Effects of the Japanese traditional medicine Bu-zhong-yi-qi-tang on Th2 responses via up-regulation of Toll-like receptor 4

To determine the mechanisms of the traditional herbal medicine Bu-zhong-yi-qi-tang (Japanese name: Hochu-ekki-to, HOT) for the control of atopic diseases, we examined the murine allergic rhinitis model orally treated with HOT. When C3H/HeN mice were orally administered with HOT at the induction phase immediately after OVA sensitization, the serum levels of OVA-specific IgE and IgG 1 were significantly decreased. IL-4 production by spleen T cells in response to OVA was also significantly suppressed, while IFN- g production was increased in mice orally treated with HOT in the induction phase. Moreover, counts of sneezing and eosinophilic infiltration significant decreased in the mice orally treated with HOT. However, when C3H/HeJ mice, TLR4 gene mutant mice, were used, there were no differences in counts of sneezing and eosinophilic infiltration between the oral HOT treatment group and non-treatment group. And, in these TLR4 gene mutant mice, neither OVA-specific IgE and IgG 1 nor Th2 cytokine production of splenic T cells decreased with the HOT treatment. Reverse transcription-PCR (RT-PCR) analysis showed that TLR4 consistently expressed on murine macrophages but lipopolysaccalides (LPS) did not directly enhance TLR4 expression in vitro . However, treatment with HOT before stimulation with LPS actually resulted in a significant increase of the level of TLR4-specific mRNA expression in murine macrophages in vitro . Furthermore, pretreatment with HOT enhanced IL-12 production by macrophages stimulated with LPS. Our results suggest that oral administration of HOT downregulates Th2 responses and consequently attenuates nasal symptom in murine allergic rhinitis model, by the enhancement of IL-12 release from macrophages via up-regulation of TLR4 expression.