Expression of class I histocompatibility antigens on human T-B lymphoblast hybrids

Expression of class I histocompatibility antigens (HLA-A and B) on hybrids of human T and B lymphoblastoid cell lines (LCL) was examined. The T-LCL CEM expressed low levels of HLA-A and B antigens. CEM^R and CEM^R.3, two 8-azaguanine- and ouabainresistant sublines of CEM used for fusion, expressed no detectable HLA-B antigens and expressed HLA-A antigens at a level below that of CEM. The three B-LCL studied expressed class I histocompatibility antigens at levels 50-to 80-fold in excess of that found on CEM as assessed by indirect immunofluorescence and flow cytometry. Total levels of class I histocompatibility antigens on hybrids of CEM^R and CEM^R.3 with B-LCL were similar to those found on the B-LCL. CEM-encoded HLA-A and B antigens were expressed on the hybrids at levels much greater than those seen on CEM itself; expression by the hybrids of CEM-encoded and B-LCL-encoded class I antigens was comparable. By RNA-DNA filter hybridization, CEM^R.3 was found to have extremely low levels of class I heavy-chain mRNA compared with two B-LCL and with HSB, a T-LCL that expresses high levels of class I histocompatibility antigens. Thus, the paucity of HLA-A and B expression by CEM^R.3 (and by inference, CEM^R and CEM), as well as the enhancement of CEM-encoded HLA-A and B antigen expression on B-LCL × T-LCL hybrids, must be due, at least in part, to modulation of the level of transcripts encoding HLA class I heavy chains.