Cytokine-like activities of a humoral opsonin from the solitary urochordate styela-clava

Previously, we have identified and purified an opsonin from the plasma of the solitary urochordate, Styela clava. Here we show that this opsonin exhibits cytokine-like activies in tunicates. The opsonin enhances incorporation of H-3-thymidine into cultures of pharyngeal tissues from S. clava and acts as a powerful chemoattractant. Cytokine-like activity is also indicated by the ability of the S. clava molecule to activate tunicate phagocytes. In addition, we show that the opsonin is produced by S. clava hemocytes and that its production is stimulated by zymosan. These data suggest that the opsonin characterized here is identical to a tunicate, cytokine-like molecule (tunIL-1beta) previously identified by its ability to stimulate mouse thymocyte proliferation.