Differential Expression of HLA-DR and DQ Molecules on Activated T Lymphocytes

Molecular genetic studies of the HLA-D region revealed an unexpected complexity in the class II gene organization in man. Three clusters of DNA sequences were identified that encode la-like alpha and beta chain molecules: DR consisting of 1α and 2 β-like sequences and DQ and DP each having 2α and 2 β-like sequences (1). Through cis and trans gene complementation, an HLA-D heterozygous individual could express more than 40 distinct la heterodimers. Since class II molecules seem to be pivotal signals in cellular interactions in the immune system it is important to understand how they are expressed in immunologically active cells. At least 2 α and 7 β chain molecules were isolated from HLA-D homozygous lymphoblastoid cell lines (LCL), indicating that the products of several genes were expressed simultaneously in mature B cells (2). On the other hand, early stage B cell leu-kemias did not express DQ-like molecules (3), however DQ expression could be induced with 12-0-tetradecanoylphorbol-l3-acetate (TPA) (4), an agent influencing cell maturation. Also, DQ-like molecules were found only on monocytes and hemopoietic cells of more differentiated stages (4,5).