Influence of the QKRAA/QRRAA/RRRAA motifs of the third hypervariable region of HLA-DRB1 in the development of rheumatoid arthritis.

Most patients with rheumatoid arthritis (RA) express HLA-DR4, HLA-DR1, or HLA-DR10. The DRB1 chains of these alleles have highly homologous 3rd hypervariable regions, with the motifs QKRAA, QRRAA, or RRRAA. The role played by the QKRAA, QRRAA, and RRRAA motifs in the development of RA is unknown. It may involve interaction with a T cell, an antigenic peptide, or an unknown ligand. We investigated the role played by the QKRAA motif and observed that it was expressed on numerous proteins from bacteria and viruses. However, we detected no anti-QKRAA autoimmunization in patients with RA. We found that QKRAA is a binding motif for bacterial and human 70 kDa heat shock proteins, and suggest that this may explain both its being expressed on so many proteins and its role in the development of RA.