Microheterogeneity of HLA-DR4 haplotypes: DNA sequence analysis of LD"KT2" and LD"TAS" haplotypes.

We have isolated and sequenced cDNA clones corresponding to the polymorphic alpha and beta chains encoded by the DR and DQ subregions of two HLA-DR4 haplotypes, LD"KT2" and LD"TAS". These two haplotypes are distinguished on the basis of mixed lymphocyte culture typing. The data indicate that the designation of LD"TAS" as a distinct subtype from Dw13 is very likely due to amino acid differences in the DQ beta chain. In contrast, LD"KT2" differs from TAS and Dw13 by a single amino acid substitution at position 37 of the DR beta 1 chain. The functional and evolutionary significance of these polymorphisms is discussed.