Glycans withN-acetyllactosamine type 2-like residues covering adultSchistosoma mansoni, and glycomimesis as a putative mechanism of immune evasion

Abstract

SUMMARYGlycans at the surface of adultSchistosoma mansoniwere investigated with gold-labelled lectins. The fragile complex of the glycans with the outer membranes could be preserved for electron microscopy by avoiding extensive pre-fixation with aldehydes and by introducing osmium-ferrocyanide as a membrane fixative. Male and female worms were entirely covered with glycans that intensely bound lectins fromErythrina cristagalliandDatura stramonium, suggesting that galactose(β1–4)N-acetylglucosamine residues occur in high numbers in the surface glycans. Similar staining was obtained with lectins fromTriticum vulgaris, Glycine maxandRicinus communisagglutinin I, which react withN-acetylglucosamine or terminal galactose residues and bind non-selectively with high affinity toN-acetyllactosamine. Fucose,N-acetylgalactose and sialic acid were not detected with lectins and sialidase treatment. The tegument contained an abundance of glycans with the same lectin reactivities as the surface-expressed molecules, indicating that the worms synthesize and replenish their surface glycans and do not merely adsorb host substances. Glycomimesis is discussed as a mechanism of immune evasion in view ofN-acetyllactosamine being a common and weakly immunogenic component in glycans of vertebrate hosts.S. mansonimight disguise themselves with the glycans against attack by immune effectors.