Cellular & Molecular Immunology

Human genetic studies have identified defects in multiple mechanisms that predispose the risk of developing inflammatory bowel diseases (IBD), which include alterations in adaptive and innate immune responses, epithelial integrity and regulation of the intestinal mucus layer. Despite the importance of intestinal barrier integrity in the pathogenesis of IBD, essentially all current therapies modulate the immune responses. In this study, we determined the high resolution cryo-EM structure of human NXPE1, a IBD associated protein. Based on the structural homology, we identified NXPE1 as an O-acetyltransferase. Since NXPE1 is a pseudo gene in mouse, we generated knockout mouse model that lacked two of the mouse NXPE1 homologs, Nxpe2 and Nxpe4. The O-acetylation of sialic acid on red blood cells was abolished in the double knockout mice, confirming the sialic acid O-acetyltransferase function of NXPE1 family members. These findings underscore the potential of NXPE1 as a novel therapeutic target of the intestinal barrier functions for the treatment of IBD.

Cross-reactive antibodies against dengue virus are known to cause antibody-dependent enhancement (ADE) of infection or disease severity under specific conditions. In our previous study, we showed that primary immunization with the COVID-19 vaccine induces induces cross-reactive IgG causing ADE against dengue. In the present study, we investigated the influence of IgG Fc-glycosylation (analyzed by LC-MS/MS) on ADE mediated by cross-reactive IgG against dengue from IgG against SARS-CoV-2. We found a clear correlation between anti-DENV2 E IgG2 galactosylation and the ADE capacity of cross-reactive IgG against dengue in individuals vaccinated against COVID-19. IgG2 sialylation increased over time; however, it was not correlated with ADE capacity. This phenomenon was restricted to IgG2, whereas anti-DENV2 E IgG1 Fc-glycosylation remained stable after COVID-19 vaccination.

Individuals with diabetes are at increased risk for severe outcomes from vaccine-preventable infections and often mount weaker immune responses to vaccination. The factors underlying this impaired immunity remain unclear, and defining them is critical to improve vaccine strategies for this vulnerable population. Here, we focused on insulin deficiency as a contributing factor. Following immunization with an alum-adjuvanted protein subunit vaccine, insulin-deficient mice exhibited reduced antigen-specific IgG antibody responses, decreased lymphocyte numbers, and lower germinal center B-cell counts within the vaccine-draining lymph node. Three-dimensional whole-organ light sheet microscopy combined with virtual reality-assisted analysis revealed significantly smaller germinal center volumes in insulin-deficient mice than controls. These findings indicate that insulin deficiency can significantly constrain germinal center responses and impair antibody production from vaccination. Our results provide foundational evidence that diabetes-associated metabolic changes can significantly and negatively influence the quality of vaccine-induced immunity and highlight insulin deficiency as a potential physiological factor.

PRV-101 is a multivalent formalin-inactivated Coxsackievirus B (CVB) vaccine developed to prevent CVB infections, which are associated with increased risk of islet autoimmunity. While PRV-101 induces robust neutralizing antibody responses, its T-cell immunogenicity is unknown. We analyzed peripheral blood mononuclear cells from 25 healthy adults receiving three high or low PRV-101 doses or placebo in a Phase I randomized, placebo-controlled trial. CVB-reactive CD8 T-cell responses were assessed using HLA Class I multimers, and CD4 and T follicular helper (Tfh) responses were measured by activation-induced marker assays following stimulation with a CVB peptide library. PRV-101 elicited minimal CVB-reactive CD8 T-cell responses but robust CD4 and Tfh responses, peaking at week 12 and persisting through week 32. Responses were observed in both seronegative and seropositive individuals, consistent with effective immune priming and boosting. Tfh frequencies correlated with neutralizing antibody titers. Female participants exhibited higher peak Tfh responses than males. We conclude that PRV-101 elicits a CVB-protective immune profile, dominated by Tfh responses supporting durable humoral immunity and devoid of potentially diabetogenic cytotoxic T-cell responses. This profile invites further investigations in vaccine trials for type 1 diabetes prevention.

