Soluble mediators of cytolytic activity in hemocytes of the Asian clam, Corbicula fluminea.

Serum-free hemocytes from the clam, Corbicula fluminea, are cytolytic to mammalian erythrocytes (RBCs) as demonstrated in a hemoglobin release assay. The reaction is hemocyte dose- and temperature-dependent, and is mediated by the release of soluble hemolytic factors from clam cells. Initiation of hemocyte secretory activity does not appear to require contact with target RBCs. The chemical nature of the secreted lysin(s) has not been determined; however, PAGE analysis of hemocyte extracts (lysates) reveals the presence of at least five peaks of lytic activity. This activity is sensitive to heat and proteolytic enzyme treatment, and can be removed by absorption with fixed, homologous RBCs. Thus it is likely that the secreted hemocyte lysin is a heat-labile protein which exerts its hemolytic activity by binding directly to target RBC membrane constituents.