Matthew G. Drake1*, Elizabeth R. Bivins-Smith1*, Becky J. Proskocil1, Zhenying Nie1, Gregory D. Scott2, James J. Lee3,Nancy A. Lee4, Allison D. Fryer1, and David B. Jacoby1
Division of Pulmonary and Critical Care Medicine, Oregon Health & Science University, Portland, Oregon; 3 Department of Biochemistry and Molecular Biology, Division of Pulmonary Medicine, and 4 Department of Biochemistry and Molecular Biology, Divisions of Hematology and Oncology, Mayo Clinic in Arizona, Scottsdale, Arizona; 2 Department of Pathology, Stanford University School of Medicine, Stanford, California ORCID ID: 0000-0002-7803-6447 (B.J.P.).
Abstract
Respiratory viruses cause asthma exacerbations. Because eosinophils are the prominent leukocytes in the airways of 60–70% of patients with asthma, we evaluated the effects of eosinophils on a common
respiratory virus, parainfluenza 1, in the lung. Eosinophils recruited to the airways of wild-type mice after ovalbumin sensitization and challenge significantly decreased parainfluenza virus RNA in the lungs 4 days after infection compared with nonsensitized animals. This antiviral effect was also seen in IL-5 transgenic mice with an abundance of airway eosinophils (NJ.1726) but was lost in transgenic eosinophil-deficient mice (PHIL) and in IL-5 transgenic mice crossed with eosinophil-deficient mice (NJ.1726-PHIL). Loss of the eosinophil granule protein eosinophil peroxidase, using eosinophil peroxidase–deficient transgenic mice, did not reduce eosinophils’ antiviral effect. Eosinophil antiviral mechanisms were also explored in vitro. Isolated human eosinophils significantly reduced parainfluenza virus titers. This effect did not involve degradation of viral RNA by eosinophil granule RNases. However, eosinophils treated with a nitric oxide synthase inhibitor lost their antiviral activity, suggesting eosinophils attenuate viral infectivity through production of nitric oxide. Consequently, eosinophil nitric oxide production was measured with an intracellular fluorescent probe. Eosinophils produced nitric oxide in response to virus and to
a synthetic agonist of the virus-sensing innate immune receptor, Toll-like receptor (TLR) 7. IFNg increased expression of eosinophil TLR7 and potentiated TLR7-induced nitric oxide production. These results suggest that eosinophils promote viral clearance in the lung and contribute to innate immune responses against respiratory virus infections in humans
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