TNF and infection: At the same time, pro-inflammatory responses are initiated by the host and involve the production of pro-inflammatory cytokines (IFN-α, IFN-γ, TNF-α and IL-6) and chemokines (KC, MIP-1α, MIP-2, CCL2, CCL5, CXCL10) which facilitate the initial phase of innate immune cell recruitment into the lungs, typically from day 1 to 5 post-infection [10].