Interferon-Mediated Immunopathological Events Are Associated with Atypical Innate and Adaptive Immune Responses in Patients with Severe Acute Respiratory Syndrome

Abstract

It is not understood how immune inflammation influences the pathogenesis of severe acute respiratory syndrome (SARS). One area of strong controversy is the role of interferon (IFN) responses in the natural history of SARS.The fact that the majority of SARS patients recover after relatively moderate illness suggests that the prevailing notion of deficient type I IFN-mediated immunity, with hypercytokinemia driving a poor clinical course, is oversimplified. We used proteomic and genomic technology to systematically analyze host innate and adaptive immune responses of 40 clinically well-described patients with SARS during discrete phases of illness from the onset of symptoms to discharge or a fatal outcome. A novel signature of high IFN-␣, IFN-␥, and IFN-stimulated chemokine levels, plus robust antiviral IFN-stimulated gene (ISG) expression, accompanied early SARS sequelae. As acute illness progressed, SARS patients entered a crisis phase linked to oxygen saturation profiles. The majority of SARS patients resolved IFN responses at crisis and expressed adaptive immune genes. In contrast, patients with poor outcomes showed deviated ISG and immunoglobulin gene expression levels, persistent chemokine levels, and deficient anti-SARS spike antibody production. We contend that unregulated IFN responses during acute-phase SARS may culminate in a malfunction of the switch from innate immunity to adaptive immunity. The potential for the use of the gene signatures we describe in this study to better assess the immunopathology and clinical management of severe viral infections, such as SARS and avian influenza (H5N1), is therefore worth careful examination.Severe acute respiratory syndrome coronavirus (SARS CoV) causes a spectrum of disease ranging from flu-like symptoms and viral pneumonia to acute respiratory distress syndrome and fatal outcomes (14,16,23,31,41). The mechanisms by which SARS CoV causes severe illness in humans are largely unknown. SARS CoV takes hold in the airways and other organs via its main putative receptor, angiotensin-converting enzyme 2 (ACE2), expressed on many cell types, including pneumocytes, enterocytes, and endothelial cells (19,25,32). SARS CoV appears to evade innate immunity during the first 10 days of infection during a period of widespread inflammation and steadily increasing viral load (39, 52). The consequent immune inflammation and hypercytokinemia, or "cytokine storm," during the course of SARS has been illustrated (22,27,33,37,51), but the molecular and cellular basis of how SARS CoV impacts host defense, resulting in a poor prognosis, is not understood. One particular area of controversy is the role of interferon (IFN) responses in human host immune responses against SARS CoV.Type I IFNs, such as IFN-␣ and -␤, are critical to innate immune responses against viral and other microbial infections and act in concert with IFN-␥ in the activation of antiviral IFN-stimulated genes (ISGs) and the immunomodulation of innate and adaptive immunity (3,36,42,48). It has been proposed that deficie...

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