A normal immune state requires balance between effector and regulatory immune functions. A normal state of immune balance can exist across a broad range of Teff and Treg functions. Imbalances between Teffs and Tregs can manifest as emergence of an autoimmune disease such as multiple sclerosis (when Teff ≫ Treg) or the development of cancer or uncontrolled infection (Teff ≪ Treg).