Direct binding of IAV to HSM. Direct binding of IAV to bead-bound HSM and PSM was tested. Virus was incubated with the mucus-coated beads in the presence of oseltamivir to inhibit NA activity. Following incubation, beads were washed to remove both non-bound virus and oseltamivir. The bound virus was quantified by measuring NA activity using 4MU-Neu5Ac-reporter method. Average of three independent experiments is shown. As control for non-specific binding, beads conjugated to non-sialylated polymer were used. Black line indicates the background. All virus strains bound to HSM, but only one strain bound to PSM.