Sialic acid commonly decorates the surface of cells and secreted proteins of Eukaryotes. It plays roles in cell signalling and adhesion, affects immune reactions and alternative complement pathways, and neurogenesis. While sialic acid is a saccharide present in high abundance in vertebrates, its minor representation was reported in arthropods and among medically necessary parasites. Ixodes ricinus tick is a significant vector of pathogens causing severe infections in humans and livestock. It has been known mainly through indirect evidence that sialylated glycoproteins are present in tick tissues. As a blood-feeding parasite, the host's blood, full of sialylated molecules, could be the source of such glycoproteins within the tick's body. To detect solely the tick sialylated glycoproteins, we used an azide-modified precursor of sialic acid to be metabolically incorporated by the tick cell line IRE/CTVM20 originating in this tick or by ticks if the corresponding biosynthetic pathway is present and active. Our I. ricinus genome screen revealed two sialyltransferase genes, which were expressed in all ticks' life stages, and we confirmed sialyltransferase activity in tick cells. We combined in vitro feeding along with Click chemistry to track the presence of sialylated glycoproteins from fed female ticks through their eggs to the larvae. Similarly, sialylated glycoproteins were produced by the IRE/CTVM20 cell line. Thus, we confirmed the ability of ticks to produce their own sialylated glycoproteins in addition to those originating from the host blood.
Sterbova et al. (Wed,) studied this question.