Proteins located on the surface of white blood cells which play an important role in our body's immune response to foreign substances. Vary from person to person. Thought that people with certain types of HLA antigens are more likely to develop insulin-dependent diabetes. These antigens are also used to determine the suitability of a match between an donor and a recipient. Patients and potential donors have their white blood cells tested for three antigens - HLA-A, -B and -DR. Each individual has two sets of these antigens, one set inherited from each parent. For this reason, it is much more likely for a brother or sister to match the patient than an unrelated individual, and much more likely for persons of the same racial and ethnic backgrounds to match each other.