Natural AhR ligands: A novel approach to dynamic immune regulation in viral infections

Isatidis Radix is effective against respiratory syncytial virus (RSV), yet its immune-regulatory mechanisms remain unclear.

To elucidate the immune-related targets and mechanisms of the active components of Isatidis Radix against RSV.

LC-MS and HPLC were used to identify the chemical profile of Isatidis Radix and its absorbed constituents in serum. Based on these serum components, network pharmacology predicted potential targets, which were validated by molecular docking, surface plasmon resonance (SPR), PCR, Western blotting, immunofluorescence, and co-immunoprecipitation (co-IP). An intranasal RSV infection model was established to assess the dynamic immunomodulatory effects of the active components.

The total alkaloids from Isatidis Radix (IRA) were primarily indole alkaloids. Six prototype components and five metabolites were identified in serum. Network pharmacology, docking, and SPR consistently indicated the aryl hydrocarbon receptor (AhR) as a core target. Mechanistic studies confirmed that IRA components, including isatin, partially activated AhR. In the RSV-infected model, IRA dynamically regulated AhR in coordination with the endogenous ligand kynurenine. This significantly reduced viral load, alleviated lung injury, and reversed the excessive immune cell infiltration and cytokine imbalance induced by RSV. The therapeutic effects were replicated using a formulation mimicking the natural component ratio.

This study is the first to demonstrate that AhR is a key mediator of IRA's dynamic therapeutic effects against RSV. Rather than exerting isolated antiviral or anti-inflammatory actions, IRA reprograms immune function by targeting AhR. This novel mechanism offers a new perspective on the dynamic therapeutic actions of traditional Chinese medicine.