The Role of the Indole-3-Acetic Acid–Aryl Hydrocarbon Receptor Axis in Inflammation and Immune Homeostasis

Indole-3-acetic acid (IAA) is produced by plants, bacteria, fungi, and human gut microbiota. IAA is increasingly recognized as a signaling molecule capable of modulating immune, inflammatory, and cellular responses in the human body. Its biological activity is linked to aryl hydrocarbon receptor (AhR) activation, a transcription factor contributing to modulation of cellular metabolism and immune response. In experimental studies, IAA-dependent AhR signaling has been associated with immunomodulatory and protective effects in models of rheumatic, renal, hepatic, respiratory, and neurological diseases. This narrative review summarizes current data on the molecular mechanisms that underlie IAA–AhR signaling and its impact on immune and tissue homeostasis, with particular emphasis on the dual and context-dependent nature of IAA activity.