**5. Conclusions**

This study describes the expression pattern of HO-1 in COVID-19 patients, both at the tissue level and the blood mRNA level. The increase of HO-1 in critically ill and disease COVID-19 patients indicates that its induction serves as a protective mechanism. Further studies are needed to determine the underlying mechanisms for HO-1 induction in COVID-19 to directly assess its potential as a therapeutic strategy against COVID-19.

**Supplementary Materials:** The following supporting information can be downloaded at https: //www.mdpi.com/article/10.3390/antiox11071300/s1. Figure S1: SARS-COV-2 absence in tissue samples from critical COVID-19 patients.

**Author Contributions:** Conceptualization, M.G.D.; formal analysis, M.G.D.; resources, A.K.; data curation, M.G.D., I.N., D.V., A.G.V., E.J., S.T. and N.A.; writing—original draft preparation, M.G.D.; writing—review and editing, H.G., I.D., S.E.O., V.G.G. and A.K.; supervision, A.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Institutional Review Board (Ethics Committee) of Evangelismos Hospital (protocol code 360 and date of approval 17 September 2020).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data is contained within the manuscript and the Supplementary Material.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

