In our preliminary data, we found that the arterial concentration of carboxyhemoglobin, which is the breakdown product of HO-1, was significantly higher in patients with acute exacerbation of idiopathic pulmonary fibrosis (IPF) (pathological DAD) than in patients with stable IPF [20, 21]. This evidence concerns the gene HMOX1 and idiopathic pulmonary fibrosis.