Mapping MHC Class II Genes and Disease-Susceptibility : Use of Polymerase Chain Reaction and Dot Hybridization for Human Leukocyte Antigen Allele Typing.

The genes of the human leukocyte antigen (HLA) region control a variety of functions involved in the immune response and influence susceptibility to over 40 diseases. The region maps to the short arm of chromosome 6 and is divided into three regions, denoted class I, II, and III. The HLA class II gene complex is approx 1000 kb in length and is arranged into three main subregions (HLA-DP, -DQ, and -DR), each of which contains genes of two types, A and B. The A genes encode α-polypeptides and B genes encode β-polypeptides; together these form the functional class II αβ dimer. Although some haplotypes contain up to 14 class II loci, not all are expressed, and limitations on functionally permissive heterodimer formation restricts the expressed repertoire to 4 class II molecules/haplotype: DPαβ, DQαβ, DRαβ(1), and DRαβ(3,4,5)(the second DR molecule is either DRαβ(3), DRαβ(4), or DRαβ(5), depending on the haplotype). With the exception of the DRA locus, the genes encoding each of these polypeptides are highly polymorphic.