments, even though Salmonella remains vital intracellularly in primary B cells. Consequently, BCR-mediated bacterial uptake induces efficient CD4+ T cell help, which boosts Salmonella-specific Ab production. BCR-mediated internalization of Salmonella by B cells is superior over extracellular Ag extraction to induce rapid and specific humoral immune responses and efficiently combat infection.

Background The spondyloarthritides (SpA) are immune-driven inflammatory diseases in which T lymphocytes are thought to have a major pathogenic role. Lymphocytes producing granulocyte-macrophage colony-stimulating factor (GM-CSF) have been shown to be especially pathogenic in murine models of SpA. This study aimed to identify and characterise the role of GM-CSF-producing lymphocytes in human SpA. Methods Peripheral blood and joint-derived mononuclear cells from adults with SpA and controls (healthy adults and adults with the inflammatory joint disease rheumatoid arthritis) were studied with flow cytometry and time of flight mass cytometry (CyTOF). The role of GM-CSF was also investigated in joint-derived innate lymphoid cells. GM-CSF-producing CD4 lymphocytes were isolated by cytokine capture, and RNA sequencing transcriptomic analysis was used to compare GM-CSF lymphocytes with T helper (Th) 1 and Th17 cells. Findings An expansion of GM-CSF-producing CD4 and CD8 T cells was noted in the blood and joints of patients with SpA. Flow cytometry and CyTOF showed that CD4 T cells were the main producers of GM-CSF. GM-CSF production occurred both independently and in combination with classic Th1 and Th17 cytokines, with increased numbers of interleukin 17A+GM-CSF+ double-producing CD4, CD8, and natural killer cells. Expansion of type 3 innate lymphoid cells in SpA also occurred, and GM-CSF was abundantly produced by these cells. Transcriptional analysis of GM-CSF+ cells isolated with a novel triple cytokine capture approach suggested that human GM-CSF+ CD4 T cells represent an effector population distinct from Th1 and Th17 cells. Interpretation GM-CSF is a key effector cytokine in human SpA and may be a valid target for therapeutic intervention. Anti-GM-CSF monoclonal antibodies are currently in phase 3 trials for rheumatoid arthritis and have been shown to be safe in patients. These data would support the use of these antibodies in SpA. Funding Wellcome Trust clinical PhD award (to MHA-M).

Aims Endothelial cells (ECs) control vascular permeability by forming a monolayer that is sealed by extracellular junctions. Various mediators modulate the endothelial barrier by acting on junctional protein complexes and the therewith connected F-actin cytoskeleton. Different Rho GTPases participate in this modulation, but their mechanisms are still partly resolved. Here, we aimed to elucidate whether the opening and closure of the endothelial barrier are associated with distinct localized RhoA activities at the subcellular level. Methods and results Live fluorescence resonance energy transfer (FRET) microscopy revealed spatially distinct RhoA activities associated with different aspects of the regulation of endothelial monolayer integrity. Unstimulated ECs were characterized by hotspots of RhoA activity at their periphery. Thrombin receptor activation in the femoral vein of male wistar rats and in cultured ECs enhanced RhoA activity at membrane protrusions, followed by a more sustained RhoA activity associated with cytoplasmic F-actin filaments, where prolonged RhoA activity coincided with cellular contractility. Unexpectedly, thrombin-induced peripheral RhoA hotspots were not spatially correlated to the formation of large inter-endothelial gaps. Rather, spontaneous RhoA activity at membrane protrusions coincided with the closure of inter-endothelial gaps. Electrical impedance measurements showed that RhoA signalling is essential for this protrusive activity and maintenance of barrier restoration. Conclusion Spontaneous RhoA activity at membrane protrusions is spatially associated with closure, but not formation of inter-endothelial gaps, whereas RhoA activity at distant contractile filaments contributes to thrombin-induced disruption of junctional integrity. Thus, these data indicate that distinct RhoA activities are associated with disruption and re-annealing of endothelial junctions.

BACKGROUND: The eradication of facultative intracellular bacterial pathogens, like Salmonella typhi, requires the concerted action of both the humoral immune response and the cytotoxic CD8(+) T cell response. Dendritic cells (DCs) are considered to orchestrate the cytotoxic CD8(+) T cell response via cross-presentation of bacterial antigens onto MHC class I molecules. Cross-presentation of Salmonella by DCs however, is accompanied by the induction of apoptosis in the DCs. Besides antibody production, B cells are required to clear Salmonella infection for other unknown reasons. METHODOLOGY/PRINCIPAL FINDINGS: Here we show that Salmonella-specific B cells that phagocytose Salmonella upon BCR-ligation reactivate human memory CD8(+) T cells via cross-presentation yielding a Salmonella-specific cytotoxic T cell response. The reactivation of CD8(+) T cells is dependent on CD4(+) T cell help. Unlike the DCs, B cell-mediated cross-presentation of Salmonella does not coincide with apoptosis. CONCLUSIONS/SIGNIFICANCE: B cells form a new player in the activation of the cytotoxic effector arm of the immune response and the generation of effective adaptive immunity in Salmonella infection.