Our conclusion is that the stimulation conditions are critical for exposing the regulatory failure in patients with T1D. The CD4+CD25hipopulation is known to be a heterogeneous mixture of cells containing recently activated effector and regulatory T cells. be suppressed contributes to this defect. Keywords:autoimmunity, diabetes, immune regulation, regulatory T cells == Introduction == Type 1 diabetes (T1D) is a T cell-mediated disease in which insulin-producing pancreatic islet beta cells are destroyed selectively, resulting in a loss of insulin production and a subsequent inability to control glucose metabolism [1]. Autoreactive T cells specific for the islet autoantigens insulin, glutamic acid decarboxylase (GAD65) and the islet tyrosine phosphatase IA-2 have been isolated from patients with T1D [25]. Several lines of evidence suggest that these cells are involved in disease pathogenesis, including their presence in islet mononuclear infiltrates, delay of disease progression using T cell-inhibiting agents [6,7] and their ability to transfer disease in the murine model of T1D the non-obese diabetic (NOD) mouse [1]. Islet autoreactive T AZD6642 cells are also present in normal non-diabetogenic individuals [3] suggesting that, in the normal immune system, mechanisms must operate in the periphery to control the potentially autoreactive cells. The CD4+CD25hiregulatory T cell population is essential for maintenance of peripheral tolerancein vivo, as highlighted by animals and humans in which a natural or experimentally induced deficit in this population exists. Deficiency of this Rabbit Polyclonal to Akt T regulatory (Treg) population leads to the development of a range of autoimmune and lymphoproliferative disorders, including autoimmune diabetes [810]. Tregscan also control the responses of autoreactive T cells stimulatedin vitro[1113]. Much evidence has been collected to suggest an important role for regulatory T cells in the control of islet autoreactivity in both mouse and man [1417]. Initial studies in human patients with T1D suggested that there may be a reduction in the frequency of CD4+CD25hiregulatory T cells in these individuals [15]. This finding was not confirmed by subsequent studies, of which some used more reliable markers to identify Tregsand appropriately age-matched control subjects [14,16,18,19]. However, careful analysis of Tregfunction indicated that the suppression of autologous responder T cells by CD4+CD25hiTregsfrom individuals with newly diagnosed T1D is reduced significantly compared with that observed in age-matched control subjects [16], findings confirmed subsequently by Brusko and colleagues [14]. In the present study, we examined whether this defective regulation was due to changes in the immune system close to diagnosis of T1D [20], or represented a stable phenotype also present in individuals with long-standing T1D (L/S T1D). In addition, we sought to determine whether the reduced regulation that we observein vitrocould be the result of a reduced frequency of true regulatory T cells within the CD25hipopulation by using additional markers of the regulatory T cell lineage, such as the transcription factor forkhead box P3 (FoxP3) [8,10,2123] and the interleukin (IL)-7R chain CD127 [24,25]. Finally, we analysed the contribution that both responder and regulatory T cells make to defectivein vitroregulation, using AZD6642 cross-over co-culture assays. == Materials and methods == == Subjects == Peripheral blood samples were obtained from 44 patients with T1D and 44 control subjects. Long-standing disease was defined as T1D duration of > 3 years AZD6642 and control subjects had no family history of T1D. Eleven patients with L/S T1D [mean standard deviation (s.d.), age 437 years 144] and 12 age- and human leucocyte antigen (HLA)-matched healthy control subjects (age 372 years 131) were recruited for analysis of Tregfrequency and function. Thirteen patients with L/S T1D (age 400 years 86) and 13 age- and HLA-matched control subjects (age 34 AZD6642 years 114) were recruited for analysis of FoxP3 expression. Fifteen patients with L/S T1D (age 415 years 144) were recruited for analysis of CD127 expression along with 15 age- and HLA-matched healthy control subjects (age 348 years 106). Finally, five patients with L/S T1D (age 392 years 8) were recruited for cross-over functional analysis along with four control subjects (age 392 years 134), forming five pairs of age- and HLA-matched subjects (one healthy control subject was paired with two patients with T1D). Peripheral blood mononuclear cells (PBMC) were obtained by density gradient centrifugation (Lymphoprep;.