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

CTLA-4 expressed by FOXP3+ regulatory T cells prevents inflammatory tissue attack and not T-cell priming in arthritis

Cytotoxic T-lymphocyte antigen 4 (CTLA-4) -mediated regulation of already tolerized autoreactive T cells is critical for understanding autoimmune responses. Although defects in CTLA-4 contribute to abnormal FOXP3⁺ regulatory T (Treg) cell function in rheumatoid arthritis, its role in autoreactive T cells remains elusive. We studied immunity towards the dominant collagen type II (CII) T-cell epitope in collagen-induced arthritis both in the heterologous setting and in the autologous setting where CII is mutated at position E266D in mouse cartilage. CTLA-4 regulated all stages of arthritis, including the chronic phase, and affected the priming of autologous but not heterologous CII-reactive T cells. CTLA-4 expression by both conventional T (Tconv) cells and Treg cells was required but while Tconv cell expression was needed to control the priming of naive autoreactive T cells, CTLA-4 on Treg cells prevented the inflammatory tissue attack. This identifies a cell-type-specific time window when CTLA-4-mediated tolerance is most powerful, which has important implications for clinical therapy with immune modulatory drugs.

T Cells Deficient in the Tyrosine Phosphatase SHP-1 Resist Suppression by Regulatory T Cells

The balance between activation of T cells and their suppression by regulatory T cells (Tregs) is dysregulated in autoimmune diseases and cancer. Autoimmune diseases feature T cells that are resistant to suppression by Tregs, whereas in cancer, T cells are unable to mount antitumor responses due to the Treg-enriched suppressive microenvironment. In this study, we observed that loss of the tyrosine phosphatase SHP-1, a negative regulator of TCR signaling, renders naive CD4⁺ and CD8⁺ T cells resistant to Treg-mediated suppression in a T cell-intrinsic manner. At the intracellular level, SHP-1 controlled the extent of Akt activation, which has been linked to the induction of T cell resistance to Treg suppression. Finally, under conditions of homeostatic expansion, SHP-1-deficient CD4⁺ T cells resisted Treg suppression in vivo. Collectively, these data establish SHP-1 as a critical player in setting the threshold downstream of TCR signaling and identify a novel function of SHP-1 as a regulator of T cell susceptibility to Treg-mediated suppression in vitro and in vivo. Thus, SHP-1 could represent a potential novel immunotherapeutic target to modulate susceptibility of T cells to Treg suppression.

A minimal unified model of disease trajectories captures hallmarks of multiple sclerosis

Multiple Sclerosis (MS) is an autoimmune disease targeting the central nervous system (CNS) causing demyelination and neurodegeneration leading to accumulation of neurological disability. Here we present a minimal, computational model involving the immune system and CNS that generates the principal subtypes of the disease observed in patients. The model captures several key features of MS, especially those that distinguish the chronic progressive phase from that of the relapse-remitting. In addition, a rare subtype of the disease, progressive relapsing MS naturally emerges from the model. The model posits the existence of two key thresholds, one in the immune system and the other in the CNS, that separate dynamically distinct behavior of the model. Exploring the two-dimensional space of these thresholds, we obtain multiple phases of disease evolution and these shows greater variation than the clinical classification of MS, thus capturing the heterogeneity that is manifested in patients.

Complement's hidden arsenal: New insights and novel functions inside the cell

A key component of both innate and adaptive immunity, new understandings of the complement system are expanding its roles beyond that traditionally appreciated. Evidence is accumulating that complement has an intracellular arsenal of components that provide not only immune defense, but also assist in key interactions for host cell functions. Although early work has primarily centered on T cells, the intracellular complement system likely functions in many if not most cells of the body. Some of these functions may trace their origins to the primitive complement system that began as a primeval form of C3 likely tasked for protection from intracellular pathogen invasion. This later expanded to include extracellular defense as C3 became a secreted protein to patrol the vasculature. Other components were added to the growing system including regulators to protect host cells from the indiscriminate effects of this potent system. Contemporary cells may retain some of these vestigial remnants. We now know that a) C3 serves as a damage-associated molecular pattern (in particular by coating pathogens that translocate into cells), b) most cells store C3 and recycle C3(H₂O) for immediate use, and c) C3 assists in cellular survival and metabolic reprogramming. Other components also are part of this hidden arsenal including C5, properdin, factors H and B, and complement receptors. Importantly, better definition of the intracellular complement system may translate into new target discovery to assist in creating the next generation of complement therapeutics.

Dimethyl Fumarate Therapy Significantly Improves the Responsiveness of T Cells in Multiple Sclerosis Patients for Immunoregulation by Regulatory T Cells

Multiple sclerosis (MS) is a chronic autoimmune disease caused by an insufficient suppression of autoreactive T lymphocytes. One reason for the lack of immunological control is the reduced responsiveness of T effector cells (Teff) for the suppressive properties of regulatory T cells (Treg), a process termed Treg resistance. Here we investigated whether the disease-modifying therapy of relapsing-remitting MS (RRMS) with dimethyl fumarate (DMF) influences the sensitivity of T cells in the peripheral blood of patients towards Treg-mediated suppression. We demonstrated that DMF restores responsiveness of Teff to the suppressive function of Treg in vitro, presumably by down-regulation of interleukin-6R (IL-6R) expression on T cells. Transfer of human immune cells into immunodeficient mice resulted in a lethal graft-versus-host reaction triggered by human CD4⁺ Teff. This systemic inflammation can be prevented by activated Treg after transfer of immune cells from DMF-treated MS patients, but not after injection of Treg-resistant Teff from therapy-naïve MS patients. Furthermore, after DMF therapy, proliferation and expansion of T cells and the immigration into the spleen of the animals is reduced and modulated by activated Treg. In summary, our data reveals that DMF therapy significantly improves the responsiveness of Teff in MS patients to immunoregulation.

The human microbiome and juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is the most common rheumatic disease in childhood. The pathogenesis of JIA is thought to be the result of a combination of host genetic and environmental triggers. However, the precise factors that determine one's susceptibility to JIA remain to be unravelled. The microbiome has received increasing attention as a potential contributing factor to the development of a wide array of immune-mediated diseases, including inflammatory bowel disease, type 1 diabetes and rheumatoid arthritis. Also in JIA, there is accumulating evidence that the composition of the microbiome is different from healthy individuals. A growing body of evidence indeed suggests that, among others, the microbiome may influence the development of the immune system, the integrity of the intestinal mucosal barrier, and the differentiation of T cell subsets. In turn, this might lead to dysregulation of the immune system, thereby possibly playing a role in the development of JIA. The potential to manipulate the microbiome, for example by faecal microbial transplantation, might then offer perspectives for future therapeutic interventions. Before we can think of such interventions, we need to first obtain a deeper understanding of the cause and effect relationship between JIA and the microbiome. In this review, we discuss the existing evidence for the involvement of the microbiome in JIA pathogenesis and explore the potential mechanisms through which the microbiome may influence the development of autoimmunity in general and JIA specifically.

T cell subpopulations in juvenile idiopathic arthritis and their modifications after biotherapies

Inflammatory T cells are thought to be central to the pathogenesis of juvenile idiopathic arthritis. In particular, recent evidence has underlined the importance of a balance between Th17 and Treg cells. Several mechanisms have come to light that control this reciprocal relationship. Moreover, it has been shown that in certain conditions, Th17 cells can shift toward a nonclassic Th1 phenotype. Anti-rheumatic biologic therapies may interfere with these mechanisms and re-establish immune tolerance.

