Shegan-Mahuang Decoction ameliorates asthmatic airway hyperresponsiveness by downregulating Th2/Th17 cells but upregulating CD4+FoxP3+ Tregs.

Shegan-Mahuang Decoction (SMD), also named Yakammaoto or Shegan-Mahuang Tang, is a classic formula of traditional Chinese medicine with nine herbs, including Asarum sieboldii Miq., Aster tataricus L.f., Ephedra sinica Stapf, Belamcanda chinensis (L.) Redouté, Pinellia ternata (Thunb.) Breit., Schisandra chinensis (Turcz.) Baill., Tussilago farfara L., Zingiber officinale Roscoe, and Ziziphus jujuba Mill. SMD was originally discovered by Zhang Zhongjing in Eastern Han dynasty. It has been widely used as traditional medicine to treat flu-like symptoms in China and Japan for around twenty centuries. It was also utilized for the treatment of the early stage of acute asthma. However, the immune mechanisms underlying its therapeutic effects remain unknown.This study was set to investigate the effects of SMD on asthmatic airway hyperresponsiveness and its impacts on adaptive immunity in a mouse model of asthma.The HPLC fingerprint profile of the water extract of SMD recorded 22 peaks, including those equivalent to guanosine, chlorogenic acid, tectoridin, 6-gingerol and wuweizisu B, as described previously (Yen et al., 2014). Airway hyperresponsiveness was assessed by measuring the airway resistance. Cellular infiltration was measured via H&E staining and immunochemistry while gene expression was analyzed using real-time RT-PCR. Treg frequency was determined through flow analysis whereas cytokine production in the supernatant was evaluated using ELISA. Finally, mTOR and NF-kB signalings were analyzed via Western blotting.

We found that SMD largely corrected the imbalance of Th cell subsets in asthmatic mice with a significant inhibition of Th2 and Th17 cytokine production, thereby reducing asthmatic airway hyperresponsiveness. Moreover, lung function tests showed that SMD reduced airway hyperresponsiveness while immunohistochemical analyses demonstrated that SMD attenuated pulmonary infiltration of CD3⁺ and CD4⁺ T cells. Further, we observed a significant increase in the proportion of CD4+Foxp3+ Tregs in SMD-treated asthmatic mice. We also found that SMD downregulated gene expression of GATA3 and ROR-γt in murine lung tissue. In addition, both mTOR- and NF-kB-related protein expressions were reduced in the lung tissue of SMD-treated mice. SMD inhibited Th2/Th17 cytokine production by CD4⁺ T cells and also their mTOR activity in vitro.

Our findings demonstrate that SMD attenuates asthmatic airway hyperresponsiveness by hindering Th2/Th17 differentiation, promoting CD4+FoxP3+ Treg generation and suppressing mTOR and NF-kB activities.