The genetics of the HLA system.

The availability of cDNA probes for Class I and Class II major histocompatibility complex (MHC) antigens has revealed the existence of more genes in both the Class I and Class II subsets than had been previously detected. The use of restriction endonucleases has demonstrated that restriction enzyme site polymorphisms exist in the flanking sequences for many of the Class I and Class II genes of the MHC. The development of locus specific probes should permit utilization of these restriction site polymorphisms in characterizing particular HLA haplotypes (combinations of HLA A, B, C, DR, DC, and SB) and the availability of allele specific probes, if feasible, would permit direct determination of genotype by DNA hybridization methods. These methods would greatly enhance our understanding of Class I and Class II HLA population genetics, linkage disequilibrium, and association of HLA with susceptibility to autoimmune diseases.