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      Complement Activation Contributes to Severe Acute Respiratory Syndrome Coronavirus Pathogenesis

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          The complement system is a critical part of host defense to many bacterial, viral, and fungal infections. It works alongside pattern recognition receptors to stimulate host defense systems in advance of activation of the adaptive immune response. In this study, we directly test the role of complement in SARS-CoV pathogenesis using a mouse model and show that respiratory disease is significantly reduced in the absence of complement even though viral load is unchanged. Complement-deficient mice have reduced neutrophilia in their lungs and reduced systemic inflammation, consistent with the observation that SARS-CoV pathogenesis is an immune-driven disease. These data suggest that inhibition of complement signaling might be an effective treatment option following coronavirus infection.


          Acute respiratory distress syndrome (ARDS) is immune-driven pathologies that are observed in severe cases of severe acute respiratory syndrome coronavirus (SARS-CoV) infection. SARS-CoV emerged in 2002 to 2003 and led to a global outbreak of SARS. As with the outcome of human infection, intranasal infection of C57BL/6J mice with mouse-adapted SARS-CoV results in high-titer virus replication within the lung, induction of inflammatory cytokines and chemokines, and immune cell infiltration within the lung. Using this model, we investigated the role of the complement system during SARS-CoV infection. We observed activation of the complement cascade in the lung as early as day 1 following SARS-CoV infection. To test whether this activation contributed to protective or pathologic outcomes, we utilized mice deficient in C3 (C3 –/–), the central component of the complement system. Relative to C57BL/6J control mice, SARS-CoV-infected C3 –/– mice exhibited significantly less weight loss and less respiratory dysfunction despite equivalent viral loads in the lung. Significantly fewer neutrophils and inflammatory monocytes were present in the lungs of C3 –/– mice than in C56BL/6J controls, and subsequent studies revealed reduced lung pathology and lower cytokine and chemokine levels in both the lungs and the sera of C3 –/– mice than in controls. These studies identify the complement system as an important host mediator of SARS-CoV-induced disease and suggest that complement activation regulates a systemic proinflammatory response to SARS-CoV infection. Furthermore, these data suggest that SARS-CoV-mediated disease is largely immune driven and that inhibiting complement signaling after SARS-CoV infection might function as an effective immune therapeutic.

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          Most cited references 71

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          Isolation of a novel coronavirus from a man with pneumonia in Saudi Arabia.

          A previously unknown coronavirus was isolated from the sputum of a 60-year-old man who presented with acute pneumonia and subsequent renal failure with a fatal outcome in Saudi Arabia. The virus (called HCoV-EMC) replicated readily in cell culture, producing cytopathic effects of rounding, detachment, and syncytium formation. The virus represents a novel betacoronavirus species. The closest known relatives are bat coronaviruses HKU4 and HKU5. Here, the clinical data, virus isolation, and molecular identification are presented. The clinical picture was remarkably similar to that of the severe acute respiratory syndrome (SARS) outbreak in 2003 and reminds us that animal coronaviruses can cause severe disease in humans.
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            Characterization of a novel coronavirus associated with severe acute respiratory syndrome.

            In March 2003, a novel coronavirus (SARS-CoV) was discovered in association with cases of severe acute respiratory syndrome (SARS). The sequence of the complete genome of SARS-CoV was determined, and the initial characterization of the viral genome is presented in this report. The genome of SARS-CoV is 29,727 nucleotides in length and has 11 open reading frames, and its genome organization is similar to that of other coronaviruses. Phylogenetic analyses and sequence comparisons showed that SARS-CoV is not closely related to any of the previously characterized coronaviruses.
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              A major outbreak of severe acute respiratory syndrome in Hong Kong.

              There has been an outbreak of the severe acute respiratory syndrome (SARS) worldwide. We report the clinical, laboratory, and radiologic features of 138 cases of suspected SARS during a hospital outbreak in Hong Kong. From March 11 to 25, 2003, all patients with suspected SARS after exposure to an index patient or ward were admitted to the isolation wards of the Prince of Wales Hospital. Their demographic, clinical, laboratory, and radiologic characteristics were analyzed. Clinical end points included the need for intensive care and death. Univariate and multivariate analyses were performed. There were 66 male patients and 72 female patients in this cohort, 69 of whom were health care workers. The most common symptoms included fever (in 100 percent of the patients); chills, rigors, or both (73.2 percent); and myalgia (60.9 percent). Cough and headache were also reported in more than 50 percent of the patients. Other common findings were lymphopenia (in 69.6 percent), thrombocytopenia (44.8 percent), and elevated lactate dehydrogenase and creatine kinase levels (71.0 percent and 32.1 percent, respectively). Peripheral air-space consolidation was commonly observed on thoracic computed tomographic scanning. A total of 32 patients (23.2 percent) were admitted to the intensive care unit; 5 patients died, all of whom had coexisting conditions. In a multivariate analysis, the independent predictors of an adverse outcome were advanced age (odds ratio per decade of life, 1.80; 95 percent confidence interval, 1.16 to 2.81; P=0.009), a high peak lactate dehydrogenase level (odds ratio per 100 U per liter, 2.09; 95 percent confidence interval, 1.28 to 3.42; P=0.003), and an absolute neutrophil count that exceeded the upper limit of the normal range on presentation (odds ratio, 1.60; 95 percent confidence interval, 1.03 to 2.50; P=0.04). SARS is a serious respiratory illness that led to significant morbidity and mortality in our cohort. Copyright 2003 Massachusetts Medical Society

                Author and article information

                Role: Editor
                Role: Solicited external reviewer
                Role: Solicited external reviewer
                American Society for Microbiology (1752 N St., N.W., Washington, DC )
                9 October 2018
                Sep-Oct 2018
                : 9
                : 5
                [a ]Department of Epidemiology, University of North Carolina, Chapel Hill, North Carolina, USA
                [b ]Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, Colorado, USA
                [c ]Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas, USA
                [d ]Department of Genetics, University of North Carolina, Chapel Hill, North Carolina, USA
                NIAID, NIH
                Centro Nacional de Biotecnologia, CNB-CSIC
                St. Jude Children's Research Hospital
                Author notes
                Address correspondence to Ralph S. Baric, rbaric@ .
                Copyright © 2018 Gralinski et al.

                This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.

                Page count
                supplementary-material: 3, Figures: 7, Tables: 0, Equations: 0, References: 68, Pages: 15, Words: 9285
                Funded by: HHS | NIH | National Institute of Allergy and Infectious Diseases (NIAID),;
                Award ID: AI100625
                Award Recipient : Award Recipient :
                Research Article
                Host-Microbe Biology
                Custom metadata
                September/October 2018

                Life sciences

                respiratory viruses, coronavirus, complement, animal models, sars-cov


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