HLA-DR typing as a predictor of MLC compatibility.

Mixed lymphocyte culture reactions between HLA-identical siblings, HLA-DR-identical parent-child and sibling pairs, HLA-DR identical unrelated normal individuals, and cadaver kidney graft donor and recipient pairs were compared for MLC compatibility. Of 34 HLA identical sibling pairs, 31 (91%) showed a percentage of relative response (RR%) of less than 5%. Forty-two of 79 HLA-DR-identical parent-child and sibling pairs (53%), 8 of 61 unrelated individuals (13%) and 4 of 7 cadaver transplant donor-recipient pairs showed %RR values of less than 20%, which is consistent with MLC compatibility. An additional 7 parent-child and sibling pairs and 8 unrelated combinations were in the borderline range yielding %RRs of 20-30%. Median %RR values were significantly increased in the DR-compatible unrelated group as compared with the DR-compatible related group (p less than .001). In the related group pairs matched for HLA-B in addition to HLA-DR had a significantly lower median %RR than pairs matched for HLA-DR only (p less than .001). In addition, a higher frequency of MLC-compatible combinations was found when B/DR-compatible antigens were present in a positive linkage disequilibrium. The same trend was observed in the unrelated population, but the number of B/DR compatible pairs in the population was low. The data demonstrate the range of MLC reactions between HLA-DR-compatible related and unrelated individuals and support the hypothesis that individuals compatible for HLA-B and DR antigens in a strong linkage disequilibrium are more likely to be MLC-compatible.