Differentiation of thymocytes in fetal organ culture: lack of evidence for the functional role of the interleukin 2 receptor expressed by prothymocytes.

Thymic rudiments of 14-day-old mouse embryos were put into organ culture in the presence of interleukin 2 (IL2) and PC.61, a monoclonal antibody that binds to the IL2 receptor (IL2R). After 5 and 7 days of culture, we found no influence of PC.61 on the growth of the thymus and the composition of the thymocyte subpopulations as studied with a panel of monoclonal antibodies. High-dose IL2 treatment of the organ culture resulted in a reduction of the number of thymocytes and a decrease in the single CD4+ and CD4+CD8+ thymocytes, whereas the number of CD8+Ly-1+ thymocytes and the number of CD4-CD8-Ly-1- IL2R+ thymocytes increased. The effect of high-dose IL2 treatment was ascribed to the induction of a nonspecific LAK activity. Our findings argue against a functional role of IL2R on prothymocytes during early T cell development.