Article

Effect of water-soluble fraction from lysozyme-treated Enterococcus faecalis FK-23 on mortality caused by influenza A virus in mice.

Central Research Laboratories, Nichinichi Pharmaceutical Corporation Ltd., Mie, Japan.
Viral immunology (Impact Factor: 1.78). 02/2012; 25(1):86-90. DOI: 10.1089/vim.2011.0056
Source: PubMed

ABSTRACT To maintain homeostasis of the immune system is considered important for the prevention of influenza A virus infection. Aberrant systemic inflammation is frequently induced by influenza A virus infection, and the severity of the symptoms is associated with pathogenicity of the virus. Lactic acid bacteria are known to have a positive effect in maintaining the immune system. Furthermore, preparations of a lactic acid bacteria strain, Enterococcus faecalis FK-23 (FK-23), have been reported to exert preferable homeostatic effects on immune diseases such as allergic rhinitis and early asthmatic responses. In this study, we examined the efficacy of the water-soluble fraction of lysed and heat-treated FK-23 (SLFK) against a lethal influenza A virus challenge. Mice were orally administered SLFK from day -7 to day 20, and intranasally infected with influenza virus A/Puerto Rico/8/34 (H1N1) at 10(3) PFU on day 0. The survival rate of SLFK-administered mice after influenza A virus infection was significantly improved compared with that of control mice. In addition, the mRNA expression level of the anti-inflammatory cytokine interleukin-10 (IL-10) in lung tissues was enhanced by the oral administration of SLFK after influenza A virus infection. These observations suggest that the oral administration of SLFK exerts a protective effect against influenza virus infection through the activation of the anti-inflammatory response.

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    ABSTRACT: Infection with influenza A virus, one of the most common life-threatening viruses, causes the accumulation of inflammatory cells in the lung, which is directly correlated with influenza-associated morbidity and mortality. In this study, we investigated the potential of lysozyme-treated Enterococcus faecalis FK-23 (LFK) to prevent influenza in influenza virus-infected mice. C57BL/6N mice were orally administered LFK and intranasally infected with influenza virus A/Puerto Rico/8/34 (H1N1) at lethal doses. After infection with influenza A virus, the survival rate of the LFK-administered mice was significantly higher than that of saline-administered mice. Staining of lung sections with hematoxylin-eosin, and cell counts of lung and bronchoalveolar lavage fluid showed that oral administration of LFK suppressed the excessive infiltration of leukocytes into the lung after viral infection. Extravasation assay revealed that the arrest was mediated by modulation of pulmonary alveolar-capillary permeability. Expression levels of genes involved in matrix degradation, which are correlated with vascular permeability, were downregulated in LFK-administered mice. These findings suggest that stabilizing the integrity of the alveolar-capillary barrier by the administration of LFK improves survival rate.
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