Figure 1. Experimental design for analyzing CTL-mediated heterosubtypic immunity against H7N9 virus infection.

8–10 week old female B6 mice were first primed intranasally with 10⁴ TCID₅₀ of an H9N2 virus or 10² TCID₅₀ of an H1N1 virus. The virus-specific primary CTL responses in the bronchoalveolar lavage (BAL) were characterized on day (d) 8 and/or d10 post inoculation (p.i). Blood was collected for Hemagglutination inhibition (HI) assays on d35. The virus-specific memory CTLs in the spleen were characterized on d38. Between 10~12 weeks after the initial priming, the primed mice were intranasally challenged with an H7N9 virus and the H7N9 virus-specific-secondary CTL response in the BAL was characterized on various days between d0 to d14 after challenge infection.