Predictability of alloreactivity among unrelated individuals: role for HLA‐DPB1

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Abstract
We compared the mixed lymphocyte culture reaction (MLR‐I) among unrelated individuals who are carriers of the extended haplotype [HLA‐B8, SC01, DR3, DRB1*0301, DQB1*0201] 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.