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Pertussis is still occurring in highly vaccinated populations, affecting individuals of all ages. Long-lived Th1 CD4+ T cells are essential for protective immunity against pertussis. For better understanding of the limited immunological memory to Bordetella pertussis, we used a panel of Pertactin and Pertussis toxin specific peptides to interrogate CD4+ T cell responses at the epitope level in a unique cohort of symptomatic pertussis patients of different ages, at various time intervals after infection. Our study showed that pertussis epitope-specific T cell responses contained Th1 and Th2 components irrespective of the epitope studied, time after infection, or age. In contrast, the breadth of the pertussis-directed CD4+ T cell response seemed dependent on age and closeness to infection. Multi-epitope specificity long-term after infection was lost in older age groups. Detailed knowledge on pertussis specific immune mechanisms and their insufficiencies is important for understanding resurgence of pertussis in highly vaccinated populations. [ABSTRACT FROM AUTHOR]

Mumps outbreaks among vaccinated young adults stress the need for a better understanding of the mumps virus (MuV)-induced immunity. Antibody responses to MuV are well-characterized, but studies on T cell responses are limited. We recently isolated a MuV-specific CD4+ T cell clone by stimulating PBMCs of a mumps case with the viral nucleoprotein (MuV-N). In this study, we further explored the identity and relevance of the epitope recognized by the CD4+ T cell clone, and ex vivo by T cells in a cohort of mumps cases. Using a 2D-matrix peptide pool of 15-mers peptides covering the complete MuV-N, the epitope recognized by the T cell clone was identified to be MuV-N110-124 GTYRLIPNARANLTA, present in a well-conserved region of the viral protein. Upon peptide-specific stimulation, the T cell clone expressed the activation marker CD137, produced IFN-γ, TNF and IL-10 in a HLA-DR4 restricted manner. Moreover, the CD4+ T cells exerted a cytotoxic phenotype and specifically killed cells presenting MuV-N110-124. Furthermore, the identified peptide is widely applicable to the general population as it is predicted to bind various common HLA-DR molecules, and epitope-specific CD4+ T cells displaying cytotoxic/Th1-type properties were found in all tested mumps cases expressing different HLA-DR alleles. This first broadly recognized human MuV-specific CD4+ T cell epitope could provide a useful tool to detect and evaluate virus-specific T cell responses upon MuV infection or following vaccination. [ABSTRACT FROM AUTHOR]

CD4 + T cell-mediated immunity against Streptococcus pneumoniae (pneumococcus) can protect against recurrent bacterial colonization and invasive pneumococcal diseases (IPDs). Although such immune responses are common, the pertinent antigens have remained elusive. We identified an immunodominant CD4 + T cell epitope derived from pneumolysin (Ply), a member of the bacterial cholesterol-dependent cytolysins (CDCs). This epitope was broadly immunogenic as a consequence of presentation by the pervasive human leukocyte antigen (HLA) allotypes DPB1 ∗ 02 and DPB1 ∗ 04 and recognition via architecturally diverse T cell receptors (TCRs). Moreover, the immunogenicity of Ply 427-444 was underpinned by core residues in the conserved undecapeptide region (ECTGLAWEWWR), enabling cross-recognition of heterologous bacterial pathogens expressing CDCs. Molecular studies further showed that HLA-DP4-Ply 427-441 was engaged similarly by private and public TCRs. Collectively, these findings reveal the mechanistic determinants of near-global immune focusing on a trans-phyla bacterial epitope, which could inform ancillary strategies to combat various life-threatening infectious diseases, including IPDs., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Pertussis, a human-specific respiratory infectious disease caused by the Gram-negative bacterium Bordetella pertussis (Bp), remains endemic with epidemic years despite high vaccination coverage. Whereas pertussis vaccines and natural infection with Bp confer immune protection, the duration of protection varies and is not lifelong. Recent evidence indicates a considerable underestimation of the pertussis burden among older adults. Whereas the impact of increasing age on Bp-specific humoral immunity has been demonstrated, little is known on immunosenescence of CD4 + T-cell responses in the context of Bp. Here, we aimed to address whether increasing age impacts responsiveness of the Bp-specific CD4 + T-cells in the memory pool following a clinically symptomatic pertussis infection in whole cell vaccine-primed pediatric and adult cases. Cytokine and proliferative responses and phenotypical profiles of CD4 + T cells specific for Bp antigens at an early and late convalescent timepoint were compared. Responses of various Th cytokines, including IFNγ, were significantly lower in older adults at early and late timepoints post diagnosis. In addition, we found lower frequencies of Bp-specific proliferated CD4 + T cells in older adults, in the absence of differences in replication profile. Phenotyping of Bp-specific CD4 + T cells suggested reduced expression of activation markers rather than increased expression of co-inhibitory markers. Altogether, our findings show that the magnitude and functionality of the Bp-specific memory CD4 + T-cell pool decrease at older age. Declined CD4 + T-cell responsiveness to Bp is suggested to contribute to the burden of pertussis in older adults., 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. The handling editor declared a shared consortium with one of the author CVE at time of review., (Copyright © 2022 Lambert, van Twillert, Beckers, Poelen, Han, Pieren and van Els.)

