We describe here a culture system for studying the development, in vitro, of antigen-specific CD4 T cells from unprimed mice. T cells from young mice are initially exposed to antigen, such as pigeon cytochrome C or keyhole limpet hemocyanin, in the presence of adherent accessory cells and then allowed to proliferate in the absence of antigen but in the presence of IL- 2, 10-8 M dexamethasone, and antibodies to IL-10. Proliferation and IL-2 production by T cells harvested from such expansion cultures are antigen- dependent but not antigen-specific and at different doses can be either stimulated or inhibited both by the priming antigen and by irrelevant proteins. Antigen-specific T cell reactions can be elicited by any of three modifications of the culture protocol: (a) absorption of nonspecific cells on accessory cell monolayers bearing irrelevant proteins; (b) increased doses of dexamethasone during the expansion phase; or (c) a second cycle of antigen activation and antigen-free expansion. These observations provide a foundation for further analysis of in vitro maturation of primary immune responses and suggest an important role for IL-10 and glucocorticoids in regulating the early stages of activation and proliferation by naive T cells.
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