title: Phytohaemagglutinin activation of T cells through the sheep red blood cell receptor.
abstract: Expression of receptors for sheep red blood cells and the ability to proliferate in response to phytohaemagglutinin (PHA) are the traditional properties of human T cells, but the function of the sheep red cell receptor (the T11 antigen) is controversial and the mechanism of PHA-induced mitogenesis unclear. Mitogenesis involves a complex series of cell-mediated and factor-dependent interactions, but a rise in intracellular free calcium concentration, [Ca2+]i, seems to be an important primary event in T-cell activation. We have now investigated the effects of three monoclonal antibodies, previously shown to inhibit mitogen-induced proliferation, on T-cell [Ca2+]i. We find that anti-LFA-2 and OKT11, which react with the sheep red cell receptor, have no effect on [Ca2+]i, nor do they inhibit the rise in [Ca2+]i induced by concanavalin A (Con A) or the mitogenic anti-T3 monoclonal antibody UCHT1 (ref. 11). They do, however, block PHA-induced Ca2+ mobilization. Anti-LFA-1, which reacts with the lymphocyte function-associated antigen, has no effect on intracellular Ca2+. These studies suggest that the sheep red blood cell receptor is an activation pathway for T cells and that the effects of PHA are mediated through this pathway.
mesh_terms: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface / Q000276:immunology; D002118:Calcium / Q000378:metabolism; D004912:Erythrocytes / Q000276:immunology; D006801:Humans; D008213:Lymphocyte Activation; D008934:Mitogens; D010835:Phytohemagglutinins / Q000494:pharmacology; D011971:Receptors, Immunologic / Q000502:physiology*; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D008934:Mitogens; D010835:Phytohemagglutinins; D011971:Receptors, Immunologic; D002118:Calcium