The expression of MUC2, a protective and antimicrobial mucoprotein, was also significantly decreased in the H9N2 infection group at 5 dpi and 12 dpi, while the mRNA expression level of MUC2 in the baicalin plus H9N2 AIV infection group was significantly upregulated (P < 0.01) (Figure 4(b)). This evidence concerns the gene MUC2 and infection.