Fig. 7. Cytokine mRNA expression from ex vivo cultures of the respiratory tract isolated from tree shrews.

Tissues isolated from different parts of the respiratory tract were infected with 10⁶ TCID₅₀/mL of H9N2 viruses (Y280-wt or Y280-PB2-E627K) at 37 °C. 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) in different ex vivo explants (n = 3 per time point) were measured by quantitative PCR. 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