Reduced CD4+,CD25- T cell sensitivity to the suppressive function of CD4+,CD25high,CD127 -/low regulatory T cells in patients with active systemic lupus erythematosus

Defective CD8+CD28+ regulatory T cell suppressor function in rheumatoid arthritis is restored by tumour necrosis factor inhibitor therapy

Balanced immunoregulatory networks are essential for maintenance of systemic tolerance. Disturbances in the homeostatic equilibrium between inflammatory mediators, immune regulators and immune effector cells are implicated directly in the pathogenesis of autoimmune diseases, including rheumatoid arthritis (RA). In this study we characterize the peripheral blood CD8(+) CD28(-) regulatory T cells (Treg) contribution to the immunoregulatory network in health and in RA. In health, CD8(+) CD28(-) Treg are suppressive but, unlike CD4(+) Treg , they function predominantly through the action of soluble mediators such as interleukin (IL)-10 and transforming growth factor (TGF)-β. Neutralization of TGF-β consistently reduced CD8(+) CD28(-) Treg suppressor function in vitro. RA, CD8(+) CD28(-) Treg are increased numerically, but have reduced expression of inducible co-stimulator (ICOS) and programmed death 1 (PD-1) compared to healthy or disease controls. They produce more IL-10 but autologous T cells express less IL-10R. This expression was found to be restored following in-vitro addition of a tumour necrosis factor inhibitor (TNFi). Deficiencies in both the CD8(+) CD28(-) Treg population and reduced sensitivity of the T responder cells impact upon their regulatory function in RA. TNFi therapy partially restores CD8(+) CD28(-) Treg ability in vivo and in vitro, despite the defects in expression of functionally relevant molecules by RA CD8(+) CD28(-) Treg compared to healthy controls. This study places CD8(+) CD28(-) Treg cells in the scheme of immune regulation alongside CD4(+) Treg cells, and highlights the importance of understanding impaired responsiveness to regulation that is common to these suppressor subsets and their restored function in response to TNFi therapy.

In active relapsing-remitting multiple sclerosis, effector T cell resistance to adaptive T(regs) involves IL-6-mediated signaling

Patients with multiple sclerosis (MS) manifest demyelination and neurodegeneration mediated in part by CD4(+) T cells that have escaped regulation. Resistance of pathogenic effector T cells (T(effs)) to suppression by regulatory T cells (T(regs)) has been demonstrated in several autoimmune diseases. Although impairment in T(reg) number and function has been observed in relapsing-remitting MS (RRMS), T(eff) resistance has not been well studied in this disease. To determine whether T(eff) resistance contributes to failed tolerance in RRMS, we performed T(reg) suppression assays with T(effs) from either RRMS patients not on immunomodulatory therapy or healthy individuals. T(eff) resistance was present in the T(effs) of RRMS patients with active disease but not from patients with inactive disease. Interleukin-6 (IL-6) and phosphorylation of signal transducer and activator of transcription 3 (pSTAT3) promote T(eff) resistance to T(regs), and we found an increase in IL-6 receptor α (IL-6Rα) expression and elevated IL-6 signaling as measured by pSTAT3 in our RRMS subjects. Further, the impaired suppression in RRMS subjects correlated with an increase in IL-6Rα surface expression on CD4(+) T cells and an increase in pSTAT3 in response to IL-6. To address whether the enhanced pSTAT3 contributed to T(eff) resistance in active RRMS patients, we blocked STAT3 phosphorylation and found that impaired suppression was reversed. Therefore, enhanced IL-6R signaling through pSTAT3, in some cases through increased IL-6Rα expression, contributed to T(eff) resistance in active RRMS. These markers may aid in determining disease activity and responsiveness to immunomodulatory therapies in RRMS.

Importance of regulatory T cells in the pathogenesis of psoriasis: review of the literature

Psoriasis is a common chronic relapsing inflammatory cutaneous disease; the main role in the inflammation of this condition is played by lymphocyte Th1, Th17 and their cytokines. The activity of these cells is modulated by a particular kind of T cells recently described: the T regulatory cells (Treg). These are able to inhibit the immunological response and to maintain the cutaneous immunological homeostasis, thus preventing autoimmunity against self antigens. Few data are available in the literature as to Treg in psoriasis; several studies demonstrate that the function of these cells is impaired in this condition and treatments for psoriasis may increase the number and activity of Treg. The role of these cells in the pathogenesis of psoriasis is very important to understand how they may contribute to the development of this cutaneous disorder. In the near future it would be possible to target therapies at these defects, improving the activity of these cells and maintaining cutaneous homeostasis, preventing psoriasis or other inflammatory cutaneous conditions.

Frequency and expression of inhibitory markers of CD4(+) CD25(+) FOXP3(+) regulatory T cells in patients with common variable immunodeficiency

Common variable immunodeficiency (CVID) is the most symptomatic primary antibody deficiency associated with recurrent infections and chronic inflammatory diseases as well as autoimmunity. CD4(+) CD25(+) FOXP3(+) regulatory T cells (Tregs) are critical T cell subsets for maintaining self-tolerance and regulation of immune response to antigens thus play a pivotal role in preventing autoimmunity. Thirty-seven CVID patients and 18 age-/sex-matched controls were enrolled. Peripheral blood mononuclear cells (PBMCs) were obtained from both groups, and the percentage of Tregs was calculated using flow cytometry method. The mRNA expression of Tregs' surface markers cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and glucocorticoid-induced tumour necrosis factor receptor (GITR), which are associated with Tregs' inhibitory function, was compared between patients and controls by quantitative real-time PCR TaqMan method. The results revealed that the frequency of Tregs was significantly lower in CVID patients than normal individuals (P < 0.001). In addition, CVID patients with autoimmunity were found to have markedly reduced proportion of Tregs compared to those cases without autoimmune diseases (P = 0.023). A significant difference was seen in factor forkhead box P3 (FOXP3) expression between CVID patients and controls (P < 0.001). The mRNAs of CTLA-4 and GITR genes were expressed at lower levels in CVID patients compared to control group (P = 0.005 and <0.001, respectively). Our findings showed reduced proportion of Tregs in CVID patients together with downregulation of FOXP3 protein and diminished expression of inhibitory Tregs' markers. It could be concluded that all of these changes may be responsible for cellular immune dysregulation observed in these patients especially those with autoimmune manifestation.

