At-Risk and Recent-Onset Type 1 Diabetic Subjects Have Increased Apoptosis in the CD4+CD25+high T-Cell Fraction

Sanja Glisic-Milosavljevic; Jill Waukau; Parthav Jailwala; Srikanta Jana; Huoy-Jii Khoo; Hope Albertz; Jeffrey Woodliff; Marilyn Koppen; Ramin Alemzadeh; William Hagopian; Soumitra Ghosh

doi:10.1371/journal.pone.0000146

Abstract

Background

In experimental models, Type 1 diabetes T1D can be prevented by adoptive transfer of CD4+CD25+ FoxP3+ suppressor or regulatory T cells. Recent studies have found a suppression defect of CD4+CD25+^high T cells in human disease. In this study we measure apoptosis of CD4+CD25+^high T cells to see if it could contribute to reduced suppressive activity of these cells.

Methods and Findings

T-cell apoptosis was evaluated in children and adolescent 35 females/40 males subjects comprising recent-onset and long-standing T1D subjects and their first-degree relatives, who are at variable risk to develop T1D. YOPRO1/7AAD and intracellular staining of the active form of caspase 3 were used to evaluate apoptosis. Isolated CD4+CD25+^high and CD4+CD25− T cells were co-cultured in a suppression assay to assess the function of the former cells. We found that recent-onset T1D subjects show increased apoptosis of CD4+CD25+^high T cells when compared to both control and long-standing T1D subjects p<0.0001 for both groups. Subjects at high risk for developing T1D 2–3Ab+ve show a similar trend p<0.02 and p<0.01, respectively. On the contrary, in long-standing T1D and T2D subjects, CD4+CD25+^high T cell apoptosis is at the same level as in control subjects p = NS. Simultaneous intracellular staining of the active form of caspase 3 and FoxP3 confirmed recent-onset FoxP3+ve CD4+CD25+^high T cells committed to apoptosis at a higher percentage 15.3±2.2 compared to FoxP3+ve CD4+CD25+^high T cells in control subjects 6.1±1.7 p<0.002. Compared to control subjects, both recent-onset T1D and high at-risk subjects had significantly decreased function of CD4+CD25+^high T cells p = 0.0007 and p = 0.007, respectively.

Conclusions

There is a higher level of ongoing apoptosis in CD4+CD25+^high T cells in recent-onset T1D subjects and in subjects at high risk for the disease. This high level of CD4+CD25+^high T-cell apoptosis could be a contributing factor to markedly decreased suppressive potential of these cells in recent-onset T1D subjects.

Citation: Glisic-Milosavljevic S, Waukau J, Jailwala P, Jana S, Khoo H-J, Albertz H, et al. (2007) At-Risk and Recent-Onset Type 1 Diabetic Subjects Have Increased Apoptosis in the CD4+CD25+^high T-Cell Fraction. PLoS ONE 2(1): e146. https://doi.org/10.1371/journal.pone.0000146

Academic Editor: Ludvig Sollid, University of Oslo, Norway

Received: December 5, 2006; Accepted: December 6, 2006; Published: January 3, 2007

Copyright: © 2007 Glisic-Milosavljevic et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: Part of the study was funded through The Max McGee National Center for Juvenile Diabetes private fund and The Children's Research Institute. The study was also funded through GCRC Grant M01-RR00058 from the National Institutes of Health. The funding source didn't have any role or influence on study design, collection of data, analysis and interpretation of results.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Type 1 diabetes T1D is an autoimmune disorder in which autoreactive T cells attack pancreatic β-cells, leading to a lifelong dependency on insulin. Twenty years ago, T1D was hypothesized to be a chronic autoimmune disorder by Eisenbarth[1]. Considerable progress has been made in understanding the pathogenesis of autoimmune disorders since then, but not enough to prevent or reverse the disease. The abrogation of central and peripheral tolerance underpins the genesis of all autoimmune diseases[2]. At the heart of these processes lies apoptosis. In central tolerance, autoreactive T cells are deleted in the thymus through apoptosis pathways. Most studies in murine T1D models have found that autoreactive T cells are resistant to apoptosis[3]. This predisposes an individual to autoimmune disease as autoreactive T cells find their way to the periphery and attack the target organ. Only a few studies have investigated apoptosis of T cells in the periphery in T1D patients and nearly all before the era of regulatory T cells[4]–[6]. There is some evidence that resistance to apoptosis of autoreactive T cells contributes to human T1D [6]. In parallel, the thymus produces regulatory T cells whose main action is in the periphery control of development, trafficking and proliferation of responder T cells. Though there are other mechanisms for peripheral tolerance[7], the role of CD4+CD25+^high T cells with regulatory function Tregs has recently attracted considerable attention.

Although the existence and function of regulatory T cells is confirmed in both in vivo and in vitro experiments, exact identification and isolation has been and continues to be a problem. The FACS isolation method that gives the high number of most potent Tregs is based on the highest surface expression of CD25 IL2-Ralpha[8]. These CD4+CD25+^high T cells are enriched in cells with regulatory properties. It has been shown in animal models that CD4+CD25+^high T cells can prevent murine T1D[9]–[11] bringing in new hope for the prevention of human autoimmune disease. However, CD4+CD25+^high also include activated CD4+CD25+ T cells that do not generally show regulatory properties. Nevertheless, high expression of CD25 on CD4+ cells has been shown to mark a small number of highly suppressive T cells. Although a specific molecule for regulatory T cells is lacking, the transcription factor FoxP3 - forkhead box P3, has been identified as necessary for their development[12]. It has also been confirmed that cells with regulatory function constitutively express high levels of the FoxP3, but this is an intracellular transcription factor, so isolation of live human cells based on FoxP3 staining is not possible. Recently however, some papers have shown correlation of high expression of FoxP3 and low or no expression of IL-7R alpha CD127low/- on the cell surface[13], [14] Humans without functional FoxP3 protein have an autoimmune disorder called IPEX with auto-antibodies against a diversity of organs[15]. However, there are still controversial data about FoxP3 involvement in regulatory function[16].

