Ian Reay Mackay is distinguished for contributions to clinical immunology, particularly autoimmune disease. Mackay wrote the first text (1963), with F. M. Burnet, on the nature of autoimmune disease. He identified autoimmunity as one cause of chronic hepatitis (1956) and established diagnostic serological assays, and showed that corticosteroid and immunosuppressive drugs reversed autoimmune inflammation in the liver (1957-1968). Mackay also described primary biliary cirrhosis as an autoimmune disease (1958) and his laboratory identified the autoantigenic mitochondrial polypeptides (1985) and the nuclear gene coding for the major polypeptide (1987), now recognized as part of the pyruvate dehydrogenase complex. His discoveries provided important insights into liver disease and autoimmunity in general.