To determine whether CsA's inhibition of viral replication was related to the host factor CypA, both 293T/CypA+ and 293T/CypA− cell lines were treated with CsA (5 μg/ml) immediately after influenza A/WSN/33 infection (MOI = 1), and a time-course experiment for antiviral activity of CsA was performed at 4 h, 6 h and 8 h p.i. by Western blot analysis. This evidence concerns the gene PPIA and infection.