Several studies with healthy control subjects and T1D patients have reported decreased regulatory function of CD4+CD25+^high T cells in T1D patients[17]–[20]. Despite accumulating data about the dysfunction of CD4+CD25+^high T cells in T1D patients, there is no compelling evidence identifying an underlying cause. Spontaneous apoptosis of Tregs in human T1D patients as a mechanism has not been fully investigated.

In this study, we measured apoptosis of CD4+CD25+^high T cells in relation to their function. Healthy control and several T1D-related clinical groups were studied. These included recent-onset T1D subjects and unrelated, unaffected subjects with one, two and three positive T1D specific auto-antibodies aAbs to GAD, IA-2 and insulin. Those with two or more aAbs are at higher risk for developing T1D in the future. We also studied longstanding T1D and T2D patients. Our results implicate a role of increased apoptosis of CD4+CD25+^high T cells in the pathogenesis of human T1D. Furthermore, intriguing data presented here shows that Tregs FoxP3+ve T cells within this population contribute most to the increased apoptosis. However, a strong inverse relationship between apoptosis of CD4+CD25+^high T cells and their function needs to be investigated on a larger sample size in different clinical groups.

Methods

Seventy-five Wisconsin study subjects 67 Caucasian, 5 Asian, 2 African-American and 1 Hispanic of both genders 35 females and 40 males were recruited through the diabetes clinics at Children's Hospital of Wisconsin CHW, Froedtert Hospital FMLH and other local hospitals and clinics that had over 1600 T1D families, through ascertainment of a proband with the T1D onset before age of 17. In families with a child proband, siblings and parents were also asked to join the study. However, just one person from each family was included in our study. Control subjects were recruited by posting flyers in areas of the hospitals that might be visited by potential “healthy” subjects, i.e. orthopedic, dental, and eye clinics. Inclusion criteria for control subjects were random blood glucose less then 110 mg/dl, no history of any autoimmune disorder including T1D in the family and an absence of T1D- specific aAbs. Although healthy subjects of all ages were included n = 28, age-matched control subjects formed a separate clinical group n = 10 because of the possible age effect on number and function of isolated CD4+CD25+high T cells[21]. At-risk subjects n = 17 were first-degree relatives of T1D patients, but unrelated to the specific probands included in this study. T1D subjects were defined according to accepted criteria: high blood glucose levels ≥200 mg/dl with symptoms of diabetes confirmed by a physician, according to WHO criteria[22]. Recent-onset T1D subjects n = 14 were recruited after metabolic stabilization and within one year of diagnosis. Long-standing T1D subjects n = 12 were diagnosed at least two years earlier. Random glucose levels at the time of recruitment in this group of subjects were at comparable levels to the glucose levels measured in recent-onset T1D subjects Table 1. Long-standing T2D subjects n = 4 were also diagnosed at least two years earlier. They were included in the study as a group with non-autoimmune diabetes. Subjects or their parents guardians provided written informed consent and completed a questionnaire.

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Table 1. Demographic data of subjects involved in the study

https://doi.org/10.1371/journal.pone.0000146.t001

All participants had aAbs and glucose levels measured at the recruitment visit. An accurate method for the detection of multiple T1D auto-antibodies developed by Hagopian and collaborators was employed[23]. His laboratory participated in the 2005 CDC/IDS Diabetes Autoantibody Standardization Program, with sensitivity/specificity of 94%/94%, 80%/93% and 76%/93% for GAD Ab, IA2 Ab and IAA, respectively.

Recent-onset and long-standing T1D and T2D subjects had HbA1c and insulin dosage recorded at each visit. Peripheral blood mononuclear cells PBMC were collected using vacutainers with ACD solution B of trisodium citrate and isolation was done using Ficoll-Hypaque density gradient centrifugation following the manufacturer's protocol Amersham Pharmacia, Uppsala, Sweden. Cells were counted and stained with a cocktail of fluorochrome-conjugated monoclonal antibodies in PBS APC-αCD4 clone RPA-T4, APC-Cy7-αCD25 clone M-A251, FITC-αCD14 clone M5E2, FITC-αCD32 clone FLI8.26, FITC-αCD116 clone M5D12, PE-Cy7-CD8 clone RPA-T8 all from BD Pharmingen, San Diego, CA and sorted on FACSAria BD Biosciences, San Diego, CA. Cells were gated first for live lymphocyte, eliminating dead cells and debris. Next, two gates were set up to eliminate non-CD4 T cells FITC- and PECy7-conjugated antibodies. CD4+ T cells were further gated as CD4+CD25- and CD4+CD25+^high using the Fluorochrome Minus One FMO method, that allows a more precise definition of cells having fluorescence above the background level[24]. The 1% of cells expressing the highest level of CD25 were collected and defined as CD4+CD25+^high T cells, known to be enriched for Tregs[25]. These cells showed expected distribution of non-unique surface markers expected for Tregs data not shown.

Apoptosis in all samples was measured using our recently published method [26]. Briefly, cells were stained with YOPRO1 250 nM for 20 minutes in the dark and 7AAD 250 ng was added 10 minutes before acquiring events. Apoptosis was measured as the percentage of apoptotic cells YOPRO1+ve/7AAD-ve amongst live cells total 7AAD-ve cells comprising both YOPRO1+ve and YOPRO1-ve cells. Using a similar computation, apoptosis was also measured by intracellular staining of the active form of caspase 3 aaCas3, in most cases combined with intracellular staining of the transcription factor FoxP3, constitutively expressed in the Treg subfraction of CD4+CD25+^high T cells[27]. Caspase 3 is a key executioner in the apoptosis pathway and detection of its active form is usually a sign of ongoing apoptosis. Before we adopted the method of dual staining of FoxP3 and the active form of caspase 3, we confirmed that the results of single staining for both proteins were similar to results generated by their simultaneous staining data not shown.