Inflammation and adaptive immunity in Parkinson's disease

The immune system is designed to protect the host from infection and injury. However, when an adaptive immune response continues unchecked in the brain, the proinflammatory innate microglial response leads to the accumulation of neurotoxins and eventual neurodegeneration. What drives such responses are misfolded and nitrated proteins. Indeed, the antigen in Parkinson's disease (PD) is an aberrant self-protein, although the adaptive immune responses are remarkably similar in a range of diseases. Ingress of lymphocytes and chronic activation of glial cells directly affect neurodegeneration. With this understanding, new therapies aimed at modulating the immune system's response during PD could lead to decreased neuronal loss and improved clinical outcomes for disease.

T cells out of control--impaired immune regulation in the inflamed joint

Since the discovery of FOXP3+ regulatory T (T(REG)) cells over 15 years ago, intensive research has focused on their presence, phenotype and function in autoimmune disease. Whether deficiencies in T(REG) cells underlie autoimmune pathology and whether, or how, therapeutic approaches based on these cells might be successful is still the subject of debate. The potential role of T(REG)-cell extrinsic factors, such as proinflammatory cytokines and resistance of effector T cells to suppression, as the cause of regulatory defects in chronic autoimmune inflammation is an intensive area of research. It is now clear that, at the site of inflammation, antigen presenting cells (APCs) and proinflammatory cytokines drive effector T cell skewing and plasticity, and that these T cells can become unresponsive to regulation. In addition, expansion and function of T(REG) cells is affected by the inflammatory environment; indeed, new data suggest that, in certain conditions, T(REG) cells promote inflammation. This Review summarizes the latest findings on changes in effector T cell homeostasis in autoimmune disease and focuses on how mechanisms that normally regulate these cells are affected in the inflamed joints of patients with arthritis. These findings have important clinical implications and will affect the development of new therapeutic strategies for autoimmune arthritis.

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.

Modulation of immune function occurs within hours of therapy initiation for multiple sclerosis

Daily administration of FDA-approved glatiramer acetate (GA) has beneficial effects on clinical course of relapsing remitting multiple sclerosis (RRMS). Although mechanisms of GA-action have been widely investigated and partially understood, immediate immune dynamics following GA-therapy are unknown. In the present study, we characterized the immediate effects of GA on phenotype, quantity and function of immune cells in MS patients. Prominent changes in immune cells were detected within 4-12h post-first GA-injection. T-cell modulation included significantly decreased CD4/CD8 ratio, perturbed homeostasis of predominantly CD8+ T-cells, significant enhancement in CD8+ T-cell mediated suppression and inhibitory potential of induced CD4-suppressors. Changes in APC were restricted to monocytes and included reduced stimulatory capacity in MLR and significantly increased IL-10 and TNF-α production. Our study provides the first evidence that GA treatment induces rapid immunologic changes within hours of first dose. Interestingly, these responses are not only restricted to innate immune cells but also include complex modulation of T-cell functionality.

Accelerated atherosclerosis in SLE: mechanisms and prevention approaches

Systemic lupus erythematosus (SLE) is a multi-organ autoimmune disease characterized by increased serum autoantibody levels and tissue damage. With improved diagnosis and more effective treatment of the resultant kidney disease, accelerated atherosclerosis has become a major cause of morbidity in patients suffering from SLE. Although the exact mechanisms for SLE-accelerated atherosclerosis are unknown, multiple factors have been established as potential players in this process. Among these potential players are dysregulation of T and B cell populations and increased circulating levels of inflammatory cytokines. In addition, SLE patients exhibit a proatherogenic lipid profile characterized by low HDL and high LDL and triglycerides. Recent therapeutic approaches have focused on targeting B cells, the producers of autoantibodies, but most studies do not consider the effects of these treatments on atherosclerosis. Evidence suggests that T cells play a major role in SLE-accelerated atherosclerosis. Therefore, therapies targeted at T cells may also prove invaluable in treating SLE and atherosclerosis.

Balance between regulatory T and Th17 cells in systemic lupus erythematosus: the old and the new

Pathogenic mechanisms underlying the development of systemic lupus erythematosus (SLE) are very complex and not yet entirely clarified. However, the pivotal role of T lymphocytes in the induction and perpetuation of aberrant immune response is well established. Among T cells, IL-17 producing T helper (Th17) cells and regulatory T (Treg) cells represent an intriguing issue to be addressed in SLE pathogenesis, since an imbalance between the two subsets has been observed in the course of the disease. Treg cells appear to be impaired and therefore unable to counteract autoreactive T lymphocytes. Conversely, Th17 cells accumulate in target organs contributing to local IL-17 production and eventually tissue damage. In this setting, targeting Treg/Th17 balance for therapeutic purposes may represent an intriguing and useful tool for SLE treatment in the next future. In this paper, the current knowledge about Treg and Th17 cells interplay in SLE will be discussed.

