A novel DRB1 Allele in DR2-positive American blacks

Abstract

Class II D region antigens of the major histocompatibility complex are naturally occurring dimeric proteins found on the surface of lymphoid cells. In most haplotypes at least two of the polymorphic β chains are associated with a nonpolymorphic α chain. The allelic variation of these proteins lies in the first domain of the expressed protein. At present, there are four known DRB genes. DRB1 encodes for the classical DR 1, 3, 4, 5, etc., specificities. DRB3 and DRB4 encode the four supertypic specificities of DRw52 and the single phenotype of DRw53, respectively. Two DRB genes are expressed in human leukocyte antigen DR2-positive individuals. While DRB1 is the more polymorphic gene in most haplotypes, in DR2 haplotypes it appears that DRB5 encodes the polymorphic DRβ chain and the DRB1 encodes a nonpolymorphic β chain. We attempted to further define the diversity of this region by direct dideoxynucleotide sequencing of polymerase-chain-reaction-amplified genomic DNA. We identified a novel DRB1 allele in DR2-positive individuals that was only observed in the American blacks sampled. This allele may code for a black specific class II antigen.