THE CYTOKINES IL-4, IFN-GAMMA, AND IL-12 REGULATE THE DEVELOPMENT OF SUBSETS OF MEMORY EFFECTOR HELPER T-CELLS IN-VITRO

We analyzed the development of cytokine-producing effector T cells fro m resting CD4 memory cells. Previously we showed that such memory effe cters are induced in vivo upon re-exposure to Ag. Here we demonstrate that effecters arise in vitro when memory CD4 cells are restimulated w ith Ag in the presence cytokines. Resting splenic CD4 cells from KLH-p rimed mice that were depleted of naive cells by adult thymectomy and w ere exclusively of memory phenotype initially secreted high titers of IL-2 and low levels of IL-4 and IFN-gamma in response to Ag. When memo ry CD4 cells were restimulated for 3 to 4 days in cultures containing rIL-2 and Ab to block endogenous IFN-gamma and IL-4 secretion, ThO-lik e effecters that produced greatly increased levels of IL-2, IL-4, and IFN-gamma developed. rIL-4 together with rIL-2 and anti-IFN-gamma indu ced Th2-like cells that secreted primarily IL-4. In contrast, Th1-like effecters that produced IL-2 and IFN-gamma developed in the presence of rIL-2 and anti-IL-4. Addition of rIFN-gamma further enhanced primin g for IFN-gamma secretion. rIL-12 also induced effecters that produced high levels of IFN-gamma, but little IL-2. Thus, cytokines direct the development of effector subsets from memory CD4 cells. Our results su ggest that memory and naive CD4 cells undergo parallel development fol lowing Ag stimulation, initially secreting predominantly IL-2 and diff erentiating in response to IL-4, IFN-gamma, and IL-12 into polarized e ffector subsets.