Flow cytometric studies on the morphology and immunological functions of hemocytes in the Iwagaki oyster Crassostrea nippona

The Iwagaki oyster Crassostrea nippona may represent an aquaculture alternative to the Pacific oyster in Korea, Japan and China. In this study, morphology and immune-related functions of hemocytes of C. nippona were characterized using light microscopy and flow cytometry. Both light microscopy and flow cytometry indicated that C. nippona hemocytes are composed of three different types: granulocytes, hyalinocytes, and blast-like cells. Hyalinocytes were the most abundant and intermediate-sized cells, while granulocytes were the largest cells, containing many granules in the cytoplasm. Blast-like cells were characterized by a smaller size and very thin cytoplasm. Granulocytes were mainly engaged in phagocytosis and oxidative activities, although hyalinocytes also exhibited a certain level of immune-related activities. On the other hand, blast-like cells exhibited an absence of phagocytosis and extremely low oxidative capacity, suggesting that this subpopulation is not directly involved in cell-mediated immune response. The flow cytometry analyses carried out in the present study confirmed that granulocytes are the major hemocyte population involved in cellular defense of C. nippona, and allow for further studies on the impact of environmental stresses or pathogens on this alternative aquaculture species.