Alterations in hemolymph and extrapallial fluid parameters in the Manila clam, Ruditapes philippinarum, challenged with the pathogen Vibrio tapetis

In a recent study, we demonstrated the presence of defense factors, compete nt hemocytes and high enzymatic activities (peptidases, hydrolases, lytic, etc.), in the extrapallial fluid, located between the mantle and the shell, of the Manila clam, Ruditapes philippinarum. In Europe, this species is af fected by brown ring disease, an epizootic disease caused by the bacterium Vibrio tapetis. The present work focused on the effect of the development o f the disease on cellular and humoral defense parameters in the hemolymph a nd the extrapallial fluid of experimentally infected clams. Results indicat e significant changes in total and dead hemocyte counts, as well as modific ations in lysozyme activity and protein content, in the hemolymph and extra pallial fluid of challenged animals. Hemocyte counts and lysozyme activity increased significantly in the hemolymph, but particularly in the extrapall ial fluid, where the highest values were observed. A healing (recalcificati on) process was observed 7 weeks following challenge, suggesting defense sy stem efficiency at neutralizing the pathogen. These results are discussed w ith emphasis on the role of extrapallial fluids in the defense process agai nst invading microorganisms, (C) 2000 Academic Press.