Inverse correlation between CD4+ CD25high CD127low/- regulatory T-cells and serum immunoglobulin A in patients with new-onset ankylosing spondylitis

This study investigated the role of regulatory T (T(reg)) cells in patients with new-onset, treatment-naïve ankylosing spondylitis (AS). Levels of CD4(+)CD25(high)CD127(low/-) T(reg) cells in the peripheral blood of 14 AS patients and 18 age-matched healthy volunteers were investigated by flow cytometry and correlations with serum levels of immunoglobulin A (IgA) and AS activity, as assessed by the Bath AS Disease Activity Index (BASDAI), were analysed. The number of peripheral blood CD4(+)CD25(high)CD127(low/-) T(reg) cells in AS patients was found to be significantly lower than in healthy controls and was inversely correlated with serum IgA levels. There was no significant correlation between CD4(+)CD25(high)CD127(low/-) T(reg) cell numbers and BASDAI scores. It is concluded that CD4(+)CD25(high)CD127(low/-) T(reg) cells may play a role in the pathogenesis and activity of AS.

Lupus nephritis: an overview of recent findings

Lupus nephritis (LN) is one of the most serious complications of systemic lupus erythematosus (SLE) since it is the major predictor of poor prognosis. In susceptible individuals suffering of SLE, in situ formation and deposit of immune complexes (ICs) from apoptotic bodies occur in the kidneys as a result of an amplified epitope immunological response. IC glomerular deposits generate release of proinflammatory cytokines and cell adhesion molecules causing inflammation. This leads to monocytes and polymorphonuclear cells chemotaxis. Subsequent release of proteases generates endothelial injury and mesangial proliferation. Presence of ICs promotes adaptive immune response and causes dendritic cells to release type I interferon. This induces maturation and activation of infiltrating T cells, and amplification of Th2, Th1 and Th17 lymphocytes. Each of them, amplify B cells and activates macrophages to release more proinflammatory molecules, generating effector cells that cannot be modulated promoting kidney epithelial proliferation and fibrosis. Herein immunopathological findings of LN are reviewed.

Role of IFN-γ in the establishment of anterior chamber-associated immune deviation (ACAID)-induced CD8+ T regulatory cells

Introduction of alloantigens into the AC induces a form of immune tolerance known as ACAID, which induces antigen-specific CD8+ Tregs, contributing to ocular immune privilege by down-regulating immune responses. Recent evidence suggests IFN-γ is needed for the suppressive function of CD8+ ACAID Tregs. This study tested the hypothesis that IFN-γ is needed for alloantigen-specific ACAID CD8+ Tregs to execute their suppressive function but is not required for the establishment of ACAID CD8+ Tregs. To address this hypothesis, ACAID was induced by injecting BALB/c spleen cells into the AC of WT C57BL/6 mice, IFN-γ(-/-) C57BL/6 mice, or anti-IFN-γ-treated WT C57BL/6 mice. LAT assays using C57BL/6 APCs as stimulators, CD4+ T cells from C57BL/6 mice previously immunized toward BALB/c alloantigens as effector cells, and IFN-γ-competent, IFN-γ(-/-), or IFN-γR(-/-) CD8+ Tregs were used to evaluate the suppressive function of CD8+ ACAID Tregs in response to IFN-γ. IFN-γ(-/-) mice or mice treated with anti-IFN-γ antibody prior to AC injection of alloantigen failed to develop ACAID. The suppressive function of IFN-γ(-/-) ACAID CD8+ Tregs was restored through the administration of exogenous IFN-γ. This suppressive responsiveness toward IFN-γ was CD8+ Treg-intrinsic, as CD8+ Tregs from IFN-γR(-/-) mice, which were primed in the AC with alloantigens, were not able to suppress alloantigen-specific DTH responses. These results indicate that IFN-γ is not needed for the induction of CD8+ ACAID Tregs but is required for ACAID Tregs to exert the suppression of allospecific DTH responses.

Regulatory T cells: banned cells for decades

Regulatory T cells (Tregs), either thymic derived or peripherally induced, suppress a variety of physiological and pathological immune responses, and the absence of this cell subset has been shown to result in severe systemic autoimmunity. Since their acceptance almost two decades ago, intensive research aiming to characterize the phenotype, to elucidate the suppressive activity, and to decipher the migratory behavior of Tregs has been performed. A substantial number of studies, however, focused on understanding whether defects in Treg numbers and function contribute to the development and progression of inflammatory, autoimmune, and malignant disorders, and how Treg numbers/function might be modulated to treat patients with autoimmune diseases or cancer. In the skin, an organ that is constantly exposed to the environment, Tregs are known to be critically involved not only in the maintenance of skin homeostasis but also in the regulation of cutaneous immune responses. In this review, we present an overview on recent data concerning Treg development and expansion, the molecular mechanisms underlying their immunosuppressive activity, and the modulation of Treg function. Furthermore, we discuss the role of Tregs in cutaneous inflammatory and autoimmune disorders.

Interaction of pregnancy and autoimmune rheumatic disease

During pregnancy, the fetus represents a natural allograft that is not normally rejected. While the maternal immune system retains the ability to respond to foreign antigens, tolerance mechanisms are up-regulated to protect the fetus from immunologic attacks by the mother. The profound immunologic adaptations during and after pregnancy do influence maternal autoimmune rheumatic diseases in several ways. One is triggering the onset of a rheumatic disease in the post partum period, the other influencing disease activity of established rheumatic disease. The review will discuss the mechanisms of increased susceptibility of rheumatoid arthritis (RA) in the first year post partum with a specific emphasis on the role of fetal cells or antigens persisting in the maternal circulation (so called microchimerism). Furthermore, the different influences of pregnancy on established rheumatic diseases will be highlighted. A marked beneficial effect of pregnancy is observed on RA whereas several other rheumatic diseases as ankylosing spondylitis (AS) and systemic lupus erythematosus (SLE) show either no particular effect or an aggravation of symptoms during pregnancy. Differences emerging in regard to modulation of disease symptoms during pregnancy seem related to response to hormones, the type of cytokine profile and immune response prevailing as well as further downstream interactions of molecular pathways that are important in disease pathogenesis.

