Protective effect of a traditional Japanese medicine Hochu-ekki-to (Chinese name: Bu-zhong-yi-qi-tang), on the susceptibility against Listeria monocytogenes in infant mice

In this study, the effect of traditional Japanese (Chinese) medicine, Hochu-ekki-to, HOT (Chinese name: Bu-zhong-yi-qi-tang), on the susceptibility against Listeria monocytogenes in postneonatal infant mice was examined. Numbers of bacteria in infant mice (infected at 4 weeks of age) were significantly higher than those in adult mice (infected at 8 weeks of age) on day 3 (non-specific resistance phase) and day 5 (specific resistance phase) after infection. Oral administration of 1,000 mg/kg of HOT for 7 days to infant mice reduced bacterial numbers in the liver and spleen at 5 days after the infection. The amount of IFN-gamma and the number of IFN-gamma-producing CD4+ T cells were lower in infant mice than adult mice but those in infant mice enhanced by HOT treatment. HOT also enhanced the antigen-presenting function along with the expression of MHC class II in infant macrophages induced by heat-killed L. monocytogenes. Further, HOT enhanced the IFN-gamma production from infant CD4+ T cells independent of the deficiency in the antigen-presenting function. These findings suggest that HOT induced simultaneously functional maturation of both infant antigen-presenting cells and T cells, and consequently developed an anti-listerial Th1 response.