SELECTIVE INDUCTION OF HEMOCYTIC RESPONSE IN RUDITAPES-PHILIPPINARUM (BIVALVIA) BY DIFFERENT SPECIES OF VIBRIO (BACTERIA)

Adult, healthy Manila clams, Ruditapes philippinarum, were inoculated in the laboratory with different, possibly pathogenic bacteria species to study the cellular immune responses. Challenging the clams with Vi brio P1, the causative agent of brown ring disease, induced significan t increased total hemocyte counts three days post-challenge. The trigg ering role of the number of bacteria in the inoculum suggested a thres hold for inducing the host response. Tn addition, a significant decrea se of hyalinocytes and an increase of granulocytes revealed a modifica tion in hemocyte population balance. No response was observed in indiv iduals that received either heat killed-Vibrio P1, V.anguillarum or V. pelagius. These experiments demonstrate in R. philippinarum the influ ence of bacterial parameters on the selective induction of host immuno defence mechanisms. The biological processes by which intra-pallial in oculation of Vibrio P1 stimulates the internal defence system of the h ost has not yet been identified but the role of some bacterial factors (toxins, adherence capacity) is discussed.