Differential surface expression of class II isotypes on activated CD4 and CD8 cells correlates with levels of locus-specific mRNA.

Class II molecules are encoded by genes located within the HLA-D region in man. Three major subregions (DR, DQ, and DP) have been identified, each containing several genes encoding the alpha- and beta-chains of the class II heterodimers. In man B lymphocytes constitutively express class II molecules, whereas T lymphocytes express class II molecules only after Ag activation. We have analyzed isotype-specific expression of class II on CD4+ and CD8+ T cell lines and clones derived from one donor after stimulation with allogeneic cells, with the soluble Ag (purified protein derivative of tuberculin), and with mitogen activation by PHA. Class II mRNA transcripts were analyzed in parallel by Northern blot hybridization with DR, DQ, and DP beta-chain-specific cDNA probes. Nearly all activated T lymphocytes expressed DR molecules and variable numbers of DP+ cells were detected in each T cell line or clone, regardless of the mode of Ag activation. DQ molecules were only found on T cell lines or clones of the CD4 phenotype. In contrast two CD8+ cytotoxic T cell lines did not bind DQ-specific mAb although they did express DR and DP molecules. The presence of DR, DQ, and DP mRNA transcripts correlated with the differential patterns of surface expression, indicating that variations in class II cell surface expression among activated T cells may relate to differential gene regulation in these cells.