HLA-DRB1 and rheumatoid arthritis: A recent study has implicated molecular mimicry as an underlying mechanism of protection against RA by certain HLA-DRB1 alleles encoding for a DERAA sequence in the cusp region due to a tri-lateral sequence homology among a self-protein named vinculin, microbial proteins, and the products of the protective DRB1 alleles (71).