TNF and infection: It has been suggested that invasion of phagocytes which are not yet activated is important for the bacteria's survival since exposure of macrophages to IFN-γ and/or TNF-α before—but not after—infection decreases the ability of pathogenic mycobacteria to inhibit phagosome maturation and function [43] at least partially by upregulating the production of reactive oxygen and nitrogen derivatives [44–48].