human leukocyte antigen (HYOO-mun LOO-koh-SITE AN-tih-jen)
One of a group of proteins found on the surface of white blood cells and other cells that play an important part in the body's immune response to foreign substances. These antigens vary from person to person, and human leukocyte antigen tests are done before organ transplantation to find out if tissues match between a donor and a recipient. Also called HLA and human lymphocyte antigen.