Respiratory infection caused by Streptococcus pneumoniae is a leading cause of morbidity and mortality in older adults. Acquired CD4 + T cell mechanism are essential for the protection against colonization and subsequent development of infections by S. pneumoniae . In this study, we hypothesized that age-related changes within the CD4 + T-cell population compromise CD4 + T-cell specific responses to S. pneumoniae , thereby contributing to increased susceptibility at older age. To this end, we interrogated the CD4 + T-cell response against the immunogenic pneumococcal protein AliB, part of the unique oligopeptide ABC transporter system responsible for the uptake of nutrients for the bacterium and crucial for the development of pneumococcal meningitis, in healthy young and older adults. Specifically, proliferation of CD4 + T cells as well as concomitant cytokine profiles and phenotypic markers implied in immunosenescence were studied. Older adults showed decreased AliB-induced CD4 + T-cell proliferation that is associated with an increased frequency of regulatory T cells and lower levels of active CD25 + CD127 + CTLA-4 - TIGIT - CD4 + T cells. Additionally, levels of pro-inflammatory cytokines IFNy and IL-17F were decreased at older age. Our findings indicate that key features of a pneumococcal-specific CD4 + T-cell immune response are altered at older age, which may contribute to enhanced susceptibility for pneumococcal infections., 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. The handling editor declared a shared consortium with one of the authors (C.V.E) at time of review., (Copyright © 2021 He, van de Garde, Pieren, Poelen, Voß, Abdullah, Hammerschmidt and van Els.)

Comprehensive analysis of the complex nature of the Human Leukocyte Antigen (HLA) class II ligandome is of utmost importance to understand the basis for CD4(+)T cell mediated immunity and tolerance. Here, we implemented important improvements in the analysis of the repertoire of HLA-DR-presented peptides, using hybrid mass spectrometry-based peptide fragmentation techniques on a ligandome sample isolated from matured human monocyte-derived dendritic cells (DC). The reported data set constitutes nearly 14 thousand unique high-confident peptides,i.e.the largest single inventory of human DC derived HLA-DR ligands to date. From a technical viewpoint the most prominent finding is that no single peptide fragmentation technique could elucidate the majority of HLA-DR ligands, because of the wide range of physical chemical properties displayed by the HLA-DR ligandome. Our in-depth profiling allowed us to reveal a strikingly poor correlation between the source proteins identified in the HLA class II ligandome and the DC cellular proteome. Important selective sieving from the sampled proteome to the ligandome was evidenced by specificity in the sequences of the core regions both at their N- and C- termini, hence not only reflecting binding motifs but also dominant protease activity associated to the endolysosomal compartments. Moreover, we demonstrate that the HLA-DR ligandome reflects a surface representation of cell-compartments specific for biological events linked to the maturation of monocytes into antigen presenting cells. Our results present new perspectives into the complex nature of the HLA class II system and will aid future immunological studies in characterizing the full breadth of potential CD4(+)T cell epitopes relevant in health and disease., (© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.)