The only reliable feature of CD4+CD25+^high T cells is their capacity to suppress proliferation of responder T cells. This capacity is measured via a proliferation assay, where responder CD4+CD25− and suppressor within the CD4+CD25+^high population T cells are stimulated in vitro separately and together in co-culture under defined conditions. The proliferation assay was performed using 10,000 responder T cells CD4+CD25− and 10,000 irradiated PBMCs 5000rad along with 1,000 CD4+CD25+^high T cells seeded in a 96-well plate. Stimulation was with aCD3-coated beads 1 ug/ml, 3 beads/cell for 5 days under 5% CO₂ and saturated humidity. Cells were left in culture after pulsing 1 µCi of [H³]-thymidine for an additional 16 hours, then harvested and after adding scintillation liquid, read for counts per minute cpm. Suppression % of Tregs was calculated as [cpm of responders in single culture − cpm of cells in co-culture/cpm of responders in single culture]×100.

The Mann-U-Whitney and Tukey-Kramer tests were used to compare results between clinical groups with p value ≤0.05 considered significant. GraphPad software was used for data presentation. We also performed Kruskal-Wallis in addition to a one-way ANOVA.

Results

We used a FACS machine for cell separation in this study. The sorter allows specific isolation of a cell population from a heterogeneous T-cell mixture, especially if the surface marker is used as a tag. To minimize the number of activated T cells that express high levels of CD25, we only collected 1% of cells with the highest CD25 expression. CD4+CD25+^high T cells.

In all clinical groups studied, two T-cell subsets CD4+CD25− and CD4+CD25+^high were collected and analyzed ex vivo for 1. proliferation/suppression; 2. apoptosis determination using nucleic acid stains YOPRO1/7AAD; 3. intracellular staining for FoxP3 and 4. intracellular staining for aaCas3. The CD4+CD25− T cells are used as responders in a suppression assay and they also served as an internal control for the measurement of apoptosis.

Within a uniformly short time after FACS isolation, in all studied subjects, fresh CD4+CD25− and CD4+CD25+^high T cells were analyzed for apoptosis using the YOPRO1/7AAD stain combination[26]. Representative FACS pictures for each group of patients are presented in Figure 1. CD4+CD25+^high T-cell apoptosis was significantly different across the clinical groups Kruskal-Wallis p<0.0001; ANOVA F = 16.07 df 6, 78, p<0.0001, Figure 2a. Based on the Tukey-Kramer post-hoc test, CD4+CD25+^high T-cell apoptosis in recent-onset T1D subjects differed significantly from all other clinical groups except from the high at-risk group Figure 2a. Concurrently, CD4+CD25− T cells, which were isolated from all subjects at the same visit, showed no differences in apoptosis levels across the clinical groups Kruskal-Wallis p = 0.25 NS; ANOVA F = 0.73 df 6, 78, p = 0.26; NS; Figure 2b. Apoptosis of CD4+CD25+^high is the highest in recent-onset T1D subjects 11.4±1.1 followed by high at-risk subjects 8.6±1.5. The lowest measured CD4+CD25+^high T-cell apoptosis level is among the longstanding T2D 3.5±0.4 and is similar to CD4+CD25+^high T-cell apoptosis among both the control and longstanding T1D subjects 3.9±0.5 and 4.0±0.5 respectively. When compared to control subjects, CD4+CD25+^high T-cell apoptosis of recent-onset T1D showed the strongest statistical difference p<0.0001. We were also able to recruit ten age-matched control subjects to rule out the possibility that increased age was associated with reduced apoptosis of CD4+CD25+^high T cells. Compared to the age-matched control group, recent-onset T1D subjects showed a significant increase in CD4+CD25+^high T cell apoptosis p<0.0001. While not as noticeable, the high at-risk clinical group both 2 Ab+ and 3 Ab+ also showed a significant increase in CD4+CD25+^high T-cell apoptosis when compared to random control subjects p = 0.008.

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Figure 1.

Representative FACS pictures of CD4+CD25− and CD4+CD25+^high T cells using YOPRO1/7AAD method from representative subjects of clinical groups. Apoptosis was calculated as the percentage of apoptotic cells YOPRO1+ve/7AAD-ve amongst live cells total 7AAD-ve cells comprising both YOPRO1+ve and YOPRO1-ve cells. This is simply designated as YOPRO1+ve.

https://doi.org/10.1371/journal.pone.0000146.g001

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Figure 2.

a Apoptosis of CD4+CD25+^high T cells in clinical groups measured by YOPRO/7AAD stain combination. CD4+CD25+^high T cells in recent-onset and in high at-risk subjects for developing T1D show significantly higher apoptosis levels: Kruskal-Wallis p<0.0001; ANOVA F = 16.07 df 6, 78 p<0.0001. Specifically, Control vs. recent-onset T1D p<0.0001; age-matched control vs. recent-onset p<0.0001; recent-onset T1D vs. long-standing T1D p<0.0001; recent-onset T1D vs. low at-risk p<0.0001; control vs. high at-risk p<0.008; high at-risk vs. long-standing T1D p = 0.01.

b Apoptosis of CD4+CD25− T cells measured by YOPRO/7AAD stain combination across studied clinical groups Kruskal-Wallis p = 0.25; ANOVA F = 0.59, df 6, 78, NS. Apoptotic cells are presented on y-axis as YOPRO1+ve.

https://doi.org/10.1371/journal.pone.0000146.g002

In order to confirm our results using YOPRO1/7AAD, we used a second apoptosis detection method. Thus, an aliquot of isolated T cells was stained for the presence of active caspase 3. Figure 3a and 3b present CD4+CD25+^high T-cell apoptosis isolated from the same subjects measured by two different apoptosis assays. The apoptosis results were similar. Furthermore, correlation of apoptosis results measured by these two methods was significant Spearman's rank correlation coefficient r = 0.59 95% CI = 0.28–0.79, p = 0.0006. A higher percentage of CD4+CD25+^high T cells in recent-onset T1D subjects produced more active caspase 3 than the same T-cell subtype in control subjects, confirming the ongoing apoptosis detected by YOPRO1/7AAD. Control subjects had significantly lower apoptosis level from both recent-onset T1D and high at-risk subjects as measured by intracellular staining of aaCas3 p = 0.0006 and p = 0.009 respectively.

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Figure 3.

