Analysis of the DR beta chains from two DRw6 cell lines (WT46 and WT52): recombination in vivo may have generated new haplotypes.

The HLA-DRw6 haplotype of the class II major histocompatibility complex (MHC) antigens exhibits unusual complexity and cannot be uniquely typed serologically. The DR beta chains expressed by consanguineous homozygous DRw6 typing cells WT46 and WT52 were biochemically analyzed using three monoclonal antibodies (mAb) that recognize denatured DR beta chains. The results of isoelectric focusing and N-terminal sequencing demonstrate that each DRw6 B-cell line expresses two DR beta chains. Evidence of an exchange of mAb epitopes involving the two DR beta chains of one of these cell lines was obtained and may be explained by a recombinational mechanism involving reciprocal exchange of genetic segments of the DR beta chains, one of which may encode the putative DRw6 chain and the other the chain carrying the MT2 allotypic determinant. Since a recombinational hot spot has been shown to occur uniquely in the mouse MHC within the E beta gene, the occurrence of a recombination within the human homolog, DR(MT2) beta, could reflect some specific feature of this MHC region. Comparison of the DR beta chains of the WT46 and WT52 cell lines with those of a third DRw6 cell line, LB, suggests that two alleles of MT2 occur.