TNF and infection: At 6-day post-infection, gene expressions of IFN-γ, IL-1β, and IL-8 were elevated significantly in the PC group compared to NC and EXP groups (P < 0.05), but no significant difference was found between NC and EXP groups (P > 0.05); additionally, no significant difference in the TNF-α production was found among EXP, NC, and PC groups (P > 0.05) (Table 5).