In the next sections, we revisit our view on the TH17 cells' role in autoimmunity [9] and provide a brief description of the double-sided role of TH17 cells and their related molecules IL-17, IL-21, and IL-22 and their participation at the initiation/induction of autoimmunity as a consequence of xenobiotic exposure. The gene discussed is IL21; the disease is Autoimmunity.