Cyclooxygenase-1 (COX-1) is classically regarded as a constitutive enzyme that produces eicosanoids with housekeeping functions, but recent evidence indicates that it may also be involved in the acute phase of severe systemic inflammation. There is evidence indicating that COX-1 is selectively activated in the spleen via post-translational mechanisms early the course of LPS-induced systemic inflammation. However, the mechanistic link between COX-1 and the spleen has not yet been demonstrated in direct experiments. The present study was conducted to fill this gap. The effects of the COX-1 inhibitor SC-560 on the LPS-induced severity triad (hypotension, hypothermia and acidosis) were evaluated in rats subjected to splenectomy or in sham-operated controls. In the sham-operated group, SC-560 significantly attenuated the severity triad independently of changes in plasma cytokines (TNF and IL-1{beta}). In the splenectomized rats, SC-560 completely lost its ability to attenuate the hypotension and the acidosis induced by LPS. The effect of SC-560 on LPS-induced hypothermia was also impaired by splenectomy, though not completely. We then conducted a lipidomic screening to identify which COX-1-derived eicosanoids might be responsible for mediating the severity triad. Based on spleen-blood correlations, the screening identified PGE2 and PGD2 as putative candidates. In conclusion, the present study provides direct evidence for a mechanistic link between the spleen and COX-1 in the mediation of severity in systemic inflammation, and identifies PGE2 and PGD2 as putative candidates involved.

Chitin is a highly abundant poly- N-acetyl-glucosamine (GlcNAc) and linked to immune recognition of fungal infections and asthma in humans. Ubiquitous in fungi and insects, in mammals and plants chitin represents a microbe-associated molecular pattern (MAMP) and whereas highly polymeric chitin is insoluble and immunologically inert, soluble chitin oligomers of 6 to 15 GlcNAc activate immediate pro-inflammatory cytokine release via TLR2 in human immune cells. However, TLR2 ligands do not the most typical activators of the NLRP3 inflammasome pathway or innate immune training, a phenomenon of long-term immunological remodeling. Here we show that especially 16-20 GlcNAc long chitin oligomers activate NLRP3-dependent IL-1{beta} and IL-18 release in human myeloid immune cells in an atypical, phagocytosis-dependent manner. Moreover, phagocytosis and methyl transferase activity were essential for innate immune training, by which the same chito-oligomer-training enhanced TNF release in primary murine and human immune cells. Collectively, this suggests that oligomer length impacts on the immune features of chitin which can be customized using glycan assembly.

RNA-binding protein LARP4 plays an important role in T cell activation and differentiation, but its role in B cell biology and the pathogenesis of systemic lupus erythematosus (SLE) remains unclear. This study found that LARP4 was specifically highly expressed in B cells of SLE patients and was positively correlated with disease activity. By constructing T cell-specific and B cell-specific conditional knockout mice, we found that deletion of LARP4 in B cells, but not in T cells, significantly alleviated pristane-induced and Bm12-induced lupus nephritis. Further analysis showed that LARP4 deletion selectively inhibited B cell differentiation into plasma cells, but did not affect germinal center B cell formation. Integrated transcriptomic and metabolomics analyses revealed that this effect is due to reduced phosphatidic acid synthesis and decreased mTORC1 activity caused by mitochondrial oxidative phosphorylation dysfunction. Furthermore, we used LIPEP, a LARP4 inhibitory peptide that effectively mimicked the therapeutic effects of LARP4 gene knockout in the MRL/lpr spontaneous lupus model and outperformed cyclophosphamide in reducing glomerular immune complex deposition and improving extrarenal dermatitis. These results indicates that LARP4 is a key metabolic checkpoint regulating B cell differentiation into Plasma cells and suggest that it may be a potential therapeutic target for SLE.

Dimeric immunoglobulin A (dIgA) is generated from IgA monomers (mIgA) via JCHAIN-dependent polymerization. DIgA is transported across epithelial barriers by the poly Ig receptor (PIGR) and confers mucosal protection, while serum contains substantial amounts of IgA monomers. Distinct plasma cell subsets have been proposed to produce either monomeric or dimeric IgA, with bone marrow plasma cells as a primary source of mIgA. Here, we addressed whether IgA plasma cell populations segregate based on mIgA or dIgA production. Flow cytometric analysis of antibody-secreting cells from bone marrow, lymphoid and mucosal tissues revealed universal intracellular JCHAIN expression across isotypes and failed to identify a discrete JCHAIN-negative IgA plasma cell population. To detect polymeric IgA, we generated a recombinant soluble PIGR that selectively bound JCHAIN-containing dIgA in Western blot, ELISA, and flow cytometry. Soluble PIGR binding was detected in all IgA plasma cells irrespective of tissue origin, arguing against a dedicated mIgA-producing plasma cell subset incapable of dIgA formation. Ex vivo cultures and single-cell DropMap secretion assays demonstrated that bone marrow and lamina propria IgA antibody-secreting cells co-secrete mIgA and dIgA. These findings suggest that dIgA assembly and secretion are general properties of IgA plasma cells and disfavor a dedicated mIgA-producing population.

