CyPA was found in the core of the influenza virion57 and was upregulated upon infection by avian H9N2 influenza virus in AGS cells (a human gastric carcinoma cell line).58 Liu et al.59 revealed that overexpression of CyPA blocked influenza A virus replication, whereas the depletion of endogenous CyPA resulted in enhanced production of influenza A virus. This evidence concerns the gene PPIA and infection.