Regulatory T cells in human autoimmune diseases

Out of balance: the role of evolutionary mismatches in the sex disparity in autoimmune disease

Over the past century autoimmune disease incidence has increased rapidly in (post-) industrialised, affluent societies, suggesting that changes in ecology and lifestyle are driving this development. Epidemiological studies show that (i) 80% of autoimmune disease patients are female, (ii) autoimmune diseases co-occur more often in women, and (iii) the incidence of some autoimmune diseases is increasing faster in women than in men. The female preponderance in autoimmunity is most pronounced between puberty and menopause, suggesting that diverging sex hormone levels during the reproductive years are implicated in autoimmune disease development. Using an evolutionary perspective, we build on the hypotheses that female immunity is cyclical in menstruating species and that natural selection shaped the female immune system to optimise the implantation and gestation of a semi-allogeneic foetus. We propose that cyclical immunomodulation and female immune tolerance mechanisms are currently out of balance because of a mismatch between the conditions under which they evolved and (post-)industrialised, affluent lifestyles. We suggest that current changes in autoimmune disease prevalence may be caused by increases in lifetime exposure to cyclical immunomodulation and ovarian hormone exposure, reduced immune challenges, increased reproductive lifespan, changed reproductive patterns, and enhanced positive energy balance associated with (post-)industrialised, affluent lifestyles. We discuss proximate mechanisms by which oestrogen and progesterone influence tolerance induction and immunomodulation, and review the effect of the menstrual cycle, pregnancy, and contraceptive use on autoimmune disease incidence and symptoms.

The potential role of cell surface complement regulators and circulating CD4+ CD25+ T-cells in the development of autoimmune myasthenia gravis

INTRODUCTION

CD4+CD25+ regulatory T-lymphocytes (T-regs) and regulators of complement activity (RCA) involving CD55 and CD59 play an important role in the prevention of autoimmune diseases. However, their role in the pathogenesis of human autoimmune myasthenia gravis (MG) remains unclear. This study aimed to determine the frequency of peripheral blood T-regs and CD4+ T-helper (T-helper) cells and the red blood cells (RBCs) level of expression of CD55 and CD59 in MG patients.

METHODS

Fourteen patients with MG in neurology outpatient clinics of Sohag University Hospital and Sohag General Hospital from March 2014 to December 2014, and 10 age-matched healthy controls participated in this case-control study. We did flowcytometric assessments of the percentage of peripheral T-regs and T-helper cells and the level of expression of CD55 and CD59 on RBCs in the peripheral blood of patients and controls.

RESULTS

There was a statistically significant decrease in the percentage of peripheral blood T-regs and T-regs/T-helper cell ratio in the MG patients group. Moreover, the level of expression of CD55, CD59, and dual expression of CD55/CD59 on RBCs were statistically significantly lower in MG patients than those of healthy controls. However, regression analysis indicated that there was no significant correlation between all the measured parameters and disease duration or staging.

CONCLUSION

Functional defects in the T-regs and RCA may play a role in the pathogenesis of autoimmune MG and their functional modulation may represent an alternative therapeutic strategy for MG treatment.

Peak inflammation in atherosclerosis, primary biliary cirrhosis and autoimmune arthritis is counter-intuitively associated with regulatory T cell enrichment

Regulatory T cells (Treg) influence the development of autoimmunity and their use is increasingly proposed for clinical applications. The well-characterized suppressive potential of Treg frequently leads to the assumption that Treg presence in prevailing numbers is indicative of immunosuppression. We hypothesized that this assumption may be false. We examined models of three different diseases caused by organ-specific autoimmune responses: primary biliary cirrhosis, atherosclerosis and rheumatoid arthritis (RA). We examined indicators of relative abundance of Treg compared to pro-inflammatory T cells, during peak inflammation. In all cases, the results were compatible with a relative enrichment of Treg at the site of inflammation or its most proximal draining lymph node. Conversely, in healthy mice or mice successfully protected from disease via a Treg-mediated mechanism, the data did not suggest that any Treg accumulation was occurring. This counter-intuitive finding may appear to be at odds with the immunosuppressive nature of Treg. Yet extensive previous studies in RA show that an accumulation of Treg occurs at peak inflammation, albeit without resulting in suppression, as the Treg suppressive function is overcome by the cytokine-rich environment. We suggest that this is a ubiquitous feature of autoimmune inflammation. Treg abundance in patient samples is increasingly used as an indicator of a state of immunosuppression. We conclude that this strategy should be revisited as it may potentially be a source of misinterpretation.

Late-onset of immunodysregulation, polyendocrinopathy, enteropathy, x-linked syndrome (IPEX) with intractable diarrhea

The syndrome of immune dysregulation, polyendocrinopathy, enteropathy, X linked (IPEX) is a rare disorder caused by mutations in the FOXP3 gene. Diarrhea, diabetes and dermatitis are the hallmark of the disease, with a typical onset within the first months of life. We describe the case of a twelve-year old male affected by a very late-onset IPEX with intractable enteropathy, which markedly improved after starting Sirolimus as second-line treatment. This case suggests that IPEX should always be considered in the differential diagnosis of watery intractable diarrhea, despite its unusual onset.

Could T cells be involved in lung deterioration and hyperglycemia in cystic fibrosis?

Cystic fibrosis-related diabetes (CFRD) is the most frequent complication of cystic fibrosis (CF) and associated with increased mortality. Why patients have an accelerated loss of lung function before the diagnosis of CFRD remains poorly understood. We reported that patients with or without CFRD had increased glucose excursions when compared to healthy peers. Studies have demonstrated that patients with CF have increased glucose fluctuations and hyperglycemia and that this may affect the clinical course of CF and lead to lymphocyte dysfunction. T-helper 17 (Th17) lymphocytes produce and secrete the pro-inflammatory cytokine IL-17. The Th17 pathway is involved in CF lung inflammation, β-cell destruction in type 1 diabetes (T1D) and Th17 cells of patients with type 2 diabetes have increased production of IL-17 when compared to healthy peers. Also, regulatory T-cells (Tregs) have been shown to be dysfunctional and produce IL-17 in T1D. Furthermore, vitamin D can affect inflammation in CF, diabetes and the differentiation of lymphocytes. In this review, we discuss the potential roles of hyperglycemia on Th17 cells, Tregs and IL-17 as a potential cause for accelerated lung function decline before CFRD and how this could be modulated by vitamin D or by directly intervening in the IL-17A pathway.

Balance of Treg vs. T-helper cells in the transition from symptomless to lesional psoriatic skin

BACKGROUND

In the pathogenesis of psoriasis, proinflammatory T cells are strongly involved in the inflammatory process, where regulatory T-cell (Treg) function is impaired.

