IL6 and infection: When mice became clinically ill (as indicated by ruffled fur, behavioral changes and decreased activity) bacterial counts in blood had increased dramatically from 101 to 105 cfu/ml at 2 and 5 days post-infection respectively, with a marked rise in proinflammatory cytokines, most notably TNF-α, IFN-γ and IL-6, in the systemic compartment.