Generation of interleukin 4 (IL-4)-producing cells in vivo and in vitro: IL-2 and IL-4 are required for in vitro generation of IL-4-producing cells.

T cell populations derived from naive mice produce very small amounts of interleukin 4 (IL-4) in response to stimulation on anti-CD3-coated dishes. IL4 production by such cells is mainly found among large- and intermediate-sized T cells and is dependent upon IL-2. Injection of anti-IgD into mice, a stimulus that leads to striking increases in serum levels of IgG1and IgE, causes a striking increase in the IL-4-producing capacity of T cells. This increase is first observed 4 d after injection of anti-IgD. IL-4 production by T cells from anti-IgD-injected donors is mainly found among large- and intermediate-sized T cells. Small, dense T cells are poor producers of IL-4. The capacity ofT cells from anti-IgD-injected donors to produce IL4 is enhanced by addition of IL2 and is largely, but not completely, inhibited by neutralization of in situ produced IL-2. These results indicate that the control of IL4 production in T cells from naive and anti-IgD-injected donors is similar. However, it is possible that a portion of the IL-4-producing activity of T cells from activated donors is IL2 independent. Although small T cells from naive donors have a very limited capacity to produce IL-4 in response to stimulation with anti-CD3, even in the presence of added IL-2, they can give rise to lL-4-producing cells upon in vitro culture on plates coated with anti-CD3 if both IL-2 and *IL-4 are added. This leads to the appearance of lL-4-producing cells within 2 d. When analyzed after 5 d of culture by harvesting and re-exposure to anti-CD3-coated culture wells and IL-2, these cells have increased their lL-4-producing capacity by ∼100-fold. The development of IL-4-producing cells in response to anti-CD3, IL-2, and IL-4 is not inhibited by interferon γ (IFN-γ), nor does IFN-γ diminish IL-4 production by these cells upon challenge with anti-CD3 plus IL-2.