AHR and Autoimmunity: Of note, recent reports have revealed that the AhR is widely expressed in the immune system and that activation of AhR by its ligands has modulatory effects on the immune system, including balancing the differentiation of regulatory T cells (Tregs) and IL-17-producing helper T cells (Th17 cells), which may be associated with autoimmunity [8, 9, 11, 12].