Tolerance induced by anti-DNA Ig peptide in (NZB×NZW)F1 lupus mice impinges on the resistance of effector T cells to suppression by regulatory T cells

We have previously shown that immune tolerance induced by the anti-DNA Ig peptide pCons in (NZB×NZW)F(1) (NZB/W) lupus mice prolonged survival of treated animals and delayed the appearance of autoantibodies and glomerulonephritis. Part of the protection conferred by pCons could be ascribed to the induction of regulatory T cells (T(Reg)) that suppressed the production of anti-DNA antibodies in a p38 MAPK-dependent fashion. Here we show that another effect of pCons in the induction of immune tolerance in NZB/W lupus mice is the facilitation of effector T cell suppression by T(Reg). These new findings indicate that pCons exerts protective effects in NZB/W lupus mice by differentially modulating the activity of different T cell subsets, implying new considerations in the design of T(Reg)-based approaches to modulate T cell autoreactivity in SLE.

CD4+FOXP3+ T regulatory cells in human autoimmunity: more than a numbers game

Regulatory T cells (Treg) play a dominant role in suppression of autoimmune pathology, as rescue of Treg number and/or function in model systems can both prevent and reverse disease. These findings have generated a series of studies addressing the role of defects in Treg number and function in human autoimmunity. However, demonstrating global defects in Treg of individuals diagnosed with autoimmune diseases has been challenging. These challenges are founded, in part, in the complexity of human autoimmune diseases in which various genetic factors and environmental triggers contribute to disease susceptibility. Moreover, contribution of failed Treg-mediated suppression to pathogenesis can extend to multiple mechanisms. In this article, we discuss what is known with respect to the number and function of CD4(+)FOXP3(+) Treg in human autoimmunity, focusing on representative autoimmunediseases in which there are diverse Treg-mediated defects. We also highlight the need to better understand Treg plasticity and function in the context of autoimmunity.

Functional human regulatory T cells fail to control autoimmune inflammation due to PKB/c-akt hyperactivation in effector cells

During the last decade research has focused on the application of FOXP3(+) regulatory T cells (Tregs) in the treatment of autoimmune disease. However, thorough functional characterization of these cells in patients with chronic autoimmune disease, especially at the site of inflammation, is still missing. Here we studied Treg function in patients with juvenile idiopathic arthritis (JIA) and observed that Tregs from the peripheral blood as well as the inflamed joints are fully functional. Nevertheless, Treg-mediated suppression of cell proliferation and cytokine production by effector cells from the site of inflammation was severely impaired, because of resistance to suppression. This resistance to suppression was not caused by a memory phenotype of effector T cells or activation status of antigen presenting cells. Instead, activation of protein kinase B (PKB)/c-akt was enhanced in inflammatory effector cells, at least partially in response to TNFα and IL-6, and inhibition of this kinase restored responsiveness to suppression. We are the first to show that PKB/c-akt hyperactivation causes resistance of effector cells to suppression in human autoimmune disease. Furthermore, these findings suggest that for a Treg enhancing strategy to be successful in the treatment of autoimmune inflammation, resistance because of PKB/c-akt hyperactivation should be targeted as well.

Regulatory T-cells in systemic lupus erythematosus and rheumatoid arthritis

Regulatory T-cells (Tregs) are the guardians of peripheral tolerance acting to prevent autoimmune diseases such as systemic lupus erythomatosus (SLE) and rheumatoid arthritis (RA). Defects in Tregs have been reported in these two diseases despite significant differences in their clinical phenotype and pathogenesis. In both diseases the potency of Treg fails to keep pace with the activation of effector cells and are unable to resist the ensuing inflammation. This review will discuss the phenotypic, numeric, and functional abnormalities in Tregs and their role in patients and murine models of SLE and RA.

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.

Cytokine disturbances in systemic lupus erythematosus

The pathogenesis of systemic lupus erythematosus (SLE) is complex, and the resulting disease manifestations are heterogeneous. Cytokine dysregulation is pervasive, and their protein and gene expression profiles may serve as markers of disease activity and severity. Importantly, biologic agents that target specific cytokines may represent novel therapies for SLE. Four cytokines (IL-6, TNFα, IFNα, and BLyS) are being evaluated as therapeutic targets in SLE. The present review will examine the roles of each of these cytokines in murine and human SLE, and will summarize results from clinical trials of agents that target these cytokines.

Human FoxP3+ regulatory T cells in systemic autoimmune diseases

Since the characterization of CD4(+)CD25(+) regulatory T (Treg) cells in mice, significant progress has been made in the definitions of the phenotype and the function of human Treg cells in health and in pathological conditions. Recent advances in the field leading to a better molecular definition of Treg subsets in humans and the description of the dynamics of differentiation of Treg cells should bring new insights in the understanding of human chronic systemic autoimmune diseases. How Treg cells are compromised in these diseases is a challenging issue because the elucidation of the mechanisms leading to such anomaly might lead to promising novel therapeutic approaches.

Human T cells induce their own regulation through activation of B cells

Regulatory functions for B lymphocytes have been reported in murine models of autoimmune diseases in which B-cell deficient mice were shown to exhibit exacerbated disease. The B cells responsible for the immune regulations were identified as a subpopulation of interleukin 10-secreting cells. However, the mechanism of induction and the characteristics of regulatory B cells in humans have been hardly studied. This study reports that regulation of T cell responses can be induced by B cells following CD40-dependent cognate interaction. T cell proliferation and cytokine production were differentially regulated. Thus, CD40-induced regulatory B cells partially inhibited T cell proliferation following CD40 interaction without requirement of soluble factor. In contrast, modulation of Th1 differentiation resulted from CD80- and CD86-dependent interactions and from IL-10 production. The suppressive effects were mediated by CD19(high)IgD+CD38(high)CD24(high)CD5(high) B cells and appeared to be indirect, through the induction of regulatory T cells as indicated by the appearance of Foxp3+CD4+CD25+T cells. These data suggest that activation signals from T cells initiate regulatory properties in B cells that modulate T cell responses involving regulatory T cells. Finally, studies in autoimmune patients revealed that regulation of T cell proliferation was defective in systemic lupus erythematosus but efficient in other diseases. Restoration of efficient B-cell regulatory activity could provide innovative B-cell based treatment of autoimmune diseases.

