Increase in T cell mitogen responsiveness in rat thymocytes by thymic epithelial culture supernatant.

Supernatants from rat thymic epithelial cultures (TES) increased [14C]thymidine incorporation into rat thymocytes stimulated with phytohemagglutinin (PHA) or concanavalin A, whereas supernatants from nonthymic control tissue cultures had no effect. It was demonstrated that the increased mitogen responsiveness was at least partially due to an increase in the number of responsive cells. Furthermore, our data suggest that the target cell for TES resides among the cortisone-sensitive population of thymocytes. The continuous presence of TES provided the best conditions for enhancement of mitogen stimulation. The addition of TES had very little effect on mitogen-stimulated spleen and lymph node lymphocyte cultures. The data suggest that, in the presence of TES, a cortisone-sensitive, PHA-nonresponsive subpopulation of rat thymocytes is induced to respond to PHA.