Authors
M E Kuipers2; E N Nolte-'t Hoen3; K F Hoffmann1; H H Smits2; C H Hokke2; 1 Aberystwyth University, UK; 2 Leiden University Medical Centre, Netherlands; 3 Utrecht University, Netherlands Discussion
Glycans play essential roles in pathogen-host interactions. Larvae and adult worms from Schistosoma mansoni release distinct subsets of glycoconjugates as excretory/secretory (ES) products. Extracellular vesicles (EVs) are also among the ES products. We previously found that schistosomula-derived EVs are glycosylated and bind to human dendritic cells (hDC) via the C-type lectin receptor (CLR) DC-SIGN, leading to increased IL-10 and IL-12 release. Here, we investigated the glycosylation of EVs released by S. mansoni adult worms, compared this to schistosomula EVs, and addressed how glycans affect EV-host interactions via CLRs.
EVs were obtained by ultracentrifugation from cultured S. mansoni parasites and purified with iodixanol density gradients. Isolated EVs were analysed by NTA and cryo EM showing that adult worm EVs have a different appearance and size distribution than schistosomula EVs, lacking the long thin filaments characteristically observed in the case of EV from schistosomula. N-glycan and lipid glycan content of EVs was determined by mass spectrometry. In contrast to schistosomula EVs, glycolipids could not be detected in the adult worm EVs. The most abundant N-glycans on the surface of adult worm EVs contained GalNAc-beta1–4GlcNAc (LacDiNAc, LDN) motifs, whereas the Gal-beta1–4(Fuc-alpha1–3)GlcNAc (Lewis X) motif dominated in the surface N-glycans of schistosomula EV. Other differences in EV glycosylation between the two life stages were observed by Western blot using anti-glycan mAbs.
In line with these structural observations, the adult worm derived EV bind to cells that express macrophage galactose-type lectin (MGL), an LDN-binding CLR expressed on hDCs and macrophages, whereas schistosomula EV primarily interact with hDC via DC-SIGN.
Overall, our observations suggest that specific glycosylation of EVs from helminths and from their different developmental stages plays a critical role in differential recognition of, and response to, helminth EVs by host immune cells. 
