Molecular Studies of the Molluscan Response to Digenean Infection

Abstract

The Mollusca is one of the largest, most diverse, and structurally complex of the animal phyla. Molluscs are of considerable importance in aquaculture, as intermediate hosts of several parasites of medical and veterinary significance, and because many molluscs are rare and endangered. Recent years have witnessed the increasing application of modern techniques to molluscan immunobiology, and there is a growing understanding of the molecules involved in molluscan defense responses. Among the notable approaches are 1) dissection of signal transduction pathways in molluscan hemocytes; 2) characterization of molecules involved in adherence of molluscan cells; 3) the identification of markers segregating with resistance of snails to digenetic trematodes; and 4) molecular characterization of a family of hemolymph proteins from planorbid snails that are induced following exposure to digeneans. The latter proteins are lectins and have similarity to fibrinogen and have been termed fibrinogen-related proteins, or FREPs. FREPs are comprised of a C-terminal domain with homology to fibrinogen and an N-terminal domain with homology to V type loops of the immunoglobulin superfamily (IgSF). Other members of the IgSF occur in molluscs and other fibrinogen-related proteins lacking Ig domains have been found in external body mucus of snails and are believed to play roles in defense.