β-l, 3 GLUCAN ACTIVATION OF CRUSTACEAN HEMOCYTESIN VITROANDIN VIVO

Abstract

The effects of 13-1 ,3 glucans on the hemocytes of the freshwater crayfish, Astacus astacus, and the shore crab, Carcinus maenas, were studied in vitro and in vivo to determine the role ofthe prophenoloxidase activating system, in the cellular defense reactions of crustaceans. In vitro, phagocytosis of the bacterium, Moraxella sp. was significantly raised by addition of laminarin, a $-l ,3 glucan, simultaneously with the test particles to the hemocytes in monolayer cultures. Both the proportion of cells ingesting one or more bacterial particles and the number of bacteria taken up by individual cells were increased, and the responses were found to be time dependent and dose related. Glucose, dextran, cellulose, and chitin had no stimulatory influence on the cells, and the agglutination of erythrocytes by crab hemocytes or serum was unchanged by glucan incubation. Examination of the monolayers under phase contrast mi croscopy, revealed that the glucans induced degranulation and occasionally lysis in the crayfish hemocytes, and vacuolation in the crab hemocytes. In vivo, injection of f3-1,3 glucans (0.2 mg laminaran/ml hemolymph) into the hemocoel of A. astacus or C. maenas caused a rapid, marked reduction in the number of circulating hemocytes, indicating that a cellular defense reaction was initiated. Since prophenoloxidase in the hemocytes is specifically activated by /3-1,3 glucans, and in the activated form phenoloxidase is “?�sticky,” it is suggested that certain proteins of the prophenoloxidase activating system may serve as opsonins, and possibly constitute an important recognition mechanism in crustaceans.