P.69 pertactin (P.69 Prn), an adhesion molecule from the causative agent of pertussis, Bordetella pertussis, is present in cellular and most acellular vaccines that are currently used worldwide. Although both humoral immunity and cellular immunity directed against P.69 Prn have been implicated in protective immune mechanisms, the identities of CD4(+) T-cell epitopes on the P.69 Prn protein remain unknown. Here, a single I-A(d)-restricted B. pertussis conserved CD4(+) T-cell epitope at the N terminus of P.69 Prn was identified by using a BALB/c T-cell hybridoma. The epitope appeared immunodominant among four other minor strain-conserved P.69 Prn epitopes recognized after vaccination and B. pertussis infection, and it was capable of evoking a Th1/Th17-type cytokine response. B. pertussis P.69 Prn immune splenocytes did not cross-react with natural variants of the epitope as present in Bordetella parapertussis and Bordetella bronchiseptica. Finally, it was found that the immunodominant P.69 Prn epitope is broadly recognized in the human population by CD4(+) T cells in an HLA-DQ-restricted manner. During B. pertussis infection, the epitope was associated with a Th1-type CD4(+) T-cell response. Hence, this novel P.69 Prn epitope is involved in CD4(+) T-cell immunity after B. pertussis vaccination and infection in mice and, more importantly, in humans. Thus, it may provide a useful tool for the evaluation of the type, magnitude, and maintenance of B. pertussis-specific CD4(+) T-cell mechanisms in preclinical and clinical vaccine studies.

Infectious agents have been implied as causative environmental factors in the development of autoimmunity. However, the exact nature of their involvement remains unknown. We describe a possible mechanism for the activation of autoreactive T cells induced by measles virus (MV) infection. The display of HLA-A*0201 associated peptides obtained from MV infected cells was compared with that from uninfected cells by mass spectrometry. We identified two abundant self peptides, IFI-6-16(74-82) and Hsp90beta(570-578), that were induced or upregulated, respectively, following infection. Their parental proteins, the type I interferon inducible protein IFI-6-16, and the beta chain of heat shock protein 90, have not been involved in MV pathogenesis. MV infection caused minor and major changes in the intracellular expression patterns of these proteins, possibly leading to altered peptide processing. CD8+ T cells capable of recognizing the self-peptides in the context of HLA-A*0201 were detectable at low basal levels in the neonatal and adult human T cell repertoire, but were functionally silent. In contrast, peptide-specific producing IFN-gamma producing effector cells were present in MV patients during acute infection. Thus, MV infection induces an enhanced display of self-peptides in MHC class I, which may lead to the temporary activation of autoreactive T cells.

Following measles virus (MV) infection, viral peptides are presented to CTL by MHC class I molecules on infected antigen presenting cells at widely different epitope densities. Whereas three MV epitopes (MV-M(211-219), MV-F(438-446) and MV-H(30-38)) derived from different structural proteins occur at regular densities, one peptide derived from the non-structural C protein (MV-C(84-92)) fully dominates the MV peptide display in HLA class I molecules on end-stage-infected human B cells. Here we demonstrate that this hierarchy in MV epitope density is not a constant, but varies with progression of infection. While MV-M(211-219), MV-F(438-446) and MV-H(30-38) epitopes were already presented by HLA class I molecules early in infection, expression of MV-C(84-92) was restricted to the later phases of infection. These dynamics in epitope densities correlated with features of MV protein expression. Synthesis of C protein mainly focused towards the final stages of infection, while the other MV proteins were more readily synthesised from earlier time points on, in line with the emergence of their respective epitopes. Furthermore, the most abundant MV epitope was derived from the most unstable viral protein and vice versa, suggesting that the stability of viral proteins may be an indicator for the final abundance of their epitopes. Thus, even though many other factors may influence the generation of peptide-MHC class I complexes, we here report that the regulation of viral protein expression seems closely linked to the viral MHC class I epitope display. Finally, the observed dynamics in viral epitope hierarchy may have important implications for the induction of antiviral T cell immunity.