Univacuolar refractile hemocytes from the tunicate Ciona intestinalis are cytotoxic for mammalian erythrocytes in vitro

A discontinuous, Percoll density gradient was used to separate hemocyte populations from the hemolymph of Ciona intestinalis. Hemocytes from each band were examined for their frequency, morphology, and cytotoxic activity against rabbit and sheep erythrocytes; results were expressed as a percentage of hemolysis. Statistical analysis revealed that only the 'univacuolar' granulocytes from Band 5, which contain a vacuole of refractile material, were cytotoxic. Cytotoxic activity was inhibited by sphingomyelin. For the first time in tunicates, lytic activity against erythrocytes was assessed by an assay based on plaque-forming cells. Plaques of lysis were revealed against rabbit erythrocytes but not against sheep erythrocytes.