Evidence for Intra HLA-DR and -DQ Subregion Crossing Over Events

The HLA-DR and -DQ region of 47 homozygous typing cell lines were analyzed by a variety of techniques such as restriction fragment length polymorphism analysis, gel electrophoretic screening of the gene products, and in some cases, by testing MHC class II restriction in antigen presentation assays (1,2). Among these 47 cell lines, 16 different HLA-DR-DQ haplotypes were observed. Their genetic make up has been summarized in Table 1. It is concluded that some cell lines that express the same type of DRβI allele may express different kinds of DRβIII alleles. For example, cell lines positive for the AVL and QBL DRw17-DQw2 haplotypes do share the same DRβI3 gene product but AVL or QBL-like cell lines express DRβIII3 and DRβIII5 gene products, respectively. This DRβIII5 gene product is often expressed by HLA-DR5 positive cell lines and is involved in the expression of the T-cell recognition epitope LB-Q1 (3,4).