T cell responses to a human cartilage autoantigen in the context of rheumatoid arthritis-associated and nonassociated HLA-DR4 alleles

Objective. To analyze the CD4+ T cell responses to the human cartilage antigen glycoprotein-39 (HCgp-39) in the context of rheumatoid arthritis (RA)-associated (DR alpha beta 1*0401) and nonassociated (DR alpha beta 1*0402) HLA class II molecules.

Methods, Large numbers of HCgp-39-specific T cell hybridomas were generated following immunization of HLA-DR4/human CD4 transgenic, murine major histocompatibility complex class II deficient mice with native HCgp-39. Fine epitope mapping of DR alpha beta 1*0401 and DR alpha beta 1*0402-restricted T cell hybridomas was performed using overlapping synthetic peptides. Antigen-specific cytokine production by lymph node T cells was evaluated after immunization with native antigen. Proliferative T cell responses of healthy human subjects were compared with the T cell responses of patients with active RA using HCgp-39 epitopes defined in HLA-DR4 transgenic mice.

Results, CD4+ T cells from DR alpha beta 1*0401 and DR alpha beta 1*0402 transgenic mice identified completely different immunodominant peptide epitopes of HCgp-39, and this was not explained by known DR4-binding motifs or direct peptide-binding studies, DR alpha beta 1*0401-restricted, antigen-specific T cells produced significantly more interferon-gamma and tumor necrosis factor alpha in response to HCgp-39 than did T cells from DR alpha beta 1*0402 transgenic mice. Finally, HCgp-39 peptides defined in DR alpha beta 1*0401 transgenic mice stimulated T cells from HLA-DR4 positive human subjects and RA patients, but not T cells from HLA-DR4 negative individuals.

Conclusion. T cell epitopes of HCgp-39 that were defined in HLA-DR4 transgenic mice stimulated T cells from human subjects carrying RA-associated HLA-DR4 alleles. HLA-DR4 molecules may influence the disease process in RA both by presentation of selected peptide epitopes and by promoting the production of proinflammatory cytokines in synovial-joints.