Authors

C Hokke¹; EN Nolte-'t Hoen²; ME Kuipers¹; HH Smits¹;  ¹ Leiden University Medical Centre, Netherlands;  ² Faculty of Veterinary Medicine, Utrecht University, Netherlands

Discussion

Glycans play an essential role in pathogen-host interactions. Larval and adult Schistosoma mansoni release distinct excretory/secretory (ES) glycoconjugates. ES products also contains extracellular vesicles (EVs). 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 adult worms, compared this to schistosomula EVs, and addressed how glycans affect EV-host cell interactions via CLRs.

EVs were obtained by ultracentrifugation and iodixanol density gradients from cultured schistosomes. Isolated EVs were analysed by NTA and cryo EM showing that adult worm EVs have a different appearance and size distribution than schistosomula EVs. N-glycan and lipid glycan content of EVs was determined by mass spectrometry.

The most abundant glycans on the surface of adult worm EVs contained GalNAcβ1–4GlcNAc (LacDiNAc, LDN) motifs, whereas the Galβ1–4(Fucα1–3)GlcNAc (Lewis X) motif dominated in the surface 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. In addition, we found that EVs from adult worms simulate cytokine responses, including IL-10, in B-cells.

Overall, our observations suggest that specific glycosylation of EVs from helminths plays a critical role in differential recognition of, and response to, helminth EVs by host immune cells.