Serological discrimination of DR4 haplotypes by radioimmunoassay.

Three new alloantigenic specificities of human major histocompatibility complex class II molecules have been defined by testing the reactivity of alloantisera at the molecular level. Two of these specificities identify different DR4 haplotypes. The Fe75 specificity is associated with the DR4/Dw10 haplotype and the CBC/MRG6 specificity with the DR4/DKT2 haplotype. Both are supertypic specificities and are associated with other DR specificities as well. Both specificities are carried by class II molecules belonging to the first DR subset. Together with previously described determinants, these specificities contribute to serological discrimination of the different DR4 haplotypes.