TNF and infection: At 6-day post-infection in the PC group, the gene expressions of IFN-γ, IL-1β, and TNF-α were elevated significantly (P < 0.05) compared to NC and EXP groups, but no difference was found between NC and EXP groups (P > 0.05); in terms of IL-8, no significant differences were found among EXP, NC, and PC groups (P > 0.05) (Table 4).