TNFα in the regulation of Treg and Th17 cells in rheumatoid arthritis and other autoimmune inflammatory diseases

TNFα is a principal pro-inflammatory cytokine vital for immunity to infections. However, its excessive production is involved in chronic inflammation and disease pathology in autoimmune diseases. Evidence for its pathogenic role is validated by the fact that its neutralisation by therapeutic agents in vivo is beneficial in ameliorating disease and controlling symptoms. Paradoxically, however, treatment with TNFα inhibitors can either have no clinical effects, or even exacerbate disease in some patients. The explanation for such contradictory outcomes may lay in how and which downstream signalling pathways are activated and drive disease. TNFα causes its effects by binding to either or both of two membrane-bound receptors, TNFR1 and TNFR2. Engagement of the receptors can induce cell death or cell proliferation. T cells both produce and respond to TNFα and depending on whether the cytokine is membrane-bound or soluble and the level of expression of its two receptors, the biological outcome can be distinct. In addition, polymorphisms in genes encoding TNFα and T cell signalling proteins can significantly impact the outcome of TNFα receptor engagement. Early studies revealed that effector T cells in patients with rheumatoid arthritis (RA) are hyporesponsive due to chronic exposure to TNFα. However, recent evidence indicates that the relationship between TNFα and T cell responses is complex and, at times, can be paradoxical. In addition, there is controversy as to the specific effects of TNFα on different T cell subsets. This review will summarise knowledge on how TNFα modulates T cell responses and the effect of engaging either of its two receptors. Furthermore, we discuss how such interactions can dictate the outcome of treatment with TNFα inhibitors.

Contribution of CD8+ T cells to inflammatory cytokine production in systemic sclerosis (SSc)

Only limited attention has been paid to the role of CD8 + T cells in the etiopathogenesis and progression of systemic sclerosis (SSc). CD8 + T cells may have autoantigen-specific and pro-inflammatory but also immunomodulatory properties. To investigate the differentiation of CD8 + T cells, staining of cell surface factors and of chemokine receptors were performed. In addition, the cytokine-producing ability of circulating CD8 + T cells and their sensitivity to suppression by regulatory T cells (Tregs) were compared between patients with diffuse (dcSSc) or limited cutaneous SSc (lcSSc) and healthy individuals. We identified CD8 + T cells as producers of pro-inflammatory type-2 cytokines with a significant contribution of memory CD8 + T cells. Memory CD8 + T cells of SSc patients stayed unaltered after suppression with autologous Tregs. Expression of chemokine receptors was significantly correlated with intracellular cytokine production in CD8 + T cells with a clear dichotomy of type 1 and type 2 cytokines. High levels of intracellular cytokines, such as interleukin-(IL)-4, IL-13 and tumor-necrosis-factor-alpha (TNFalpha) were positively associated with the presence of Scl-70 or anti-centromere antibodies and negatively with the administration of glucocorticoids. Administration of glucocorticoids was positively associated with higher IFNgamma production. Lack of anti-centromere antibodies and therapy with methotrexate were positively associated with higher intracellular IL-10 production. CD8 + T cells may significantly contribute to inflammation in SSc. Our findings suggest to not only focus on T helper cells in the development of therapeutic strategies but also to consider the role of CD8 + T cells in the etiopathogenesis and perpetuation of SSc.

Infliximab therapy balances regulatory T cells, tumour necrosis factor receptor 2 (TNFR2) expression and soluble TNFR2 in sarcoidosis

Sarcoidosis is a systemic granulomatous disease of unknown aetiology that most commonly affects the lungs. Although elevated levels of regulatory T cells (Tregs ) have been reported, the extent to which they play a role in sarcoidosis pathogenesis remains unclear. Tumour necrosis factor (TNF) is thought to be one of the driving forces behind granuloma formation, illustrated by the efficacy of infliximab in severe sarcoidosis. Tregs express TNF receptor 2 (TNFR2) highly. Here, we examined the influence of infliximab therapy on Tregs and (soluble) TNFR2 levels in sarcoidosis, and correlated these with response to therapy. We observed that relative frequencies of Tregs were significantly higher in patients (n = 54) compared to healthy controls (n = 26; median 6·73 versus 4·36%; P < 0·001) and decreased following therapy (4·95; P < 0·001). Baseline TNFR2 expression on Tregs was increased significantly in patients versus controls (99·4 versus 96·2%; P = 0·031), and also in responders to therapy versus non-responders (99·6 versus 97·3%; P = 0·012). Furthermore, baseline soluble TNFR2 (sTNFR2) was higher in responders than in non-responders (mean 174 versus 107 pg/ml; P = 0·015). After treatment, responders showed a significant reduction in sTNFR2 levels in peripheral blood (-44·7 pg/ml; P < 0·001), in contrast to non-responders (+3·59 pg/ml). Our results demonstrated that Treg frequencies and TNFR2 expression on Tregs are increased in sarcoidosis, followed by a decline during infliximab therapy, suggesting a pathophysiological role of this T cell subset. Interestingly, sTNFR2 levels at baseline differed significantly between responders and non-responders, making it a potential marker in predicting which patients might benefit from infliximab.

TCR repertoire sequencing identifies synovial Treg cell clonotypes in the bloodstream during active inflammation in human arthritis

OBJECTIVES

The imbalance between effector and regulatory T (Treg) cells is crucial in the pathogenesis of autoimmune arthritis. Immune responses are often investigated in the blood because of its accessibility, but circulating lymphocytes are not representative of those found in inflamed tissues. This disconnect hinders our understanding of the mechanisms underlying disease. Our goal was to identify Treg cells implicated in autoimmunity at the inflamed joints, and also readily detectable in the blood upon recirculation.

METHODS

We compared Treg cells of patients with juvenile idiopathic arthritis responding or not to therapy by using: (i) T cell receptor (TCR) sequencing, to identify clonotypes shared between blood and synovial fluid; (ii) FOXP3 Treg cell-specific demethylated region DNA methylation assays, to investigate their stability and (iii) flow cytometry and suppression assays to probe their tolerogenic functions.

RESULTS

We found a subset of synovial Treg cells that recirculated into the bloodstream of patients with juvenile idiopathic and adult rheumatoid arthritis. These inflammation-associated (ia)Treg cells, but not other blood Treg cells, expanded during active disease and proliferated in response to their cognate antigens. Despite the typical inflammatory-skewed balance of immune mechanisms in arthritis, iaTreg cells were stably committed to the regulatory lineage and fully suppressive. A fraction of iaTreg clonotypes were in common with pathogenic effector T cells.

CONCLUSIONS

Using an innovative antigen-agnostic approach, we uncovered a population of bona fide synovial Treg cells readily accessible from the blood and selectively expanding during active disease, paving the way to non-invasive diagnostics and better understanding of the pathogenesis of autoimmunity.

