HLA-DQA2 and osteoarthritis, knee: HLA‐DQA2 and HLA‐DQB1 encode HLA class II molecules, including HLA‐DQ α and β chains, which are expressed in antigen‐presenting cells.15 HLA class II molecules play an important role in the immune system by presenting peptides derived from extracellular proteins.16 Nakajima et al17 conducted GWAS and replication study using 4800 Japanese subjects and found the association of rs7775228 with susceptibility to knee osteoarthritis.