Quantitative and functional profiles of CD4+ lymphocyte subsets in systemic lupus erythematosus patients with lymphopenia

Lymphopenia is a common clinical manifestation in patients with systemic lupus erythematosus (SLE). However, its physiopathogenic role and the contribution of different T cell subsets in this setting have not been addressed fully. The aim of this study was to characterize T cell subsets quantitatively and functionally and their association with lymphopenia and azathioprine treatment in SLE. We included 84 SLE patients and 84 healthy controls and selected 20 patients for a 6-month longitudinal analysis. Peripheral blood mononuclear cells were isolated, and T cell subsets were analysed by flow cytometry. Functional analyses included autologous and allogeneic co-cultures of T cells. Our data show persistently lower absolute numbers of CD4(+) CD25(high) T cells [regulatory T cells (T(regs) )] (1·9 versus 5·2, P < 0·01) and CD4(+) CD69(+) T cells (3·2 versus 9·3, P = 0·02) and higher activity scores (4·1 versus 1·5, P = 0·01) in SLE patients with lymphopenia compared with those without lymphopenia. Lymphopenia increased the risk for decreased numbers of CD4(+) CD25(high) cells (relative risk 1·80, 95% confidence interval 1·10-2·93; P = 0·003). In addition, azathioprine-associated lymphopenia was characterized by decreased absolute numbers of CD4(+) CD69(+) and CD4(+) interleukin (IL)-17(+) cells compared to disease activity-associated lymphopenia. Functional assays revealed that SLE effector T cells were highly proliferative and resistant to suppression by autologous T(regs) . In summary, lymphopenia was associated with deficient numbers of CD4(+) CD25(high) and CD4(+) CD69(+) cells and resistance of effector T cells to suppression by T(regs) , which could contribute to the altered immune responses characteristic of SLE. Furthermore, azathioprine treatment was associated with decreased numbers of CD4(+) CD69(+) and CD4(+) IL-17(+) cells and diminished T(reg) suppressive activity.

The type of responder T-cell has a significant impact in a human in vitro suppression assay

Background

In type 1 diabetes (T1D), a prototypic autoimmune disease, effector T cells destroy beta cells. Normally, CD4⁺CD25^+high, or natural regulatory T cells (Tregs), counter this assault. In autoimmunity, the failure to suppress CD4⁺CD25^low T cells is important for disease development. However, both Treg dysfunction and hyperactive responder T-cell proliferation contribute to disease.

Methods/Principal Findings

We investigated human CD4⁺CD25^low T cells and compared them to CD4⁺CD25^- T cells in otherwise equivalent in vitro proliferative conditions. We then asked whether these differences in suppression are exacerbated in T1D. In both single and co-culture with Tregs, the CD4⁺CD25^low T cells divided more rapidly than CD4⁺CD25^- T cells, which manifests as increased proliferation/reduced suppression. Time-course experiments showed that this difference could be explained by higher IL-2 production from CD4+CD25^low compared to CD4+CD25- T cells. There was also a significant increase in CD4+CD25^low T-cell proliferation compared to CD4+CD25- T cells during suppression assays from RO T1D and at-risk subjects (n = 28, p = 0.015 and p = 0.024 respectively).

Conclusions/Significance

The in vitro dual suppression assays proposed here could highlight the impaired sensitivity of certain responder T cells to the suppressive effect of Tregs in human autoimmune diseases.

Mechanisms of impaired regulation by CD4(+)CD25(+)FOXP3(+) regulatory T cells in human autoimmune diseases

A lack of regulatory T (T(Reg)) cells that express CD4, CD25 and forkhead box P3 (FOXP3) results in severe autoimmunity in both mice and humans. Since the discovery of T(Reg) cells, there has been intense investigation aimed at determining how they protect an organism from autoimmunity and whether defects in their number or function contribute to the development of autoimmunity in model systems. The next phase of investigation - that is, to define the role that defects in T(Reg) cells have in human autoimmunity - is now underway. This Review summarizes our progress so far towards understanding the role of CD4(+)CD25(+)FOXP3(+) T(Reg) cells in human autoimmune diseases and the impact that this knowledge might have on the diagnosis and treatment of these diseases.

Human regulatory T cells in autoimmune diseases

Human regulatory T cells (Tregs) play a critical role in preventing autoimmunity, and their failure contributes to autoimmune diseases. In recent years, our understanding of human Tregs has been greatly enhanced by improvements in the definition and isolation of pure human Tregs, as well as by the discovery of phenotypically and functionally distinct human Treg subsets. This progress has also yielded a better understanding of the mechanisms of human Treg suppression and the role of human Tregs in autoimmune diseases. An unexpected discovery is that human Tregs have considerable plasticity that allows them to produce the pro-inflammatory cytokine IL-17 under certain conditions. These recent advances highlight the importance of studying the roles of both mouse and human Tregs in autoimmunity.

CD8(+) T regulatory/suppressor cells and their relationships with autoreactivity and autoimmunity

Regulatory T lymphocytes (Treg) are fundamental for immune homeostasis since they contribute to the induction of peripheral tolerance to autologous antigens and regulate effector immune responses. Treg subsets are present within both the CD4+and the CD8(+) T cell compartments. Considering the CD8(+) Treg, in the last decades several subpopulations, provided with different phenotypes and mechanisms of action, have been characterized. This review is an attempt of integrating in an organic scenario the different CD8(+) Treg subpopulations. Moreover, it summarizes the findings so far achieved on the existence of CD8(+) Treg alterations in autoimmune diseases.

