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

Abstract

Glycans at the surface of adult Schistosoma mansoni were 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 from Erythrina cristagalli and Datura stramonium, suggesting that galactose(beta 1-4)N-acetylglucosamine residues occur in high numbers in the surface glycans. Similar staining was obtained with lectins from Triticum vulgaris, Glycine max and Ricinus communis agglutinin I, which react with N-acetylglucosamine or terminal galactose residues and bind non-selectively with high affinity to N-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 of N-acetyllactosamine being a common and weakly immunogenic component in glycans of vertebrate hosts. S. mansoni might disguise themselves with the glycans against attack by immune effectors.

Effects of benzimidazole anthelmintics as microtubule-active drugs on the synthesis and transport of surface glycoconjugates in Hymenolepis microstoma , Echinostoma caproni , and Schistosoma mansoni

“…Electron-lucent vesicles of E. caproni and vesicles of H. microstoma, which resemble those observed in H. nana (Verheyen et al 1976), were found to contain glycoconjugates in the present study and in unpublished investigations. Previously these glycoconjugates had been localized in the surface coat of Hymenolepis species and Schistosoma mansoni (Schmidt 1988(Schmidt , 1995. They are characterized by a high binding capacity for the lectins WGA and DSL.…”

“…One of the possible reasons for this might be that the surface of S. mansoni has a rather low turnover in vivo (Saunders et al 1987). Also, the outer membranes of S. mansoni are covered only by a very thin glycoconjugate coating, and glycoconjugate vesicles in the tegument are sparse (Schmidt 1995). The rate of secretion of glycoconjugates of the tegument of S. mansoni could be signi®cantly lower than that of E. caproni and other gut-inhabiting platyhelminths.…”

“…Gold sols were produced according to Slot and Geuze (1985). Lectin from Datura stramonium (Sigma) was adsorbed onto gold particles measuring about 10 nm in diameter (Schmidt 1988(Schmidt , 1995. Lectin from Triticum vulgare (WGA; Serva, Heidelberg, Germany) was coupled to bovine serum albumin and adsorbed onto gold particles of about 12-nm diameter.…”

“…An essential surface constituent involves peculiar glycoconjugates, which have largely remained unexplored to date. These glycoconjugates have been suggested in Hymenolepis and Schistosoma to play an important role in evasion of the hosts' immune defense (Schmidt 1988(Schmidt , 1995.…”

Metabolic enzymes of helminth parasites: potential as drug targets

“…Unlike in trypanosomes, there is no evidence that the enzyme is essential for the production of galactose. However, the tegument of many helminths contains complex glycoproteins and it is likely that the disruption of the Leloir pathway would lead to alterations in this structure potentially altering parasite-host interactions [218][219][220][221][222][223][224][225][226]. Like many of the glycolytic enzymes, GALE may also have potential as a vaccine against helminth infections [227].…”