The involvement of Tregs was suggested by the analysis of patients with immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX), who harbor dysfunctional Tregs due to loss-of-function FOXP3 mutations and show elevated frequencies of circulating autoreactive mature naive B cells (50). Here, FOXP3 is linked to immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.