OBJECTIVES

As effective Treg function is associated with a numerical balance between Treg and effector T cells, we wondered whether Treg/T-helper cell ratios may be associated with certain stages of the inflammatory process. We opted for the margin zone model as a dynamic approach.

METHODS

From nine patients with chronic plaque psoriasis, 3-mm punch biopsies were obtained from the centre and margin of the lesion, perilesional skin and distant uninvolved skin. Skin biopsies of 10 healthy volunteers were included as a control. Samples were analysed using immunohistochemistry and immunofluorescence.

RESULTS

In the transition from symptomless to lesional skin, a significant increase of CD3+, CD4+ and Foxp3+ cells was found. In seven of nine patients the ratio of Treg (Foxp3+) vs. CD4+ T cells was higher in the distant uninvolved skin than in the perilesional and lesional skin. Interestingly, the Foxp3/CD4 ratio in the distant uninvolved skin was even higher than in the skin of healthy controls. Notably, we found that most of the interleukin (IL)-17 expression was not related to CD4+ cells, but to mast cells.

CONCLUSIONS

The relatively high Foxp3/CD4 ratio in symptomless skin of patients with psoriasis suggests an active immune controlling mechanism distant from the psoriatic plaque. In the margin and centre of the plaque the ratio appears skewed towards effector cells associated with inflammation. IL-17, an important driver of the psoriatic process, is mostly related to mast cells, and only sporadically to T cells.

Imbalance between circulating CD4+ regulatory T and conventional T lymphocytes in patients with HBV-related acute-on-chronic liver failure

BACKGROUND & AIMS

The important pathophysiological role of immune dysfunction, especially innate immune dysfunction in patients with acute-on-chronic liver failure (ACLF), has been investigated in recent years, but dysregulation of adaptive immunity remains poorly elucidated. The aim of this study was to (i) determine the CD3(+) T-lymphocyte count and the balance between CD4(+) regulatory T (Tregs) and conventional T cells (Tconv) in hepatitis B virus (HBV)-related ACLF patients; (ii) analyse the frequencies of Tregs subpopulations; and (iii) assess the suppressive potency of CD4(+) Tregs and each fraction.

METHODS

We enrolled 20 HBV-ACLF patients, 10 septic shock subjects, 20 chronic hepatitis B (CHB) patients and 20 healthy volunteers (HC). Based on flow cytometry, we performed the absolute counting of circulating T lymphocytes and phenotyping of CD4(+) Tregs and quantified the effects of Tregs and each subpopulation on Tconv proliferation by CFSE staining.

RESULTS

Compared with CHB patients and HC, we observed an equal reduction in peripheral T subsets in HBV-ACLF and septic shock subjects; the number of CD4(+) Tregs remained unchanged and the Tconv count declined, promoting elevation of the Treg-to-Tconv ratio. The frequencies of Treg-II and -III were elevated in HBV-ACLF. Functional studies showed that the suppressive capacity of Tregs was preserved in the HBV-ACLF group and Treg-II came first.

CONCLUSIONS

Similar to septic shock subjects, in HBV-ACLF patients there exists a reduction in CD4(+) T lymphocytes, predominantly CD4(+) Tconv, and the development of suppressive CD4(+) Tregs greatly prevails over Tconv, constituting important characteristics of adaptive immune dysfunction of HBV-ACLF.

T helper cell polarization in healthy people: implications for cardiovascular disease

Atherosclerosis is a chronic inflammatory disease characterized by T lymphocyte infiltration into the atherosclerotic plaque. Assessments of T cell subtypes have demonstrated a predominance of CD4(+) T helper (Th) cells, implicated Th1 and Th17 immunity in both human and mouse atherogenesis, and provided some evidence suggesting protective roles of Th2 and T regulatory cells. Observations that certain inbred mouse strains have an inherent T helper bias suggest a genetic predisposition toward developing a particular T helper phenotype. This review summarizes our current understanding of mechanisms of antigen processing for major histocompatibility complex molecules, describes the different T helper cell subsets and their roles in atherosclerosis, and discusses mechanisms of genetic predisposition toward Th1/Th2 bias in mice. We also present data from our laboratory demonstrating inherent Th1/Th2 phenotypes in apparently healthy human volunteers that are stable over time and discuss the potential implications for cardiovascular disease.

Functional defect in regulatory T cells in myasthenia gravis

Forkhead box P3 (FOXP3) is a transcription factor necessary for the function of regulatory T cells (T(reg) cells). T(reg) cells maintain immune homeostasis and self-tolerance and play an important role in the prevention of autoimmune disease. Here, we discuss the role of T(reg) cells in the pathogenesis of myasthenia gravis (MG) and review evidence indicating that a significant defect in T(reg) cell in vitro suppressive function exists in MG patients, without an alteration in circulating frequency. This functional defect is associated with a reduced expression of key functional molecules, such as FOXP3 on isolated T(reg) cells, and appears to be more pronounced in immunosuppression-naive MG patients. In vitro administration of granulocyte macrophage-colony-stimulating factor (GM-CSF) enhanced the suppressive function of T(reg) cells and upregulated FOXP3 expression. These findings indicate a clinically relevant T(reg) cell-intrinsic defect in immune regulation in MG that may reveal a novel therapeutic target.

Association of FOXP3 (rs3761548) promoter polymorphism with nondermatomal vitiligo: A study from India

BACKGROUND

The rs3761548 polymorphism (-3279 C>A) of FOXP3 gene is associated with several autoimmune disorders.

OBJECTIVE

We sought to determine whether rs3761548 polymorphism is associated with nondermatomal vitiligo in Indian subjects.

METHODS

Genomic DNA was isolated from blood samples of 303 patients and 305 control subjects and genotyping was done by allele-specific primers. Data analysis was carried out for the entire cohort and separately for male and female participants as FOXP3 is an X-linked marker. Statistics were performed using software.

RESULTS

The genotype frequencies differed significantly from patients to control subjects (P = .002). Further analysis demonstrated female participants with CC genotype were protected (CC vs CA+AA; odds ratio 0.38, 95% confidence interval 0.238-0.615) and those with CA genotype were at higher risk to develop vitiligo (CA vs CC+AA; odds ratio 2.634, 95% confidence interval 1.604-4.325). However, no such statistical difference was observed in male participants.

LIMITATIONS

Our study is, to our knowledge, the first report from India with respect to vitiligo and rs3761548; however, we lack adequate literature assistance.

CONCLUSIONS

The rs3761548 of FOXP3 gene in our population may be associated with susceptibility to vitiligo because of altered expression. CC genotype appears to be protective and CA genotype seems to impart nearly 3-fold risk to develop vitiligo in women and girls.

