HLA-DR and DQ antigens in chronic lymphocytic leukemia: dissociation of expression revealed by cell surface, protein, and mRNA studies.

We studied peripheral blood lymphocytes (PBL) of eight B chronic lymphocytic leukemia (CLL) patients for the expression of the human leucocyte antigens, HLA-DR and HLA-DQ. Cell surface expression of HLA class II epitopes was analyzed by fluorescent activated cell sorter (FACS) using three monomorphic anti-HLA class II monoclonal antibodies (mAb) specific for DR (D1.12) and DQ (TU22, L2) and a polymorphic anti-DQ (G2A5). The DR and DQ molecules were characterized by two-dimensional gel electrophoresis (2D-PAGE) of the specific immunoprecipitates from biosynthetically labeled cells. DR, DQ specific probes were used to characterize the class II transcripts of the corresponding genes. The data obtained with immunofluorescence disclosed two distinct patterns of HLA class II expression leading to two cell surface phenotypes: (DR+DQ+) and (DR+DQ-). In all cases the cells expressed normal amounts of HLA-DR gene products in terms of mRNA. DR cell surface determinants were present in more than 80% of cells in every sample. By 2-D gel analysis DR proteins disclosed the normal classical pattern associating the alpha, beta, and invariant chain gamma with normal level of biosynthesis for alpha and gamma but decreased biosynthesis for one of the beta gene products. Moreover, the three chains demonstrated defect in glycosylation process. In half of the cases studied the cells lacked DQ molecules at the cell surface. DQ alpha and DQ beta transcripts were detected in all cases, although the amount was extremely low in one case. DQ proteins were variable in the DQ+ phenotype and absent in the DQ- one. Interestingly, TPA and rIFN gamma treatment could restore normal glycosylation process of the DR isotype and increase biosynthesis of DQ alpha and beta chains. Those combined results support the view that transcriptional, post-transcriptional, and posttranslational mechanisms underlie the heterogeneity of class II expression observed in CLL. Moreover, 2-D gel analysis may be an invaluable tool for the analysis of the biosynthetic process of class II molecules.