Schistosoma mansoni eggs excrete specific free oligosaccharides that are detectable in the urine of the human host

Abstract

In infections with Schistosoma mansoni the paired adult worms produce hundreds of eggs daily, of which many get trapped in various organs of the human host. The eggs produce complex and unique protein- and lipid-linked glycans, which are important activators and modulators of the host's immune response. The same parasite-derived glycoconjugates are also attractive immunodiagnostic targets in enzyme-linked immunosorbent assays (ELISAs), which detect circulating antigens in serum or urine of the host. Here, we report for the first time that in addition to glycoprotein and glycolipid antigens, schistosome eggs also excrete unique unconjugated oligosaccharides. Employing the schistosome-specific anti-carbohydrate monoclonal antibody 114-4D12 in an affinity purification approach, a specific set of free oligosaccharides was detected by matrix-assisted laser-desorption-ionisation time-of-flight mass spectrometry (MALDI-TOF MS) in human S. mansoni infection urine as well as in egg-incubation medium, but not in worm-culture medium. Nano-scale reverse-phase liquid chromatography-mass spectrometry (nano-RP-LC-MS) analysis of the purified egg-derived oligosaccharides indicated that the captured compounds form a series of multi-fucosylated multimeric N-acetylhexosamine chains with a non-reducing terminal Fucalpha1-2Fucalpha1-3GalNAcbeta1-4(Fucalpha1-2Fucalpha1-3)GlcNAcbeta1- (DF-LDN-DF) sequence which forms the epitope of mAb 114-4D12. Since fucosylated (egg) glycoconjugates have been shown to harbour immunogenic properties, we anticipate that these unconjugated oligosaccharides also play a role in the immunobiology associated with schistosome eggs. Moreover, our data indicate that mass spectrometric detection of a set of signature molecules in urine has potential as a new approach for the diagnosis of schistosomiasis and possibly other helminth infections.