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␣1*0401) and nonassociated (DR␣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␣1*0401and DR␣1*0402-restricted T cell hybridomas was performed using overlapping synthetic peptides. Antigenspecific 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␣1*0401 and DR␣1*0402 transgenic mice identified completely dif-ferent immunodominant peptide epitopes of HCgp-39, and this was not explained by known DR4-binding motifs or direct peptide-binding studies. DR␣1*0401restricted, antigen-specific T cells produced significantly more interferon-␥ and tumor necrosis factor ␣ in response to HCgp-39 than did T cells from DR␣1*0402 transgenic mice. Finally, HCgp-39 peptides defined in DR␣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.
Rheumatoid arthritis (RA) is a chronic inflammatory disease of the synovial joints that affects ϳ1% of the Caucasian population (1). Although the pathogenesis of RA is multifactorial, the major histocompatibility complex (MHC) in humans accounts for one-third to one-half of the total genetic contribution to disease susceptibility (2). A consensus motif encoded by the third hypervariable region of the HLA-DRB1 sequence of RA-associated alleles (DRB1*0401, *0404, *0405, *0408, and *0101) has been identified as one of the critical genetic elements of RA susceptibility (3-6), and the baseline frequency of expression of this diseaselinked "shared epitope" motif correlates very closely with the prevalence of RA in a given population (7). RA patients carrying 2 copies of disease-associated HLA-DRB1 alleles may have both an earlier disease onset and more severe erosive disease (8). Despite these strong