Figure 2: Immune responses induced by cold-adapted H9N2 vaccine in chickens.

(A) SD-01-10-wt specific antibody levels assessed by HI assay. Groups of three-week-old SPF white Leghorn chickens (n = 36) were immunized intranasally with 10⁶ EID₅₀ of cold-adapted H9N2 viruses in 0.2 mL or phosphate-buffered saline (mock immunized) in 0.2 mL. Serum HI antibodies were measured against SD-01-10-wt pre-vaccination and on day 14 after vaccination. Black dashed lines indicate the lower limit of detection. *P < 0.05, by one-way analysis of variance to evaluate the difference between the value tested pre vaccination and 14 days post vaccination. (B) The frequency of IFN-γ⁺CD4⁺ or IFN-γ⁺CD8⁺ T cells in the lungs after cold-adapted H9N2 virus vaccination. Groups of three-week-old SPF white Leghorn chickens (n = 5) were immunized intranasally with 0.2 mL 10⁶ EID₅₀ of cold-adapted H9N2 or phosphate-buffered saline (mock immunized). The lungs of five SD-01-10-ca vaccinated and five mock-vaccinated chickens were harvested pre-vaccination and on day 7 post vaccination. IFN-γ⁺CD4⁺ or IFN-γ⁺CD8⁺ T cells after stimulation of the lung cells with SD-01-10-wt were measured by intracellular cytokine staining. Percentages of IFN-γ⁺CD4⁺ or IFN-γ⁺CD8⁺ T cells within CD4⁺ or CD8⁺ T cells were analyzed. *P < 0.05, by one-way analysis of variance of the difference between the value tested pre vaccination and 14 days post vaccination.