The viral protein expression levels were detected by western blot with anti-gp85 of ALV-J or anti-env of REV, and the results showed that the synergistic infection of ALV-J and REV increased each virus protein expression at 48 hpi, 72 hpi and 96 hpi (Fig. 1c, 1d and 1e). Here, ERVW-1 is linked to infection.