VLP composition was determined by western blot analysis. Briefly, purified VLPs resuspended in endotoxin free PBS were lysed by resuspending them in equal amount of 2x SDS proteinloading buffer and loaded into a 12% SDS-polyacrylamide gel with a 4% stacking gel. 293T cell lysates processed similarly were run in parallel as negative cell control. Following electrophoresis to resolve the protein bands, and transfer to membrane, the blot was incubated with NiV-specific HMAF primary antibody at a dilution of 1:1000 dilution, overnight at 4uC, and HRP-conjugated antimouse secondary antibody (from GE Healthcare) at a 1: 20,000 dilution for one hour at room temperature. The proteins were revealed using western blot detection reagents according to instructions provided by the manufacturer (GE Healthcare).