A conserved flagellar pocket exposed high mannose moiety is used by African trypanosomes as a host cytokine binding molecule

Trypanosomes use antigenic variation of their variant- specific surface gly coprotein (VSG) coat as defense against the host immune system. However, in order to sustain their growth, they need to expose conserved epitopes, all owing host macromolecule binding and receptor-mediated endocytosis. Here we show that Trypanosoma bruce! uses the conserved chitobiose-oligomannose G1 (L)CNAc2-Man(5-9)) moieties of its VSG as a binding ligand for tumor necros is factor TNF), a host cytokine with lectin-like properties. As endocytosis , in trypanosomes is restricted to the flagellar pocket, we show that solub le flagellar pocket extracts, and in particular soluble VSG, inhibit the bi nding of I-125-TNF to trypanosomes. The interaction between TNF and VSG is confirmed by affinity chromatography, biosensor, and dot-blot affinity meas urements, and soluble VSG inhibition of TNF-mediated trypanolysis. In all a pproaches, removal of N-linked carbohydrates abrogates the TNF-VSG interact ion. In addition, synthetic high mannose oligosaccharides can block TNF-VSG interactions, and a VSG glycopeptide carrying the G1(L)CNAc2-Man(5-9) moie ty is shown to inhibit TNF-mediated trypanosome killing in mixed parasite m acrophage cell cultures. Together, these results support the observation th at TNF plays a role in growth control of trypanosomes and, moreover, sugges t that, by the use of conserved VSG carbohydrates as lectin-binding epitope s, trypanosomes can limit the necessity to express large numbers of invaria nt surface exposed receptors.