Comparison of apoptosis measurement in the same subjects using two different methods. a CD4+CD25+^high T cells apoptosis in three clinical groups using YOPRO/7AAD stain combination; control subjects CD4+CD25+^high T cells apoptosis significantly differs from both recent-onset T1D and high at-risk subjects p = 0.0001 and p = 0.01, respectively. Apoptotic cells are presented on y-axis as YOPRO1+ve. b CD4+CD25+^high T cells apoptosis in the same subjects using intracellular staining of aaCas3. CD4+CD25+^high T cells apoptosis from control subjects significantly differs from both recent-onset T1D and high at-risk subjects p = 0.0006 and p = 0.009, respectively. Spearman's rank correlation coefficient between two apoptosis measurement methods in control and recent-onset T1D subjects is significant r = 0.59 and p = 0.0006. Apoptotic cells are presented on y-axis as aaCas3+ve.

https://doi.org/10.1371/journal.pone.0000146.g003

Since CD4+CD25+^high T cells comprise FoxP3+ Tregs[27] as well as activated T cells, we checked whether cells that were dying by apoptosis were FoxP3 positive. Simultaneous intracellular staining of the active form of caspase 3 and FoxP3 confirmed recent-onset FoxP3+ve CD4+CD25+^high T cells committed to apoptosis at a higher percentage 15.3±2.2 compared to FoxP3+ve CD4+CD25+^high T cells in control subjects 6.1±1.7; Figure 4, p<0.002. Of great interest, while FoxP3+ve and FoxP3-ve CD4+CD25+^high T cells in both control and longstanding T1D subjects did not show differences in the apoptosis rate, FoxP3+ve CD4+CD25+^high in recent-onset T1D subjects were significantly more apoptotic than FoxP3-ve CD4+CD25+^high T cells from the same individual Figure 4, p = 0.01.

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Figure 4.

CD4+CD25+^high T cells apoptosis levels within FoxP3+ve and FoxP3-ve cell subpopulation across three clinical groups. FoxP3+ve CD4+CD25+^high T cells show significantly higher apoptosis level intracellular staining of aaCas3 compared to FoxP3-ve CD4+CD25+^high T cells in recent-onset T1D only Kruskal-Wallis, p = 0.0066; recent-onset T1D CD4+CD25+^high T cells FoxP3+ve vs. FoxP3-ve p = 0.01; FoxP3+ve CD4+CD25+^high T cells control vs. FoxP3+ve CD4+CD25+^high T cells recent-onset T1D p<0.002. FoxP3-ve CD4+CD25+^high T cells control vs. FoxP3-ve CD4+CD25+^high T cells recent-onset T1D p = 0.01. Apoptotic cells are presented on y-axis as aaCas3+ve.

https://doi.org/10.1371/journal.pone.0000146.g004

FACS-isolated CD4+CD25+^high T cells were also tested for their suppressive function using standardized in vitro suppression assays. Analysis of CD4+CD25−/CD4+CD25+^high T cell co-culture at a ratio of 1∶10 indicated that CD4+CD25+^high T cells in control subjects showed average suppression of 46.0.±5.9% while high at-risk and recent-onset T1D subjects showed similar suppression of 10.±9.9% and 9.9±5.5% respectively, Figure 5. Compared to control subjects, both recent-onset T1D and high at-risk subjects had significantly decreased function of CD4+CD25+^high T cells p = 0.0007 and p = 0.007, respectively. Although suppressive potential of CD4+CD25+^high T cells isolated from longstanding T1D subjects was higher than in recent-onset T1D subjects, it was significantly lower when compared to healthy controls p = 0.04.

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Figure 5.

CD4+CD25+^high T cells suppressive potential across major clinical groups. Control subjects show statistically higher suppression compared to the other three groups recent-onset T1D, high at-risk and longstanding T1D subjects p = 0.0007, p = 0.007 and p = 0.04, respectively. Standardized suppression assay was performed with 1×10⁴ responder T cells, 10⁴ irradiated PBMCs 5000rad alone and in co-culture with CD4+CD25+^high T cells in 1∶10 ratio, stimulated with aCD3 coated beads 1ug/ml, 3 beads/per cell.

https://doi.org/10.1371/journal.pone.0000146.g005

One must be aware of other factors associated with increased apoptosis of T cells in the clinical setting. These include ambient glucose[28] and insulin[29] levels. We provide evidence that these factors play only a minor role in our apoptosis results. In our sample, longstanding T1D subjects have similar glucose levels to recent-onset T1D subjects p = 0.52, NS, similar CD4+CD25− T cells apoptosis levels p = 0.21, but completely disparate apoptosis levels of their fresh CD4+CD25+^high T cells p<0.0001. Although exogenous insulin levels are significantly different because of the honeymoon phase p = 0.004, our data for CD4+CD25− T cells do not show apoptosis differences, which confirm a non-significant role of insulin or any other factor in the protection from or genesis of apoptosis. Age-dependent differences in the frequency of have been shown before[20]. However, in the present study, no differences in apoptosis of CD4+CD25+^high T cells dependent on donor age were observed Mann-Whitney U-test p = 0.19.

Discussion

In this study, we aimed to measure apoptosis and function of CD4+CD25+^high T cells in T1D families and control subjects. Although a recent study shows that 2–3% of the highest CD25-expressing T cells can be safely sorted as Tregs[30], we only collect the top 1%. This is because subjects with ongoing autoimmune disease have more activated T cells that also express CD25, even though these cells possess no regulatory properties. For now, the presence of true Tregs is best defined by their functional activity, which in vitro, is monitored by suppression of the proliferation of responder T cells. In fact, recent studies in vivo have confirmed that Tregs probably act in a similar manner by inhibiting the interaction between antigen-presenting cells and responder T cells, leading to reduced proliferation of the latter cells[31]. Most groups have reported regulatory T-cell CD4+CD25+^high dysfunction in T1D [17], [20]. None have found a cause for this dysfunction.

