Receptor Density-Dependent Motility of Influenza Virus Particles on Surface Gradients

Influenza viruses can move across the surface of hostcells whileinteracting with their glycocalyx. This motility may assist in findingor forming locations for cell entry and thereby promote cellular uptake.Because the binding to and cleavage of cell surface receptors formsthe driving force for the process, the surface-bound motility of influenzais expected to be dependent on the receptor density. Surface gradientswith gradually varying receptor densities are thus a valuable toolto study binding and motility processes of influenza and can functionas a mimic for local receptor density variations at the glycocalyxthat may steer the directionality of a virus particle in finding theproper site of uptake. We have tracked individual influenza virusparticles moving over surfaces with receptor density gradients. Weanalyzed the extracted virus tracks first at a general level to verifyneuraminidase activity and subsequently with increasing detail toquantify the receptor density-dependent behavior on the level of individualvirus particles. While a directional bias was not observed, most likelydue to limitations of the steepness of the surface gradient, the surfacemobility and the probability of sticking were found to be significantlydependent on receptor density. A combination of high surface mobilityand high dissociation probability of influenza was observed at lowreceptor densities, while the opposite occurred at higher receptordensities. These properties result in an effective mechanism for findinghigh-receptor density patches, which are believed to be a key featureof potential locations for cell entry.