PTPN22 and Autoimmunity: However, increased inhibition of T-cell receptor signaling caused by the PTPN22 C1858T polymorphism could predispose towards autoimmunity, either by affecting thymic deletion of autoreactive T-cells or by affecting development or function of peripheral regulatory T-cells.27 Indeed, recently, PTPN22 was found to be among the gene targets of FoxP3 in CD4+CD25+ regulatory T-cells.28