Granulocyte macrophage colony-stimulating factor treatment of a patient in myasthenic crisis: effects on regulatory T cells

INTRODUCTION

In this study we describe a patient with a prolonged myasthenic crisis refractory to conventional immunomodulatory therapy who was treated with GM-CSF (granulocyte macrophage colony-stimulating factor, sargramostim).

METHODS

T-regulatory cell (Treg) suppressive function and Foxp3 expression were evaluated before and after treatment with GM-CSF.

RESULTS

Treatment with GM-CSF was associated with clinical improvement, expansion in the circulating numbers of Foxp3(+) cells, increase in Foxp3 expression levels in Tregs, early improvement in Treg suppressive capacity for AChR-α-induced T-cell proliferation, and subsequent enhancement in Treg suppression of polyclonal T-cell proliferation.

CONCLUSION

Although definitive conclusions cannot be drawn from a single case, the correlation with similar findings in GM-CSF-treated animals with experimental autoimmune myasthenia gravis suggests further exploration of the effects of GM-CSF in myasthenia gravis should be studied in a clinical trial setting.

Impaired regulatory function in circulating CD4(+)CD25(high)CD127(low/-) T cells in patients with myasthenia gravis

Previous studies have reported alterations in numbers or function of regulatory T (Treg) cells in myasthenia gravis (MG) patients, but published results have been inconsistent, likely due to the isolation of heterogenous "Treg" populations. In this study, we used surface CD4, CD25(high), and CD127(low/-) expression to isolate a relatively pure population of Tregs, and established that there was no alteration in the relative numbers of Tregs within the peripheral T cell pool in MG patients. In vitro proliferation assays, however, demonstrated that Treg-mediated suppression of responder T (Tresp) cells was impaired in MG patients and was associated with a reduced expression of FOXP3 in isolated Tregs. Suppression of both polyclonal and AChR-activated Tresp cells from MG patients could be restored using Tregs isolated from healthy controls, indicating that the defect in immune regulation in MG is primarily localized to isolated Treg cells, and revealing a potential novel therapeutic target.

The IL-2 diphtheria toxin fusion protein denileukin diftitox modulates the onset of diabetes in female nonobese diabetic animals in a time-dependent manner and breaks tolerance in male nonobese diabetic animals

Denileukin diftitox, also known as DAB(389)IL-2 or Ontak, is a fusion protein toxin consisting of the full-length sequence of the IL-2 protein and as toxophore the truncated diphtheria toxin. As a consequence, it delivers the toxic agent to CD25-bearing cells, whereby CD25 represents the high-affinity α-subunit of the IL-2 receptor. Initially it was developed for the treatment of patients with cutaneous T cell lymphoma. Meanwhile, denileukin diftitox is also used as an adjuvant in other tumor therapies and neoplastic disorders. In this study, to our knowledge we report for the first time that denileukin diftitox has also dramatic effects regarding the pathology of type 1 diabetes using the NOD mouse model. Repeated injections of denileukin diftitox into female NOD mice at 12 wk of age led to a clear acceleration of disease onset, whereas injection at 7 wk of age did not. Using male NOD mice, which are much less susceptible to diabetes, we demonstrate that the injection of denileukin diftitox leads to a dramatic development of type 1 diabetes within days after injection, thereby obviously breaking pre-existing tolerance mechanisms. This is accompanied by an increased IFN-γ production of autoreactive splenic cells and a decreased presence of regulatory CD4(+)CD25(+)Foxp3(+) T cells. In contrast, transfer of CD4(+)CD25(+)Foxp3(+) T cells could correct the defect after denileukin diftitox treatment. Furthermore, whereas IFN-γ production was increased in the pancreata of treated animals, insulin expression was strongly reduced. These finding should be considered when denileukin diftitox is used for the treatment of patients suffering from tumors and/or autoimmune disorders.

Is multiple sclerosis an autoimmune disease?

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) with varied clinical presentations and heterogeneous histopathological features. The underlying immunological abnormalities in MS lead to various neurological and autoimmune manifestations. There is strong evidence that MS is, at least in part, an immune-mediated disease. There is less evidence that MS is a classical autoimmune disease, even though many authors state this in the description of the disease. We show the evidence that both supports and refutes the autoimmune hypothesis. In addition, we present an alternate hypothesis based on virus infection to explain the pathogenesis of MS.

GM-CSF-induced regulatory T cells selectively inhibit anti-acetylcholine receptor-specific immune responses in experimental myasthenia gravis

We and others have demonstrated the ability of granulocyte-macrophage colony-stimulating factor (GM-CSF) to suppress autoimmunity by increasing the number of CD4(+)CD25(+) regulatory T cells (Tregs). In the current study, we have explored the critical role of induced antigen specific Tregs in the therapeutic effects of GM-CSF in murine experimental autoimmune myasthenia gravis (EAMG). Specifically, we show that Tregs from GM-CSF treated EAMG mice (GM-CSF/AChR-induced-Tregs) adoptively transferred into animals with EAMG suppressed clinical disease more potently than equal numbers of Tregs from either GM-CSF untreated EAMG mice or healthy mice treated with GM-CSF. In addition, GM-CSF/AChR-induced-Tregs selectively suppressed antigen specific T cell proliferation induced by AChR relative to that induced by an irrelevant self antigen, (thyroglobulin) and failed to significantly alter T cell proliferation in response to an exogenous antigen (ovalbumin). These results are consistent with the hypothesized mechanism of action of GM-CSF involving the mobilization of tolerogenic dendritic cell precursors which, upon antigen (AChR) capture, suppress the anti-AChR immune response through the induction/expansion of AChR-specific Tregs.

Clinical and molecular characteristics of immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome in China

Immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare X-linked recessive disorder causing life-threatening systemic autoimmunity because of immunodysregulation. The FOXP3 gene had been reported as the responsible gene, which was critical for the functions of CD4(+) CD25(+) FOXP3(+) regulatory T cells (Tregs) and maintenance of peripheral immunologic tolerance. So far, no IPEX patients with definite mutations in the FOXP3 gene had been reported in China. In this study, the genotypes and phenotypes were investigated in three IPEX infants from three unrelated Chinese families. Patient 1 (P1) presented with a classical clinical phenotype, whose mutation was a novel frameshift insertion in exon 11, led to the complete abrogation of Tregs. Patient 2 (P2) showed incomplete IPEX phenotype. He carried a missense mutation in exon 11 with slightly increased frequency of Tregs, whereas Patient 3 (P3) presented with a relatively mild classical phenotype and had a previously reported missense mutation in exon 10 with decreased frequency of Tregs. We firstly report three Chinese IPEX patients with definite mutations of FOXP3 gene. Our study indicated the potential correlation between the genotype and the phenotype of IPEX, which was different from the previous reports.

