Growth of fetal thymocytes in organ culture: effect of recombinant lymphokines on thymocyte maturation.

Interleukin 2 (IL2) has a dose-dependent inhibitory effect on the growth and phenotypic maturation of thymocyte populations grown in fetal thymus organ culture. Addition of IL2 (100 U/ml) to 14-day fetal thymus organ cultures induces the appearance of a population of lymphokine-activated killer (LAK) cells which lyse allogeneic, syngeneic, and syngeneic tumor cell targets. The addition of the monoclonal antibody, PC-61, blocks the IL2-dependent growth and activation of LAK cells but does not influence the maturation of CD4+ CD8+ fetal thymocytes. These data imply that IL2 is not a major regulator of normal fetal thymocyte maturation. The effects of a range of recombinant lymphokines (IL1 alpha, IL1 beta, IL3, IL4, GM-CSF, G-CSF, M-CSF) on the proliferation and phenotypic maturation of fetal 14-day thymocytes in organ culture has been analysed. Two significant changes were seen. First, IL1 alpha and IL1 beta inhibited growth and the expression of the CD4 and CD8 antigens in organ culture, and second, GM-CSF increased the expression of Mac-1+ cells. IL4, which has known T cell growth-promoting activity, IL3, G-CSF, and M-CSF did not alter either normal growth or surface antigen expression in fetal thymocytes. While some of these lymphokines may function as accessory molecules in fetal thymocyte development, our experiments suggest that they do not have a significant influence on thymocyte maturation when used alone.