TNF and infection: Transcripts encoding the proinflammatory cytokines IL-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α were markedly increased in late-stage animals (average fold increase at day 5 after infection: IL-1β, 3.9; IL-6, 4.3; IL-8, 11.3; and TNF-α, 5.2; Figure 2b).