HLA-DRB1 and rheumatoid arthritis: These citrullinated proteins are believed to trigger an immune response by binding to HLA-DRB1 SE molecules on antigen presenting cells, leading to activation of pathogenic T and B cells, and ultimately promoting anti-CCP antibodies formation.1 The anti-CCP antibodies form immune complexes with these citrullinated proteins results in release of mediators of inflammation and joint destruction in RA.10,11