RESPONSES OF HUMAN FETAL SPLENOCYTES AND THYMOCYTES TO INTERLEUKIN-2 AND COMPARISON WITH ADULT PERIPHERAL-BLOOD LYMPHOCYTES

By means of cytotoxicity and thymidine uptake assays, the effect of hu man recombinant interleukin-2 (rIL-2) on the induction of lymphokine-a ctivated killer (LAK) cell activity and cellular proliferation in sple nocytes and thymocytes from human fetuses (18-22 weeks) was studied an d compared with that in mononuclear cells from adult peripheral blood. It was shown that the fetal splenocytes and thymocytes incubated with low doses of rIL-2 (10-100 U/ml) developed a broad spectrum of antitu mor activity (LAK cytotoxicity), although the kinetics and magnitudes of the responses were different. It was also suggested that LAK precur sors were present in fetal spleen and thymus. Furthermore, rIL-2 induc ed a stronger proliferative and cytotoxic response in splenocytes than in thymocytes. The human fetal LAK cells isolated from the spleen wer e found to be 10-20 times more potent than those from adult peripheral blood with regard to cell proliferation and cytotoxicity in vitro.