CD8(+) T cells in human autoimmune arthritis: the unusual suspects

CD8(+) T cells are key players in the body's defence against viral infections and cancer. To date, data on the role of CD8(+) T cells in autoimmune diseases have been scarce, especially when compared with the wealth of research on CD4(+) T cells. However, growing evidence suggests that CD8(+) T-cell homeostasis is impaired in human autoimmune diseases. The contribution of CD8(+) T cells to autoimmune arthritis is indicated by the close association of MHC class I polymorphisms with disease risk, as well as the correlation between CD8(+) T-cell phenotype and disease outcome. The heterogeneous phenotype, resistance to regulation and impaired regulatory function of CD8(+) T cells - especially at the target organ - might contribute to the persistence of autoimmune inflammation. Moreover, newly identified populations of tissue-resident CD8(+) T cells and their interaction with antigen-presenting cells might have a key role in disease pathology. In this Review, we assess the link between CD8(+) T cells, autoimmune arthritis and the basis of their homeostatic changes under inflammatory conditions. Improved insight into CD8(+) T cell-specific pathogenicity will be essential for a better understanding of autoimmune arthritis and the identification of new therapeutic targets.

Regulatory T Cells Control Th2-Dominant Murine Autoimmune Gastritis

Pernicious anemia and gastric carcinoma are serious sequelae of autoimmune gastritis (AIG). Our study indicates that in adult C57BL/6-DEREG mice expressing a transgenic diphtheria toxin receptor under the Foxp3 promoter, transient regulatory T cell (Treg) depletion results in long-lasting AIG associated with both H(+)K(+)ATPase and intrinsic factor autoantibody responses. Although functional Tregs emerge over time during AIG occurrence, the effector T cells rapidly become less susceptible to Treg-mediated suppression. Whereas previous studies have implicated dysregulated Th1 cell responses in AIG pathogenesis, eosinophils have been detected in gastric biopsy specimens from patients with AIG. Indeed, AIG in DEREG mice is associated with strong Th2 cell responses, including dominant IgG1 autoantibodies, elevated serum IgE, increased Th2 cytokine production, and eosinophil infiltration in the stomach-draining lymph nodes. In addition, the stomachs exhibit severe mucosal and muscular hypertrophy, parietal cell loss, mucinous epithelial cell metaplasia, and massive eosinophilic inflammation. Notably, the Th2 responses and gastritis severity are significantly ameliorated in IL-4- or eosinophil-deficient mice. Furthermore, expansion of both Th2-promoting IFN regulatory factor 4(+) programmed death ligand 2(+) dendritic cells and ILT3(+) rebounded Tregs was detected after transient Treg depletion. Collectively, these data suggest that Tregs maintain physiological tolerance to clinically relevant gastric autoantigens, and Th2 responses can be a pathogenic mechanism in AIG.

Breaking Free of Control: How Conventional T Cells Overcome Regulatory T Cell Suppression

Conventional T (Tcon) cells are crucial in shaping the immune response, whether it is protection against a pathogen, a cytotoxic attack on tumor cells, or an unwanted response to self-antigens in the context of autoimmunity. In each of these immune settings, regulatory T cells (Tregs) can potentially exert control over the Tcon cell response, resulting in either suppression or activation of the Tcon cells. Under physiological conditions, Tcon cells are able to transiently overcome Treg-imposed restraints to mount a protective response against an infectious threat, achieving clonal expansion, differentiation, and effector function. However, evidence has accumulated in recent years to suggest that Tcon cell resistance to Treg-mediated suppression centrally contributes to the pathogenesis of autoimmune disease. Tipping the balance too far in the other direction, cancerous tumors utilize Tregs to establish an overly suppressive microenvironment, preventing antitumor Tcon cell responses. Given the wide-ranging clinical importance of the Tcon/Treg interaction, this review aims to provide a better understanding of what determines whether a Tcon cell is susceptible to Treg-mediated suppression and how perturbations to this finely tuned balance play a role in pathological conditions. Here, we focus in detail on the complex array of factors that confer Tcon cells with resistance to Treg suppression, which we have divided into two categories: (1) extracellular factor-mediated signaling and (2) intracellular signaling molecules. Further, we explore the therapeutic implications of manipulating the phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway, which is proposed to be the convergence point of signaling pathways that mediate Tcon resistance to suppression. Finally, we address important unresolved questions on the timing and location of acquisition of resistance, and the stability of the “Treg-resistant” phenotype.

Self-Sustained Resistance to Suppression of CD8+ Teff Cells at the Site of Autoimmune Inflammation Can Be Reversed by Tumor Necrosis Factor and Interferon-γ Blockade

OBJECTIVE

Resistance of Teff cells to Treg cell-mediated suppression contributes to the breakdown of peripheral tolerance in the inflamed joints of patients with juvenile idiopathic arthritis (JIA). However, unanswered questions are whether this resistant phenotype is self-sustained and whether CD8+ and CD4+ Teff cells share the same mechanism of resistance to suppression. We undertook this study to investigate intrinsic resistance of CD8+ Teff cells to suppression and to determine how this can be targeted therapeutically.

METHODS

CD8+ or CD4+ Teff cells were cultured with or without antigen-presenting cells (APCs) in Treg cell-dependent and -independent suppression assays. Synovial fluid (SF)-derived Teff cells were crosscultured with peripheral blood (PB) Treg cells from JIA patients or healthy controls. Tumor necrosis factor (TNF) or interferon-γ (IFNγ) blocking agents were used to restore Teff cell responsiveness to suppression.

RESULTS

Suppression of cell proliferation and cytokine production in CD8+ Teff cells from the SF of JIA patients was severely impaired compared to that in CD8+ Teff cells from the PB of JIA patients, regardless of the presence of APCs and CD4+ Teff cells. Similar to CD4+ Teff cells, impaired suppression of CD8+ Teff cells was shown to be an intrinsic feature of this cell population. While TNF blockade restored both CD8+ and CD4+ Teff cell susceptibility to suppression, autocrine release of IFNγ selectively sustained CD8+ Teff cell resistance, which could be relieved by IFNγ blockade.

CONCLUSION

Unlike CD4+ Teff cells, resistance of CD8+ Teff cells to suppression at the site of autoimmune inflammation is maintained by autocrine release of IFNγ, and blockade of IFNγ restores CD8+ Teff cell responsiveness to suppression. These findings indicate a potential therapeutic value of blocking IFNγ to restore immune regulation in JIA.

In vivo activation of Treg cells with a CD28 superagonist prevents and ameliorates chronic destructive arthritis in mice

Although regulatory T (Treg) cells are necessary to prevent autoimmune diseases, including arthritis, whether Treg cells can ameliorate established inflammatory disease is controversial. Using the glucose-6-phosphate isomerase (G6PI)-induced arthritis model in mice, we aimed to determine the therapeutic efficacy of increasing Treg cell number and function during chronic destructive arthritis. Chronic destructive arthritis was induced by transient depletion of Treg cells prior to immunization with G6PI. At different time points after disease induction, mice were treated with a CD28 superagonistic antibody (CD28SA). CD28SA treatment during the induction phase of arthritis ameliorated the acute signs of arthritis and completely prevented the development of chronic destructive arthritis. CD28SA treatment of mice with fully developed arthritis induced a significant reduction in clinical and histological signs of arthritis. When given during the chronic destructive phase of arthritis, 56 days after disease induction, CD28SA treatment resulted in a modest reduction of clinical signs of arthritis and a reduction in histopathological signs of joint inflammation. Our data show that increasing the number and activation of Treg cells by a CD28SA is therapeutically effective in experimental arthritis.

