Indolelactic acid (Indole-3-lactic acid), a metabolite of tryptophan (Trp), plays a role in immune cell differentiation and cytokine production by activating aryl hydrocarbon receptors (AhR). This regulation supports immune responses and aids in anti-inflammatory and anti-allergic activities. It also plays an important role in the balance of Th17/Treg cells by reprogramming CD4+ Th cells into CD4+CD8+ Treg cells and inhibiting the polarization of Th17 cells.