Hemolymph factors responsible for defense reactions against pollutants and bacteria, Vibrio alginolyticus, in the Indian edible oyster, Crassostrea madrasensis (Preston) (Th 133)

The study of the defense mechanisms in invertebrates started with marine animals. The first report on the cellular defense in invertebrates was the observation of phagocytosis in starfish larvae and Daphnia (Metchnikoff, 1884). It was suggested that phagocytes play a significant role in the defense mechanisms of all evolutionary stages of animals starting from unicellular animals to mammals. The study of hemolysins in the horse-shoe crab by Noguchi (1903) was the first study on the humoral immunity of invertebrates. Since 1960, there was a renewed interest in the study of defense mechanisms in invertebrates, which was suggested to be because of two reasons: (1) to find out those mechanisms in invertebrates that are also discovered in vertebrates and (2) the development of intensive mariculture requires better knowledge of the factors that may lead to mortality of the crustaceans and mollusc due to failure of their defense systems. Marine invertebrates served as experimental materials for phylogenetic study of defense mechanisms in Animal Kingdom from late 191h century to the beginning of20lh century (Mori, 1990). Among invertebrates, the defense systems of molluscs and insects are being studied extensively in order to understand the basics of invertebrate inullune system. During the past three decades, there has evolved a considerable interest in how the molluscs defend themselves against the invaders. Immunity of molluscs is comprised of cell-mediated immunity and humoral mechanisms. The cell-mediated immunity is the function of hemocytes, while humoral immunity is provided by the serum factors. There are many evidences, which suggest that these two are interrelated (Cheng, 1990). Hemolymph in invertebrates is analogous to blood in vertebrates. The blood of vertebrates consists of plasma and cells. The cells are red blood corpuscles and white blood corpuscles