SEROLOGIC AND MOLECULAR STUDIES OF 2 KINDREDS EXPRESSING RECOMBINANT HLA DR1 DR2 HAPLOTYPES/

We have recently identified two unrelated kindreds in which DR1 and DR 2 co-segregate as a single haplotype spanning several generations. Ser ology, PCR-RFLP and sequence-specific oligonucleotide probes were used to characterize the presence and segregation of the DRB1 and DRB5 loc i in these two kindreds. In both families, the recombination resulted in co-expression of a DRB1 locus that encoded a DR1 serologic phenotyp e and a DRB5 locus that encoded a ''short'' DR2 serologic phenotype. O ne of these kindreds co-expressed the DR1 and DR15 (DRB501). The othe r kindred co-expressed the DR1 and DR16 (DRB502). Our data indicate t hat the recombination event occurred in the region between the DRB1 lo cus and the DRB5 locus. This recombinant haplotype produces a DR2 phen otype which lacks the epitopes normally encoded by the DRB1 locus, res ulting in a serologic ''short'' antigen. The clinical significance of such a recombinational event becomes evident when patients with such a genotype require allogeneic bone marrow transplantation.