| Research Abstract |
In order to determine and discuss functional profiles associated with the host defense process of the Pacific oyster, Crassostrea gigas, we investigated for the occurrence of subtypes, phagocytosis, and the reactive oxygen intermediate (ROI)-genenrating system of C.gigas hemocytes. Light microscopy revealed two morphological types of C.gigas hemocytes : granulocytes and agranulocytes. Granulocytes were distinguished from other hemocytes by the possession of many cytoplasmic granules. The ratios between the granulocytes and agranulocytes varied during the year, however, the number of agranulocytes was always greater than that of granulocytes ; approximately 70% of the total cell population was composed of agranulocytes. In order to determine and compare the phagocytic ability of both granulocytes and agranulocytes, we examined in vitro phagocytosis against three species of bacteria, heat-killed yeast cells, formalinized erythrocytes, and latex beads. Granulocytes were more active phagoc
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ytes against all species of bacteria tested and the phagocytic percentage ranged from 48.0% to 64.6% of the granulocytes and from 12.9% to 44.6% of the agranulocytes. Yeast cells were also extensively phagocytized by the granulocytes, but the agranulocytes produced a little phagocytosis of yeast cells. On the other hand, agranulocytes were more phagocytically active than granulocytes against erythrocytes and latex beads. These results suggest that most non-self particles, if not all, are more actively phagocytized by granulocytes than by agranulocytes. A rapid increase in oxygen consumption was observed accompanying a cyanide-independent respiratory burst when C.gigas hemocytes were stimulated with phorbol ester. As a result, granulocytes produced large amount of superoxide anion after phorbol ester stimulation or phagocytosis of zymosan particles, but agranulocytes did not or only slightly produced superoxide anion. We also found myeloperoxidase-like activity in C.gigas granulocytes, but not in agranulocytes. In summary, hemocytes in C.gigas have a strong phagocytic ability against various foreign particles and microbes and a potent microbicidal action. Less
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