Differentiation of prothymocytes induced by trypsin

Treatment in vitro of nude mouse spleen prothymocytes with relatively low concentrations (1-50 micrograms/ml) of trypsin induce the Thy 1- to Thy 1+ conversion. The effect of trypsin was inhibited by prior heating or by addition of soybean trypsin inhibitor. The maximal effect achieved by trypsin treatment, approximately 25% conversion of spleen cells from layer B of an albumin gradient into theta-positive cells, was equivalent to that obtained with thymic hormone preparation (TP-1) at 10 ng/ml. Maximal conversion required 120 min incubation with TP-1 or trypsin. We conclude that both trypsin and TP-1 act by perturbation of a membrane receptor which can send a signal initiating the differentiation process.