A healthy gut immune system balances pathogen defense and tolerance to beneficial microbes. This equilibrium is sustained by coordinated mechanisms where B cells (BCs) play a central role, and secretory immunoglobulin A (SIgA) regulates microbiome composition. In ulcerative colitis (UC), impaired tolerogenic pathways result in exaggerated immune activation, epithelial dysfunction, and tissue damage; however, the contribution of BCs to disease pathogenesis remains unclear. Notably, sialylation is crucial to B-cell function, but its relevance in the intestinal IgA B-cell response has been scarcely explored. Here, we show that SIgA from active UC patients displays an inflammation-dependent reduction in (2,6)-sialylation. This desiaylation is recapitulated in dextran sodium sulfate-induced colitis, where IgA plasma cells (IgA+ PCs) and BCs exhibit a similar glycophenotype. Functional analyses reveal that BCs lacking (2,6)-sialylation on N-glycans exhibit defective differentiation into IgA PCs and diminished capacity to suppress intestinal inflammation in vivo, with increased neutrophil infiltration. Moreover, transcriptomic analyses of UC patient samples suggest a synergistic contribution of neuraminidase activity and reduced bioavailability of sialic acid precursors, leading to SIgA desialylation. Collectively, these findings uncover a glycosylation-dependent pathological circuit in which altered sialylation of SIgA and BCs disrupts their function, compromising mucosal homeostasis in intestinal inflammation.

Acute respiratory distress syndrome (ARDS) is a devastating complication of respiratory infections; however, the biological mechanisms that initiate its onset are poorly defined. Here we show that TNFRSF13B polymorphisms increase the risk of ARDS following SARS-CoV-2 infection up to 7.4-fold compared to the WT genotype. The increased risk was not due to immune-deficiency or impaired virus neutralization. On the contrary, TNFRSF13B mutant subjects mounted better antibody neutralization compared to subjects with WT TNFRSF13B. However, IgG from subjects expressing TNFRSF13B variants had less sialic acid, terminal galactose, and fucose than IgG from subjects with a WT genotype. Moreover, IgG from TNFRSF13B mutant subjects exhibited increased recruitment of complement factors. Thus, besides well-known actions governing plasma cell differentiation, TNFRSF13B impacts both affinity maturation and effector functions of IgG in ways that independently govern complement activation controlling inflammatory responses known to trigger ARDS.

Streptococcus pneumoniae remains a global health threat, particularly to young children, the elderly, and immunocompromised individuals. Pneumococcal vaccines targeting the bacterial capsule polysaccharide do not protect against all 100+ pneumococcal serotypes, contributing to non-vaccine serotype infections and antibiotic resistance. To address these limitations, we isolated human monoclonal antibodies (mAbs) targeting pneumococcal surface proteins and identified a first-in-class mAb, derived from a patient with prior pneumococcal infection, namely mAb 5995-40. mAb 5995-40 bound multiple pneumococcal proteins, including PcpA and PspA, through a conserved choline-binding domain shared across serotypes. Functionally, mAb 5995-40 provided complete protection in lethal pneumococcal challenge models and improved survival in influenza A, influenza B, and respiratory syncytial virus-associated bacterial coinfection models. Mechanistic studies showed enhanced opsonophagocytic killing, reduced bacterial dissemination, and blocked epithelial translocation. Cryo-electron microscopy identified a repeating motif within the choline-binding domain targeted by mAb 5995-40, highlighting its potential as a broadly protective pneumococcal therapeutic.

Aberrant activation of type I interferon (IFN-I) is closely related to the development of autoimmune diseases. The metabolic regulation of cytokine signaling is essential for immune homeostasis. In this study, we characterized Urolithin A(UA), a natural gut-derived metabolite, as an inhibitor of Janus kinase (JAK) signaling. UA was found to broadly dampen JAK phosphorylation and the downstream signaling induced by cytokines such as type I interferons (IFN-I), type II interferons (IFN-II), and interleukin-6 (IL-6). UA can directly bind to JAK1 JH1 domain and treatment with UA attenuated autoimmune pathogenesis in Trex1-KO mice, IMQ-induced SLE and psoriasis models. Our findings unveil that UA is an anti-inflammatory metabolite that promotes immune homeostasis and could be used to treat inflammatory and autoimmune diseases.

