Human class II major histocompatibility antigen beta-chains are derived from at least three loci.

Class II antigens of the major histocompatibility complex (MHC) consist of two glycosylated, membrane-integrated polypeptide chains. These cell surface-expressed molecules are involved in several immunobiological events involving cell-cell interactions, most of which seem to require that genetically identical class II antigens, or other molecules controlled by the same region of the MHC, are expressed on the interacting cells. The extensive genetic polymorphism of the class II antigens has rendered analyses in the human system of the number of non-allelic species of class II antigens difficult, although several laboratories have reported the existence of at least two types of human class II antigens. Here we present the results of experiments using restriction enzyme digestions and separation of DNA from individuals homozygous for the MHC followed by hybridization to human class II antigen alpha- and beta-chain cDNA probes. While the alpha-chain probe gave only a single hybridization band, the various beta-chain probes revealed a more complex pattern that is consistent with the existence of at least three separate beta-chain genes or pseudogenes in the human MHC.