Lactobacillus pentosus strain S-PT84 isolated from Kyoto pickles enhances splenic natural killer (NK) cell activity and exhibit anti-allergic effects by modulating the Th1/Th2 (T-helper1/T-helper2) balance. In the present study, we investigated whether the immune response could be activated by intranasal administration of S-PT84 in the respiratory immune system and protected against influenza virus infection in mice. When BALB/c mice received intranasal administration of S-PT84 once daily for 3 consecutive days, S-PT84 strongly induced interleukin-12 (IL-12) and gamma interferon (IFN-gamma) production in mediastinal lymph node (MLN) cells. At intranasal infection with influenza virus PR8 (a mouse-adapted H1N1 strain) after S-PT84 treatment, the survival rates of mice improved in a dose-dependent manner, and the titer of influenza virus in bronchoalveolar lavage fluids (BALF) was significantly decreased by S-PT84 administration. Production of IL-12 and alpha-interferon (IFN-alpha) in BALF were significantly higher in mice treated with S-PT84 compared to the control mice. Lung NK activity was also significantly augmented in S-PT84-treated mice. These results suggested that the L. pentosus strain S-PT84 showed inhibitory activity against influenza virus infection.
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