Exocytosis and uptake of bacteria by isolated haemocyte populations of two crustaceans: evidence for cellular co-operation in the defence reactions of arthropods

Abstract

The role of exocytosis in the cellular defence reactions of arthropods was investigated using in vitro cultures of isolated haemocytes (blood cells) from the freshwater crayfish Pacifastacus leniusculus, and the shore crab Carcinus maenas. In both species, activated lysates of those cell types that contain the prophenoloxidase activating system (granular cells of crab and crayfish and semigranular cells of crayfish) were found to induce degranulation (exocytosis) of semigranular and granular cells. A cell lysate, in which the prophenoloxidase system was kept inactive, did not have this effect. Limited degranulation of granular cells of crab was also induced by lipopolysaccharides as has earlier been shown for crayfish semigranular cells. The phagocytic capability of semigranular cells from crayfish was lost after exocytosis induced by the Ca2+ ionophore A23187, and under no conditions were the granular cells of crabs or crayfish seen to ingest bacteria in vitro. An opsonic function for the attaching proteins of a β1,3-glucan-activated haemocyte lysate was demonstrated using the phagocytic hyaline cells from crabs. Phenoloxidase appeared to lack opsonic properties.