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 lymphop oiesis. We examined Bcl-2 expression and the cell cycle status of imma ture thymocyte subsets in these mice. In IL-7-deficient mice, developm ental transition to a T cell-committed fate was accompanied by a strik ing loss of Bcl-2 protein expression and an increased relative proport ion 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 protei n and cell survival. These data specify a T cell lineage developmental transition point, prior to T cell antigen receptor rearrangement, whe re IL-7 signal transduction is linked to an anti-apoptosis mechanism a nd the cell cycle.