Population kinetics of precursors of IL 2-producing peripheral T lymphocytes: evidence for short life expectancy, continuous renewal, and post-thymic expansion.

The fate of spleen T cell populations able to produce IL 2 after stimulation with Con A (IL 2p) was evaluated at different times after injection into IL 2p-deficient, syngeneic nude recipients. Precise enumeration of transferred cell populations in recipient organs was performed by limiting dilution analysis. The results obtained confirm previous findings on the short life-span of IL 2p cells. They also demonstrate that: the transferred populations containing IL 2p were capable of continuous renewal and expansion in the host; IL 2p cell expansion, a transient event that takes place predominantly in lymph nodes, is much reduced when injected cells are depleted of recent thymus migrants; in steady-state conditions, IL 2p T cells do not lose their self-renewal ability and maintain population sizes by continuous cell production and death in peripheral pools. The self-renewal capacity, the expansion potential of peripheral IL 2p T cells and, in particular, of recent thymus migrants may allow extensive post-thymic modulation of peripheral T cell specificities, suggesting that post-thymic selection may have a major role in the establishment of the available and actual mature IL 2p T cell repertoire.