Cells were harvested 24 hours later and washed with FACs wash (1% FCS/5 mM EDTA in PBS) before fixation in 1% paraformaldehyde in PBS. To examine cellular association of VLPs, cell fluorescence was analysed by flow cytometry (FACSCaliber, Becton Dickinson, USA). For examination of intracellular uptake of VLPs, extracellular fluorescence was quenched by addition of an equal volume of 0.1 M citrate buffer (pH 4.0) containing 250 mg/ml trypan blue (Merck, Damstadt, Germany) prior to analysis [27] . Data were analysed using FlowJo software (Tree Star, San Carlos, CA).