Alterations of peripheral CD4⁺CD25⁺Foxp3⁺ T regulatory cells in mice with STZ-induced diabetes

Abstract

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 CD4⁺Helios⁺Foxp3⁺ 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 from CD4⁺CD25⁻ T cells by transforming growth factor (TGF)-β, high glucose enhanced the efficiency of CD4⁺CD25⁺Foxp3⁺ inducible Tregs (iTregs) induction. In addition, CD4⁺CD25⁻ T cells from diabetic mice were more susceptible to CD4⁺CD25⁺Foxp3⁺ iTreg differentiation than those cells from control mice. These data, together with the enhanced frequency of CD4⁺Helios⁻Foxp3⁺ iTregs in the periphery of mice with diabetes, indicate that enhanced CD4⁺CD25⁺Foxp3⁺ 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⁺ Tregs in mice, which may result in late-state immune dysfunction in patients with diabetes.