El copyright pertenece a The Rockefeller University PressWe have analyzed the effect of human recombinant interleukin 4 (rIL4) on the growth and differentiation of human intrathymic pre-T cells (CD7+2+1-3-4-8-) . We describe that this population of T cell precursors proliferates in response to rIL4 (in the absence of mitogens or other stimulatory signals) in a dose-dependent way. The IL-4-induced proliferation is independent of the IL-2 pathway, as it cannot be inhibited with an anti-IL2 receptor a chain antibody. In our culture conditions, rIL4 also promotes the differentiation of preT cells into phenotypically mature T cells. Although both CD3/T cell receptor (TCR)-[alfa/beta]+ and CD3-[gamma/delta]+ T cells were obtained,the preferential differentiation into TCR-y/a+ cells was a consistent finding. These results suggest that, in addition to IL-2, IL4 plays a critical role in promoting growth and differentiation of intrathymic T cell precursors at early stages of T cell developmentPeer reviewed