HLA Class II Gene Polymorphism: DNA Typing, Evolution, and Relationship to Disease Susceptibility

Abstract

The detection of HLA class II polymorphism is valuable in the areas of individual identification, tissue typing for transplantation, and genetic susceptibility to specific autoimmune diseases. Polymorphism in the HLA class II region (see Figure 1 for map) has been identified using serologic reagents (HLA-DR and -DQ specificities), by cellular techniques (Dw and DPw specificities) and, more recently, by restriction fragment length polymorphism (RFLP) analysis. For HLA class II typing, RFLP analysis is based on the presence or absence of polymorphic restriction sites located primarily in non-coding regions which are in linkage disequilibrium with allelic variation in coding sequences. Until recently, the direct analysis of coding sequence polymorphism has been difficult. However, the enzymatic amplification of specific DNA sequences using the PCR has provided a new approach to genetic typing.^1-4 The capacity of the PCR to amplify a specific segment of genomic DNA has made it an invaluable tool in the study of polymorphism and evolution, as well as in the analysis of genetic susceptibility to disease. In all of these areas, a particular gene must be examined in a variety of individuals; either within a species, in different closely related species, or in patient and in healthy control populations. We have used PCR, initially with the Klenow fragment of E. colf DNA polymerase I and more recently with the thermostable Taq DNA polymerase, to determine the allelic sequence diversity of the HLA class II genes (HLA-DRβ, HLA-DQα, HLA-DQβ, and HLA-DPβ).