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

The mechanism of cytotoxicity by the hemocytes from the solitary ascid ian, Ciona intestinalis, against the target cell WEHI, a mouse myelomo nocytic leukemic cell (strain 3B), was investigated in vitro. Experime nts using chelators of Mg2+ and Ca2+ show that the cytotoxic activity by these hemocytes involves at least two stages distinguishable by the ir divalent cation requirements. In particular removal of both Ca2+ an d Mg2+ by EDTA inhibits effector Co target cell conjugate formation an d target cell lysis, whereas selective removal of Ca2+ by EGTA inhibit s target cell lysis but does not reduce the formation of effector to t arget sell conjugates. Evidence that cytotoxic activity is reduced by sodium azide, cytochalasin B, colchicine, vinblastine sulfate, and mon ensin, indicates that the response involves energy metabolism, require s an intact cytoskeleton, and entails active secretory processes iri t he effector cells. In addition, cytotoxic activity is probably not med iated by superoxide anions or hydrogen peroxide, because the antioxida nt enzymes, superoxide dismutase, and catalase did not affect target e el lysis. It is therefore likely that cytotoxic activity by the hemocy tes from C. intestinalis is mediated by mechanisms similar to those of vertebrate cytotoxic cells. (C) 1994 Wiley-Liss, Inc.