Unique sequences for two HLA-DRB1 genes expressed on distinct DRw6 haplotypes

Abstract

We have used restriction fragment length polymorphism (RFLP) analysis and DNA sequencing to characterize two distinct DRB1 alleles expressed on DRw52 and DQw7-associated haplotypes but not readily defined by conventional DR serology. These two haplotypes, designated HLA-D “HAG” and “PEV”, react variably with DRw13(w6), DRw14(w6), and the more broad DR “3+6” antisera. Analysis of RFLP revealed that HLA-D “HAG” and “PEV” are associated with different DRw52 variants, and that “HAG” is indistinguishable from DRw18(3) haplotypes. Sequencing of the “HAG” and “PEV” DRB1 genes showed each to represent novel alleles. Nevertheless, these sequences show similarities with the other alleles of the DR5, w6, and w8 family. “HAG” (DRB1*1303) appears to have arisen either from two recombinational events involving at least three DRB1 sequences (DRB1*1101, DRB1*0803, DRB1*0401) or from a single recombinational event together with multiple point mutational events. “PEV” appears to represent a DRB1*1301-1302/DRB1*1101 recombinant allele, with recombination having occured in the region of bases 175 – 198. The results of this study suggest that the DRw52 family haplotypes is derived from a relatively restricted number of ancestral sequences, with diversity among DRB1 alleles within this family arising through gene conversion or recombination events.