Gasdermins are a family of pore-forming proteins that regulate the release of pro-inflammatory cytokine, interleukin-1{beta} (IL-1{beta}) from infected or PAMP-stimulated cells. During infection or injury, IL-1{beta} is released by both human and mouse macrophages. IL-1{beta} release from mouse macrophages is associated with cell death, often termed "pyroptosis". Mouse macrophages undergoing pyroptosis assemble an exit channel termed gasdermin D (GSDMD). Both the processing of IL-1{beta} and the formation of the exit channel are caspase-1 dependent. Here, in bacterial endotoxin, lipopolysaccharide (LPS), treated mouse bone marrow-derived macrophages (BMDMs), we studied the pharmacologic inhibition of the intracellular nucleotide-binding domain, leucine-rich-containing family, pyrin domain- containing-3 (NLRP3) inflammasome by OLT1177. BMDMs stimulated with LPS plus the potassium efflux inducer nigericin triggered the formation of the NLRP3 inflammasome. Treatment of these BMDMs with OLT1177 suppressed cell death by 42% and ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain)-speck formation by approximately 60%. In addition, OLT1177 dose-dependently inhibited IL-1{beta}, CCL3, and myeloperoxidase (MPO) secretion and the pore-forming (GSDMD) from LPS-primed BMDMs, suggesting the existence of a vicious cycle controlled by IL-1{beta} release. Overall, our study demonstrates that OLT1177 prevents IL-1{beta} release from BMDMs by inhibiting caspase-1 and the conversion of (GSDMD) into its active N-terminal fragment (GSDMD-N). This study thus supports the concept that orally administered OLT1177 can be used to prevent local as well as systemic inflammation in humans.

One major aftermath of COVID-19 pandemic is cardiovascular consequences. SARS-CoV-2 binds to ACE2 and downregulates vasodilation. Dengue favors hypotension by weakening endothelial glycocalyx leading to plasma leakage. C1q levels, immune complexes (ICs), and proteomic profiles in serum samples from 52 COVID-19 and 19 pre-pandemic Dengue cases were studied. Unlike Dengue, COVID-19 serums showed elevated coagulation proteins promoting vaso-occlusion and peripheral artery diseases. The stress-induced chaperone and atherosclerosis marker, GRP78 (gene/ protein) was found upregulated upon SARS-CoV-2 spike expression in cardiac/ lung cell lines. Elevated GRP78 levels were also observed in serum samples from COVID-19-diagnosed individuals and subjects with myocardial infarction (MI) in post COVID-era. Surprisingly, spike antibodies (Abs) showed cross-binding to GRP78 and possibly contributed to the observed higher-level ICs in COVID-19 serums (cardiovascular embolism?). Co-localization studies showed that spike Abs (analogous to pro-atherosclerotic GRP78 auto-Abs) could directly bind to upregulated cellular GRP78 (type II hypersensitivity?). Both pathways could worsen vascular injury and atherosclerosis, leading to cardiac complications in COVID-19 cases with narrowed vessels.

