Expression of MHC class II antigens in human B-cell leukaemia, and increased levels of class II antigens and DR-specific mRNA after stimulation with 12-O-tetradecanoyl phorbol-13-acetate.

Cells from the peripheral blood of B-cell chronic lymphocytic leukaemia (CLL) patients were examined serologically for the expression of cell surface MHC class II antigens with monoclonal antibodies (mAbs) specific for the products of HLA-DP, -DQ and -DR genes, and mRNAs from the cells of three patients were analysed with a cDNA probe specific for DR beta chain genes. In 12 cases of CLL studied by indirect immunofluorescence and FACS analysis, a variable proportion of cells failed to express detectable levels of HLA-DP and HLA-DQ antigens at the cell surface, although greater than 90% of the cells had detectable expression of HLA-DR antigens. In all cases, greater than 90% of the cells expressed MHC class I antigens and the majority of cells reacted with the Leu-1 (CD5) mAb. Cells from different patients expressed variable levels of MHC class II antigens, and this was reflected in the finding of variable levels of mRNA detectable with the cDNA probe. Culture of cells with the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) induced much increased levels of expression of MHC class II antigens. HLA-DP and -DQ antigens were expressed on greater than 90% of the cells in all cases studied after culture of the cells with TPA, and MHC class II specific mRNA transcripts were correspondingly increased. In a single case of plasma cell leukaemia studied, MHC class II antigens were not detectable at the cell surface and their expression was not induced after culture of the cells with TPA.