T-cell specific defect in expression of the NTPDase CD39 as a biomarker for lupus

Regulatory T cells (T(regs)) are critical for maintenance of peripheral tolerance via suppression of T-cell responses, and absence of T(regs) results in autoimmunity. The role of aberrations in the T(reg) pool for the development of systemic lupus erythematosus (SLE, lupus) remains uncertain. T(reg)-mediated generation of adenosine, dependent on the ectonucleotidase CD39, is an important mechanism for suppression of T-cell responses. We tested whether decreases in numbers of T(regs), and specifically CD39-expressing T(regs), are associated with human lupus. We studied 15 SLE patients, six patients with rheumatoid arthritis (RA) and 24 healthy controls. T(reg) phenotypic markers, including CD39 expression, were studied by flow cytometry. Varying numbers of sorted T(regs) cells were co-cultured with responder T (T(resp)) cells, with proliferation assessed by (3)H-thymidine incorporation. The proportion of T(regs) as defined by Foxp3(+) CD25(+high) CD127(-/low) was similar in lupus and control populations. CD39-expressing T(regs) comprised 37±13% of the T(reg) population in healthy controls and 36±21% in lupus subjects using nonsteroidal immunosuppressants to control active disease, but was nearly absent in five of six lupus subjects with minimally active disease. In contrast to healthy controls and lupus subjects without the CD39 defect, in SLE subjects with the CD39 defect, adenosine-dependent T(reg)-mediated suppression was nearly absent. These results suggest that functional defects in T(regs), rather than reduced T(reg) numbers, are important for the loss of peripheral tolerance in lupus. Presentation of this defect may serve as a biomarker for untreated disease.

Cross-talk between cd1d-restricted nkt cells and γδ cells in t regulatory cell response

CD1d is a non-classical major histocompatibility class 1-like molecule which primarily presents either microbial or endogenous glycolipid antigens to T cells involved in innate immunity. Natural killer T (NKT) cells and a subpopulation of γδ T cells expressing the Vγ4 T cell receptor (TCR) recognize CD1d. NKT and Vγ4 T cells function in the innate immune response via rapid activation subsequent to infection and secrete large quantities of cytokines that both help control infection and modulate the developing adaptive immune response. T regulatory cells represent one cell population impacted by both NKT and Vγ4 T cells. This review discusses the evidence that NKT cells promote T regulatory cell activation both through direct interaction of NKT cell and dendritic cells and through NKT cell secretion of large amounts of TGFβ, IL-10 and IL-2. Recent studies have shown that CD1d-restricted Vγ4 T cells, in contrast to NKT cells, selectively kill T regulatory cells through a caspase-dependent mechanism. Vγ4 T cell elimination of the T regulatory cell population allows activation of autoimmune CD8+ effector cells leading to severe cardiac injury in a coxsackievirus B3 (CVB3) myocarditis model in mice. CD1d-restricted immunity can therefore lead to either immunosuppression or autoimmunity depending upon the type of innate effector dominating during the infection.

Tolerogenic dendritic cells in autoimmune diseases: crucial players in induction and prevention of autoimmunity

The immune system has evolved to coordinate responses against numerous invading pathogens and simultaneously remain silent facing self-antigens and those derived from commensal organisms. But, if both processes are not maintained in strict balance, a potential threat can emerge due to the risk of chronic inflammation and/or autoimmunity development. Therefore, there is a negative immune regulation where tolerogenic dendritic cells (tDCs) participate actively. Under steady-state conditions, tDC are notably involved in the elimination of autoreactive T cells at the thymus, and in the control of T cells specific to self and harmless antigens in the periphery. But in the presence of foreign antigens in an inflammatory milieu, dendritic cells (DCs) mature and induce T cells activation and their migration to B cell areas to assist in antibody production. Additionally, there are other factors such as infections, anti tumoral immune responses, trauma-mediated disruption, etc. that may induce alterations in the balance between tolerogenic and immunogenic functions of DCs and instigate the development of autoimmune diseases (ADs). Therefore, in recent years, DCs have emerged as therapeutic targets to control of ADs. Diverse strategies in vitro and/or in animal models of ADs have explored the tolerogenic functions of DCs and demonstrated their feasibility to prevent or control an autoimmune process, but still leaving a void in their application in clinical assays. The purpose of this paper is to give a general overview of the current literature on the significance of tDCs in tolerance maintenance to self and innocuous antigens, the most relevant alterations involved in the pathophysiology of ADs, the cellular and molecular mechanisms involved in their tolerogenic function and the current strategies used to exploit their tolerogenic potential.

Mouse Models of Systemic Lupus Erythematosus Reveal a Complex Pathogenesis

The mammalian immune system is remarkable in that it can respond to an essentially infinite number of foreign antigens. The ability to mount a long-lasting (adaptive) immune response against foreign antigen requires the participation of cells selected from an enormously diverse population of B and T cells. Because the B and T cell receptors expressed by these cells are generated at random, a significant percentage of B and T cells are invariably directed against self-antigen. Under normal circumstances, autoreactive B and T cells are eliminated, reprogrammed, or inactivated in the primary and secondary lymphoid organs. Despite these checks and balances, a small but significant number of people and animals still develop autoimmune disease. One such autoimmune disease—systemic lupus erythematosus—is characterized by the loss of B- and T-cell tolerance to self-antigens (principally nuclear), culminating in multisystemic inflammation. Multiple genetic defects, drug exposure, infectious agents, and environmental factors can contribute to the pathogenesis of the disease. Loss of B- and T-cell tolerance precipitates activation of plasmacytoid and myeloid dendritic cells; collectively, these cells cooperate to form a complex positive feedback loop, continually stimulated by the persistence of self-antigen. Novel treatment strategies now focus on specific inhibition of various aspects of the feedback loop. These specific inhibitors have the potential to be more effective and lack the side effects associated with generalized immunosuppression.

Development of thymically derived natural regulatory T cells

Natural regulatory T cells (nTregs) are defined by their inherent ability to establish and maintain peripheral self-tolerance. In recent years, the development of nTregs has come under close examination with the advent of Forkhead Box P3 protein (FOXP3)-green fluorescent protein reporter mice that pinpointed the initiation of FOXP3 expression within the thymus. The mechanism and pathway of nTreg development has only recently been studied in detail and to a large degree remains unclear. In this review, we will discuss our current understanding of nTreg lineage choice and development from a cellular and intracellular standpoint.