Phenotypic, Functional, and Gene Expression Profiling of Peripheral CD45RA+ and CD45RO+ CD4+CD25+CD127(low) Treg Cells in Patients With Chronic Rheumatoid Arthritis

OBJECTIVE

Conflicting evidence exists regarding the suppressive capacity of Treg cells in the peripheral blood (PB) of patients with rheumatoid arthritis (RA). The aim of this study was to determine whether Treg cells are intrinsically defective in RA.

METHODS

Using a range of assays on PB samples from patients with chronic RA and healthy controls, CD3+CD4+CD25+CD127(low) Treg cells from the CD45RO+ or CD45RA+ T cell compartments were analyzed for phenotype, cytokine expression (ex vivo and after in vitro stimulation), suppression of Teff cell proliferation and cytokine production, suppression of monocyte-derived cytokine/chemokine production, and gene expression profiles.

RESULTS

No differences between RA patients and healthy controls were observed with regard to the frequency of Treg cells, ex vivo phenotype (CD4, CD25, CD127, CD39, or CD161), or proinflammatory cytokine profile (interleukin-17 [IL-17], interferon-γ [IFNγ], or tumor necrosis factor [TNF]). FoxP3 expression was slightly increased in Treg cells from RA patients. The ability of Treg cells to suppress the proliferation of T cells or the production of cytokines (IFNγ or TNF) upon coculture with autologous CD45RO+ Teff cells and monocytes was not significantly different between RA patients and healthy controls. In PB samples from some RA patients, CD45RO+ Treg cells showed an impaired ability to suppress the production of certain cytokines/chemokines (IL-1β, IL-1 receptor antagonist, IL-7, CCL3, or CCL4) by autologous lipopolysaccharide-activated monocytes. However, this was not observed in all patients, and other cytokines/chemokines (TNF, IL-6, IL-8, IL-12, IL-15, or CCL5) were generally suppressed. Finally, gene expression profiling of CD45RA+ or CD45RO+ Treg cells from the PB revealed no statistically significant differences between RA patients and healthy controls.

CONCLUSION

Our findings indicate that there is no global defect in either CD45RO+ or CD45RA+ Treg cells in the PB of patients with chronic RA.

Translating Treg Therapy in Humanized Mice

Regulatory T cells (Treg) control immune cell function as well as non-immunological processes. Their far-reaching regulatory activities suggest their functional manipulation as a means to sustainably and causally intervene with the course of diseases. Preclinical tools and strategies are however needed to further test and develop interventional strategies outside the human body. “Humanized” mouse models consisting of mice engrafted with human immune cells and tissues provide new tools to analyze human Treg ontogeny, immunobiology, and therapy. Here, we summarize the current state of humanized mouse models as a means to study human Treg function at the molecular level and to design strategies to harness these cells for therapeutic purposes.

The Interplay Between Monocytes/Macrophages and CD4(+) T Cell Subsets in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by inflammation of the synovial lining (synovitis). The inflammation in the RA joint is associated with and driven by immune cell infiltration, synovial hyperproliferation, and excessive production of proinflammatory mediators, such as tumor necrosis factor α (TNFα), interferon γ (IFNγ), interleukin (IL)-1β, IL-6, and IL-17, eventually resulting in damage to the cartilage and underlying bone. The RA joint harbors a wide range of immune cell types, including monocytes, macrophages, and CD4(+) T cells (both proinflammatory and regulatory). The interplay between CD14(+) myeloid cells and CD4(+) T cells can significantly influence CD4(+) T cell function, and conversely, effector vs. regulatory CD4(+) T cell subsets can exert profound effects on monocyte/macrophage function. In this review, we will discuss how the interplay between CD4(+) T cells and monocytes/macrophages may contribute to the immunopathology of RA.

Interferon-Beta Therapy of Multiple Sclerosis Patients Improves the Responsiveness of T Cells for Immune Suppression by Regulatory T Cells

Multiple sclerosis (MS) is an inflammatory autoimmune disease characterized by imbalanced immune regulatory networks, and MS patient-derived T effector cells are inefficiently suppressed through regulatory T cells (Treg), a phenomenon known as Treg resistance. In the current study we investigated T cell function in MS patients before and after interferon-beta therapy. We compared cytokine profile, responsiveness for Treg-mediated suppression ex vivo and evaluated reactivity of T cells in vivo using a humanized mouse model. We found that CD4⁺ and CD8⁺ T cells of therapy-naive MS patients were resistant to Treg-mediated suppression. Treg resistance is associated with an augmented IL-6 production, enhanced IL-6 receptor expression, and increased PKB/c-Akt phosphorylation. These parameters as well as responsiveness of T cells to Treg-mediated suppression were restored after interferon-beta therapy of MS patients. Following transfer into immunodeficient mice, MS T cells induced a lethal graft versus host disease (GvHD) and in contrast to T cells of healthy volunteers, this aggressive T cell response could not be controlled by Treg, but was abolished by anti-IL-6 receptor antibodies. However, magnitude and lethality of GvHD induced by MS T cells was significantly decreased after interferon-beta therapy and the reaction was prevented by Treg activation in vivo. Our data reveals that interferon-beta therapy improves the immunoregulation of autoaggressive T effector cells in MS patients by changing the IL-6 signal transduction pathway, thus restoring their sensitivity to Treg-mediated suppression.

Polyfunctional, Pathogenic CD161+ Th17 Lineage Cells Are Resistant to Regulatory T Cell-Mediated Suppression in the Context of Autoimmunity

In autoimmune diseases such as rheumatoid arthritis (RA), regulatory T cells (Tregs) fail to constrain autoimmune inflammation; however, the reasons for this are unclear. We investigated T cell regulation in the RA joint. Tregs from RA synovial fluid suppressed autologous responder T cells; however, when compared with Tregs from healthy control peripheral blood, they were significantly less suppressive. Despite their reduced suppressive activity, Tregs in the RA joint were highly proliferative and expressed FOXP3, CD39, and CTLA-4, which are markers of functional Tregs. This suggested that the reduced suppression is due to resistance of RA synovial fluid responder T cells to Treg inhibition. CD161(+) Th17 lineage cells were significantly enriched in the RA joint; we therefore investigated their relative susceptibility to Treg-mediated suppression. Peripheral blood CD161(+) Th cells from healthy controls were significantly more resistant to Treg-mediated suppression, when compared with CD161(-) Th cells, and this was mediated through a STAT3-dependant mechanism. Furthermore, depletion of CD161(+) Th cells from the responder T cell population in RA synovial fluid restored Treg-mediated suppression. In addition, CD161(+) Th cells exhibited pathogenic features, including polyfunctional proinflammatory cytokine production, an ability to activate synovial fibroblasts, and to survive and persist in the inflamed and hypoxic joint. Because CD161(+) Th cells are known to be enriched at sites of autoinflammation, our finding that they are highly proinflammatory and resistant to Treg-mediated suppression suggests an important pathogenic role in RA and other autoimmune diseases.

Methotrexate treatment affects effector but not regulatory T cells in juvenile idiopathic arthritis

OBJECTIVE

The balance between Treg and effector T cells (Teff) is crucial for immune regulation in JIA. How MTX, the cornerstone treatment in JIA, influences this balance in vivo is poorly elucidated. The aim of this study was to investigate quantitative and qualitative effects of MTX on Treg and Teff in JIA patients during MTX treatment.

