Etude des effets de polluants sur les paramètres hémocytaires de l'huître creuse, Crassostrea gigas - Interactions entre environnement, mécanismes de défense et maladies infectieuses

Shellfish industry is mostly realized in estuary zones, which are subjected to pollutions due to anthropic activities. The harmful effects of pollutants on animals inhabiting these estuarine zones are poorly known. Among these animals, Pacific oyster, Crassostrea gigas, may represent a model because they are sedentary and they filter water intensively. Among all physiological functions possibly disturbed by pollutants, defence mechanisms are poorly studied in bivalves. Moreover, animals presenting impaired defence mechanisms may be more sensitive to infectious diseases. In this context, effects of pollutants on hemocyte functions and on sensitiveness to diseases were tested in C. gigas. After adjusting the protocols for the monitoring of hemocyte parameters using flow cytometry, contamination experiments were conducted in vitro and in vivo. In vitro experiments allowed to demonstrate the effects of several pollutants on selected hemocyte parameters. In vivo contamination with a pesticide mixture induced a decrease of phagocytosis activity and a down-regulation of immune genes monitored by real-time PCR. In other experiments involving the same pesticide contamination followed by an injection of bacteria (Vibrio), mortality was higher and several immune genes were up-regulated in infected contaminated animals compared to infected non contaminated animals. In situ experiments allowed to define the defence status of different oyster populations (triploids, diploids from sea bed and hatchery diploids). This study is the first to explore a relationship between a modulation of hemocyte parameters and a dysfunctioning of response to bacteria in Pacific oyster, C. gigas.