Molecular localization of LB-Q1, a DRw52-like T-cell recognition epitope and identification at the genomic level of associated shared hybridizing fragments

Abstract

In this paper we report on the molecular localization of LB-Q1, a supertypic HLA class II determinant which we previously identified by the use of proliferative T cells. The population distribution shows that each of the DRw52 associated specificities DR3, DR5, and DRw6 may occur with and without LB-Q1. DNA from nine DR3, six DR5, and 14 DRw6 homozygous B-cell lines were digested with the enzymes TaqI, EcoRI, and PvuII. Using a DR beta cDNA probe, shared hybridizing fragments were observed that correlate completely with the presence or absence of LB-Q1. T-cell recognition of LB-Q1 can be blocked with a monoclonal antibody (7.3.19.1) which in some haplotypes selectively reacts with the DR beta III chains, but cannot be blocked with a monoclonal antibody (I-LR2) reacting in those same haplotypes exclusively with DR beta I chains. Therefore, LB-Q1 maps to the DR beta III molecule. These data suggest the occurrence of relatively frequent previous recombinations between the two DR beta chain genes present in DRw52 haplotypes.