Serum levels of CC chemokine ligands in cutaneous leishmaniasis patients

The crucial functions of chemokine/receptors in numerous parasitic infections, including leishmaniasis, are well documented. This study aimed to assess the serum levels of CC ligand (CCL) 2, CCL5, and CCL11 in cutaneous leishmaniasis (CL) patients. 64 patients, suffering from CL and 100 healthy people were selected, and their blood serum concentrations of CCL2, CCL5, and CCL11 were measured using enzyme-linked immunosorbent assay. The results demonstrated that while the mean serum levels of CCL5 and CCL11 increased significantly in CL patients, the mean serum levels of CCL2 decreased, compared to the control group. Despite the sufficient production of CCL5 and CCL11 in CL patients, they suffered from CCL2 deficiency, as the defense mechanism against parasitic infection. These findings suggest a mechanism that might partially explain the patients' susceptibility to persistent infection and their inability to clear the parasites.

Mesenchymal Stem Cells Attenuate Acute Liver Failure by Promoting Expansion of Regulatory T Cells in an Indoleamine 2,3-Dioxygenase-Dependent Manner

The influence of mesenchymal stem cells (MSCs) on the phenotype and function of CD4+CD49b+FoxP3- regulatory cells has not been elucidated. We used Concanavalin A (ConA) - and α-galactosylceramide (α-GalCer)-induced acute liver injury to estimate the effects of MSCs on liver-infiltrating CD4+CD49b+FoxP3-regulatory cells. MSCs significantly reduced ConA- and α-GalCer-mediated liver injury in C57BL/6 mice, as demonstrated by biochemical tests, reduced influx of inflammatory CD4+ T cells, and increased presence of CD4+CD49b+FoxP3- regulatory cells in the injured livers. The number of CD4+CD49b+FoxP3-regulatory cells was also significantly increased in α-GalCer-treated mice that received MSC-derived conditioned medium (MSC-CM). The presence of 1-methyltryptophan, a specific inhibitor of indoleamine 2,3-dioxygenase (IDO), in MSC-CM completely abrogated the hepatoprotective eff ect of MSCs and significantly decreased the total number of liver-infiltrated CD4+CD49b+FoxP3- regulatory cells, indicating the crucial importance of MSC-derived IDO for the expansion of CD4+CD49b+FoxP3- regulatory cells and the consequent MSC-dependent attenuation of acute liver injury.

Resolution of inflammation during multiple sclerosis

Multiple sclerosis (MS) is a frequent autoimmune demyelinating disease of the central nervous system (CNS). There are three clinical forms described: relapsing-remitting multiple sclerosis (RRMS), the most common initial presentation (85%) among which, if not treated, about half will transform, into the secondary progressive multiple sclerosis (SPMS) and the primary progressive MS (PPMS) (15%) that is directly progressive without superimposed clinical relapses. Inflammation is present in all subsets of MS. The relapsing/remitting form could represent itself a particular interest for the study of inflammation resolution even though it remains incomplete in MS. Successful resolution of acute inflammation is a highly regulated process and dependent on mechanisms engaged early in the inflammatory response that are scarcely studied in MS. Moreover, recent classes of disease-modifying treatment (DMTs) that are effective against RRMS act by re-establishing the inflammatory imbalance, taking advantage of the pre-existing endogenous suppressor. In this review, we will discuss the active role of regulatory immune cells in inflammation resolution as well as the role of tissue and non-hematopoietic cells as contributors to inflammation resolution. Finally, we will explore how DMTs, more specifically induction therapies, impact the resolution of inflammation during MS.

ITK signalling via the Ras/IRF4 pathway regulates the development and function of Tr1 cells

Type 1 regulatory T (Tr1) cells differentiate in response to signals engaging the T cell receptor (TCR), express high levels of the immunosuppressive cytokine IL-10, but not Foxp3, and can suppress inflammation and promote immune tolerance. Here we show that ITK, an important modulator of TCR signalling, is required for the TCR-induced development of Tr1 cells in various organs, and in the mucosal system during parasitic and viral infections. ITK kinase activity is required for mouse and human Tr1 cell differentiation. Tr1 cell development and suppressive function of Itk deficient cells can be restored by the expression of the transcription factor interferon regulatory factor 4 (IRF4). Downstream of ITK, Ras activity is responsible for Tr1 cell induction, as expression of constitutively active HRas rescues IRF4 expression and Tr1 cell differentiation in Itk-/- cells. We conclude that TCR/ITK signalling through the Ras/IRF4 pathway is required for functional development of Tr1 cells.

