Respiratory secretions, such as saliva and bronchoalveolar fluid, contain anti-influenza activity. Multiple soluble factors have been described that exert anti-influenza activity and are believed to be responsible for the anti-influenza activity in respiratory secretions. It was previously shown that a bronchial epithelial cell culture could produce exosome-like particles with anti-influenza activity. Whether such extracellular vesicles in respiratory secretions have anti-influenza activity is unknown. Therefore, we characterized bronchoalveolar lavage fluid and found microparticles, which mostly stained positive for epithelial cell markers and both α2,3- and α2,6-linked sialic acid. Microparticles were purified from bronchoalveolar lavage fluid and shown to exhibit anti-influenza activity by a hemagglutination inhibition (HI) assay and a neutralization (NT) assay. In addition, physical binding between influenza virions and microparticles was demonstrated by electron microscopy. These findings indicate that respiratory microparticles containing viral receptors can exert anti-viral activity by probably trapping viral particles. This innate mechanism may play an important role in the defense against respiratory viruses.
Hemagglutinin (HA) of seasonal influenza virus evolves under positive selection pressure exerted by host immunity. It was previously shown that antigenic drift in different influenza B sublineages during different time periods distributed unevenly among different epitopes, and that more recent viruses up to 2007 might have their antigenic drift more focused on certain epitope. We further analyzed whether more recent influenza B viruses up to 2016 followed that same pattern of antigenic evolution. By using Shannon entropy and relative entropy to characterize HA antigenic epitopes, the most recent viruses of both Victoria and Yamagata lineages had residues with high relative entropy located most frequently on the 120-loop region. In addition to residues in the known epitopes, possible antigenic residues were also identified outside of the known epitope regions. The data provide an insight into the antigenic evolution of current influenza B viruses and expand our knowledge on their antigenic sites.
Microparticles (MPs) are vesicles that are released by budding from plasma membrane of living cells. Recently, the role of MPs in antiviral activity has been proposed. We investigated quantity and anti-influenza activity of MPs from human alveolar epithelial cells A549, human bronchial epithelial cells BEAS-2B, human colon adenocarcinoma cells HT-29, and the human lung fibroblast cells MRC-5. MPs were found from all four cell lines. However, anti-influenza activity against an H1N1 influenza virus was found only from MPs of A549 and BEAS-2B. BEAS-2B cell differentiation did not increase MP release. Methyl-β-cyclodextrin (MβCD) increased MP release and anti-influenza activity in HT-29 and A549. MP release increased after calcium ionophore A23187 treatment in three cell lines but only in HT-29 after forskolin treatment. These findings provide in vitro data supporting the role of MPs as an innate defense against influenza virus and as an approach to enhance the defense.
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