ERVW-1 and infection: First, to confirm infection, undifferentiated SH-SY5Y cells were infected and analyzed by FACS at 2 dpi, positive viral envelope protein (E) staining was observed in a large percentage (65.1%) of the infected cells (Figure 5A) and viral RNA, detected in the supernatant, increased over time (Figure 5B), confirming that these cells were susceptible to infection.