PTPN22 and autoimmune disease: Currently, several phosphatases have been identified as contributors to the pathogenesis of autoimmune diseases, including members of the PSP family, such as protein phosphatase 2A (PP2A), and of the PTP family, such as T-cell PTP (TC-PTP), Src homology-2 domain-containing PTP1 (SHP1), Src homology-2 domain-containing PTP2 (SHP2), PTP non-receptor type 22 (PTPN22), dual specificity phosphatase 22 (DUSP22), dual specificity phosphatase 2 (DUSP2), and CD45 (Table 1).