Polymorphism and Regulation of HLA Class II Genes of the Major Histocompatibility Complex

Until recently, immunology had remained a controversial field for molecular biologists, with provocative and subtle theories outnumbering hard facts. In the last 10 years however, due in large part to the availability of cDNA cloning (Rougeon et al. 1975), dramatic progress in molecular immunology has clarified the genetic basis of immune diversity and of the control of the immune response. The diversity of immunoglobulins and of T-lymphocyte receptors is a somatic phenomenon, with each clone of a B or T cell exhibiting a distinct specificity. On the other hand, the diversity of major histocompatibility complex (MHC) antigens results from allelic polymorphism at the population level, with all cells of a given individual expressing the same specificity. The MHC encodes two major groups of antigens: class I, also known as transplantation antigens, and class II, involved in the control of the immune response. In man, the MHC antigens are referred to...