Refractoriness of host haemocytes to parasite immunosuppressive factors as a putative resistance mechanism in the Biomphalaria glabrata-Echinostoma caproni system.

In contrast to the growing knowledge accumulated on plant resistance to pathogens, mechanisms of parasite resistance largely remain to be elucidated in animal species. In the present study we investigated mechanisms underlying resistance/susceptibility in the snail-trematode system Biomphalaria glabrata-Echinostoma caproni. In particular, we compared the effect of the parasite excretory-secretory (E-S) products on the defence functions of haemocytes from 2 susceptible and 2 resistant snail strains. In vitro experiments showed that E. caproni E-S products inhibit adhesion and phagocytosis of haemocytes from susceptible snails. A partial biochemical characterization also suggested that the interfering factor(s) is (are) heat-labile glycosylated polypeptides of molecular mass between 10 and 30 kDa. Interestingly, haemocytes from resistant snails remained unaffected by the parasite E-S products, suggesting that a constitutive difference results in their refractoriness to the parasite's immunosuppressive factor(s).