Role of regulatory T cells in rheumatoid arthritis: facts and hypothesis

Regulatory T cells (Treg) are a CD4⁺ lymphocyte subset involved in self-tolerance and autoimmunity prevention. There is evidence for a phenotypic and/or functional impairment of this cell subset during the natural history of several chronic autoimmune/inflammatory diseases, including rheumatoid arthritis (RA). Although the intracellular transcription factor FoxP3 is thought to be the master regulator of Treg cell function, a number of other molecules expressed on the cell surface have been proposed for the identification of Treg cells. This is important in order to favour their possible selective isolation and in the development of new therapeutic strategies. In the present paper, available data on phenotypic and functional characterization of Treg cells in both peripheral blood and synovial fluid from RA patients are reviewed and their possible pathogenic role in triggering and perpetuating rheumatoid joint inflammation is discussed.

Interferon alpha in systemic lupus erythematosus

The pleiotropic cytokine interferon alpha is involved in multiple aspects of lupus etiology and pathogenesis. Interferon alpha is important under normal circumstances for antiviral responses and immune activation. However, heightened levels of serum interferon alpha and expression of interferon response genes are common in lupus patients. Lupus-associated autoantibodies can drive the production of interferon alpha and heightened levels of interferon interfere with immune regulation. Several genes in the pathways leading to interferon production or signaling are associated with risk for lupus. Clinical and cellular manifestations of excess interferon alpha in lupus combined with the genetic risk factors associated with interferon make this cytokine a rare bridge between genetic risk and phenotypic effects. Interferon alpha influences the clinical picture of lupus and may represent a therapeutic target. This paper provides an overview of the cellular, genetic, and clinical aspects of interferon alpha in lupus.

Treating arthritis by immunomodulation: is there a role for regulatory T cells?

The discovery of regulatory T cells almost 15 years ago initiated a new and exciting research area. The growing evidence for a critical role of these cells in controlling autoimmune responses has raised expectations for therapeutic application of regulatory T cells in patients with autoimmune arthritis. Here, we review recent studies investigating the presence, phenotype and function of these cells in patients with RA and juvenile idiopathic arthritis (JIA) and consider their therapeutic potential. Both direct and indirect methods to target these cells will be discussed. Arguably, a therapeutic approach that combines multiple regulatory T-cell-enhancing strategies could be most successful for clinical application.

[Regulatory T cells and systemic autoimmune diseases: systemic lupus erythematosus, rheumatoid arthritis, primary Sjögren's syndrome]

Regulatory/suppressor T cells (Tregs) maintain immunologic homeostasis and prevent autoimmunity. They are the guardians of dominant tolerance. Recent research reveals quantitative and/or functional defect of Tregs in systemic autoimmune diseases. In this article, past and recent studies of Tregs in human systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and primary Sjögren's syndrome (pGSS) are reviewed. Most studies report that Tregs are decreased in peripheral blood of subjects with active SLE. A population of CD4+CD25-Foxp3+ is specifically described in SLE. Tregs functions are still discussed. Tregs counts in peripheral blood of RA patients vary across studies. Enrichment of synovial fluid in Tregs contrasts with inflammation. Tregs suppressive effects are altered in vivo in RA secondary to proinflammatory cytokines environment and resistance of effector T cells to Tregs. In pGSS, the conflicting place of Tregs in the balance prevention of autoimmunity/antitumor immunity is unspecified. Immunosuppressive treatments, like corticosteroids and anti-TNF, modulate Tregs cells population. There is increasing interest in the use of Tregs as a biological therapy to preserve and restore tolerance to self-antigen. However, difficulties to characterize these lymphocytes and controversies in the results of studies refrain their use in current clinical practice.

Regulatory T cell (Treg) subsets return in patients with refractory lupus following stem cell transplantation, and TGF-beta-producing CD8+ Treg cells are associated with immunological remission of lupus

Compared with conventional drug therapy, autologous hemopoietic stem cell transplantation (HSCT) can induce very-long-term remission in refractory lupus patients. Herein, we show that in posttransplant patients, both CD4(+)CD25(high)FoxP3(+) and an unusual CD8(+)FoxP3(+) Treg subset return to levels seen in normal subjects; accompanied by almost complete inhibition of pathogenic T cell response to critical peptide autoepitopes from histones in nucleosomes, the major lupus autoantigen from apoptotic cells. In addition to a stably sustained elevation of FoxP3, posttransplant CD8 T cells also maintained markedly higher expression levels of latency-associated peptide (LAP), CD103, PD-1, PD-L1, and CTLA-4, as compared with pretransplant CD8 T cells that were identically treated by a one-time activation and rest in short-term culture. The posttransplant CD8 regulatory T cells (Treg) have autoantigen-specific and nonspecific suppressive activity, which is contact independent and predominantly TGF-beta dependent. By contrast, the pretransplant CD8 T cells have helper activity, which is cell contact dependent. Although CD4(+)CD25(high) Treg cells return during clinical remission of conventional drug-treated lupus, the posttransplant patient's CD8 Treg cells are considerably more potent, and they are absent in drug-treated patients in whom CD4 T cell autoreactivity to nucleosomal epitopes persists even during clinical remission. Therefore, unlike conventional drug therapy, hemopoietic stem cell transplantation generates a newly differentiated population of LAP(high)CD103(high) CD8(TGF-beta) Treg cells, which repairs the Treg deficiency in human lupus to maintain patients in true immunological remission.

Regulatory T cells and autoimmunity

PURPOSE OF REVIEW

The identification of regulatory T cells (Tregs) as regulators of immunological self-tolerance has stimulated tremendous interest in the field. Over the past 12 months, new studies have added greatly to our understanding of the role of Tregs in autoimmune disease, details of which are presented here.

RECENT FINDINGS

In this review, the mechanism of action of Tregs, their antigen specificity and their frequency and function in different autoimmune diseases is explored. Currently available data on the role of transforming growth factor-beta, the reciprocal relationship between Tregs and Th17 cells, Treg markers, and current therapeutic approaches are evaluated. Other regulatory cells, which have been recently identified to play a significant role in autoimmunity, are described.