IgA nephropathy (IgAN) is a common primary glomerulonephritis characterized by glomerular immune-complex deposits with (co)dominant IgA. These deposits are enriched for IgA1 glycoforms with some O-glycans deficient in galactose (Gd-IgA1). Circulating Gd-IgA1 is bound by IgG autoantibodies to form immune complexes, some of which deposit in glomeruli. Genomic and immunologic studies indicate involvement of pro-inflammatory signaling pathways in the production of Gd-IgA1 in IgAN. Genomic studies identified multiple genetic loci associated with IgAN and suggested a convergence on the NF-{kappa}B pathway, including RELA, the gene encoding the NF-{kappa}B subunit p65. However, the mechanisms by which NF-{kappa}B pathways may affect O-glycosylation in IgA1-producing cells are unknown. Using EBV-immortalized B cells derived from peripheral-blood mononuclear cells of IgAN patients and healthy controls that have constitutively activated NF-{kappa}B, we report that inhibition of NF-{kappa}B/p65 by a selective IKK{beta} inhibitor TPCA-1 reduced phosphorylation of NF-{kappa}B/p65 at S536 and decreased production of IgA1 and, conversely, increased Gd-IgA1 production. This was likely related to reduced expression of C1GALT1 gene that encodes the enzyme responsible for galactosylation of IgA1 O-glycans. Flow-cytometry imaging revealed changes in nuclear translocation and co-localization of the NF-{kappa}B/p65 with co-transcriptional factor SP1, a transcriptional activator of C1GALT1, suggesting that NF-{kappa}B pathway affects IgA1 O-glycosylation via SP1 transcriptional control of C1GALT1 expression. Furthermore, prolonged IKK{beta} inhibition altered B cell subpopulations, enhancing generation of cells with a plasmablast-like phenotype, characterized by high SSC MFI and CD138 expression. Together, these findings provide functional evidence for involvement of NF-{kappa}B/p65 and its transcriptional partners in IgA1 O-glycosylation. HighlightsO_LIIKK{beta} inhibition reduced C1GALT1 expression and thereby increased galactose-deficient IgA1 (Gd-IgA1) production in immortalized human B cells. C_LIO_LISP1+ subpopulations, a transcriptional activator of C1GALT1, declined after sustained NF-{kappa}B inhibition. C_LIO_LINF-{kappa}B inhibition shifted a subpopulation of B cells into a plasmablast-like phenotype. C_LIO_LIThis study links NF-{kappa}B signaling with the GWAS-identified RELA susceptibility locus and IgA1 O-glycosylation. C_LI

Introduction: Synthetic oligopeptides provide a rapid and cost-efficient approach to developing antibodies and diagnostics for emerging viral variants. Methods: This study computationally and experimentally characterized a synthetic peptide analog of the SARS-CoV-2 spike subdomain 2 major disulfide loop (SD2MDL), designated S621 (CPVAIHADQLTPTWRVYSTC). Binding affinity was computationally estimated using the Heuristic Affinity Prediction Tool for Immune Complexes (HAPTIC), while experimental validation was performed using enzyme-linked immunosorbent assay (ELISA) with rabbit-derived antipeptide antibodies. Clinical diagnostic accuracy testing was done using plasma samples from RT-PCR-confirmed COVID-19 patients and pre-COVID-19 controls. Results: S621 demonstrated nanomolar binding affinity (Kdapp = 1.14 nM) and high avidity (3.67 nM), closely matching HAPTIC predictions (3.54 nM). Diagnostic evaluation yielded a sensitivity of 89.92% and specificity of 27.79%, corresponding to an overall accuracy of 71.79%. Discussion: These findings demonstrate that a single synthetic peptide derived from a conserved spike subdomain can function as a high-affinity surrogate for full-length antigens, supporting its potential application in rapid peptide-based immunodiagnostics.

We have previously demonstrated a critical role of c-Maf SUMOylation in the regulation of autoimmune diabetogenesis, but its physiological relevance to and potential clinical impact on gut inflammation need further elucidation. Here, integrating a 14-year population-based time-trend cohort study of 139,204 type 1 diabetes patients with experiments in non-obese diabetic mice, we illustrated that autoimmune diabetes confers resistance to colitis mediated by an impaired c-Maf SUMOylation-driven IL-21-IgA axis. Utilizing T cell-specific c-Maf SUMOylation site-mutated mice, we further demonstrated that SUMOylation-defective c-Maf enhances IL-21 expression in CD4+ T cells to promote fecal IgA production and colitis resistance via microbiota remodeling, specifically through Lactobacillus johnsonii enrichment and activating lithocholic acid (LCA)-mediated AMPK anti-inflammatory pathway. Pharmacological HDAC2 inhibition by BRD6688 promotes c-Maf-mediated IL-21 and suppresses colitis in PBMC-humanized mice. Altogether, we revealed how SUMOylation reciprocally modulates the inflammatory process between autoimmune diabetes and colitis in a T cell-restricted and single transcription factor-based manner.

