Tic‐tac‐toe does not provide lessons for appreciating the HLA–rheumatoid arthritis relationship: Comment on the editorial by Bridges et al

Protection against anti–citrullinated protein antibody–positive rheumatoid arthritis is predominantly associated with HLA–DRB1*1301: A meta‐analysis of HLA–DRB1 associations with anti–citrullinated protein antibody–positive and anti–citrullinated protein antibody–negative rheumatoid arthritis in four European populations

“…The 3 best known classifications postulate that HLA-DRB1 alleles with a protective effect harbor the "shared sequence" DERAA at positions 70-74 (18), an aspartic acid at position 70 (D70 allele) (16), or an isoleucine at position 67 (I67 allele) of the HLA-DRB1 molecule (15). The DERAA and D70 alleles have been shown to be protective in both the presence and absence of SE alleles (19,20), which demonstrates that their protective effect is not solely attributable to the absence of SE alleles (21,22). A new classification of HLA-DRB1 alleles has recently been put forward that incorporates both predisposing and protective effects (23,24).…”