AhR activation by metabolites such as indole-3-acetate, indole-3-aldehyde, and tryptamine enhances immune tolerance by promoting Treg differentiation and suppressing pro-inflammatory Th2 cytokine production, particularly IL-5, IL-13, and IL-33, all of which are central to the allergic responses observed in asthma.191–194 AhR also modulates innate lymphoid cells (ILC3), leading to IL-22 production,194 which enhances epithelial barrier integrity. This evidence concerns the gene AHR and asthma.