METHODS

Peripheral blood samples were obtained from JIA patients at the start of MTX and 3 and 6 months thereafter. Treg numbers and phenotypes were determined by flow cytometry and suppressive function in allogeneic suppression assays. Teff proliferation upon stimulation with anti-CD3, activation status and intracellular cytokine production were determined by flow cytometry. Effector cell responsiveness to suppression was investigated in autologous suppression assays. Effector cell cytokines in supernatants of proliferation and suppression assays and in plasma were measured by cytokine multiplex assay.

RESULTS

MTX treatment in JIA did not affect Treg phenotype and function. Instead, MTX treatment enhanced, rather than diminished, CD4(+) and CD8(+) T cell proliferation of JIA patients after 6 months of therapy, independent of clinical response. Effector cells during MTX treatment were equally responsive to Treg-mediated suppression. MTX treatment did not attenuate Teff activation status and their capacity to produce IL-13, IL-17, TNF-α and IFN-γ. Similarly to Teff proliferation, plasma IFN-γ concentrations after 6 months were increased.

CONCLUSION

This study provides the novel insight that MTX treatment in JIA does not attenuate Teff function but, conversely, enhances T cell proliferation and IFN-γ plasma concentrations in JIA patients.

Nonapoptotic and extracellular activity of granzyme B mediates resistance to regulatory T cell (Treg) suppression by HLA-DR-CD25hiCD127lo Tregs in multiple sclerosis and in response to IL-6

In autoimmune patients, regulatory T cells (Tregs) are increasingly found to be unable to suppress patient-derived T cells, an outcome referred to as Treg resistance. In this study, we show that CD4 T cells from patients with multiple sclerosis resist suppression by patient-derived or healthy donor-derived ex vivo Tregs. Importantly, we report that granzyme B (GzmB) contributes to this Treg resistance via a novel, apoptosis-independent mechanism. We show that memory CD4(+)CD127(lo)FOXP3(+) Treg subsets do not express GzmB, whereas activated, nonregulatory CD4 T cells isolated from patients with multiple sclerosis express higher levels of GzmB than do cells from healthy donors. In contrast to the intracellular GzmB that mediates apoptosis, GzmB can be found in extracellular fluids where it is hypothesized to regulate other cellular processes. In this study, we show that providing extracellular GzmB strongly inhibits Treg suppression, without altering Treg viability. However, when GzmB and GzmB-specific inhibitor are both provided to the cocultures, Treg suppression occurs. Thus, these data suggest that a novel activity of extracellular GzmB is to regulate Treg suppression. Additionally, we find that the suppression-abrogating cytokine IL-6 augments GzmB expression by human CD4 T cells, and it inhibits Treg suppression via this nonapoptotic GzmB-mediated mechanism. Lastly, in examining the mechanism whereby GzmB inhibits Treg function, we show that extracellular GzmB reduces Treg expression of CD39 and programmed death ligand 1. Collectively, these data indicate that extracellular GzmB plays an unexpected, nonapoptotic role in regulating Treg suppression and suggest that inactivation of specifically the extracellular activity of GzmB may be an efficacious therapeutic in autoimmunity.

The impact of biological therapy on regulatory T cells in rheumatoid arthritis

Regulatory T cells (Treg) are functionally defective in patients with RA. Restoring their function may not only control inflammation but also restore tolerance in these patients. Biologic therapies have been tremendously successful in treating RA. Here we review numerous reports suggesting that these immunomodulatory therapies have an impact on Treg and that this may contribute to their beneficial effects. Better understanding of their mode of action may not only lead to improvements in therapies and sustained remission but also enable the development of biomarkers of response, which would be the first steps towards personalized medicine.

Control of tissue-localized immune responses by human regulatory T cells

Treg cells control immune responses to self and nonharmful foreign antigens. Emerging data from animal models indicate that Treg cells function in both secondary lymphoid organs and tissues, and that these different microenvironments may contain specialized subsets of Treg cells with distinct mechanisms of action. The design of therapies for the restoration of tissue-localized immune homeostasis is dependent upon understanding how local immune responses are influenced by Treg cells in health versus disease. Here we review the current state of knowledge about human Treg cells in four locations: the skin, lung, intestine, and joint. Despite the distinct biology of these tissues, there are commonalities in the biology of their resident Treg cells, including phenotypic and functional differences from circulating Treg cells, and the presence of cytokine-producing (e.g. IL-17(+)) FOXP3(+) cells. We also highlight the challenges to studying tissue Treg cells in humans, and opportunities to use new technologies for the detailed analysis of Treg cells at the single-cell level. As emerging biological therapies are increasingly targeted toward tissue-specific effects, it is critical to understand their potential impact on local immune regulation.

Rebamipide attenuates autoimmune arthritis severity in SKG mice via regulation of B cell and antibody production

Oxidative stress is involved in the pathophysiology of rheumatoid arthritis (RA). We investigated the therapeutic potential of rebamipide, a gastroprotective agent with a property of reactive oxygen species scavenger, on the development of inflammatory polyarthritis and the pathophysiological mechanisms by which rebamipide might confer anti-arthritic effects in SKG mice, an animal model of RA. Intraperitoneal (i.p.) injection of rebamipide attenuated the severity of clinical and histological arthritis. Rebampide treatment reduced the number of T helper type 1 (Th1), Th2, Th17, inducible T cell co-stimulator (ICOS)(+) follicular helper T (Tfh) transitional type (T2) and mature B cells in the spleen, but increased the number of regulatory T (Treg ), CD19(+) CD1d(high) CD5(high) , CD19(+) CD25(high) forkhead box protein 3 (FoxP3)(+) regulatory B (Breg ) cells, memory B cells, and transitional type 1 (T1) B cells. In addition, flow cytometric analysis revealed significantly decreased populations of FAS(+) GL-7(+) germinal centre B cells and B220(-) CD138(+) plasma cells in the spleens of rebamipide-treated SKG mice compared to controls. Rebamipide decreased germinal centre B cells and reciprocally induced Breg cells in a dose-dependent manner in vitro. Rebamipide-induced Breg cells had more suppressive capacity in relation to T cell proliferation and also inhibited Th17 differentiation from murine CD4(+) T cells. Together, these data show that i.p. administration of rebamipide suppresses arthritis severity by inducing Breg and Treg cells and suppressing Tfh and Th17 cells in a murine model of RA.

Regulatory T-cell homeostasis: steady-state maintenance and modulation during inflammation

Regulatory T (Treg) cells play a vital role in the prevention of autoimmunity and the maintenance of self-tolerance, but these cells also have an active role in inhibiting immune responses during viral, bacterial, and parasitic infections. Although excessive Treg activity can lead to immunodeficiency, chronic infection, and cancer, too little Treg activity results in autoimmunity and immunopathology and impairs the quality of pathogen-specific responses. Recent studies have helped define the homeostatic mechanisms that support the diverse pool of peripheral Treg cells under steady-state conditions and delineate how the abundance and function of Treg cells changes during inflammation. These findings are highly relevant for developing effective strategies to manipulate Treg cell activity to promote allograft tolerance and treat autoimmunity, chronic infection, and cancer.

