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JCI Insight. 2018 Dec 20;3(24). pii: 99022. doi: 10.1172/jci.insight.99022. [Epub ahead of print]

Matrix metalloproteinase-9 deficiency protects mice from severe influenza A viral infection.

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Division of Pulmonary and Critical Care Medicine, Brigham and Women's Hospital, and Harvard Medical School, Boston, Massachusetts, USA.
Department of Anesthesiology and Perioperative Medicine, Division of Molecular and Translational Biomedicine, School of Medicine, University of Alabama-Birmingham, Birmingham, Alabama, USA.
Laboratory of Immunobiology and Genetics, and Intensive Care Unit, Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas, Mexico City, Mexico.
Lovelace Respiratory Research Institute, Albuquerque, New Mexico, USA.
Escuela de Medicina y Ciencias de la Salud, Tecnologico de Monterrey, Mexico City, Mexico.


Matrix metalloproteinase-9 (MMP-9) cleaves various proteins to regulate inflammatory and injury responses. However, MMP-9's activities during influenza A viral (IAV) infections are incompletely understood. Herein, plasma MMP-9 levels were increased in patients with pandemic H1N1 and seasonal IAV infections. MMP-9 lung levels were increased and localized to airway epithelial cells and leukocytes in H1N1-infected WT murine lungs. H1N1-infected Mmp-9-/- mice had lower mortality rates, reduced weight loss, lower lung viral titers, and reduced lung injury, along with lower E-cadherin shedding in bronchoalveolar lavage fluid (BALF) samples than WT mice. H1N1-infected Mmp-9-/- mice had an altered immune response to IAV with lower BALF PMN and macrophage counts, higher Th1-like CD4+ and CD8+ T cell subsets, lower T regulatory cell counts, reduced lung type I interferon levels, and higher lung interferon-γ levels. Mmp-9 bone marrow-chimera studies revealed that Mmp-9 deficiency in lung parenchymal cells protected mice from IAV-induced mortality. H1N1-infected Mmp-9-/- lung epithelial cells had lower viral titers than H1N1-infected WT cells in vitro. Thus, H1N1-infected Mmp-9-/- mice are protected from IAV-induced lung disease due to a more effective adaptive immune response to IAV and reduced epithelial barrier injury due partly to reduced E-cadherin shedding. Thus, we believe that MMP-9 is a novel therapeutic target for IAV infections.


Infectious disease; Influenza; Mouse models; Pulmonology

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