Characterization of the requirements for human T cell mitogenesis by using suboptimal concentrations of phytohemagglutinin.
To characterize the requirements for T cell proliferation, we have studied the response of purified populations of human T cells to varying concentrations of the mitogen phytohemagglutinin (PHA). Concentrations of PHA which induce optimal proliferative responses induce increases in cytosolic free calcium ([Ca2+]i), expression of interleukin 2 (IL 2) receptors, and production of IL 2. As the concentration of PHA is decreased, each of these processes decreases in parallel. At suboptimal concentrations of PHA, the addition of exogenous IL 2 reconstitutes both the proliferative response and the expression of the IL 2 receptor, as measured by immunofluorescence with antibodies directed against the TAC/IL 2 receptor molecule, but without reconstituting the increase in [Ca2+]i. Therefore, the concentration dependence of responses to PHA appears to be secondary to an absence of IL 2 production due to a failure to induce an increase in [Ca2+]i. The addition of the calcium ionophores A23187 and ionomycin or of accessory cells to low concentrations of PHA induces increases in [Ca2+]i and subsequent proliferative responses, suggesting that the two events are linked. The proliferative response can be inhibited by antibodies directed towards IL 2 or the IL 2 receptor, indicating that the proliferative response was at least partially dependent on the production and action of IL 2. This suggests that, although increases in [Ca2+]i are an integral event in the induction of proliferation by PHA, the increase in [Ca2+]i is required for the production but not the action of IL 2. In addition, low concentrations of PHA deliver an additional signal to cells, independent of an increase in [Ca2+]i, which induces IL 2 receptor expression and allows a proliferative response in the presence of exogenous IL 2.
D000938:Antigen-Presenting Cells / Q000276:immunology; D000954:Antigens, Surface / Q000096:biosynthesis; D002118:Calcium / Q000502:physiology; D002469:Cell Separation; D004306:Dose-Response Relationship, Immunologic; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology; D008213:Lymphocyte Activation; D010835:Phytohemagglutinins / Q000494:pharmacology*; D011971:Receptors, Immunologic / Q000096:biosynthesis; D015375:Receptors, Interleukin-2; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7
D000954:Antigens, Surface; D007376:Interleukin-2; D010835:Phytohemagglutinins; D011971:Receptors, Immunologic; D015375:Receptors, Interleukin-2; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7; D002118:Calcium