SUMMARY

Increasing insights into understanding the complex mechanisms of action of Tregs have already led to exciting therapeutic advances. This review provides an in-depth analysis of recent advances in the field of Tregs in autoimmunity. It highlights targets for future immunomodulatory therapy that may treat and potentially cure autoimmune disease, and it identifies areas for future research.

Increased numbers of IL-7 receptor molecules on CD4+CD25-CD107a+ T-cells in patients with autoimmune diseases affecting the central nervous system

Background

High content immune profiling in peripheral blood may reflect immune aberrations associated with inflammation in multiple sclerosis (MS) and other autoimmune diseases affecting the central nervous system.

Methods and Findings

Peripheral blood mononuclear cells from 46 patients with multiple sclerosis (MS), 9 patients diagnosed with relapsing remitting MS (RRMS), 13 with secondary progressive multiple sclerosis (SPMS), 9 with other neurological diseases (OND) and well as 15 healthy donors (HD) were analyzed by 12 color flow cytometry (TCRαβ, TCRγδ, CD4, CD8α, CD8β, CD45RA, CCR7, CD27, CD28, CD107a, CD127, CD14) in a cross-sectional study to identify variables significantly different between controls (HD) and patients (OND, RRMS, SPMS). We analyzed 187 individual immune cell subsets (percentages) and the density of the IL-7 receptor alpha chain (CD127) on 59 individual immune phenotypes using a monoclonal anti-IL-7R antibody (clone R34.34) coupled to a single APC molecule in combination with an APC-bead array. A non-parametric analysis of variance (Kruskal-Wallis test) was conducted in order to test for differences among the groups in each of the variables. To correct for the multiplicity problem, the FDR correction was applied on the p-values. We identified 19 variables for immune cell subsets (percentages) which allowed to segregate healthy individuals and individuals with CNS disorders. We did not observe differences in the relative percentage of IL-7R-positive immune cells in PBMCs. In contrast, we identified significant differences in IL-7 density, measured on a single cell level, in 2/59 variables: increased numbers of CD127 molecules on TCRαβ+CD4+CD25 (intermed) T-cells and on TCRαβ+CD4+CD25−CD107a+ T-cells (mean: 28376 Il-7R binding sites on cells from HD, 48515 in patients with RRMS, 38195 in patients with SPMS and 33692 IL-7 receptor binding sites on cells from patients with OND).

Conclusion

These data show that immunophenotyping represents a powerful tool to differentiate healthy individuals from individuals suffering from neurological diseases and that the number of IL-7 receptor molecules on differentiated TCRαβ+CD4+CD25−CD107a+ T-cells, but not the percentage of IL-7R-positive cells, segregates healthy individuals from patients with neurological disorders.

Increased frequency and compromised function of T regulatory cells in systemic sclerosis (SSc) is related to a diminished CD69 and TGFbeta expression

Background

Regulatory T cells (Tregs) are essential in the control of tolerance. Evidence implicates Tregs in human autoimmune conditions. Here we investigated their role in systemic sclerosis (SSc).

Methods/Principal Findings

Patients were subdivided as having limited cutaneous SSc (lcSSc, n = 20) or diffuse cutaneous SSc (dcSSc, n = 48). Further subdivision was made between early dcSSc (n = 24) and late dcSSc (n = 24) based upon the duration of disease. 26 controls were studied for comparison. CD3+ cells were isolated using FACS and subsequently studied for the expression of CD4, CD8, CD25, FoxP3, CD127, CD62L, GITR, CD69 using flow cytometry. T cell suppression assays were performed using sorted CD4CD25^highCD127^- and CD4CD25^lowCD127^high and CD3⁺ cells. Suppressive function was correlated with CD69 surface expression and TGFβ secretion/expression. The frequency of CD4⁺CD25⁺ and CD25^highFoxP3^highCD127^neg T cells was highly increased in all SSc subgroups. Although the expression of CD25 and GITR was comparable between groups, expression of CD62L and CD69 was dramatically lower in SSc patients, which correlated with a diminished suppressive function. Co-incubation of Tregs from healthy donors with plasma from SSc patients fully abrogated suppressive activity. Activation of Tregs from healthy donors or SSc patients with PHA significantly up regulated CD69 expression that could be inhibited by SSc plasma.

Conclusions/Significance

These results indicate that soluble factors in SSc plasma inhibit Treg function specifically that is associated with altered Treg CD69 and TGFβ expression. These data suggest that a defective Treg function may underlie the immune dysfunction in systemic sclerosis.

The Nature of Increased Circulating CD4CD25Foxp3 T Cells in Patients with Systemic Lupus Erythematosus: A Novel Hypothesis

The forkhead family transcriptional factor (Foxp3) is an important lineage marker for regulatory T (Treg) cells. Foxp3 expression is primarily restricted to CD4+CD25+ cell population. Recently, an intriguing phenomenon is highlighted that there is a considerable amount of CD4⁺CD25^-Foxp3⁺ T cells present in the peripheral blood of patients with systemic lupus erythematosus (SLE). Up to now, it is still an open question as to the nature of this cell subset. Following an analyses of the available phenotypic characteristics of CD4⁺CD25^-Foxp3⁺ T cell subset along with some new findings in research of Treg in human SLE, we propose the hypothesis: the increased circulating CD4⁺CD25^-Foxp3⁺ T cells in patients with SLE may constitute a peripheral reservoir of CD4⁺CD25⁺ Foxp3⁺ Treg cells. Under the condition of autoimmune response reactivated, CD4⁺CD25^-Foxp3⁺ T cells could be recruited to expand the Treg pool upon CD25 regaining, for the effort to try to reverse a homeostatic imbalance shift to more aggressive expansion of autoreactive T cells and B cells. This hypothesis, if confirmed, would provide a new strategy for the treatment of SLE via the generation of therapeutic regulatory T cells.