We present evidence that increased apoptosis of Tregs could potentially play a role in the pathogenesis of human T1D, a major autoimmune disease. Apoptosis was measured in freshly isolated CD4+CD25+^high T cells from T1D families and control subjects. The highest levels of apoptosis were found in recent-onset T1D subjects and in individuals at high risk 2+3Ab+ve for disease Figure 2. This important observation was only possible after we developed a novel, sensitive stain combination YOPRO1/7-AAD for the detection of early apoptosis [26]. YOPRO1 is a small molecule that enters the apoptotic cells readily compared to other stains.

Our data suggest that individuals who are positive for one Ab low risk to develop T1D have a low apoptosis level of CD4+CD25+^high T cells that is similar to control subjects. The percentage of apoptosis increases with the number of Abs detected in the serum, reaching the highest level in subjects at the onset of the disease staying high during the period immediately following diagnosis. It is during this period that requirements for exogenous insulin drop dramatically and beta cell function improves “honeymoon” phase. Later on, when the autoimmune destruction is complete and insulin requirements increase, CD4+CD25+^high T-cell apoptosis goes back to the level detected in healthy control subjects.

Our results with the new stain combination are confirmed with a second, independent, apoptosis detection method on the same samples. The second method was the intracellular staining for the active form of caspase 3. Generated results parallel the apoptosis data in the CD4+CD25+^high T-cell fraction using YOPRO1/7-AAD Figure 3. These results also suggest that apoptosis in recent-onset T1D subjects involves pathways with caspase 3. Furthermore, with the simultaneous staining for the active form of caspase 3 and the transcription factor FoxP3, we are able to differentiate apoptosis based on FoxP3 expression in CD4+CD25+^high T cells Figure 4. These results suggest that it is the true Tregs FoxP3+CD4+CD25+^high T cells that contribute most to the apoptosis seen in highest CD25-expressing T cells.

Even though under intense investigation during the last several years, it has not been completely determined why CD4+CD25+^high T cells have reduced in vitro suppressive capacity in T1D. Some of the possible causes include insufficient amount of ambient IL2[32], mutations in FoxP3[33] prevention of CD4+CD25+^high T cells development or non-functional TGF-βR on the surface of responder T cells [34]. The only report that we are aware of shows increased apoptosis of human CD4+CD25+^high T cells after FACS isolation but under specific conditions Fritzsching et al., 2005 [35]. No reports have yet appeared to link increased apoptosis in the unmanipulated CD4+CD25+^high T-cell fraction with respect to autoimmune disease.

How does increased apoptosis of Tregs affect their function? Since in vitro suppression is the only functional test, we have developed a robust assay Jana et al, in preparation. High suppression in control subjects using our high co-culture ratio ensures that functionally these are true suppressor cells. Significant suppression differences between control and recent-onset T1D subjects following the same experimental conditions, point to a functional impairment of regulatory cells seen in the recent-onset T1D clinical group Figure 5. This result is in agreement with previous studies done with recent-onset T1D patients[17]. Another comprehensive study also reported T1D patients having deficient function of CD4+CD25+^high T cells[20].

The novel stain combination for apoptosis measurement used here for the first time in a study involving diabetic patients correlates well with the number of diabetes-specific auto-antibodies. A future longitudinal study on more subjects will give direct proof that ongoing apoptosis of CD4+CD25+^high T cells leads to reduced suppression and the beginning of T1D. Although other tests for the prediction of T1D exist family history and HLA genotyping, we believe that this easy-to-use method that captures early apoptosis of CD4+CD25+^high T cells may be of value as a marker for individuals at T1D risk and that it opens up a new area in T1D investigation.

Acknowledgments

The authors would like to thank Dr. Robert Truitt and Dr. Shigemi Matsuyama for valuable advice during data generation. The authors would also like to thank to patients and their families for enthusiastic involvement in this study as well as to Karen Zeqiri and Corbett Reinbold for technical support of our work. We are grateful to Drs. Martin Hessner and Howard Jacob for review of the manuscript.

Author Contributions

Other: Principal investigator and corresponding author, was instrumental in study design, analysis guidance, interpretation and writing the manuscript: SG. Actively participated in study design, experimental execution, analysis of generated data and writing the manuscript: SG. Participated in generation of results for the manuscript: JW. Participated in analysis of results for the manuscript: PJ. Participated in generation of results for the manuscript: SJ. Was responsible for database configuration and manipulation helping in better control of results for the manuscript: HK. Performed FACS analysis for subjects taking part in the manuscript: HA JW. Recruited subjects and coordinated clinical analysis and data base entry for the study: MK. Helped in the design of the study, facilitating recruitment and providing clinical expertise in characterizing subjects for the manuscript: RA. Provided expertise in type 1 diabetes measuring autoantibodies in subjects for the manuscript: WH.

