Autoimmune rheumatologic diseases
The presence of anti-citrullinated protein antibodies in rheumatoid arthritis (RA) indicates that an immune response directed toward citrullinated antigens participates in disease development. Using a combinatorial HLA class II tetramer staining approach and applying a new computational algorithm for phenotyping rare cell populations, we characterized cit-specific CD4+ T cells in a cross-sectional cohort of 80 RA subjects and 30 matched healthy control (HC) subjects. We assayed the frequency and phenotype of CD4+ T cells specific for five citrullinated autoantigens expressed in the joint: alpha-enolase, aggrecan, cartilage intermediate layer protein (CILP), fibrinogen and vimentin. While the overall frequency of cit-specific CD4+ T cells was increased in RA subjects compared to HC subjects, antigen-specific differences were observed. Further, antigen-specificity influenced the predominant immunophenotype of cit-specific CD4+ T cells. Cit-aggrecan-specific cells were primarily Th2-like; cit-alpha-enolase-specific cells were principally Th1; and CILP-specific cells were mostly naïve. Lastly, certain cit-specific cell immunophenotypes were significantly associated with disease characteristics. Th17-like cit-aggrecan-specific cells were more frequent in early disease whereas Th1-like cells were abundant in longstanding RA. CILP-specific cells shifted out of the naïve compartment with increased disease duration. Vimentin/fibrinogen-specific stem cell memory cells were more frequent than predicted from the CD4+ landscape and were linked to disease activity. These data reveal the heterogeneity of autoantigen-specific CD4+ T cells across and within individuals and suggest that specific antigens may drive distinct immune responses. Future work may help classify RA subjects based on the specificity and dominant phenotype of their T cell response, leading to more targeted therapies.