The critical role of this pathway is demonstrated by the fact that HO-1 gene knockout (HO-1-/-) or pharmacological inhibition with tin protoporphyrin (SnPP) significantly reduces intracellular bacterial load, whereas HO-1 induction with cobalt protoporphyrin (CoPP) exacerbates infection in both macrophages and mouse models (41, 49). This evidence concerns the gene HMOX1 and infection.