References

1. Eisenbarth GS (1986) Type I diabetes mellitus. A chronic autoimmune disease. N Engl J Med 314: 1360–1368.
- View Article
- Google Scholar
2. Mathis D, Benoist C (2004) Back to central tolerance. Immunity 20: 509–516.
- View Article
- Google Scholar
3. Liston A, Lesage S, Gray DH, O'Reilly LA, Strasser A, et al. (2004) Generalized resistance to thymic deletion in the NOD mouse; a polygenic trait characterized by defective induction of Bim. Immunity 21: 817–830.
- View Article
- Google Scholar
4. Giordano C, De Maria R, Stassi G, Todaro M, Richiusa P, et al. (1995) Defective expression of the apoptosis-inducing CD95 Fas/APO-1 molecule on T and B cells in IDDM. Diabetologia 38: 1449–1454.
- View Article
- Google Scholar
5. Giordano C, Stassi G, Todaro M, De Maria R, Richiusa P, et al. (1995) Low bcl-2 expression and increased spontaneous apoptosis in T-lymphocytes from newly-diagnosed IDDM patients. Diabetologia 38: 953–958.
- View Article
- Google Scholar
6. Dosch H, Cheung RK, Karges W, Pietropaolo M, Becker DJ (1999) Persistent T cell anergy in human type 1 diabetes. J Immunol 163: 6933–6940.
- View Article
- Google Scholar
7. Buckner JH, Ziegler SF (2004) Regulating the immune system: the induction of regulatory T cells in the periphery. Arthritis Res Ther 6: 215–222.
- View Article
- Google Scholar
8. Sakaguchi S, Sakaguchi N, Asano M, Itoh M, Toda M (1995) Immunologic self-tolerance maintained by activated T cells expressing IL-2 receptor alpha-chains CD25. Breakdown of a single mechanism of self-tolerance causes various autoimmune diseases. J Immunol 155: 1151–1164.
- View Article
- Google Scholar
9. Tang Q, Henriksen KJ, Bi M, Finger EB, Szot G, et al. (2004) In vitro-expanded antigen-specific regulatory T cells suppress autoimmune diabetes. J Exp Med 199: 1455–1465.
- View Article
- Google Scholar
10. Tarbell KV, Yamazaki S, Olson K, Toy P, Steinman RM (2004) CD25+ CD4+ T cells, expanded with dendritic cells presenting a single autoantigenic peptide, suppress autoimmune diabetes. J Exp Med 199: 1467–1477.
- View Article
- Google Scholar
11. Lundsgaard D, Holm TL, Hornum L, Markholst H (2005) In vivo control of diabetogenic T-cells by regulatory CD4+CD25+ T-cells expressing Foxp3. Diabetes 54: 1040–1047.
- View Article
- Google Scholar
12. Sakaguchi S (2005) Naturally arising Foxp3-expressing CD25+CD4+ regulatory T cells in immunological tolerance to self and non-self. Nat Immunol 6: 345–352.
- View Article
- Google Scholar
13. Liu W, Putnam AL, Xu-Yu Z, Szot GL, Lee MR, et al. (2006) CD127 expression inversely correlates with FoxP3 and suppressive function of human CD4+ T reg cells. J Exp Med 203: 1701–1711.
- View Article
- Google Scholar
14. Seddiki N, Santner-Nanan B, Martinson J, Zaunders J, Sasson S, et al. (2006) Expression of interleukin IL-2 and IL-7 receptors discriminates between human regulatory and activated T cells. J Exp Med 203: 1693–1700.
- View Article
- Google Scholar
15. Wildin RS, Smyk-Pearson S, Filipovich AH (2002) Clinical and molecular features of the immunodysregulation, polyendocrinopathy, enteropathy, X linked IPEX syndrome. J Med Genet 39: 537–545.
- View Article
- Google Scholar
16. Allan SE, Passerini L, Bacchetta R, Crellin N, Dai M, et al. (2005) The role of 2 FOXP3 isoforms in the generation of human CD4+ Tregs. J Clin Invest 115: 3276–3284.
- View Article
- Google Scholar
17. Lindley S, Dayan CM, Bishop A, Roep BO, Peakman M, et al. (2005) Defective suppressor function in CD4+CD25+ T-cells from patients with type 1 diabetes. Diabetes 54: 92–99.
- View Article
- Google Scholar
18. Kukreja A, Cost G, Marker J, Zhang C, Sun Z, et al. (2002) Multiple immuno-regulatory defects in type-1 diabetes. J Clin Invest 109: 131–140.
- View Article
- Google Scholar
19. Putnam AL, Vendrame F, Dotta F, Gottlieb PA (2005) CD4+CD25high regulatory T cells in human autoimmune diabetes. J Autoimmun 24: 55–62.
- View Article
- Google Scholar
20. Brusko TM, Wasserfall CH, Clare-Salzler MJ, Schatz DA, Atkinson MA (2005) Functional defects and the influence of age on the frequency of CD4+ CD25+ T-cells in type 1 diabetes. Diabetes 54: 1407–1414.
- View Article
- Google Scholar
21. Gregg R, Smith CM, Clark FJ, Dunnion D, Khan N, et al. (2005) The number of human peripheral blood CD4+ CD25high regulatory T cells increases with age. Clin Exp Immunol 140: 540–546.
- View Article
- Google Scholar
22. (1999) Definition, diagnosis and classification of diabetes mellitus and its complications. Report of a WHO Consultation, Part I: Diagnosis and Classification of Diabetes Mellitus, Geneva, World Health Organization.
23. Woo W, LaGasse JM, Zhou Z, Patel R, Palmer JP, et al. (2000) A novel high-throughput method for accurate, rapid, and economical measurement of multiple type 1 diabetes autoantibodies. J Immunol Methods 244: 91–103.
- View Article
- Google Scholar
24. Perfetto SP, Chattopadhyay PK, Roederer M (2004) Seventeen-colour flow cytometry: unravelling the immune system. Nat Rev Immunol 4: 648–655.
- View Article
- Google Scholar
25. Baecher-Allan C, Viglietta V, Hafler DA (2002) Inhibition of human CD4+CD25+high regulatory T cell function. J Immunol 169: 6210–6217.
- View Article
- Google Scholar
26. Glisic-Milosavljevic S, Waukau J, Jana S, Jailwala P, Rovensky J, et al. (2005) Comparison of apoptosis and mortality measurements in peripheral blood mononuclear cells PBMCs using multiple methods. Cell Prolif 38: 301–311.
- View Article
- Google Scholar
27. Hori S, Sakaguchi S (2004) Foxp3: a critical regulator of the development and function of regulatory T cells. Microbes Infect 6: 745–751.
- View Article
- Google Scholar
28. Federici M, Hribal M, Perego L, Ranalli M, Caradonna Z, et al. (2001) High glucose causes apoptosis in cultured human pancreatic islets of Langerhans: a potential role for regulation of specific Bcl family genes toward an apoptotic cell death program. Diabetes 50: 1290–1301.
- View Article
- Google Scholar
29. Otton R, Soriano FG, Verlengia R, Curi R (2004) Diabetes induces apoptosis in lymphocytes. J Endocrinol 182: 145–156.
- View Article
- Google Scholar
30. Baecher-Allan C, Wolf E, Hafler DA (2005) Functional analysis of highly defined, FACS-isolated populations of human regulatory CD4+ CD25+ T cells. Clin Immunol 115: 10–18.
- View Article
- Google Scholar
31. Tadokoro CE, Shakhar G, Shen S, Ding Y, Lino AC, et al. (2006) Regulatory T cells inhibit stable contacts between CD4+ T cells and dendritic cells in vivo. J Exp Med 203: 505–511.
- View Article
- Google Scholar
32. Thornton AM, Donovan EE, Piccirillo CA, Shevach EM (2004) Cutting edge: IL-2 is critically required for the in vitro activation of CD4+CD25+ T cell suppressor function. J Immunol 172: 6519–6523.
- View Article
- Google Scholar
33. Bennett CL, Christie J, Ramsdell F, Brunkow ME, Ferguson PJ, et al. (2001) The immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome IPEX is caused by mutations of FOXP3. Nat Genet 27: 20–21.
- View Article
- Google Scholar
34. Fahlen L, Read S, Gorelik L, Hurst SD, Coffman RL, et al. (2005) T cells that cannot respond to TGF-beta escape control by CD4+CD25+ regulatory T cells. J Exp Med 201: 737–746.
- View Article
- Google Scholar
35. Fritzsching B, Oberle N, Eberhardt N, Quick S, Haas J, et al. (2005) In contrast to effector T cells, CD4+CD25+FoxP3+ regulatory T cells are highly susceptible to CD95 ligand- but not to TCR-mediated cell death. J Immunol 175: 32–36.
- View Article
- Google Scholar