Increased presence of FOXP3+ regulatory T cells in inflamed muscle of patients with active juvenile dermatomyositis compared to peripheral blood

Juvenile dermatomyositis (JDM) is an immune-mediated inflammatory disease affecting the microvasculature of skin and muscle. CD4+ CD25+ FOXP3+ regulatory T cells (Tregs) are key regulators of immune homeostasis. A role for Tregs in JDM pathogenesis has not yet been established. Here, we explored Treg presence and function in peripheral blood and muscle of JDM patients. We analyzed number, phenotype and function of Tregs in blood from JDM patients by flow cytometry and in vitro suppression assays, in comparison to healthy controls and disease controls (Duchenne's Muscular Dystrophy). Presence of Tregs in muscle was analyzed by immunohistochemistry. Overall, Treg percentages in peripheral blood of JDM patients were similar compared to both control groups. Muscle biopsies of new onset JDM patients showed increased infiltration of numbers of T cells compared to Duchenne's muscular dystrophy. Both in JDM and Duchenne's muscular dystrophy the proportion of FOXP3+ T cells in muscles were increased compared to JDM peripheral blood. Interestingly, JDM is not a self-remitting disease, suggesting that the high proportion of Tregs in inflamed muscle do not suppress inflammation. In line with this, peripheral blood Tregs of active JDM patients were less capable of suppressing effector T cell activation in vitro, compared to Tregs of JDM in clinical remission. These data show a functional impairment of Tregs in a proportion of patients with active disease, and suggest a regulatory role for Tregs in JDM inflammation.

Pathophysiology of JIA-associated uveitis

Juvenile idiopathic arthritis (JIA)-associated uveitis is an intriguing manifestation of JIA and an important contributor of long-term damage. Its pathophysiology is still poorly understood. This review summarizes current concepts. JIA is both a multifactorial and polygenetic disease. In the past 2 decades, multiple studies have indicated that the genetic contribution to both JIA and JIA-associated uveitis is modest. From an ophthalmological point of view, much of the pathophysiological data is derived from studies in experimental uveitis animal models. The pathophysiology of the arthritic manifestations of JIA has been studied extensively in humans. These studies have focused on the principal cells of the adaptive immune system, in particular different subsets of regulatory and effector T cells, as well as on antigen presenting cells or dendritic cells. With advancing technology and advancing knowledge of the underlying mechanisms of JIA-associated uveitis, new targets for therapy might evolve in the coming years.

TREG-cell therapies for autoimmune rheumatic diseases

Naturally occurring Foxp3(+)CD25(+)CD4(+) regulatory T (TREG) cells maintain immunological self-tolerance and prevent a variety of autoimmune diseases, including rheumatic diseases such as rheumatoid arthritis and systemic lupus erythematosus. In animal models of rheumatic disease, autoimmune responses can be controlled by re-establishing the T-cell balance in favour of TREG cells. Here we discuss three potential strategies for the clinical use of TREG cells to treat autoimmune rheumatic disease: expansion of self-antigen-specific natural TREG cells in vivo; propagation of antigen-specific natural TREG cells ex vivo, by in vitro antigenic stimulation, and subsequent transfer back into the host; or conversion of antigen-specific conventional T cells into TREG cells in vivo or ex vivo. These strategies require depletion of the effector T cells that mediate autoimmunity before initiating TREG-cell-based therapies. Immunotherapies that target TREG cells, and the balance of TREG cells and autoreactive T cells, are therefore an important modality for the treatment of autoimmune rheumatic disease.

Myasthenia Gravis: paradox versus paradigm in autoimmunity

Myasthenia Gravis (MG) is a paradigm of organ-specific autoimmune disease (AID). It is mediated by antibodies that target the neuromuscular junction. The purpose of this review is to place MG in the general context of autoimmunity, to summarize the common mechanisms between MG and other AIDs, and to describe the specific mechanisms of MG. We have chosen the most common organ-specific AIDs to compare with MG: type 1 diabetes mellitus (T1DM), autoimmune thyroid diseases (AITD), multiple sclerosis (MS), some systemic AIDs (systemic lupus erythematous (SLE), rheumatoid arthritis (RA), Sjogren's syndrome (SS)), as well as inflammatory diseases of the gut and liver (celiac disease (CeD), Crohn's disease (CD), and primary biliary cirrhosis (PBC)). Several features are similar between all AIDs, suggesting that common pathogenic mechanisms lead to their development. In this review, we address the predisposing factors (genetic, epigenetic, hormones, vitamin D, microbiota), the triggering components (infections, drugs) and their interactions with the immune system [1,2]. The dysregulation of the immune system is detailed and includes the role of B cells, Treg cells, Th17 and cytokines. We particularly focused on the role of TNF-α and interferon type I whose role in MG is very analogous to that in several other AIDS. The implication of AIRE, a key factor in central tolerance is also discussed. Finally, if MG is a prototype of AIDS, it has a clear specificity compared to the other AIDS, by the fact that the target organ, the muscle, is not the site of immune infiltration and B cell expansion, but exclusively that of antibody-mediated pathogenic mechanisms. By contrast, the thymus in the early onset subtype frequently undergoes tissue remodeling, resulting in the development of ectopic germinal centers surrounded by high endothelial venules (HEV), as observed in the target organs of many other AIDs.

Imbalance of Th17 and T-regulatory cells in peripheral blood and synovial fluid in treatment naïve children with juvenile idiopathic arthritis

Objectives

The imbalance between Th17 and T regulatory cells (Tregs) may be a key event in development of autoimmunity. The problem is poorly explored in juvenile idiopathic arthritis (JIA) so far. In this study, peripheral blood (PB) and synovial fluid (SF) Tregs and Th17 cells from were assessed in untreated JIA children.

Material and methods

In 50 children with JIA the PB or SF percentages of Tregs and Th17 cells were assessed by flow cytometry, in comparison with PB Tregs and Th17 cells from 28 healthy controls. Additionally, in both groups the levels of proinfammatory cytokines, such as interleukin (IL)-1β, IL -6, IL -17, IL -21, IL -23 and tumor necrosis factor α (TN F-α) were assessed using ELI SA method.

Results

The proportion of JIA PB Th17 cells was significantly higher than in the controls (p = 0.01). Serum levels of IL -1β, IL -6, IL -17, IL -23 were also significantly higher in JIA (p = 0.011, p = 0.007, p = 0.008 and p = 0.023, respectively). The highest serum IL -6 levels were observed in oligoarthritis JIA (p = 0.031). Synovial fluid IL -21 concentration was distinctly higher in polyarticular JIA. Synovial fluid levels of TN F-α, IL -1β and IL -6 were significantly higher than in JIA PB (p = 0.038, p = 0.013 and p < 0.001, respectively). There was a significant correlation between IL -6 and PB Tregs (p = 0.02).

Conclusions

The results of this comprehensive analysis indicate a role of Th17 cell activation in the pathogenesis of JIA.

