Complications arising from abnormal immune responses are the major causes of mortality and morbidity in diabetic patients.CD4^(+)CD25^(+)T regulatory cells(Tregs)play pivotal roles in controlling immune homeostasis,immunity and tolerance.The effect of hyperglycemia on CD4^(+)CD25^(+)Tregs has not yet been addressed.Here we used streptozotocin(STZ)-induced diabetic mice to study the effects of long-term hyperglycemia on CD4^(+)CD25^(+)Tregs in vivo.Four months after the onset of diabetes,the frequency of CD4^(+)CD25^(+)Foxp3^(+)T regulatory cells was significantly elevated in the spleen,peripheral blood lymphocytes(PBLs),peripheral lymph nodes(pLNs)and mesenteric LNs(mLNs).CD4^(+)CD25^(+)Tregs obtained from mice with diabetes displayed defective immunosuppressive functions and an activated/memory phenotype.Insulin administration rescued these changes in the CD4^(+)CD25^(+)Tregs of diabetic mice.The percentage of thymic CD4^(+)CD25^(+)naturally occurring Tregs(nTregs)and peripheral CD41Helios1Foxp31 nTregs were markedly enhanced in diabetic mice,indicating that thymic output contributed to the increased frequency of peripheral CD4^(+)CD25^(+)Tregs in diabetic mice.In an in vitro assay in which Tregs were induced fromCD4^(+)CD25^(+)T cells by transforming growth factor(TGF)-b,high glucose enhanced the efficiency of CD4^(+)CD25^(+)Foxp3^(+)T inducible Tregs(iTregs)induction.In addition,CD4^(+)CD25^(+)T cells from diabetic mice were more susceptible to CD4^(+)CD25^(+)Foxp3^(+)TiTreg differentiation than those cells from control mice.These data,together with the enhanced frequency of CD4^(+)CD25^(+)Foxp3^(+)T iTregs in the periphery of mice with diabetes,indicate that enhanced CD4^(+)CD25^(+)Foxp3^(+)T iTreg induction also contributes to a peripheral increase in CD4^(+)CD25^(+)Tregs in diabetic mice.Our data show that hyperglycemia may alter the frequency of CD4^(+)CD25^(+)Foxp3^(+)T Tregs in mice,which may result in late-state immune dysfunction in patients with diabetes.
CD4＋CD25＋ regulatory T cells （Tregs） play an important role in maintaining host immune tolerance via regulation of the phenotype and function of the innate and adaptive immune cells. Whether allogeneic CD4＋CD25＋ Tregs can regulate recipient mouse macrophages is unknown. The effect of allogeneic donor CD4＋CD25＋ Tregs on recipient mouse resident F4/80＋macrophages was investigated using a mouse model in which allogeneic donor CD4＋CD25＋ Tregs were adoptively transferred into the peritoneal cavity of host NOD-scid mice. The phenotype and function of the recipient macrophages were then assayed. The peritoneal F4/80＋ macrophages in the recipient mice that received the allogeneic CD4＋CD25＋ Tregs expressed significantly higher levels of CD23 and programmed cell death-ligand I（PD-L1） and lower levels of CD80, CD86, CD40 and MHC II molecules compared to the mice that received either allogeneic CD4＋CD25- T cells （Teffs） or no cells. The resident F4/80＋ macrophages of the recipient mice injected with the allogeneic donor CD4＋CD25＋ Tregs displayed significantly increased phagocytosis of chicken red blood cells （cRBCs） and arginase activity together with increased IL-IO production, whereas these macrophages also showed decreased immunogenicity and nitric oxide （NO） production. Blocking arginase partially but significantly reversed the effects of CD4＋CD25＋ Tregs with regard to the induction of the M2 macrophages in vivo. Therefore, the allogeneic donor CD4＋CD25＋ Tregs can induce the M2 macrophages in recipient mice at least in part via an arginase pathway. We have provided in vivo evidence to support the unknown pathways by which allogeneic donor CD4＋CD25＋ Tregs regulate innate immunity in recipient mice by promoting the differentiation of M2 macrophages.
