IFNG and infection: following infection with the H strain, the expression levels of IFN-γ and IL-12p40 genes (Figure 2A and 2E) in bursal tissues were significantly up-regulated compared with uninfected birds (P < 0.05) and the expression of IL-2 genes was markedly increased at 3 dpi with no differences at 1 and 5 dpi (P > 0.05) (Figure 2C).