Human dendritic cell functional specialization in steady-state and inflammation

Dendritic cells (DC) represent a heterogeneous population of antigen-presenting cells that are crucial in initiating and shaping immune responses. Although all DC are capable of antigen-uptake, processing, and presentation to T cells, DC subtypes differ in their origin, location, migration patterns, and specialized immunological roles. While in recent years, there have been rapid advances in understanding DC subset ontogeny, development, and function in mice, relatively little is known about the heterogeneity and functional specialization of human DC subsets, especially in tissues. In steady-state, DC progenitors deriving from the bone marrow give rise to lymphoid organ-resident DC and to migratory tissue DC that act as tissue sentinels. During inflammation additional DC and monocytes are recruited to the tissues where they are further activated and promote T helper cell subset polarization depending on the environment. In the current review, we will give an overview of the latest developments in human DC research both in steady-state and under inflammatory conditions. In this context, we review recent findings on DC subsets, DC-mediated cross-presentation, monocyte-DC relationships, inflammatory DC development, and DC-instructed T-cell polarization. Finally, we discuss the potential role of human DC in chronic inflammatory diseases.

Anti-tumor necrosis factor α targets protein kinase B/c-Akt-induced resistance of effector cells to suppression in juvenile idiopathic arthritis

OBJECTIVE

To determine whether therapeutic strategies that block interleukin-6 (IL-6) or tumor necrosis factor α (TNFα) can improve the responsiveness of Teff cells to suppression in patients with juvenile idiopathic arthritis (JIA).

METHODS

Synovial fluid mononuclear cells (SFMCs) from the inflamed joints of patients with JIA were cultured in the presence of etanercept or anti-IL-6 in vitro, and protein kinase B (PKB)/c-Akt activation and responsiveness to suppression were measured. In addition, the in vivo effects of TNFα blockade were investigated using peripheral blood mononuclear cells obtained from patients before and after the start of etanercept therapy.

RESULTS

In vitro treatment of SFMCs with anti-IL-6 led to improved Treg cell-mediated suppression of cell proliferation in some but not all patients. Blocking TNFα with etanercept, however, clearly enhanced suppression, especially that of CD8+ T cells. In the presence of etanercept, PKB/c-Akt activation of Teff cells was reduced, and cells became more susceptible to transforming growth factor β-mediated suppression, indicating that anti-TNFα directly targets resistant Teff cells.

CONCLUSION

This study is the first to show that anti-TNFα targets the resistance of Teff cells to suppression, resulting in improved regulation of inflammatory effector cells.

Both Treg cells and Tconv cells are defective in the Myasthenia gravis thymus: roles of IL-17 and TNF-α

Myasthenia gravis (MG) is an autoimmune disease in which the thymus frequently presents follicular hyperplasia and signs of inflammation and T cells display a defect in suppressive regulation. Defects in a suppressive assay can indicate either the defective function of Treg cells or the resistance of Tconv cells to suppression by Treg cells. The aim of this study was to determine which cells were responsible for this defect and to address the mechanisms involved. We first performed cross-experiment studies using purified thymic Treg cells and Tconv cells from controls (CTRL) and MG patients. We confirmed that MG Treg cells were defective in suppressing CTRL Tconv proliferation, and we demonstrated for the first time that MG Tconv cells were resistant to Treg cell suppression. The activation of MG Tconv cells triggered a lower upregulation of FoxP3 and a higher upregulation of CD4 and CD25 than CTRL cells. To investigate the factors that could explain these differences, we analyzed the transcriptomes of purified thymic Treg and Tconv cells from MG patients in comparison to CTRL cells. Many of the pathways revealed by this analysis are involved in other autoimmune diseases, and T cells from MG patients exhibit a Th1/Th17/Tfh signature. An increase in IL-17-related genes was only observed in Treg cells, while increases in IFN-γ, IL-21, and TNF-α were observed in both Treg and Tconv cells. These results were confirmed by PCR studies. In addition, the role of TNF-α in the defect in Tconv cells from MG patients was further confirmed by functional studies. Altogether, our results indicate that the immunoregulatory defects observed in MG patients are caused by both Treg cell and Tconv cell impairment and involve several pro-inflammatory cytokines, with TNF-α playing a key role in this process. The chronic inflammation present in the thymus of MG patients could provide an explanation for the escape of thymic T cells from regulation in the MG thymus.

Enhanced activity of Akt in Teff cells from children with lupus nephritis is associated with reduced induction of tumor necrosis factor receptor-associated factor 6 and increased OX40 expression

OBJECTIVE

The breakdown of peripheral tolerance mechanisms is central to the pathogenesis of systemic lupus erythematosus (SLE). Although true Treg cells in patients with SLE exhibit intact suppressive activity, Teff cells are resistant to suppression. The underlying mechanisms are incompletely understood. This study was undertaken to examine the Akt signaling pathway and molecules that may alter its activity in T cells in lupus patients.

METHODS

The Akt pathway and its regulators were analyzed in Teff and Treg cells from children with lupus nephritis and controls using flow cytometry and real-time quantitative polymerase chain reaction. T cell proliferation was assessed by analysis of 5,6-carboxyfluorescein succinimidyl ester dilution.

RESULTS

CD4+CD45RA-FoxP3(low) and FoxP3- Teff cells from children with lupus nephritis expressed high levels of activated Akt, resulting in the down-regulation of the proapoptotic protein Bim and an enhanced proliferative response. The induction of tumor necrosis factor receptor-associated factor 6 (TRAF6) was impaired, and TRAF6 levels inversely correlated with Akt activity. Although the expression of OX40 was enhanced on Teff cells from children with lupus nephritis compared to controls, OX40 stimulation failed to significantly increase TRAF6 expression in cells from patients, in contrast to those from healthy controls, but resulted in further increased Akt activation that was reversed by blockade of OX40 signaling. Moreover, inhibition of Akt signaling markedly decreased the proliferation of Teff cells from lupus patients.

CONCLUSION

Our findings indicate that hyperactivation of the Akt pathway in Teff cells from children with lupus nephritis is associated with reduced induction of TRAF6 and up-regulation of OX40, which may cause Teff cell resistance to Treg cell-mediated suppression.

Intracellular complement activation sustains T cell homeostasis and mediates effector differentiation

Complement is viewed as a critical serum-operative component of innate immunity, with processing of its key component, C3, into activation fragments C3a and C3b confined to the extracellular space. We report here that C3 activation also occurred intracellularly. We found that the T cell-expressed protease cathepsin L (CTSL) processed C3 into biologically active C3a and C3b. Resting T cells contained stores of endosomal and lysosomal C3 and CTSL and substantial amounts of CTSL-generated C3a. While “tonic” intracellular C3a generation was required for homeostatic T cell survival, shuttling of this intracellular C3-activation-system to the cell surface upon T cell stimulation induced autocrine proinflammatory cytokine production. Furthermore, T cells from patients with autoimmune arthritis demonstrated hyperactive intracellular complement activation and interferon-γ production and CTSL inhibition corrected this deregulated phenotype. Importantly, intracellular C3a was observed in all examined cell populations, suggesting that intracellular complement activation might be of broad physiological significance.

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Complement C3 is activated intracellularly in human T cells by cathepsin L

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Intracellular C3 activation mediates cell survival and Th1 induction

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Increased intracellular C3 activation underlies T effector dysregulation in arthritis

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Patients with serum C3-deficiency retain intracellular C3a generation

T regulatory cells in childhood arthritis--novel insights

In recent years, there have been many new developments in the field of regulatory T cells (Treg), challenging the consensus on their behaviour, classification and role(s) in disease. The role Treg might play in autoimmune disease appears to be more complex than previously thought. Here, we discuss the current knowledge of regulatory T cells through animal and human research and illustrate the recent developments in childhood autoimmune arthritis (juvenile idiopathic arthritis (JIA)). Furthermore, this review summarises our understanding of the fields and assesses current and future implications for Treg in the treatment of JIA.

