HMOX1 and COVID-19: As a new biomarker candidate for ILD, we have previously demonstrated that evaluating the degree of oxidative stress by measuring HO-1 in the peripheral blood known as a rate-limiting enzyme in heme catabolism with antioxidative activities was useful for assessing disease activities and predicting prognosis in patients with such as ARDS, COVID-19, and acute exacerbation of ILDs22,27–30.