Immune parameters in carpet shell clams naturally infected with Perkinsus atlanticus

Defence parameters of non-infected clams (Ruditapes decussatus) and clams h eavily infected with Perkinsus atlanticus were assessed. Cellular (haemocyt e density and phagocytic activity) and humoral (lysozyme and anti-bacterial activities, protein concentration and agglutination titre) parameters were measured in clams collected in an area enzootic for P. atlanticus. The inf ection intensity of each clam was assessed, and the immune parameters measu red in the most infected clams were compared with those measured in the non infected ones. Only the serum anti-bacterial activity and the agglutination titre were significantly different between infected and non-infected clams . The phagocytic rate, haemocyte density, lysozyme concentration and protei n concentration were not statistically different but they showed the same t rend in the two trials performed. Phagocytic rate, haemocyte concentration and anti-bacterial activity were higher in non-infected clams, while they h ad lower lysozyme concentration, serum protein concentration and agglutinat ion titre than infected clams. Although infected and healthy clams were not different for every parameter measured, probably due to the high variabili ty among individuals, P. atlanticus seems to affect the clam immune system, at least in advanced stages of the infection. (C) 2000 Academic Press.