Regulatory T cells in the skin lesions and blood of patients with systemic sclerosis and morphoea

BACKGROUND

Systemic sclerosis (SSc) and morphoea are connective tissue diseases characterized by fibrosis of the skin. Although to date their pathogenesis has not been clearly defined, it is thought that autoimmunity may play a role in the development of the skin lesions observed in both these diseases. As regulatory T cells (Tregs) play a key role in the modulation of immune responses, it has recently been suggested that Treg impairment may lead to the development of autoimmune diseases.

OBJECTIVES

To investigate the presence of Tregs and their immunomodulatory cytokines, transforming growth factor (TGF)-beta and interleukin (IL)-10, in patients with SSc and morphoea.

PATIENTS/METHODS

Fifteen patients with SSc and 15 with morphoea were enrolled. Immunohistochemistry was applied to identify FoxP3+ (forkhead/winged helix transcription factor) Tregs, TGF-beta+ cells and IL-10+ cells in the skin, cytofluorometry to detect CD4+CD25+FoxP3+ Tregs in the blood, and enzyme-linked immunosorbent assays to analyse TGF-beta and IL-10 serum levels.

RESULTS

Fewer FoxP3+ Tregs and TGF-beta+ and IL-10+ cells were found in the skin of patients with scleroderma than in controls. Similarly, there were reduced TGF-beta and IL-10 serum levels and fewer circulating CD4+CD25brightFoxP3+ cells in patients with SSc or morphoea, than in controls.

CONCLUSIONS

The quantitative reduction of Tregs, together with that of TGF-beta and IL-10 serum levels, may be responsible for the loss of tolerance observed in both SSc and morphoea.

Frequency of Treg cells is reduced in CVID patients with autoimmunity and splenomegaly and is associated with expanded CD21lo B lymphocytes

INTRODUCTION

Common variable immunodeficiency is a heterogeneous antibody deficiency syndrome with autoimmune and inflammatory complications in a significant proportion of patients. The study was designed to evaluate the role of T regulatory (Treg) cells in common variable immunodeficiency (CVID) patients with autoimmunity.

METHODS

The number and frequency of Treg cells (CD4(+), CD25(hi), Foxp3(+)) were evaluated in patients and controls, and Foxp3 expression in different subgroups of CVID patients with common clinical manifestations was compared.

RESULTS

CVID patients had significantly fewer Treg cells than controls, and low frequency of Treg cells was associated with expansion of CD21(lo) B cells in patients. Patients with autoimmunity had significantly reduced frequency but normal numbers of regulatory T cells, whilst patients with splenomegaly had significant reduction in frequency and number of regulatory T cells.

CONCLUSION

Foxp3 is useful on its own or as an adjunct to classify CVID patients although the possibility of reduction in Treg cells as a secondary phenomenon cannot be excluded.

Critical role of IFN-gamma in CFA-mediated protection of NOD mice from diabetes development

IFN-gamma signaling-deficient non-obese diabetic (NOD) mice develop diabetes with similar kinetics to those of wild-type NOD mice. However, the immunization of IFN-gamma signaling-deficient NOD mice with CFA failed to induce long-term protection, whereas wild-type NOD mice receiving CFA remained diabetes-free. CFA also failed to protect IFN-gamma receptor-deficient (IFN-gammaR(-/-)) NOD mice from the autoimmune rejection of transplanted islets, as it does in diabetic NOD mice, and from disease transfer by spleen cells from diabetic NOD mice. These data clearly show that the pro-inflammatory cytokine IFN-gamma is necessary for the CFA-mediated protection of NOD mice from diabetes. There is no difference in the T(h)1/T(h)17 balance between IFN-gammaR(-/-) NOD and wild-type NOD mice. There is also no difference in the total numbers and percentages of regulatory T (Treg) cells in the lymph node CD4(+) T-cell populations between IFN-gammaR(-/-) NOD and wild-type NOD mice. However, pathogenic T cells lacking IFN-gammaR are resistant to the suppressive effect of Treg cells, both in vivo and in vitro. Therefore, it is likely that CFA-mediated protection against diabetes development depends on a change in the balance between Treg cells and pathogenic T cells, and IFN-gamma signaling seems to control the susceptibility of pathogenic T cells to the inhibitory activity of Treg cells.

Can infections protect against autoimmunity?

PURPOSE OF REVIEW

It has often been suggested that autoimmune diseases are initiated by certain infectious agents that mimic self-antigens or polyclonally activated autoreactive lymphocytes. An alternative, and not necessarily mutually exclusive, hypothesis that some infections might inhibit the onset of some autoimmune conditions has more recently been explored. In this review, the evidence suggesting that the current rise in the incidence of some autoimmune diseases is attributable to a decrease in the incidence of exposure to certain infections will be discussed.

RECENT FINDINGS

Studies using animal models have shown that some infectious agents or products derived from them have the potential to inhibit the onset of autoimmunity. These studies have led to the suggestion that human autoimmune or allergic diseases might be alleviated by the use of microbial products. There are some data that would support such an observation.

SUMMARY

The incidence of some autoimmune diseases has increased dramatically in recent years in the developed world. Many autoimmune diseases are governed by both genetic and environmental factors. Our immune system has coevolved with infectious agents. There have been marked changes in the exposure to certain infectious agents over the last 70 years. It has been proposed that certain infections of historical importance might inhibit the development of autoimmune disorder. This review highlights studies addressing the ways in which infectious agents might inhibit onset of autoimmunity, and how this might lead to the development of novel therapeutic approaches.

From autoimmune enteropathy to the IPEX (immune dysfunction, polyendocrinopathy, enteropathy, X-linked) syndrome

The term autoimmune enteropathy (AIE) was applied to a form of "intractable diarrhoea" with serum gut autoantibodies, characterized by male predominance, early onset, poor response to parenteral nutrition and several autoimmune diseases, mainly type 1 diabetes. In recent years the vague concept of AIE has became more precise thanks to the discovery of its genetic and molecular basis. The FOXP3 molecule is crucial for the generation and maturation of regulatory T cells (Treg) expressing CD4+ and CD25+ molecules. Mutations of the FOXP3 gene, located in X chromosome, produce a syndrome with Immune dysfunction, Polyendocrinopathy, Enteropathy and X-linked inheritance (IPEX). The majority of the ancient so-called AIE cases probably correspond to the new IPEX syndrome, even in female patients who may have some autosomal genetic variants. Besides FOXP3, other molecules are likely to be involved in the generation and function of Treg and its deficiency may also enhance autoimmune disease and IPEX-like syndromes. Meanwhile, the important pathogenic role previously ascribed to gut autoantibodies has vanished, with it remaining as having only certain screening usefulness.

