The cytokines IL-4, IFN-γ, 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 from resting CD4 memory cells. Previously we showed that such memory effectors are induced in vivo upon re-exposure to Ag. Here we demonstrate that effectors arise in vitro when memory CD4 cells are restimulated with Ag in the presence cytokines. Resting splenic CD4 cells from KLH-primed mice that were depleted of naive cells by adult thymectomy and were 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 memory 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, Th0-like effectors that produced greatly increased levels of IL-2, IL-4, and IFN-gamma developed. rIL-4 together with rIL-2 and anti-IFN-gamma induced Th2-like cells that secreted primarily IL-4. In contrast, Th1-like effectors that produced IL-2 and IFN-gamma developed in the presence of rIL-2 and anti-IL-4. Addition of rIFN-gamma further enhanced priming for IFN-gamma secretion. rIL-12 also induced effectors 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 suggest that memory and naive CD4 cells undergo parallel development following Ag stimulation, initially secreting predominantly IL-2 and differentiating in response to IL-4, IFN-gamma, and IL-12 into polarized effector subsets.