[ref1] 1. Eisenbarth GS (1986) Type I diabetes mellitus. A chronic autoimmune disease. N Engl J Med 314: 1360–1368.
View Article
Google Scholar

[2] View Article

[3] Google Scholar

[ref2] 2. Mathis D, Benoist C (2004) Back to central tolerance. Immunity 20: 509–516.
View Article
Google Scholar

[5] View Article

[6] Google Scholar

[ref3] 3. Liston A, Lesage S, Gray DH, O'Reilly LA, Strasser A, et al. (2004) Generalized resistance to thymic deletion in the NOD mouse; a polygenic trait characterized by defective induction of Bim. Immunity 21: 817–830.
View Article
Google Scholar

[8] View Article

[9] Google Scholar

[ref4] 4. Giordano C, De Maria R, Stassi G, Todaro M, Richiusa P, et al. (1995) Defective expression of the apoptosis-inducing CD95 Fas/APO-1 molecule on T and B cells in IDDM. Diabetologia 38: 1449–1454.
View Article
Google Scholar

[11] View Article

[12] Google Scholar

[ref5] 5. Giordano C, Stassi G, Todaro M, De Maria R, Richiusa P, et al. (1995) Low bcl-2 expression and increased spontaneous apoptosis in T-lymphocytes from newly-diagnosed IDDM patients. Diabetologia 38: 953–958.
View Article
Google Scholar

[14] View Article

[15] Google Scholar

[ref6] 6. Dosch H, Cheung RK, Karges W, Pietropaolo M, Becker DJ (1999) Persistent T cell anergy in human type 1 diabetes. J Immunol 163: 6933–6940.
View Article
Google Scholar

[17] View Article

[18] Google Scholar

[ref7] 7. Buckner JH, Ziegler SF (2004) Regulating the immune system: the induction of regulatory T cells in the periphery. Arthritis Res Ther 6: 215–222.
View Article
Google Scholar

[20] View Article

[21] Google Scholar

[ref8] 8. Sakaguchi S, Sakaguchi N, Asano M, Itoh M, Toda M (1995) Immunologic self-tolerance maintained by activated T cells expressing IL-2 receptor alpha-chains CD25. Breakdown of a single mechanism of self-tolerance causes various autoimmune diseases. J Immunol 155: 1151–1164.
View Article
Google Scholar

[23] View Article

[24] Google Scholar

[ref9] 9. Tang Q, Henriksen KJ, Bi M, Finger EB, Szot G, et al. (2004) In vitro-expanded antigen-specific regulatory T cells suppress autoimmune diabetes. J Exp Med 199: 1455–1465.
View Article
Google Scholar

[26] View Article

[27] Google Scholar

[ref10] 10. Tarbell KV, Yamazaki S, Olson K, Toy P, Steinman RM (2004) CD25+ CD4+ T cells, expanded with dendritic cells presenting a single autoantigenic peptide, suppress autoimmune diabetes. J Exp Med 199: 1467–1477.
View Article
Google Scholar

[29] View Article

[30] Google Scholar

[ref11] 11. Lundsgaard D, Holm TL, Hornum L, Markholst H (2005) In vivo control of diabetogenic T-cells by regulatory CD4+CD25+ T-cells expressing Foxp3. Diabetes 54: 1040–1047.
View Article
Google Scholar

[32] View Article

[33] Google Scholar

[ref12] 12. Sakaguchi S (2005) Naturally arising Foxp3-expressing CD25+CD4+ regulatory T cells in immunological tolerance to self and non-self. Nat Immunol 6: 345–352.
View Article
Google Scholar

[35] View Article

[36] Google Scholar

[ref13] 13. Liu W, Putnam AL, Xu-Yu Z, Szot GL, Lee MR, et al. (2006) CD127 expression inversely correlates with FoxP3 and suppressive function of human CD4+ T reg cells. J Exp Med 203: 1701–1711.
View Article
Google Scholar

[38] View Article

[39] Google Scholar

[ref14] 14. Seddiki N, Santner-Nanan B, Martinson J, Zaunders J, Sasson S, et al. (2006) Expression of interleukin IL-2 and IL-7 receptors discriminates between human regulatory and activated T cells. J Exp Med 203: 1693–1700.
View Article
Google Scholar

[41] View Article

[42] Google Scholar

[ref15] 15. Wildin RS, Smyk-Pearson S, Filipovich AH (2002) Clinical and molecular features of the immunodysregulation, polyendocrinopathy, enteropathy, X linked IPEX syndrome. J Med Genet 39: 537–545.
View Article
Google Scholar

[44] View Article

[45] Google Scholar

[ref16] 16. Allan SE, Passerini L, Bacchetta R, Crellin N, Dai M, et al. (2005) The role of 2 FOXP3 isoforms in the generation of human CD4+ Tregs. J Clin Invest 115: 3276–3284.
View Article
Google Scholar

