Increased Reactive Oxygen Intermediate Production by Hemocytes Withdrawn from Crassostrea virginica Infected with Perkinsus marinus

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Abstract
Perkinsus marinus is a protozoan parasite responsible for a major infectious disease of the Eastern oyster, Crassostrea virginica. Nonspecific immunity was assayed in oysters with known intensities of infection so that the physiological responses of the host elicited by the parasite could be better understood. This report describes the capacity of hemocytes to generate reactive oxygen intermediates during the progression of the disease. The hemocytes constitute the major internal defense effector system of oysters, and cytotoxic oxygen species are thought to play central roles in antimicrobial activities of hemocytes and other phagocytic cells. Production of oxyradicals by both resting and phagocytically stimulated hemocytes was quantified by luminol-augmented chemiluminescence. Hemocytes from oysters with heavy Perkinsus infections produced significantly higher levels of chemiluminescence than their counterparts withdrawn from lightly or moderately infected individuals. Furthermore, in addition to a higher chemiluminescent activity per cell, the total circulating hemocyte count was elevated in the heavily infected animals. Therefore, advanced cases of this disease seem to be characterized by hemocyte activation and recruitment, with concomitant exuberant production of hemocyte-derived reactive oxygen intermediates. The resultant oxidant load may participate in the pathogenesis of the disease.

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