TNF and infection: At 2-day post-infection, gene expression for pro-inflammatory cytokine TNF-α was significantly elevated in 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); with regard to IFN-γ, IL-1β, and IL-8 production, no significant difference was observed among EXP, PC, and NC groups (P > 0.05).