Competition binding experiments and schematic representation of the localization of Nb binding on VSG.

<p>A) Flow cytometry profiles showing binding competition among different Nbs. Left panels: profile of parasites in the absence of Nbs (black), or bound by ALEXA-labelled Nbs (red). Right panels: FACS profiles of parasites bound by ALEXA-labelled Nbs (red) or when binding of the ALEXA-labelled Nb was competed by prior incubation with unlabelled Nb as indicated at the top of the first row (green profile). B) Schematic representation of the location of the Nbs bound on GPI-anchored VSG at the parasite surface as inferred from the flow cytometry data. Nb_An33 binds close to the membrane, Nb_An05 interacts close to the membrane-distal region of VSG, and Nb_Ab46 binds at an intermediate location. Attachment of trypanolytic Nbs at the surface (Nb_An05), or slightly deeper (Nb_An46) on the VSG prevents binding of molecules to epitopes that are located more proximal to the membrane.