We evaluated the therapeutic efficacy of ethanol extracts of two Korean herbal medicines in an intranasal influenza virus infection model in mice. The ethanol extracts of Jahyang-dokgamaek (JD) 1 (2.26 g/kg) and 2 (1.64 or 4.92 g/kg) were orally administered to mice infected with influenza A/PR/8/34 virus twice or three times daily for 7 days after infection. Extracts JD1 (2.26 g/kg) and 2 (1.64 or 4.92 g/kg) significantly prevented body weight loss and/or prolonged survival times of infected mice. Extract JD2 moderately but significantly reduced virus titers in bronchoalveolar lavage fluid (BALF) on days 1 to 3 after infection. Both extracts exhibited significant anti-influenza virus activity in a plaque reduction assay, but their active concentrations were very high. Neither JD1 or 2 significantly affected the total numbers of infiltrated cells or the levels of interferon (IFN)-β in BALF on days 1 to 3. However, JD2 significantly elevated the levels of interleukin (IL)-12 and IFN-γ on day 1, promoted infiltration of neutrophils on day 2, and reduced the levels of tumor necrosis factor (TNF)-α on day 3. Similar trends were seen in infected mice with JD1 administration. Administration of the two extracts was suggested to promote infiltration of neutrophils into the lungs in the early phase of infection, resulting in activation of innate immunity and thereafter alleviation of inflammation as indicated by the reduction of the TNF-α level in the BALF. Thus, the efficacy of the two extracts against influenza virus infection was possibly based on the activation of early host immunity.
