TNF and infection: In this model, there is an initial phase of partial resistance dominated by Th1 cytokines plus TNF-α and the expression of iNOS, followed by a late phase of progressive disease after 1 month of infection, characterized by a lower expression of IFN-γ, TNF-α, or iNOS, progressive pneumonia, extensive interstitial fibrosis, high bacillary counts and very high levels of immunosuppressive factors such as TGF-β1 and Prostaglandin E-2 (PGE2) [26,37,38].