When the venerid clam Tapes decussatus is parasitized by the protozoan Perkinsus sp. it synthesizes a defensive polypeptide that is closely related to p225

Abstract

Molluscs, like other invertebrates, have primitive defense systems. These are based on chemotaxis, recognition and facultative phagocytosis of foreign elements. Previously, we have described one of these systems: a cellular reaction involving infiltrated granulocytes against Perkinsus sp. parasitizing the Manila clam Tapes semidecussatus, in which the parasites are encapsulated by a defensive host product, the polypeptide p225. The aim of this study is to determine the similarities between the defense mechanisms of 2 venerid clams, T. semidecussatus and T. decussatus, when they are infected by Perkinsus sp. The hemocytes of both species infiltrate the connective tissue, redifferentiate, and ultimately, express and secrete the polypeptide which constitutes the main product of the capsule that surrounds the parasites. The main secretion product of T. decussatus shows a high degree of homology to that of T. semidecussatus, since it has a similar electrophoretic mobility and the polypeptide is recognized by the polyclonal serrum against p225 from T. semidecussatus, as confirmed by Western blotting and immunocytochemistry. In conclusion, we demonstrate the existence of 2 polypeptides that are closely related at the molecular and functional level, and are specific in the defense of some molluscs against infection by these protozoan parasites.