IL-7 is critical for homeostatic proliferation and survival of naive T cells

In T cell-deficient conditions, naive T cells undergo spontaneous "homeosta tic" proliferation in response to contact with self-MHC/ peptide ligands. W ith the aid of an in vitro system, we show here that homeostatic proliferat ion is also cytokine-dependent. The cytokines IL-4, IL-7, and IL-15 enhance d homeostatic proliferation of naive T cells in vitro. Of these cytokines, only IL-7 was found to be critical; thus, naive T cells underwent homeostat ic proliferation in IL-4(-) and IL-15(-) hosts but proliferated minimally i n IL-7(-) hosts. In addition to homeostatic proliferation, the prolonged su rvival of naive T cells requires IL-7. Thus, naive T cells disappeared grad ually over a 1-month period upon adoptive transfer into IL-7(-) hosts. Thes e findings indicate that naive T cells depend on IL-7 for survival and home ostatic proliferation.