HMOX1 and tuberculosis: Treatment of macrophages or mice with a HO-1 inhibitor leads to enhanced control of mycobacterial replication (278, 279); it is believed that HO-1 expression increases iron availability in activated macrophages, which benefits Mtb growth (276). HO-1 levels correlate directly with the level of active TB but this relationship by itself does not inform whether HO-1 is host-protective or not (280).