Current SARS-CoV-2 vaccines provide limited breadth of protection, underscoring the need for vaccine strategies that optimize immune responses. Virosomesoffer a modular vaccine platform that enables multivalent antigen display and incorporation of adjuvants which can steer immune responses. We evaluated the immune response in BALB/c mice with virosomes displaying SARS-CoV-2 Wuhan or Delta spike antigens and coupled with various distinct adjuvants. Adjuvant selection differentially influenced both humoral and cellular immune outcomes. The TLR7/8 agonist 3M -052 induced a strong Th1-biased response, characterized by elevated IgG2a/IgG1 ratios and robust type 1 cytokine induction with suppression of Th2-associated cytokines. In contrast, the saponin QS-21 enhanced antibody functional quality, illustrated by improved virus neutralization potency and breadth. Furthermore, the combined incorporation of both 3M-052 and QS-21 induced an elevated Th1-biased response without improving neutralization capacity. In conclusion, different adjuvants added onto our virosome-basedvaccine led to distinct antibody responses and splenic T-cell profiles, reflective of differences in immune programming. This information guides the selection of adjuvants for respiratory virus vaccines.

Neisseria gonorrhoeae causes gonorrhea and poses a growing global health threat driven by antimicrobial resistance and the lack of an effective vaccine. The lipooligosaccharide (LOS) epitope recognized by monoclonal antibody (mAb) 2C7 is expressed by most clinical isolates, making it an attractive therapeutic target. To determine the molecular basis for mAb 2C7 recognition, we conducted structural studies of mAb 2C7 in complex with an octasaccharide derived from LOS. NMR epitope mapping demonstrated that mAb 2C7 contacts two of three glycan chains: the {beta}-chain (lactose) and the {gamma}-chain (N-acetylglucosamine). The 1.6-[A] resolution crystal structure of the Fab 2C7-octasaccharide complex revealed that these chains make extensive hydrogen bonds and hydrophobic contacts within a cleft of the Fab. Molecular dynamics (MD) simulations showed that the {beta} and {gamma} chains adopt stable, specific conformations, contrasted with transient interactions of the chain. Informed by these structural data, we synthesized a tetrasaccharide comprising the {beta} and {gamma} chains joined by heptose II. The tetrasaccharide conjugated to a carrier protein bound mAb 2C7 by ELISA and Western blotting. Isothermal titration calorimetry showed that the tetrasaccharide and octasaccharide bound mAb 2C7 with similar affinities, indicating that the smaller oligosaccharide retains the key binding determinants. Binding was enthalpically driven, consistent with the polar interactions observed crystallographically and by MD. NMR experiments with the tetrasaccharide confirmed interactions with all four residues, establishing it as the minimal 2C7 epitope. Together, these studies provide a structural framework for rational design of glycan-based vaccines and antibody therapeutics against antimicrobial-resistant N. gonorrhoeae.

Langerhans cells express the nonpolymorphic antigen-presenting molecule CD1a, positioning them as contributors to host immunity against Mycobacterium leprae in human leprosy. CD1a was originally shown to present non-canonical lipopeptide antigens such as dideoxymycobactin and chemically diverse hydrophobic ligands. Here, we generated CD4 T cell lines from leprosy lesions that recognized M. leprae in a CD1a-restricted manner. Unexpectedly, antigen recognition was protease-sensitive, prompting biochemical purification that identified two microbial protein antigens: LppX, a 25-kDa lipoglycoprotein, and Ag85A, a 30-kDa secreted protein with no known lipid modification. Recombinant proteins activated the corresponding T cell lines in a CD1a-dependent manner. Epitope mapping identified 12-mer peptides that fully reconstituted antigenicity, were conserved between M. leprae and M. tuberculosis, and elicited robust, dose-dependent IFN-{gamma} production and T cell proliferation, establishing that DNA-encoded, ribosomally translated peptides serve as CD1a-restricted cognate antigens. Biochemical analyses showed peptide binding to CD1a, supported by isoelectric focusing and surface plasmon resonance (KD [~]75 M for Ag85A). CD1a-peptide tetramers specifically stained cognate T cells, soluble CD1a was sufficient to present peptide antigen, and transfer of the LppX-specific TCR into naive T cells restored antigen responsiveness. Using CD1a-peptide tetramers, we identified antigen-specific T cells enriched in patients undergoing reversal reactions compared with patients with lepromatous leprosy and healthy donors. The CD1a-restricted T cell lines secreted IFN-{gamma} and IL-26, cytokines with established antimicrobial activity. Together, these findings demonstrate that CD1a can present canonical microbial peptides as part of a cell-mediated immune response in leprosy, extending the known spectrum of CD1a ligands. Because CD1a is nonpolymorphic and presents antigens to antimicrobial T cells, CD1a-peptide complexes may provide a broadly applicable platform for studying, detecting, and potentially targeting mycobacterial immunity.