MECHANISM OF CYTOTOXIC ACTIVITY BY HEMOCYTES OF THE SOLITARY ASCIDIAN, CIONA-INTESTINALIS

The mechanism of cytotoxicity by the hemocytes from the solitary ascidian, Ciona intestinalis, against the target cell WEHI, a mouse myelomonocytic leukemic cell (strain 3B), was investigated in vitro. Experiments using chelators of Mg2+ and Ca2+ show that the cytotoxic activity by these hemocytes involves at least two stages distinguishable by their divalent cation requirements. In particular removal of both Ca2+ and Mg2+ by EDTA inhibits effector Co target cell conjugate formation and target cell lysis, whereas selective removal of Ca2+ by EGTA inhibits target cell lysis but does not reduce the formation of effector to target sell conjugates. Evidence that cytotoxic activity is reduced by sodium azide, cytochalasin B, colchicine, vinblastine sulfate, and monensin, indicates that the response involves energy metabolism, requires an intact cytoskeleton, and entails active secretory processes iri the effector cells. In addition, cytotoxic activity is probably not mediated by superoxide anions or hydrogen peroxide, because the antioxidant enzymes, superoxide dismutase, and catalase did not affect target eel lysis. It is therefore likely that cytotoxic activity by the hemocytes from C. intestinalis is mediated by mechanisms similar to those of vertebrate cytotoxic cells. (C) 1994 Wiley-Liss, Inc.