Homocitrullinated Peptides Drive Pro-Inflammatory T-Cell Responses in a Humanized Mouse Model of Rheumatoid Arthritis

ObjectiveAnti-homocitrullinated protein/peptide antibodies (AHCPA) are specific to rheumatoid arthritis (RA) and predictive of worse prognosis, suggesting a pathogenic role for autoreactivity to homocitrullinated antigens. However, T-cell responses to homocitrullinated peptides remain largely unexplored. We investigated these responses in a humanized HLA-DR4-transgenic (DR4tg) mouse model of RA, which expresses the strongest genetic risk factor for this disease. MethodsDR4tg mice were injected subcutaneously with a homocitrullinated peptide called HomoCitJED while control mice received phosphate-buffered saline. After 10 days, T-cells were analyzed for their phenotypic characteristics, cytokine production, and proliferative capacities in the draining lymph nodes (dLNs) and spleens by flow cytometry, enzyme-linked immunosorbent assays, and ProQuantum immunoassays. ResultsHomoCitJED immunization drove robust expansion of T helper (Th) 1, Th17 and hybrid Th1/Th17 CD4+ T cells in dLNs, alongside elevated CD25 activation marker within these subsets. Intracellular cytokine staining confirmed effector activity, revealing higher frequencies of IL-17A+, TNF-+IL-17A+, and IFN-{gamma}+IL-17A+ CD4+ T cells. CD4+ T cells from dLNs also up-regulated the exhaustion markers LAG-3 and Tim-3. CD8+ T cells (Tc) mirrored these findings, as HomoCitJED immunization augmented CD25 and KLRG1 expression, Tc1/Tc17-type IL-17A and IFN-{gamma}/IL-17A production, and antigen-specific proliferation. Additionally, Tim-3, LAG-3 and PD-1 expression on these subsets was augmented. ConclusionsA homocitrullinated peptide elicited Th1/Th17 and Tc1/Tc17 responses marked by concurrent activation and exhaustion signatures, pointing to a dysregulated T-cell state. These findings position homocitrulline-driven T-cell imbalance across both CD4+ and CD8+ T-cell compartments as a potential mechanistic contributor to RA pathogenesis and a target for future immunomodulatory therapies.