Guizhi Gegen Decoction alleviates influenza-associated intestinal injury by balancing lung-gut ILC2 distribution via the S1P/S1PR1 axis.

ETHNOPHARMACOLOGICAL RELEVANCE: Influenza virus primarily affects the respiratory system but frequently induces gastrointestinal complications as well. Guizhi Gegen Decoction (GGD), a classical traditional Chinese herbal formula, has been used to treat influenza patients presenting with gastrointestinal symptoms such as vomiting and diarrhea, yet its underlying pharmacological mechanisms remain to be clarified.

AIM OF THE STUDY: This study aimed to elucidate the molecular mechanisms by which GGD ameliorates influenza-associated intestinal injury through the regulation of lung-gut ILC2 homeostasis.

MATERIALS AND METHODS: A influenza mouse model was established using H1N1/PR8 influenza virus. Inflammatory injury of the lung and intestinal segments (duodenum, jejunum, ileum, and colon) was systematically evaluated. Multi-timepoint transcriptomic sequencing, flow cytometry, and pharmacological interventions were employed to characterize the imbalance of group 2 innate lymphoid cells (ILC2s) along the lung-gut axis and to establish their causal relationship with intestinal pathology. Based on these findings, the therapeutic effects of GGD were comprehensively assessed in terms of antiviral, anti-inflammatory, and ILC2 homeostasis-modulating activities. Furthermore, molecular biology techniques and computational simulations were combined to explore the molecular targets and mechanisms by which GGD regulates ILC2 homeostasis.

RESULTS: Influenza virus infection not only induced pneumonia but also triggered abnormal expansion of intestinal ILC2s, leading to disruption of immune homeostasis and activation of ILC3-mediated intestinal inflammation. Notably, intestinal ILC2 levels increased markedly during disease progression, whereas pulmonary ILC2 levels gradually declined. Mechanistically, the sphingosine-1-phosphate (S1P)/S1PR1 signaling axis played a pivotal role in this lung-gut ILC2 imbalance. Administration of the S1PR1 antagonist fingolimod (FTY720) reversed this phenomenon, restoring pulmonary ILC2 levels while reducing intestinal ILC2 accumulation. GGD treatment significantly reduced viral load, downregulated key proinflammatory cytokines (IFN-γ, IL-17, and IL-6) in both lung and intestine, and effectively alleviated inflammation. Further mechanistic studies demonstrated that GGD suppressed S1PR1 overexpression and directly modulated its signaling activity in the lung, thereby restoring ILC2 homeostasis between lung and intestine. Restoration of ILC2 balance in turn suppressed aberrant intestinal ILC3 activation and downstream production of IL-6, TNF-α, and IL-17A.

CONCLUSION: The S1P-S1PR1 axis-mediated imbalance of ILC2s between lung and intestine is one of the key molecular mechanism driving influenza-induced intestinal injury. By inhibiting S1PR1 signaling, GGD restores inter-organ ILC2 homeostasis while exerting synergistic antiviral and anti-inflammatory effects, thereby achieving therapeutic efficacy against influenza. This study provides new insights into the pathophysiological progression of influenza-associated intestinal injury and supports the modernization of GGD in clinical practice.