HMOX1 and tuberculosis: HO-1 is protective and promotes granuloma formation in M. avium infection (273). In mice, HO-1 deficiency leads to increased susceptibility to Mtb infection with increased bacterial loads and mortality due, in part, to failure to mount a protective TH1-mediated granulomatous response (274, 275). HO-1 catalyzes the oxidation of heme (as seen with TB hemorrhage) to produce iron, biliverdin, and carbon monoxide that have anti-oxidant, anti-inflammatory, and anti-apoptotic properties to attenuate TB immunopathology (276, 277).