Hemocyte aggregation in the oyster Crassostrea gigas: In vitro measurement and experimental modulation by xenobiotics

The hemolymph of aquatic invertebrates is the target of many environmental contaminants. Different events of the cellular immune response constitute potential models for the development of sensitive bioassays. Here, a new methodology is described to quantify in vitro spontaneous aggregation by Crassostrea gigas hemocytes. Preliminary assays indicated that the aggregation index was altered when the cells were incubated at low or high temperature. The chelator EDTA or the drug caffeine added to the medium were powerful inhibitors. The effects of xenobiotics actually found in polluted marine waters [tributyltin (TBT) and trace metals] were tested by exposure of either the cells or whole individuals and appeared as efficient potential inhibitors. A higher sensitivity to cadmium than to copper has been revealed. Exposure of individuals in the laboratory to pesticides or TBT at peak environmental concentrations resulted in moderate changes in hemocyte aggregation, a response that could, however, be enhanced by synergistic effects of these concentrations with other contaminants or with physicochemical factors in the field. The alteration of spontaneous hemocyte aggregation is thought to reflect an impairment of hemocyte functions in homeostasis keeping and even in internal defense. This simple assay may constitute an additional tool to experiment the toxic effects of xenobiotics in molluscs.