[47] View Article

[48] Google Scholar

[ref17] 17. Lindley S, Dayan CM, Bishop A, Roep BO, Peakman M, et al. (2005) Defective suppressor function in CD4+CD25+ T-cells from patients with type 1 diabetes. Diabetes 54: 92–99.
View Article
Google Scholar

[50] View Article

[51] Google Scholar

[ref18] 18. Kukreja A, Cost G, Marker J, Zhang C, Sun Z, et al. (2002) Multiple immuno-regulatory defects in type-1 diabetes. J Clin Invest 109: 131–140.
View Article
Google Scholar

[53] View Article

[54] Google Scholar

[ref19] 19. Putnam AL, Vendrame F, Dotta F, Gottlieb PA (2005) CD4+CD25high regulatory T cells in human autoimmune diabetes. J Autoimmun 24: 55–62.
View Article
Google Scholar

[56] View Article

[57] Google Scholar

[ref20] 20. Brusko TM, Wasserfall CH, Clare-Salzler MJ, Schatz DA, Atkinson MA (2005) Functional defects and the influence of age on the frequency of CD4+ CD25+ T-cells in type 1 diabetes. Diabetes 54: 1407–1414.
View Article
Google Scholar

[59] View Article

[60] Google Scholar

[ref21] 21. Gregg R, Smith CM, Clark FJ, Dunnion D, Khan N, et al. (2005) The number of human peripheral blood CD4+ CD25high regulatory T cells increases with age. Clin Exp Immunol 140: 540–546.
View Article
Google Scholar

[62] View Article

[63] Google Scholar

[ref22] 22. (1999) Definition, diagnosis and classification of diabetes mellitus and its complications. Report of a WHO Consultation, Part I: Diagnosis and Classification of Diabetes Mellitus, Geneva, World Health Organization.

[ref23] 23. Woo W, LaGasse JM, Zhou Z, Patel R, Palmer JP, et al. (2000) A novel high-throughput method for accurate, rapid, and economical measurement of multiple type 1 diabetes autoantibodies. J Immunol Methods 244: 91–103.
View Article
Google Scholar

[66] View Article

[67] Google Scholar

[ref24] 24. Perfetto SP, Chattopadhyay PK, Roederer M (2004) Seventeen-colour flow cytometry: unravelling the immune system. Nat Rev Immunol 4: 648–655.
View Article
Google Scholar

[69] View Article

[70] Google Scholar

[ref25] 25. Baecher-Allan C, Viglietta V, Hafler DA (2002) Inhibition of human CD4+CD25+high regulatory T cell function. J Immunol 169: 6210–6217.
View Article
Google Scholar

[72] View Article

[73] Google Scholar

[ref26] 26. Glisic-Milosavljevic S, Waukau J, Jana S, Jailwala P, Rovensky J, et al. (2005) Comparison of apoptosis and mortality measurements in peripheral blood mononuclear cells PBMCs using multiple methods. Cell Prolif 38: 301–311.
View Article
Google Scholar

[75] View Article

[76] Google Scholar

[ref27] 27. Hori S, Sakaguchi S (2004) Foxp3: a critical regulator of the development and function of regulatory T cells. Microbes Infect 6: 745–751.
View Article
Google Scholar

[78] View Article

[79] Google Scholar

[ref28] 28. Federici M, Hribal M, Perego L, Ranalli M, Caradonna Z, et al. (2001) High glucose causes apoptosis in cultured human pancreatic islets of Langerhans: a potential role for regulation of specific Bcl family genes toward an apoptotic cell death program. Diabetes 50: 1290–1301.
View Article
Google Scholar

[81] View Article

[82] Google Scholar

[ref29] 29. Otton R, Soriano FG, Verlengia R, Curi R (2004) Diabetes induces apoptosis in lymphocytes. J Endocrinol 182: 145–156.
View Article
Google Scholar

[84] View Article

[85] Google Scholar

[ref30] 30. Baecher-Allan C, Wolf E, Hafler DA (2005) Functional analysis of highly defined, FACS-isolated populations of human regulatory CD4+ CD25+ T cells. Clin Immunol 115: 10–18.
View Article
Google Scholar

[87] View Article

[88] Google Scholar

[ref31] 31. Tadokoro CE, Shakhar G, Shen S, Ding Y, Lino AC, et al. (2006) Regulatory T cells inhibit stable contacts between CD4+ T cells and dendritic cells in vivo. J Exp Med 203: 505–511.
View Article
Google Scholar

[90] View Article

[91] Google Scholar

[ref32] 32. Thornton AM, Donovan EE, Piccirillo CA, Shevach EM (2004) Cutting edge: IL-2 is critically required for the in vitro activation of CD4+CD25+ T cell suppressor function. J Immunol 172: 6519–6523.
View Article
Google Scholar

[93] View Article

[94] Google Scholar

[ref33] 33. Bennett CL, Christie J, Ramsdell F, Brunkow ME, Ferguson PJ, et al. (2001) The immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome IPEX is caused by mutations of FOXP3. Nat Genet 27: 20–21.
View Article
Google Scholar

[96] View Article

[97] Google Scholar

[ref34] 34. Fahlen L, Read S, Gorelik L, Hurst SD, Coffman RL, et al. (2005) T cells that cannot respond to TGF-beta escape control by CD4+CD25+ regulatory T cells. J Exp Med 201: 737–746.
View Article
Google Scholar

[99] View Article

[100] Google Scholar

[ref35] 35. Fritzsching B, Oberle N, Eberhardt N, Quick S, Haas J, et al. (2005) In contrast to effector T cells, CD4+CD25+FoxP3+ regulatory T cells are highly susceptible to CD95 ligand- but not to TCR-mediated cell death. J Immunol 175: 32–36.
View Article
Google Scholar

[102] View Article

[103] Google Scholar

Figures

Abstract

Background

Methods and Findings

Conclusions

Introduction

Methods

Results

Discussion

Acknowledgments

Author Contributions

References