| الوصف: |
Objective The shared epitope hypothesis posits that amino acids QR/KRAA in positions 70–74 of the DRΒ1 chain are responsible for rheumatoid arthritis susceptibility. However, even DRB1*04 alleles containing the shared epitope vary greatly with respect to degrees of susceptibility. This study was undertaken to conduct a molecular examination of the shared epitope hypothesis by measuring binding of arthritogenic peptides to susceptibility and resistance alleles. Methods We measured binding of native and citrullinated forms of vimentin66–78 and α-enolase11–25 and noncitrullinated type II collagen258–272 to 88 class II alleles on Luminex beads (which includes alleles of many varying degrees of susceptibility and resistance). We expressed DRΒ1*04:01, *04:02, and *08:01 in T2 cells and mutated DRΒ1*04:01 at positions 67, 70, 71, 74, and 86 to corresponding residues in DRB1*04:02, *04:03, *04:04, *04:05, and *08:01. Finally, we measured responses of 4 DRΒ1*04:01 restricted collagen258–272 T cell hybridomas against wild-type DRΒ1*04:01, *04:02, and all mutated alleles. Results The most susceptible allele, DRΒ1*04:01, preferentially bound citrullinated vimentin66–78 and citrullinated α-enolase11–25 over the native forms. DRΒ1*04:02 exhibited no preference for citrullinated peptides, and *08:01 preferred native peptides. Similarly, DRB1*04:01 bound collagen258–272, but *04:02 and *08:01 did not. Mutating DRΒ1*04:01 at positions 70, 71, 74, and 86 to the corresponding residues in DRΒ1*04:02 or *08:01 dramatically reduced the specificity for citrullinated peptides and collagen258–272 binding. Conclusion These observations demonstrate that while amino acids at positions 70, 71, and 74 within the shared epitope in DRΒ1 mediate binding and T cell responses of arthritogenic peptides, position 86 outside the shared epitope also plays a critical role. |
