Flow cytometric assessment of haemocyte sub-populations in the European flat oyster, Ostrea edulis, haemolymph

The morphology and functions of haemocytes from the haemolymph of the European oyster, Ostrea edulis, were analysed by flow cytometry on the basis of cellular structures and incorporation of fluorescent markers. O. edulis circulating haemocytes appear to be composed of one to three cell populations based on cell size and granularity, with many individual variations. Analysis of haemocytes after propidium iodide staining indicated that the majority of oyster haemocytes are alive after sampling. The phagocytic activity level of haemocytes was analysed using fluorescent beads and this cell activity varied greatly depending on the oysters. The use of 3,3'dihexyloxacarbocyanine iodide (DIOC6) allowed the demonstration of several cell populations on the basis of labelled intensity. One to three cell sub-populations can be observed depending on the oysters. The haemocytes characterised by high granularity showed a strong fluorescence intensity related to high mitochondrial activity.