Heme oxygenase-1 and carbon monoxide regulate intestinal homeostasis and mucosal immune responses to the enteric microbiota.

Heme oxygenase-1 (HO-1) and its enzymatic by-product carbon monoxide (CO) have emerged as important regulators of acute and chronic inflammation. Mechanisms underlying their anti-inflammatory effects are only partially understood. In this addendum, we summarize current understanding of the role of the HO-1/CO pathway in regulation of intestinal inflammation with a focus on innate immune function. In particular, we highlight our recent findings that HO-1 and CO ameliorate intestinal inflammation through promotion of bacterial clearance. Our work and that of many others support further investigation of this global homeostatic pathway in the human inflammatory bowel diseases (IBDs).