Kinetics of IL-6 production defines T effector cell responsiveness to regulatory T cells in multiple sclerosis

In multiple sclerosis (MS) autoaggressive T effector cells (Teff) are not efficiently controlled by regulatory T cells (Treg) but the underlying mechanisms are incompletely understood. Proinflammatory cytokines are key factors facilitating Teff activity in chronic inflammation. Here we investigated the influence of IL-6 on Treg sensitivity of Teff from therapy-naïve MS patients with or without active disease. Compared to healthy volunteers and independent of disease course CD4⁺ and especially CD8⁺ MS-Teff were insensitive against functional active Treg from healthy controls. This unresponsiveness was caused by accelerated production of IL-6, elevated IL-6 receptor expression and phosphorylation of protein kinase B (PKB)/c-Akt in MS-Teff. In a positive feedback loop, IL-6 itself induced its accelerated synthesis and enhanced phosphorylation of PKB/c-Akt that finally mediated Treg resistance. Furthermore, accelerated IL-6 release especially by CD8⁺ Teff prevented control of surrounding Teff, described here as “bystander resistance”. Blockade of IL-6 receptor signaling or direct inhibition of PKB/c-Akt phosphorylation restored Treg responsiveness of Teff and prevented bystander resistance. In Teff of healthy controls (HC) exogenous IL-6 also changed the kinetics of IL-6 production and induced Treg unresponsiveness. This modulation was only transient in Teff from healthy volunteers, whereas accelerated IL-6 production in MS-Teff maintained also in absence of IL-6. Hence, we showed that the kinetics of IL-6 production instead of elevated IL-6 levels defines the Teff responsiveness in early Treg-T cell communication in MS independent of their disease course and propose IL-6 and associated PKB/c-Akt activation as effective therapeutic targets for modulation of Teff activity in MS.

How numbers, nature, and immune status of foxp3(+) regulatory T-cells shape the early immunological events in tumor development

The influence of CD4(+)CD25(+)Foxp3(+) regulatory T-cells (Tregs) on cancer progression has been demonstrated in a large number of preclinical models and confirmed in several types of malignancies. Neoplastic processes trigger an increase of Treg numbers in draining lymph nodes, spleen, blood, and tumors, leading to the suppression of anti-tumor responses. Treg-depletion before or early in tumor development may lead to complete tumor eradication and extends survival of mice and humans. However this strategy is ineffective in established tumors, highlighting the critical role of the early Treg-tumor encounters. In this review, after discussing old and new concepts of immunological tumor tolerance, we focus on the nature (thymus-derived vs. peripherally derived) and status (naïve or activated/memory) of the regulatory T-cells at tumor emergence. The recent discoveries in this field suggest that the activation status of Tregs and effector T-cells (Teffs) at the first encounter with the tumor are essential to shape the fate and speed of the immune response across a variety of tumor models. The relative timing of activation/recruitment of anti-tumor cells vs. tolerogenic cells at tumor emergence appears to be crucial in the identification of tumor cells as friend or foe, which has broad implications for the design of cancer immunotherapies.

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.

The effect of autoimmune arthritis treatment strategies on regulatory T-cell dynamics

PURPOSE OF REVIEW

Since their discovery over 15 years ago, intensive research has focused on the presence, phenotype and function of FOXP3(+) regulatory T cells (Treg) in autoimmune diseases such as rheumatoid arthritis (RA). The questions of whether Treg deficiencies underlie autoimmune pathology and whether or how Treg-related therapeutic approaches might be successful are still a subject of a vivid debate. In this review we give an overview of how current therapies influence Treg numbers and function in RA and juvenile idiopathic arthritis (JIA) and discuss these findings in the light of new Treg-based intervention strategies for autoimmune arthritis.

RECENT FINDINGS

The attempt to relate rheumatic diseases like rheumatoid arthritis and juvenile idiopathic arthritis to Treg has led to somewhat heterogeneous observations. So far, no clear defects in Treg numbers or function have been identified in autoimmune arthritis. The current standard therapies, that is methotrexate and biologicals, are generally effective, but the exact mechanism of action and their effect on Treg is not fully known. Nevertheless, the majority of in-vitro and ex-vivo data point towards a positive influence of these treatments on Treg number and function. These observations are not all consistent, however, and it is not known whether the observed effects on Treg are primary or secondary effects. To safely conduct targeted regulatory T-cell therapy in rheumatic diseases more knowledge about regulatory T-cell function in an inflammatory environment is needed that coincides with the initiative to elucidate the exact mechanism of current therapies.

Heat shock proteins can be targets of regulatory T cells for therapeutic intervention in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterised by excessive immune responses resulting in inflammation of the joints. Although current therapies can be successful in dampening inflammation, a long-lived state of tolerance is seldom achieved. Therefore, novel therapies are needed that restore and maintain tolerance in patients with RA. Targeting regulatory T cells (Tregs) is a successful strategy to achieve tolerance, as was shown in studies performed in animal models and in human clinical trials. The antigen-specificity of Tregs is crucial for their effectiveness and allows for very specific targeting of these cells. However, which antigen is suitable for autoimmune diseases such as RA, for which the autoantigens are largely unknown? Heat shock proteins (HSPs) are ubiquitously expressed and can be up-regulated during inflammation. Additionally, HSPs, or HSP-derived peptides are immunogenic and can be recognised by a variety of immune cells, including Tregs. Therefore, this review highlights the potential of HSP-specific Tregs to control inflammatory immune responses. Targeting HSP-specific Tregs in RA can be achieved via the administration of HSPs (derived peptides), thereby controlling inflammatory responses. This makes HSPs attractive candidates for therapeutic intervention in chronic autoimmune diseases, with the ultimate goal of inducing long-lasting tolerance.

CD161 expression characterizes a subpopulation of human regulatory T cells that produces IL-17 in a STAT3-dependent manner

Treg cells are critical for the prevention of autoimmune diseases and are thus prime candidates for cell-based clinical therapy. However, human Treg cells are “plastic”, and are able to produce IL-17 under inflammatory conditions. Here, we identify and characterize the human Treg subpopulation that can be induced to produce IL-17 and identify its mechanisms. We confirm that a subpopulation of human Treg cells produces IL-17 in vitro when activated in the presence of IL-1β, but not IL-6. “IL-17 potential” is restricted to population III (CD4⁺CD25^hiCD127^loCD45RA⁻) Treg cells expressing the natural killer cell marker CD161. We show that these cells are functionally as suppressive and have similar phenotypic/molecular characteristics to other subpopulations of Treg cells and retain their suppressive function following IL-17 induction. Importantly, we find that IL-17 production is STAT3 dependent, with Treg cells from patients with STAT3 mutations unable to make IL-17. Finally, we show that CD161⁺ population III Treg cells accumulate in inflamed joints of patients with inflammatory arthritis and are the predominant IL-17-producing Treg-cell population at these sites. As IL-17 production from this Treg-cell subpopulation is not accompanied by a loss of regulatory function, in the context of cell therapy, exclusion of these cells from the cell product may not be necessary.

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.