PHENOLOXIDASE-DEPENDENT CYTOTOXIC MECHANISM IN ASCIDIAN (STYELA-PLICATA) HEMOCYTES ACTIVE AGAINST ERYTHROCYTES AND K562 TUMOR-CELLS

The cytotoxic activity against rabbit erythrocytes (RE) and human K562 tumor cells by Styela plicata hemocytes was significantly related to the phenoloxidase (PO) which converts phenols to quinone and initiates the melanogenic pathway The effector hemocyte population, separated i n a Percoll density gradient band, enriched in a granulocyte type name d ''morula cells'', was examined with RE in a hemocyte cytotoxic assay and plaque forming cell assay. Inhibition experiments with the copper chelating agents 1-phenyl-2-thiourea and tropolone, the substrate ana logue sodium benzoate and sodium ascorbate support the notion that hem ocyte cytotoxic activity is a PO-dependent mechanism, Treatments of he mocytes with the antioxidant enzymes, superoxide dismutase and catalas e rule out oxy radicals produced by the melanogenic process as respons ible of erythrolysis. Such a result suggests that quinone compounds de rived from the melanogenic pathway might be the cytotoxic molecules. T he PO-dependent anti-RE activity was also shown in a plaque forming as say in which ''morula cells'', containing polyphenols and PO, were ide ntified as cytotoxic.