CLDN3 and infection: The results show that the mRNA expression of the cytoplasmic protein ZO-1 and the cell membrane protein Claudin-3 significantly decreased at 5 dpi and 12 dpi, while the mRNA expression of Claudin-3 and ZO-1 significantly increased in the baicalin plus H9N2 AIV infection group (P < 0.01) (Figures 4(c) and 4(d)).