Human leukocyte antigens (HLAs) are molecules found on the surface of most cells in the body that regulate the immune system. It is not entirely clear how HLA-B27, which appears on white blood cells, influences immune dysfunction. The connection between HLA-B27 and the inflammatory rheumatic disorder ankylosing spondylitis was discovered in 1972. Since then, the role it plays in a number of disorders, including anterior uveitis, has become more apparent.