HLA-DR TYPING AT THE DNA LEVEL - RFLPS AND SUBTYPES DETECTED WITH A DR-BETA CDNA PROBE

Abstract

The HLA-DR.BETA. gene, used as a hybridization probe, detects RFLPs that correlate with HLA-DR specificities. Using genomic DNA from more than 200 individuals, we have carried out a population study with a cDNA probe for the DR.beta. chain, which, under appropriate conditions, does not cross-hybridize with genes from other HLA-D subregions (e.g., DP and DQ). We first assessed the correspondence between serologically defined HLA-DR types and DNA patterns obtained after digestion with TaqI and found that DNA patterns allowed us to identify most specificities. Only two pairs of antigens are not distinguishable: with the DR.BETA. probe alone we cannot distinguish DR3 from DRw6 or DR7 from DRw9. However, the correct assignment can always be made for the first pair by hybridizing the same digests with a DQ.alpha. or DQ.beta. probe. Thus DR typing from the DNA patterns is practical and accurate. We also looked for serologically undetectable subtypes. RFLPs revealed high-frequency subtypes for the specificities DR 2, 3, 5, w6, 7, and w9. Some of these are more accurately viewed as variant haplotypes, since the relevant variations is probably not at the DR.beta. locus that determines the serological specificities but rather at other closely linked and highly homologous DR.beta. locus such as DR.beta.-III. Nevertheless, the existence of variant haplotypes for so many specificities indicates a wealth of polymorphic variation beyond that detected serologically and provides more specific markers for studies of various diseases associated with HLA-DR specificities.