In vitro model for the activation of CD4 and CD8 T cell receptors

Previously, most models that sought to explain the misregulation of immune cell function assumed molecular similarities between the disease-causing pathogens and the host's proteins. In recent time several different models have been proposed and in this study, these concepts are compared to a new hypothesis proposing another explanation for this immune dysregulation: the possibility that the mislocalization of proteins may be responsible for autoimmune activity. Based on this hypothesis, proteins are recognized as self or non-self depending on where they appear in sufficiently high concentrations. To examine this new idea, the intracellular human proteins beta-actin, GAPDH, and hemoglobin as well as the extracellular human proteins insulin and albumin, were added to human whole blood samples. After an incubation period, the activation of whole-blood T lymphocytes in the samples was measured. The observed activation pattern of the T lymphocytes fit well with the proposed hypothesis. Therefore, these data suggest that protein mislocalization and/or errors within protein trafficking might be important in the development of autoimmune diseases.

Regulatory T cells in type 1 diabetic patients with autoimmune chronic atrophic gastritis

Type A chronic atrophic gastritis (CAG) is increased in type 1 diabetic patients (DM1). To address this issue, we determined and analyzed the number of peripheral blood regulatory T cells (Tregs) in 15 DM1-CAG patients, 15 DM1 patients without associated autoantibodies (DM1) and 15 healthy controls by flow cytometry and compared gastric Tregs expression (CD4+Foxp3+/CD4+) in DM1-CAG patients with that observed in 10 control Helicobacter pylori CAG-infected biopsies. The percentage of peripheral Tregs was higher in DM1-CAG patients compared to DM1 and controls (CD4+Foxp3+: 7.67 +/- 1.91% vs. 5.38 +/- 1.57% and 5.65 +/- 1.76%, P < 0.001, respectively), with no differences between DM1 and controls. Gastric mucosal Tregs were higher in H. pylori CAG than in DM1-CAG patients (31.31 +/- 5.52% vs. 7.68 +/- 3.70%; P < 0.001). Data suggest that Tregs are stimulated in patients with more than one autoimmune disease (DM1 + CAG) in an ineffectual attempt to control autoimmune response and that the number of Tregs in gastric mucosa implicated in the chronification of gastritis differs according to the etiology.

Persistent systemic inflammation and atypical enterocolitis in patients with NEMO syndrome

The NEMO syndrome is a primary immunodeficiency with immune and non-immune manifestations. The immune deficiency is heterogeneous showing defects in humoral, innate, and cell-mediated immunity. While the clinical aspects of the immunodeficiency are increasingly well understood, little is known about autoimmune manifestations in NEMO patients. We therefore sought to examine serologic markers of systemic inflammation and intestinal pathology in a kindred of patients with the NEMO syndrome. We observed persistent elevation of erythrocyte sedimentation rates in five patients, and two were symptomatic, with a chronic but atypical enterocolitis. Though pathologic lesions in these two patients were consistent with acute inflammation, sustained clinical improvement was only achieved with systemic and/or topical glucocorticoid therapy. Our data suggest that some patients with the NEMO syndrome exhibit persistent elevation of inflammatory markers similar to systemic autoimmune diseases and may subsequently develop an atypical enterocolitis.

Treatment of lupus patients with a tolerogenic peptide, hCDR1 (Edratide): immunomodulation of gene expression

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by dysregulation of cytokines, apoptosis, and B- and T-cell functions. The tolerogenic peptide, hCDR1 (Edratide), ameliorated the clinical manifestations of murine lupus via down-regulation of pro-inflammatory cytokines and apoptosis, up-regulation of the immunosuppressive cytokine TGF-beta, and the induction of regulatory T-cells. In the present study, gene expression was determined in peripheral blood mononuclear cells of 9 lupus patients that were treated for 26 weeks with either hCDR1 (five patients), or placebo (four patients). Disease activity was assessed by SLEDAI-2K and the BILAG scores. Treatment with hCDR1 significantly down-regulated the mRNA expression of the pathogenic cytokines IL-1beta, TNF-alpha, IFN-gamma, and IL-10, of BLyS (B-lymphocyte stimulator) and of the pro-apoptotic molecules caspase-3 and caspase-8. In contrast, the treatment up-regulated in vivo gene expression of both TGF-beta and FoxP3. Furthermore, hCDR1 treatment resulted in a significant decrease in SLEDAI-2K (from 8.0+/-2.45 to 4.4+/-1.67; P=0.02) and BILAG (from 8.2+/-2.7 to 3.6+/-2.9; P=0.03) scores. Thus, the tolerogenic peptide hCDR1, immunomodulates, in vivo, the expression of genes that play a role in SLE, consequently restoring the global immune dysregulation of lupus patients. Hence, hCDR1 has a potential role as a novel disease-specific treatment for lupus patients.

IL-12R beta 2 promotes the development of CD4+CD25+ regulatory T cells

We have previously shown that mice lacking the IL-12-specific receptor subunit beta2 (IL-12Rbeta2) develop more severe experimental autoimmune encephalomyelitis than wild-type (WT) mice. The mechanism underlying this phenomenon is not known; nor is it known whether deficiency of IL-12Rbeta2 impacts other autoimmune disorders similarly. In the present study we demonstrate that IL-12Rbeta2(-/-) mice develop earlier onset and more severe disease in the streptozotocin-induced model of diabetes, indicating predisposition of IL-12Rbeta2-deficient mice to autoimmune diseases. T cells from IL-12Rbeta2(-/-) mice exhibited significantly higher proliferative responses upon TCR stimulation. The numbers of naturally occurring CD25(+)CD4(+) regulatory T cells (Tregs) in the thymus and spleen of IL-12Rbeta2(-/-) mice were comparable to those of WT mice. However, IL-12Rbeta2(-/-) mice exhibited a significantly reduced capacity to develop Tregs upon stimulation with TGF-beta, as shown by significantly lower numbers of CD25(+)CD4(+) T cells that expressed Foxp3. Functionally, CD25(+)CD4(+) Tregs derived from IL-12Rbeta2(-/-) mice were less efficient than those from WT mice in suppressing effector T cells. The role of IL-12Rbeta2 in the induction of Tregs was confirmed using small interfering RNA. These findings suggest that signaling via IL-12Rbeta2 regulates both the number and functional maturity of Treg cells, which indicates a novel mechanism underlying the regulation of autoimmune diseases by the IL-12 pathway.

