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A7572 - Alveolar Macrophage-Derived Microvesicles Protect Alveolar Epithelial Cells from Influenza Infection
Author Block: D. Schneider1, A. Podsiad1, C. Wilke1, L. Penke1, D. Lyons2, B. B. Moore1, M. Peters-Golden1; 1Internal Medicine, Division of Pulmonary and Critical Care, University of Michigan, Ann Arbor, MI, United States, 2Internal Medicine, Microbiology and Immunology, University of Michigan, Ann Arbor, MI, United States.
Rationale: Influenza is a global health problem with limited treatment options. A better understanding of host defense mechanisms may suggest new therapeutic approaches. The principle cell types infected and responsible for initial defense against influenza are airway/alveolar epithelial cells (AECs) and macrophages (AMs). While AM-dependent protection against influenza has been ascribed to their classic phagocytic functions, immunomodulatory interactions between AMs and AECs have received little attention in this context. Extracellular vesicles (EVs) are emerging as paracrine signaling vectors in a broad range of (patho)physiologic contexts including anti-viral immunity. However, a role for EV signaling in host defense against influenza remains unexplored. We have previously reported that AM-derived microvesicles (MVs), a defined subset of EVs, modulate the immune response in AECs to diverse airway challenges. Thus, we hypothesized that uptake of AM-derived MVs by AECs protects against influenza infection. Methods: We utilized a plasmid containing cDNA corresponding to the WSN33 influenza strain polymerase A gene segment fused to a luciferase reporter. This plus seven additional plasmids containing the remaining WSN33 wild type gene segments were transfected into standard cell lines to create a functional viral stock expressing luciferase (Luc-WSN33). We also sought to confirm findings using an additional strain of influenza (purified A/PR/8/34 virus). Mouse epithelial cells (MLE-12) were infected for various times with virus at a range of concentrations (MOI) with and without MVs, isolated from conditioned medium from mouse MH-S cells by ultracentrifugation. MVs were defined by forward and side scatter characteristics and the presence of phosphatidylserine using flow cytometry. Viral replication was determined by qPCR of M1 gene (for A/PR/8/34) or quantification of luminescence (for Luc-WSN33). The impact of MVs on virus binding to the AEC surface was interrogated by confocal immunofluorescence detection of influenza nucleoprotein (NP). Results: AECs incubated with different concentrations of MVs demonstrated a dose-dependent reduction in Luc-WSN33 replication as measured by luminescence. These effects were present at a range of MOI (0.01 - 0.2). There was no significant difference in detection of influenza NP by confocal microscopy in AECs incubated at 4 degrees C with and without MVs. AECs incubated with A/PR/8/34 strain also demonstrated significantly reduced viral replication by qPCR when incubated with MVs. Conclusion: AM-derived MVs inhibit influenza infection in AECs independent of affecting virus binding. This suggests the presence of constituents within AM-derived MVs with anti-viral properties, the nature of which remain to be defined.