Initial analysis of T cell phenotypes in Ptpn22-/- mouse models demonstrated that in the absence of PTPN22, naïve T cell functions were comparable to wild-type T cells whereas effector T cell responses were enhanced leading to lymphadenopathy, splenomegaly and the accumulation of elevated numbers of effector/memory phenotype T cells and increased serum immunoglobulin (Ig).23 Here, PTPN22 is linked to Lymphadenopathy.