The neoplastically transformed (CD30hi) Marek's disease lymphoma cell phenotype most closely resembles T-regulatory cells

INTRODUCTION

Marek's disease (MD), a herpesvirus-induced lymphoma of chickens is a unique natural model of CD30-overexpressing (CD30hi) lymphoma. We have previously proposed that the CD30hi neoplastically transformed CD4+ T cells in MD lymphomas have a phenotype antagonistic to cell mediated immunity. Here were test the hypothesis that the CD30hi neoplastically transformed MD lymphoma cells have a phenotype more closely resembling T-helper (Th)-2 or regulatory T (T-reg) cells.

MATERIALS AND METHODS

We separated ex vivo-derived CD30hi, from the CD30lo/- (non-transformed), MD lymphoma cells and then quantified the relative amounts of mRNA and proteins for cytokines and other genes that define CD4+ Th-1, Th-2 or T-reg phenotypes.

RESULTS AND DISCUSSION

Gene Ontology-based modeling of our data shows that the CD30hi MD lymphoma cells having a phenotype more similar to T-reg. Sequences that could be bound by the MD virus putative oncoprotein Meq in each of these genes' promoters suggests that the MD herpesvirus may play a direct role in maintaining this T-reg-like phenotype.

Mechanisms of disease: the evolving role of regulatory T cells in atherosclerosis

Atherosclerosis and related complications still represent the major cause of morbidity and mortality in the western world. The mechanisms that govern the progression and destabilization of atheromatous lesions are multiple and complex. Despite their widespread use, lipid-lowering agents do not provide sufficient protection from future clinical cardiovascular-associated events. Interest in the role of immunity in atherosclerosis and support for this relationship has grown significantly over recent years. This paradigm, in which inflammation is an instrumental process in plaque development and rupture, is further supported by studies showing that immune subsets are operative in atherosclerosis. Regulatory T-cell subpopulations consist of lymphocytes--with several phenotypic markers--that share the ability to suppress, by various mechanisms, inflammatory responses. These regulatory T cells consist of subsets such as interleukin-10 secreting type I regulatory cells, type 3 effector T-helper cells that produce transforming growth factor-beta, as well as adaptive and natural CD4(+)CD25(+) regulatory T cells. In this Review, I focus on the direct and indirect evidence for the involvement of regulatory T cells in atherogenesis in experimental models and in humans. The growing knowledge of the role of regulatory T cells could result in the future development of novel therapeutic modalities to attenuate atherosclerosis and stabilize vulnerable plaques.

Natural naive CD4+CD25+CD127low regulatory T cell (Treg) development and function are disturbed in multiple sclerosis patients: recovery of memory Treg homeostasis during disease progression

Patients with relapsing-remitting multiple sclerosis (RR-MS) show a suboptimal CD4(+)CD25(+) regulatory T cell (Treg) function, whereas no Treg alterations are observed in secondary progressive MS (SP-MS) patients. To clarify the difference in Treg activity between early and chronic disease stages in MS, we analyzed the functional capacity and homeostatic parameters of naive CD4(+)CD25(+)CD127(low)CD45RA(+) Tregs (nTregs) and their memory counterparts CD4(+)CD25(+)CD127(low)CD45RO(+) Tregs (mTregs) in untreated MS patients and healthy controls. Interestingly, whereas the suppressive capacity of FACS-sorted nTregs was impaired in both early and chronic MS patients, only the latter group showed a restored mTreg function. Consistent with this observation, chronic MS patients had increased numbers of mTregs as compared with age-matched early MS patients, whereas nTreg frequencies did not differ significantly. TCR excision circle numbers were reduced in nTregs of early MS patients, suggestive of a diminished nTreg thymic output. Moreover, a decreased number of CD31(+) mTregs were observed in early vs chronic MS patients, indicating that inflammatory processes drive the homeostatic turnover of mTregs during the early disease stage. Additionally, early MS patients showed a more restricted nTreg and mTreg TCR BV gene profile as compared with healthy controls and chronic MS patients. Finally, analysis of IFN-beta and glatiramer acetate-treated MS patients showed that these immunomodulatory drugs modify nTreg homeostasis. Taken together, this study provides strong evidence for a disturbed thymic nTreg development and function in MS patients. Moreover, memory Treg but not naive Treg homeostasis recovers during disease progression.

IPEX as a result of mutations in FOXP3

Immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare disorder caused by mutations in the FOXP3 gene that result in the defective development of CD4+CD25+ regulatory T cells which constitute an important T cell subset involved in immune homeostasis and protection against autoimmunity. Their deficiency is the hallmark of IPEX and leads to severe autoimmune phenomena including autoimmune enteropathy, dermatitis, thyroiditis, and type 1 diabetes, frequently resulting in death within the first 2 years of life. Apart from its clinical implications, IPEX illustrates the importance of immunoregulatory cells such as CD4+CD25+ regulatory T cells.

Understanding systemic lupus erythematosus physiopathology in the light of primary immunodeficiencies

INTRODUCTION

Associations between systemic lupus erythematosus (SLE) and primary immunodeficiencies (PIDs) were analyzed to gain insight into the physiopathology of SLE. Some PIDs have been consistently associated with SLE or lupus-like manifestations: (a) homozygous deficiencies of the early components of the classical complement pathway in the following decreasing order: in C1q, 93% of affected patients developed SLE; in C4, 75%; in C1r/s, 57%; and in C2, up to 25%; (b) female carriers of X-linked chronic granulomatous disease allele; and (c) IgA deficiency, present in around 5% of juvenile SLE.

DISCUSSION

In the first two groups, disturbances of cellular waste-disposal have been proposed as the main mechanisms of pathogenesis. On the other hand and very interestingly, there are PIDs systematically associated with several autoimmune manifestations in which SLE has not been described, such as autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED), immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX), and autoimmune lymphoproliferative syndrome (ALPS), suggesting that mechanisms considered as critical players for induction and maintenance of tolerance to autoantigens, such as (1) AIRE-mediated thymic negative selection of lymphocytes, (2) Foxp3+ regulatory T cell-mediated peripheral tolerance, and (3) deletion of auto-reactive lymphocytes by Fas-mediated apoptosis, could not be relevant in SLE physiopathology. The non-description of SLE and neither the most characteristic SLE clinical features among patients with agammaglobulinemia are also interesting observations, which reinforce the essential role of B lymphocytes and antibodies for SLE pathogenesis.

CONCLUSION

Therefore, monogenic PIDs represent unique and not fully explored human models for unraveling components of the conundrum represented by the physiopathology of SLE, a prototypical polygenic disease.

