Effect of a traditional Chinese medicine, Bu-zhong-yi-qi-tang on the protection against an oral infection with Listeria monocytogenes.

The protective effect against an oral infection with Listeria monocytogenes was observed in BALB/c mice who were orally administered a traditional Chinese medicine, Bu-zhong-yi-qi-tang (Japanese name: Hochu-ekki-to, HOT) daily for 7 days. Bacterial numbers in the Peyer's patch (PP) at 18 h, in the mesenteric lymph nodes (MLN) at 18 h, 1 day and 3 days and in the liver at 3 days after infection were significantly suppressed in HOT-treated mice, although there was no difference in the bacterial number in the small intestinal contents. The enhanced bactericidal activities of PP and liver macrophages by pretreatments of HOT were observed. The protective effect of HOT was not observed in athymic nu/nu and IFN-gamma deficient mice. The administration of HOT increased IFN-gamma-producing cells in the intestinal intraepithelial lymphocytes (IEL) but did not in the PP, MLN and liver. HOT exerts effects mainly on CD8alphabeta+ IEL which are thymus-dependent, and induced IFN-gamma production from their cells. These results suggest that HOT acts on the gut-associated lymphoid tissues and induces IFN-gamma from CD8alphabeta+ IEL, which activates PP and liver macrophages and consequently the resistance to L. monocytogenes is augmented in the mice.