The earliest T lineage-committed cells depend on IL-7 for Bcl-2 expression and normal cell cycle progression.

Interleukin-7 (IL-7)-deficient mice exhibit an early defect in lymphopoiesis. We examined Bcl-2 expression and the cell cycle status of immature thymocyte subsets in these mice. In IL-7-deficient mice, developmental transition to a T cell-committed fate was accompanied by a striking loss of Bcl-2 protein expression and an increased relative proportion of cells in the G0/G1 stage of the cell cycle. Short-term culture of immature thymocytes with rIL-7 caused up-regulation of Bcl-2 protein and cell survival. These data specify a T cell lineage developmental transition point, prior to T cell antigen receptor rearrangement, where IL-7 signal transduction is linked to an anti-apoptosis mechanism and the cell cycle.