Mosquito cell line glycoproteins: an unsuitable model system for the Plasmodium ookinete-mosquito midgut interaction?

Background: Mosquito midgut glycoproteins may act as key recognition sites for the invading malarial ookinete. Effective transmission blocking strategies require the identification of novel target molecules. We have partially characterised the surface glycoproteins of two cell lines from two mosquito species; Anopheles stephensi and Anopheles gambiae, and investigated the binding of Plasmodium berghei ookinetes to carbohydrate ligands on the cells. Cell line extracts were run on SDS-PAGE gels and carbohydrate moieties determined by blotting against a range of biotinylated lectins. In addition, specific glycosidases were used to cleave the oligosaccharides. Results: An. stephensi 43 and An. gambiae 55 cell line glycoproteins expressed oligosaccharides containing oligomannose and hybrid oligosaccharides, with and without alpha 1-6 core fucosylation; N-linked oligosaccharides with terminal Gal beta 1-3GalNAc or GalNAc beta 1-3Gal; O-linked alpha/beta GalNAc. An. stephensi 43 cell line glycoproteins also expressed N-linked Gal beta 1-4R and O-linked Gal beta 1-3GalNAc. Although P. berghei ookinetes bound to both mosquito cell lines, binding could not be inhibited by GlcNAc, GalNAc or Galactose. Conclusions: Anopheline cell lines displayed a limited range of oligosaccharides. Differences between the glycosylation patterns of the cell lines and mosquito midgut epithelial cells could be a factor why ookinetes did not bind in a carbohydrate inhibitable manner. Anopheline cell lines are not suitable as a potential model system for carbohydrate-mediated adhesion of Plasmodium ookinetes.