MMP9 and COVID-19: Matrix metalloproteinase-9 (MMP9) plays a multifaceted role in COVID-19, contributing to both lung tissue damage and potential repair mechanisms. Initially, MMP9, produced by neutrophils and monocytes, is upregulated during inflammation, where it breaks down the alveolar-capillary barrier, leading to increased lung permeability and worsening inflammation, but its persistent elevation during recovery phase may aid in tissue remodeling and repair, supporting the reorganization of the extracellular matrix as inflammation subsides (Gelzo et al., 2022)