Isolation of cytolytic granules from sea urchin amoebocytes.

Calcium-dependent, heat-labile lytic activity was detected in whole Paracentrotus lividus coelomocytes. The molecules responsible for this activity were mainly expressed by an enriched amoebocyte population and were contained in cytoplasmic granules which could be isolated by Percoll density gradient centrifugation. The isolated cytoplasmic granules were small (0.1-0.25 micron) organelles containing the lysosomal marker arylsulfatase. The functional implication of our results is that P. lividus amoebocytes represent cytotoxic cells which mediate the killing event by a secretory phenomenon involving the release of cytolytic material from cytoplasmic granules.