CCL2 and infection: Compared with the blank group, the levels of IL-1β, TNF-α, and CCL2 in the lung tissue of the H9N2-infected mice were significantly increased at 3, 5, 7 and 9 days (P < 0.05) (Fig. 8a–c), and the levels of CXCL10 were significantly increased at 5 and 7 days (P < 0.05) (Fig. 8d), whereas the levels of IFN-α and IFN-β were only significantly increased at 3 days post-infection (P < 0.05) (Fig. 8e, f).