The use of FoxP3 as a biomarker and prognostic factor for malignant human tumors

Only since the early 21st century has it been proven that the immune system can actively defend the body against the development of malignant tumors. Escape from this process, termed immunosurveillance, has been shown to be required for the development of many tumors in both mice and humans, and may be a necessary prerequisite for the establishment of many malignancies. Serendipitously, an evolution in the understanding and characterization of immunosuppressor cells, regulatory T cells, has coincided with the establishment of tumor immunosurveillance. These two fields merged when it was found that the recruitment of regulatory T cells within tumors was a dominant mechanism tumors used to escape immunosurveillance. Regulatory T cells are specifically identified with antibodies which recognize the transcription factor, FoxP3. The presence of FoxP3+ cells within tumors has been shown to predict the prognosis, invasiveness, and metastatic ability of some tumors by modulating the ability of the immune system to target tumor cells. Furthermore, depletion of regulatory T cells from tumors could lead to the rejection of both early- and late-stage tumors by the host immune system. These findings suggest that the widespread use of FoxP3 as a biomarker should be explored for human tumors to enable physicians to make better decisions in oncologic care and to prepare the field for novel therapeutic agents directed at the elimination of regulatory T cells within tumors.

CD8+CD122+ T cells, a newly identified regulatory T subset, negatively regulate Graves' hyperthyroidism in a murine model

Graves' disease is a thyroid-specific autoimmune disease mediated by stimulatory autoantibodies against the TSH receptor (TSHR). We have previously shown in our mouse model with adenovirus expressing the TSHR that antibody mediated depletion of CD4(+)CD25(+) regulatory T cells (Tregs) enhances incidence and severity of hyperthyroidism in resistant and susceptible mouse strains, respectively. These data indicate that balance between effector T cells and Tregs is critical for disease development. This study was designed to evaluate the role played by another recently identified type of Treg, CD8(+)CD122(+) T cells, in our mouse model to delineate the significance of different types of Tregs in Graves' disease. Flow cytometry analysis showed that CD4(+)CD25(+) and CD8(+)CD122(+) T cells are distinct cell types, and anti-CD122 antibody effectively and selectively depleted CD8(+)CD122(+) T cells. As for CD4(+)CD25(+) Treg, CD8(+)CD122(+) T cell depletion increased the incidence of hyperthyroidism both in resistant and susceptible mice. Of interest, intrathyroidal lymphocytic infiltration was observed in some CD8(+)CD122(+) T cell-depleted, hyperthyroid resistant mice. These results indicate that in addition to CD4(+)CD25(+) T cells, CD8(+)CD122(+) T cells also play a crucial role in disease susceptibility in mouse Graves' disease. Thus, different types of Tregs appear to be involved in tolerance to a self-antigen, the TSHR.

The role of apoptosis in thyroid autoimmunity

There is increasing evidence showing that apoptosis plays a role in the development of the autoimmune thyroid diseases-Hashimoto's (lymphocytic) thyroiditis (HT) and Graves' disease (GD). The immune pathogenesis of HT and GD is not yet fully understood, but evidence points toward several steps. A defect in CD4(+)CD25(+) T regulatory cells breaks the immunological tolerance of the host and induces an abnormal production of cytokines, which facilitates the initiation of apoptosis. Though apoptosis appears to play a role in the pathogenesis of both HT and GD, the mechanisms that mediate these processes appear different. The induction of apoptosis in HT results in the destruction of thyrocytes, while apoptosis in the GD leads to damage of thyroid-infiltrating lymphocytes. The differences in the apoptotic mechanisms produce two very different forms of thyroid autoimmune responses, eventually developing into HT and GD, respectively.

Role of regulatory T cells and FOXP3 in human diseases

Immune regulation and tolerance are specific functions of the immune system, meaning at prevention or limitation of effector immune responses against inner and external insults. Regulatory T (Treg) cells are crucial players in this immune balance network. Research over the last 10 years has significantly contributed to characterizing Treg cell features, their mechanisms of function, and their role in human pathologies. The discovery of FOXP3 as an essential transcription factor not only for differentiation and function of naturally occurring Treg cells but also for regulation of intracellular molecules related to effector T-cell responses has provided new insights into the pathogenesis of immune-mediated diseases. Interestingly, there is increasing evidence that the individual signature of genes relevant for immune regulation definitely influences the final outcome of an immune response.

CD4+CD25+ naturally occurring regulatory T cells and not lymphopenia play a role in the pathogenesis of iodide-induced autoimmune thyroiditis in NOD-H2h4 mice

NOD-H2(h4) mice, which express I-A(k) on the NOD background, spontaneously develop autoimmune thyroiditis, a model of Hashimoto thyroiditis in humans, by adding iodide in the drinking water. Parental NOD mice have previously been shown to have intrinsic numerical abnormalities in peripheral lymphocytes and lymphocyte subpopulations such as CD4(+)CD25(+) naturally occurring regulatory T cells (Treg). Therefore we first investigated whether the similar abnormalities exist in NOD-H2(h4) mice. We observed that, compared with other non-autoimmune disease prone BALB/c and C57BL/6 mice, NOD-H2(h4) mice have lower numbers of splenocytes, CD3(+)T, CD4(+)T and CD8(+)T cells but the ratios of Treg to CD4(+)T cells were comparable. Increasing the numbers of peripheral lymphocytes by Complete Freund's Adjuvant immunization or splenocyte transfer did not affect development of thyroiditis, indicating that lymphopenia does not play a critical role in the pathogenesis of thyroiditis. We next examined the significance of Treg by depleting this lymphocyte subset with anti-CD25 antibody. Treg depletion, performed 4days before the administration of NaI water for 8 weeks, significantly exacerbated thyroiditis (p<0.01). Anti-thyroglobulin antibody titers also increased by Treg depletion (p<0.01) without changing the IgG2b to IgG1 ratios. In addition, expression levels of mRNA for IFN-gamma and IL-4 were enhanced in parallel. However, T(4) levels were similar between antibody-treated and untreated groups. Additional anti-CD25 administration at 3 weekly intervals did not influence these results. These data, together with previous studies on other mouse models of inducible thyroiditis and Graves' disease, indicate the role played by Treg in keeping anti-thyroid autoimmune reaction in check in experimental autoimmune thyroid diseases.

Regulatory T cells in health and disease

The healthy host does not normally develop tissue destructive autoimmunity in part because of the presence of natural regulatory T cells. These cells are best identified by their expression of a unique transcription factor forkhead box transcription factor (Foxp3) that controls their regulatory function. Several other types of regulatory T cells also occur most of which are induced in response to antigen stimulation. Some of these express the Foxp3 transcription factor but many do not. The role of natural T-regulatory cells as well as induceable regulatory cells in autoimmunity, cancer, allergy and infectious disease is described. The current status of therapeutic approaches that modulate regulatory T-cell responses on the outcome of experimental animal and human disease is also discussed.