Regulatory T cells overturned: the effectors fight back

In the past 15 years, regulatory T cell (Treg) suppression has graduated from a phenomenon that 'dare not speak its name' to a field at the centre of a global research effort. It is now accepted that Tregs can target numerous cell populations to elicit potent immunosuppression. Intriguingly, emerging data suggest that certain signals can confer resistance to Treg suppression. Moreover, such resistance may be relevant to the pathogenesis of autoimmune diseases. In this article I review various pathways linked to resistance to Treg suppression. These include Toll-like receptor (TLR) signals, cytokines [in particular those that use the common gamma chain, such as interleukin (IL)-7 and IL-21] and the triggering of tumour necrosis factor (TNF) receptor family members (such as glucocorticoid induced tumor necrosis factor receptor (GITR), OX40 and 4-1BB). I also propose a model of 'tuned suppression' in which inflammatory stimuli and TLR ligation actively promote Treg function, such that as soon as effector cells re-acquire sensitivity to suppression the immune response can be efficiently curtailed.

Surveillance of antigen-presenting cells by CD4+ CD25+ regulatory T cells in autoimmunity: immunopathogenesis and therapeutic implications

CD4+CD25+ regulatory T cells (Tregs) play a critical role in preventing immune aggression. One way in which Tregs exert immune surveillance activities is by modifying the function of antigen presenting cells (APCs) such as dendritic cells, macrophages, and B cells. Tregs can induce apoptosis of APCs or inhibit their activation and function, thereby regulating subsequent innate and adaptive immune responses. These actions of Tregs are mediated by both soluble factors (interleukin [IL]-10, transforming growth factor-beta, perforins, granzymes) and cell-associated molecules (cytotoxic T lymphocyte antigen 4, lymphocyte activation gene-3, CD18, neuropilin-1, LFA-1/CD11a, CD39), of which cytotoxic T lymphocyte antigen 4 has a key role. However, in autoimmunity, chronically activated APCs under the influence of intracellular signaling pathways, such as phosphatidyl inositol 3 kinase, JAK-STAT, MAPK, and nuclear factor-kappaB pathways, can escape surveillance by Tregs, leading to the activation of T cells that are refractory to suppression by Tregs. Moreover, APCs and APC-derived inflammatory cytokines such as tumor necrosis factor, IL-6, IL-1beta, and IL-23 can render Tregs defective and can also reciprocally enhance the activity of the IL-17-producing pathogenic Th17 T cell subset. Emerging knowledge of the importance of APC-Treg interactions in maintaining immune tolerance and aberrations in this cross talk in autoimmune diseases provides a rationale for therapeutic approaches specifically targeting this axis of the immune system.

Identification of regulatory T cells in systemic lupus erythematosus

The concept that regulatory T cells (Treg) play a key role in both development and maintenance of autoimmune response in rheumatic diseases is well accepted. In recent years, several studies analyzed Treg cell phenotype and function in systemic lupus erythematosus (SLE), the prototypical systemic autoimmune disorder in humans. Although qualitative and/or quantitative abnormalities of Treg cells have been shown, data are often conflicting. This may depend on the selection of patients with different degrees of disease activity or on immunosuppressive treatments that can alter Treg cell findings. Among several proposed surface or intracellular Treg cell markers, CD25 at high level of expression and the transcription factor Foxp3 are the two most investigated in SLE. Despite the glucocorticoid-induced TNF receptor-related protein (GITR) represents a reliable phenotypic marker of murine Treg cells, little is known about its role in humans, in particular in the course of systemic autoimmune disorders. Preliminary data seems to suggest that this marker may represent a good tool to identify cell populations included within Treg cell subsets.

The effector T cells of diabetic subjects are resistant to regulation via CD4+ FOXP3+ regulatory T cells

Defects in immune regulation have been implicated in the pathogenesis of diabetes in mouse and in man. In vitro assays using autologous regulatory (Treg) and responder effector (Teff) T cells have shown that suppression is impaired in diabetic subjects. In this study, we addressed whether the source of this defect is intrinsic to the Treg or Teff compartment of diabetic subjects. We first established that in type 1 diabetes (T1D) individuals, similar levels of impaired suppression were seen, irrespective of whether natural (nTreg) or adaptive Treg (aTreg) were present. Then using aTreg, we examined the ability of T1D aTreg to suppress Teff of healthy controls, as compared with the ability of control aTreg to suppress Teff of diabetic subjects. Taking this approach, we found that the aTregs from T1D subjects function normally in the presence of control Teff, and that the T1D Teff were resistant to suppression in the presence of control aTreg. This escape from regulation was seen with nTreg as well and was not transferred to control Teff coincubated with T1D Teff. Thus, the "defective regulation" in T1D is predominantly due to the resistance of responding T cells to Treg and is a characteristic intrinsic to the T1D Teff. This has implications with respect to pathogenic mechanisms, which underlie the development of disease and the target of therapies for T1D.

Regulatory T cells in systemic lupus erythematosus: past, present and future

Regulatory/suppressor T cells (Tregs) maintain immunologic homeo-stasis and prevent autoimmunity. In this article, past studies and recent studies of Tregs in mouse models for lupus and of human systemic lupus erythematosus are reviewed concentrating on CD4⁺CD25⁺Foxp3⁺ Tregs. These cells consist of thymus-derived, natural Tregs and peripherally induced Tregs that are similar phenotypically and functionally. These Tregs are decreased in young lupus-prone mice, but are present in normal numbers in mice with established disease. In humans, most workers report CD4⁺Tregs are decreased in subjects with active systemic lupus erythematosus, but the cells increase with treatment and clinical improvement. The role of immunogenic and tolerogenic dendritic cells in controlling Tregs is discussed, along with new strategies to normalize Treg function in systemic lupus erythematosus.