title: Mechanisms of HLA-DR antigen expression in phytohemagglutinin-activated T cells in man. Requirement of T cell recognition of self HLA-DR antigen expressed on the surface of monocytes.
abstract: Signals required for expression of HLA-DR (DR) antigen in phytohemagglutinin (PHA)-activated human peripheral blood T cells were examined. T cells were purified by a four-step procedure, which included depletion of glass-adherent cells, 53% Percoll gradient centrifugation, nylon wool column passage, and treatment with mouse monoclonal antibodies directed to human HLA-DR antigen and Leu M1 antigen plus complement. Purified T cells responded poorly to PHA but with the combination stimuli of PHA and recombinant human interleukin 2 (rIL-2), resting T cells proliferated as well as T cells cultured with 10% monocytes and PHA. But well proliferated T cells in the absence of monocytes expressed very poor DR antigen after 7 to 8 days of culture. DR expression of T cells was restored by the addition of 10% monocytes. Allogeneic monocytes also helped proliferative responses of PHA-activated T cells but did not help the expression of DR antigen. These results suggested that signals required for T cell proliferation (PHA and rIL-2) were not sufficient for DR expression in this system and further monocytes were essentially required in a HLA-restricted manner. In the next experiment, we examined the role of membrane molecules in monocytes for transmission of signals that induce activated T cells to express DR antigen. Autologous monocytes were fixed with 1% paraformaldehyde and added to T cells in the presence of PHA and rIL-2. Fixed monocytes could help DR antigen expression of PHA-activated T cells as well as viable monocytes. But when fixed monocytes were pretreated with anti-HLA-DR monoclonal antibody, they could not help DR expression of T cells any longer. These results suggested that for the expression of DR antigen, PHA-activated T cells had to first recognize self DR antigen expressed on the surface of monocytes before proliferation occurred.
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D002455:Cell Division; D002469:Cell Separation; D004357:Drug Synergism; D005786:Gene Expression Regulation / Q000187:drug effects; D006681:HLA-D Antigens / Q000096:biosynthesis*; D006684:HLA-DR Antigens / Q000096:biosynthesis*; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology; D007963:Leukocytes, Mononuclear / Q000502:physiology*; D008213:Lymphocyte Activation / Q000187:drug effects; D008297:Male; D010835:Phytohemagglutinins / Q000494:pharmacology; D011994:Recombinant Proteins / Q000494:pharmacology; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D006681:HLA-D Antigens; D006684:HLA-DR Antigens; D007376:Interleukin-2; D010835:Phytohemagglutinins; D011994:Recombinant Proteins