Influenza A viruses (IAV) are a continuing global threat and cause of highly contagious respiratory tract infections with high morbidity and mortality rates despite available anti-viral drugs and vaccines. Excessive anti-viral inflammation is the likely root cause of IAV-induced acute lung injury (ALI) and the more fatal form adult respiratory distress syndrome (ARDS). There is a great need for Goldilocks therapies that target unexploited aspects of IAV infection in the host. Pathogenic influenza strains are known to by-pass neutralizing and immunoregulatory functions of surfactant proteins A (SP-A) and D (SP-D). Importantly, SP-A gene polymorphisms have been associated with increased morbidity and mortality from pandemic influenza-induced ARDS. However, we have found a novel role for the surfactant protein A receptor SP-R210 in IAV infection in vivo, a finding that may overcome this critical knowledge barrier and lead to new therapeutics. Specifically, we found that IAV co-opts the SP-R210 isoform SP-R210L to infect macrophages initiating the disease process of viral replication and inflammation in the lung. We have found an unexpected function for SP-R210L: IAV utilizes the SP-R210L variant to infect macrophages. Furthermore, depletion of SP-R210L in vitro enhances macrophage responsiveness to inflammatory stimuli through a mechanism that impairs apoptotic cell clearance and NFkB inflammatory signal termination by activating transcription factor 3 (ATF-3). Accordingly, studies in vivo demonstrate that conditional disruption of SP-R210L in myeloid cells leads to increased mortality rates in SP-R210L-deficient mice vs. littermate controls consistent with inability to resolve inflammation. The central hypothesis is that SP-R210L is required for both IAV entry and resolution of inflammation through coordination of ATF-3 activation and clearance of apoptotic cells. However, by co-opting SP-R210L, IAV causes a functional `knock-down', reducing the beneficial function of SP-R210L and leading to enhanced inflammation. We will test this hypothesis by 1) evaluating apoptotic cell (AC) clearance, by investigating the impact of SP-R210 deletion on the inflammatory response to IAV infection, and by defining the expression of SP-R210 isoforms in the myeloid compartment using novel isoform-specific monoclonal antibodies; and 2) by characterizing the role of SP-R210L in binding and endocytic trafficking of IAV, by assessing efficacy of blocking SP-R210 function in vivo using monoclonal antibodies, and by examining the role of SP-A gene variants with protective and pathogenic polymorphisms in coordinating ATF-3 and NFkB activation during IAV infection. These studies provide a new rationale for therapies directed toward critical host cells rather than at the virus. These studies provide crucial data for further studies with highly pathogenic IAV strains such as H5N1 and H7N7 that have the capacity to evolve into worldwide pandemics.
Influenza infection is a major pathogen of global public health significance having the capacity to cause regular pandemic, regional, and seasonal outbreaks with high morbidity and mortality despite the availability of antiviral drugs and vaccines. Inflammation is a key aspect of influenza pneumonia that leads to high morbidity and mortality that has not been tackled pharmaceutically. This proposal will investigate a novel pathway through which influenza infects and activates inflammatory responses in macrophages and alveolar epithelial cells in mice and humans.
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