Abstract
Influenza viruses cause infectious respiratory disease characterized by fever, myalgia, and congestion, ranging in severity from mild to life-threating. Although enormous efforts have aimed to prevent and treat influenza infections, seasonal and pandemic influenza outbreaks remain a major public health concern. This is largely because influenza viruses rapidly undergo genetic mutations that restrict the long-lasting efficacy of vaccine-induced immune responses and therapeutic regimens. In this review, we discuss the virological features of influenza A viruses and provide an overview of current knowledge of the innate sensing of invading influenza viruses and the protective immune responses in the host.
Highlights
The influenza virus, or ‘flu’, causes an acute respiratory disease that results in moderate to severe symptoms including fever, runny nose, cough, muscle pain, headaches, and sometimes even death
TLR7 signaling induces the activation of IRF7 and nuclear factor-κB (NF-κB) via the MyD88-mediated pathway, which initiates the expression of proinflammatory cytokines and type I IFNs
TLR7 deficiency results in attenuated production of type I IFN by Plasmacytoid DCs (pDCs) [69], reduced IL-1β secretion from bone marrow-derived dendritic cells (DCs) [71], and impaired activation and production of IFN-γ by lung natural killer cells (NK cells) during infection [72], suggesting that TLR7 is responsible for efficient innate immune responses against the influenza virus
Summary
The influenza virus, or ‘flu’, causes an acute respiratory disease that results in moderate to severe symptoms including fever, runny nose, cough, muscle pain, headaches, and sometimes even death. Three classes of anti-influenza drugs have been approved by the Food and Drug Administration (FDA) These drugs target several distinct steps of the viral replication cycle to inhibit influenza propagation in hosts. The cap-dependent endonuclease inhibitor, which received FDA approval for the treatment of influenza in 2018 [2,3], targets the influenza polymerase acidic (PA) endonuclease to prevent viral replication [4]. While these drugs are currently effective, they are only capable of reducing symptoms by a few days. We describe the virological characteristics of influenza A viruses that facilitate viral propagation in host cells and the mechanisms by which host cells recognize invading influenza viruses and produce a protective response against infection
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