PTPN22 and Autoimmunity: PTPN22 plays an important role in determining TCR signal strength during central tolerance; PTPN22-deficient mice show increased positive selection in the thymus as well as increased Treg numbers both in the thymus and periphery, leading to protection from the experimental autoimmune encephalomyelitis (EAE) model of autoimmunity (Maine et al., 2012; Hasegawa et al., 2004; Fousteri et al., 2014).