Syncytium formation is a classical feature of NiV and other paramyxovirus-induced cytopathology that can be blocked by virus-specific neutralizing antibody. A similar observation was made when 293 cells were ''infected'' with the NiV VLPs. Briefly, the VLPs were pre-incubated with NiV-specific antibody, Junin virus (JV)-specific antibody, and with OPTI-MEM I (Invitrogen Inc) medium only for one hour at 37uC before inoculating onto near confluent 293 cell monolayers grown overnight in 60 mm dishes. The inoculum was removed after incubation for 3 hours at 37uC, replaced with OPTI-MEM I, and the plates were further incubated overnight at 37uC overnight. The monolayers were then viewed for the formation of syncytia after staining with crystal violet. The results in Figure 4 show that 293 cells exposed to NiV VLPs induced syncytium formation and that this process was neutralized by NIV-specific antibodies; prior incubation with the unrelated JV antibodies failed to block this process.