Mechanism of cytotoxic activity by hemocytes of the solitary ascidian, <i>Ciona intestinalis</i>

Abstract

Abstract 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 Mg 2+ and Ca 2+ show that the cytotoxic activity by these hemocytes involves at least two stages distinguishable by their divalent cation requirements. In particular removal of both Ca 2+ and Mg 2+ by EDTA inhibits effector to target cell conjugate formation and target cell lysis, whereas selective removal of Ca 2+ by EGTA inhibits target cell lysis but does not reduce the formation of effector to target cell 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 cyto‐skeleton, and entails active secretory processes in 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 cell 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. © Wiley‐Liss, Inc.