TNF and infection: In order to compare the concentrations of the pro-inflammatory cytokines TNF-α, IL-6, and the chemokine KC in cerebellum homogenates and serum of aged and young mice in the acute phase of infection, 36 aged (18.8 ± 0.9 months) and 37 young mice (2.8 ± 0.3 months) were intracerebrally infected with a higher dose of E. coli K1 (7.5 × 105 CFU/mouse) and sacrificed 24 hours later.