Fig. 5. Cytokine mRNA expression in different tissues of the tree shrew respiratory tract.

The mRNA expression levels of TNF-α (a), IFN-β (b), IL-4 (c), IL-6 (d), CXCL8 (e), IL-10 (f), IL-13 (g), CXCL10 (h), CCL5 (i), CXCL9 (j), and CCL2 (k) were determined by quantitative PCR in the nasal turbinate, throat, trachea, and lung tissue of tree shrews (n = 4 per time point) that were infected with H9N2 viruses (Y280-wt or Y280-PB2-E627K). The expression of the target genes was standardized to the mRNA expression of the GAPDH gene and the expression in mock-infected tree shrews. *p < 0.05