UNIVACUOLAR REFRACTILE HEMOCYTES FROM THE TUNICATE CIONA-INTESTINALISARE CYTOTOXIC FOR MAMMALIAN ERYTHROCYTES IN-VITRO

A discontinuous, Percoll density gradient was used to separate hemocyt e populations from the hemolymph of Ciona intestinalis. Hemocytes from each band were examined for their frequency, morphology, and cytotoxi c activity against rabbit and sheep erythrocytes; results were express ed as a percentage of hemolysis. Statistical analysis revealed that on ly the ''univacuolar'' granulocytes from Band 5, which contain a vacuo le of refractile material, were cytotoxic. Cytotoxic activity was inhi bited by sphingomyelin. For the first time in tunicates, lytic activit y against erythrocytes was assessed by an assay based on plaque-formin g cells. Plaques of lysis were revealed against rabbit erythrocytes bu t not against sheep erythrocytes.