Perkinsus marinus secretory products modulate superoxide anion production by oyster (Crassostrea virginica) haemocytes

Superoxide anion (O-2(-)) generation by Eastern oyster haemocytes before an d after phagocytosis of living or dead Perkinsus marinus was quantified by lucigenin-augmented chemiluminescence (CL). Superoxide is the initial produ ct formed during the respiratory burst; this radical and its more cytotoxic metabolites are thought to play roles in the oxygen-dependent defence mech anisms available to the oyster. The haemocytes, in the absence of added par ticles, produced a constant, very low-level CL activity. Phagocytosis of os motically-killed P. marinus triggered a rapid CL response that peaked at a value 5-7-fold greater than the CL level of the untreated cells. However, p hagocytosis of viable P. marinus was associated with minor, short-lived CL stimulation followed by a period (>2 h) of sustained inhibition of O-2(-) g eneration. Phagocytosis of zymosan produced an immediate CL response, which was maintained for the >2 h course of the experiment. Haemocytes simultane ously exposed to zymosan and osmotically-killed P. marinus produced higher levels of O-2(-) than those receiving zymosan alone. Cells similarly expose d to both zymosan and living P. marinus produced significantly lower levels of O-2(-) than the zymosan-stimulated haemocytes. The stimulatory and inhi bitory effects of killed and living P. marinus on CL were apparently both d ose-dependent. The data suggest that both living and dead P. marinus are av idly phagocytosed, but only live P. marinus cells produce excretory/secreto ry products that scavenge O-2(-) and/or suppress aspects of the oxygen-depe ndent immune system. In this fashion the parasites can survive within the h aemocytes, multiply in the haemolymph, and eventually produce lethal infect ions. (C) 1999 Academic Press.