HLA-DR and the development of rheumatoid arthritis. 
Susceptibility to develop Rheumatoid arthritis (RA) maps to a highly conserved amino acid motif ("the shared epitope") expressed in the third hypervariable region of different HLA-DRB1 alleles.  This motif, namely QKRAA, QRRAA or RRRAA helps the development of RA by an unknown mechanism.  However, it is now established that the shared epitope can 1.  Shape the T cell repertoire.  2.  Interact with 70 kD heat shock proteins.