Developmentally controlled expression of IL 2 receptors and of sensitivity to IL 2 in a subset of embryonic thymocytes.

At various times of gestation murine fetal thymocytes were tested for IL 2 receptor (IL 2-R) and T cell differentiation antigen expression. The majority of 14 to 15 day fetal thymocytes were IL 2-R and Thy-1 antigen positive, yet negative for the Lyt and L3T4 marker. A subset of IL 2-R-positive fetal thymocytes could be induced by recombinant IL 2 to proliferate over at least 10 days. Growth of these proliferating cells could not be enhanced by syngeneic feeder cells nor suppressed by monoclonal anti-I-A or anti-I-E antibodies. No antigen-specific effector functions could be induced in the proliferating Thy-1, IL 2-R-positive cells. As a whole, the results suggest a developmentally controlled rather than antigen-induced expression of IL 2-R during embryogenesis of thymocytes.