HLA-DQA2 (Human Leukocyte Antigen DQ Alpha 2): HLA-DQA2 is a gene within the HLA complex that plays a key role in immune system regulation through antigen presentation. It encodes an alpha chain that pairs with a beta chain to form the HLA-DQ molecule, which presents foreign antigens to T cells to trigger immune responses. Variations in HLA-DQA2 are linked to susceptibility to certain autoimmune diseases, highlighting its importance in immune tolerance and autoimmunity.