A protein with lectin activity in penetration glands of Diplostomum pseudospathaceum cercariae

Homogenates of Diplostomum pseudospathaceum cercariae agglutinated mouse er ythrocytes. The haemagglutination could be inhibited by certain glycoconjug ates containing beta -1,3- and beta -1,4-glycan chains and also by some sim ple saccharides. The most potent inhibitors were heparin and some other gly cosaminoglycans, bacterial lipopolysaccharides, laminarin (a beta -1,3-gluc an) and lactulose. After electrophoresis of cercarial proteins, a dominant double band appeared in the 22-24 kDa region of gels. On blots, this protei n bound labelled laminarin and it was also one of the few proteins recognis ed by mouse antibodies raised against cercarial haemagglutinins. In additio n, mouse polyclonal antibodies against the beta -1,3-glucan-binding protein bound exclusively to the 22-24 kDa region on Western blots. Histochemistry revealed strong binding of labelled laminarin to cercarial penetration gla nds; this reaction was fully blocked by unlabelled laminarin. Other labelle d glycoconjugates such as heparin, hyaluronic acid and a bacterial lipopoly saccharide also bound to the glands. Immunohistochemistry confirmed the loc alisation of the P-l,3-glucan-binding protein in penetration glands. Reacti on of the cercarial protein with immunoglobulins from non-immunised mice wa s observed on both nitrocellulose membranes and histological sections; this could be blocked by laminarin in incubation buffers. We consider the cerca rial haemagglutinin to be a lectin which is identical with the 22-24 kDa be ta -1,3-glucan-binding protein. According to the binding specificity and lo calisation we speculate on a role of this lectin in cercarial penetration i nto the host, probably as a tissue recognition or antibody rendering factor . (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier S cience Ltd. All rights reserved.