TNF and infection: To examine cytokine responses to infection with each virus, the mRNA expression of the inflammatory cytokines IFN-γ, IL-1β, IL-6, and TNF-α and the antiviral cytokine IFN-α was determined in the brains, lungs, and spleens of the chickens inoculated with Ty/Italy, Ck/NL, or Ck/Ibaraki, respectively (Figure 3A–C).