Predictability of alloreactivity among unrelated individuals: role for HLA-DPB1.

We compared the mixed lymphocyte culture reaction (MLR-1) among unrelated individuals who are carriers of the extended haplotype [HLA-B8,SC01,DR3,DRB10301,DQB10201] on one chromosome and the generic specificity HLA-DR4 on the second chromosome. Genomic DNA samples from the same individuals were also analyzed for HLA-DRB1, DQB1 and DPB1 alleles by PCR and SSOPH typing and for DOB polymorphism by RFLP. HLA-DRB1 alleles, in paired MLR responses between unrelated individuals indicated that matching of HLA-DRB1 was a better predictor of non-reactivity than identity in HLA-DR generic types, (43% vs 22%). Moreover, 90% of the DRB1 matched pairs had nonreactive and weakly reactive MLR, whereas only 37% of DRB1 mismatched unrelated individuals gave weak or no reactions. Matching for HLA-DRB1 and HLA-DPB1 alleles eliminates a significant number of cell mixtures with MLR-I reactivity. Furthermore, some DPB1 mismatches, but not all, do not seem to elicit MLR-I reactivity.