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HLA class II molecules were isolated from a large panel of Epstein Barr virus-transformed B-cell lines by immunoprecipitation with the monoclonal antibodies Tu22, IA3, and SPV-L3. The radiolabeled immunocomplexes were analyzed by two-D gel electrophoresis. Such assays demonstrated that SPV-L3 (not used in this Workshop; therefore, see reference 1) is truly locus-specific and isolates only one type of HLA-DQ molecules from HLA-DR-DQ homozygous B-cell lines that originate from consanguineous origin.

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).

Previous reports have demonstrated the existence of an alloantigenic system not detectable on resting T and B lymphocytes, which is expressed on renal capillary endothelium and monocytes (1,2). In contrast to resting B lymphocytes, EBV-transformed B cells appeared to express EM antigens as shown by absorption studies. These endothelium monocyte (EM) antigens appear to be important in transplantation immunology since EM antibodies are present in the circulation during acute graft rejection and can be eluted from biopsies taken from a graft that is being rejected (2–6). Although the genetics is not completely clear, EM antigens have shown to be polymorphic (7). However, the molecular localization of these antigens has been a question of debate. Therefore, this was studied by analyzing immunoprecipitates obtained of EBV-transformed B cells using EM alloantisera. Gel electrophoretic techniques showed that EM alloantigenic determinants are located on a subset of HLA-DR molecules.