CCR8+FOXp3+ Treg cells as master drivers of immune regulation

The current study identifies CCR8⁺ regulatory T cells (T_reg cells) as drivers of immunosuppression. We show that in human peripheral blood cells, more than 30% of T_reg up-regulate CCR8 following activation in the presence of CCL1. This interaction induces STAT3-dependent up-regulation of FOXp3, CD39, IL-10, and granzyme B, resulting in enhanced suppressive activity of these cells. Of the four human CCR8 ligands, CCL1 is unique in potentiating T_reg cells. The relevance of these observations has been extended using an experimental model of multiple sclerosis [experimental autoimmune encephalomyelitis, (EAE)] and a stabilized version of mouse CCL1 (CCL1-Ig). First, we identified a self-feeding mechanism by which CCL1 produced by T_reg cells at an autoimmune site up-regulates the expression of its own receptor, CCR8, on these cells. Administration of CCL1-Ig during EAE enhanced the in vivo proliferation of these CCR8⁺ regulatory cells while inducing the expression of CD39, granzyme B, and IL-10, resulting in the efficacious suppression of ongoing EAE. The critical role of the CCL1-CCR8 axis in T_reg cells was further dissected through adoptive transfer studies using CCR8^-/- mice. Collectively, we demonstrate the pivotal role of CCR8⁺ T_reg cells in restraining immunity and highlight the potential clinical implications of this discovery.

Mechanisms of immunological tolerance in central nervous system inflammatory demyelination

Multiple sclerosis is a complex autoimmune disease of the central nervous system that results in a disruption of the balance between pro-inflammatory and anti-inflammatory signals in the immune system. Given that central nervous system inflammation can be suppressed by various immunological tolerance mechanisms, immune tolerance has become a focus of research in the attempt to induce long-lasting immune suppression of pathogenic T cells. Mechanisms underlying this tolerance induction include induction of regulatory T cell populations, anergy and the induction of tolerogenic antigen-presenting cells. The intravenous administration of encephalitogenic peptides has been shown to suppress experimental autoimmune encephalomyelitis and induce tolerance by promoting the generation of regulatory T cells and inducing apoptosis of pathogenic T cells. Safe and effective methods of inducing long-lasting immune tolerance are essential for the treatment of multiple sclerosis. By exploring tolerogenic mechanisms, new strategies can be devised to strengthen the regulatory, anti-inflammatory cell populations thereby weakening the pathogenic, pro-inflammatory cell populations.

T cell subsets and their signature cytokines in autoimmune and inflammatory diseases

CD4(+) T helper (Th) cells are critical for proper immune cell homeostasis and host defense, but are also major contributors to pathology of autoimmune and inflammatory diseases. Since the discovery of the Th1/Th2 dichotomy, many additional Th subsets were discovered, each with a unique cytokine profile, functional properties, and presumed role in autoimmune tissue pathology. This includes Th1, Th2, Th17, Th22, Th9, and Treg cells which are characterized by specific cytokine profiles. Cytokines produced by these Th subsets play a critical role in immune cell differentiation, effector subset commitment, and in directing the effector response. Cytokines are often categorized into proinflammatory and anti-inflammatory cytokines and linked to Th subsets expressing them. This article reviews the different Th subsets in terms of cytokine profiles, how these cytokines influence and shape the immune response, and their relative roles in promoting pathology in autoimmune and inflammatory diseases. Furthermore, we will discuss whether Th cell pathogenicity can be defined solely based on their cytokine profiles and whether rigid definition of a Th cell subset by its cytokine profile is helpful.

Regulatory T-cell vaccination independent of auto-antigen

To date, efforts to treat autoimmune diseases have primarily focused on the disease symptoms rather than on the cause of the disease. In large part, this is attributed to not knowing the responsible auto-antigens (auto-Ags) for driving the self-reactivity coupled with the poor success of treating autoimmune diseases using oral tolerance methods. Nonetheless, if tolerogenic approaches or methods that stimulate regulatory T (T_reg) cells can be devised, these could subdue autoimmune diseases. To forward such efforts, our approach with colonization factor antigen I (CFA/I) fimbriae is to establish bystander immunity to ultimately drive the development of auto-Ag-specific T_reg cells. Using an attenuated Salmonella vaccine expressing CFA/I fimbriae, fimbriae-specific T_reg cells were induced without compromising the vaccine's capacity to protect against travelers' diarrhea or salmonellosis. By adapting the vaccine's anti-inflammatory properties, it was found that it could also dampen experimental inflammatory diseases resembling multiple sclerosis (MS) and rheumatoid arthritis. Because of this bystander effect, disease-specific T_reg cells are eventually induced to resolve disease. Interestingly, this same vaccine could elicit the required T_reg cell subset for each disease. For MS-like disease, conventional CD25⁺ T_reg cells are stimulated, but for arthritis CD39⁺ T_reg cells are induced instead. This review article will examine the potential of treating autoimmune diseases without having previous knowledge of the auto-Ag using an innocuous antigen to stimulate T_reg cells via the production of transforming growth factor-β and interleukin-10.

Liver type I regulatory T cells suppress germinal center formation in HBV-tolerant mice

The liver plays a critical role in inducing systemic immune tolerance, for example, during limiting hypersensitivity to food allergy and in rendering acceptance of allotransplant or even hepatotropic pathogens. We investigated the unknown mechanisms of liver tolerance by using an established hepatitis B virus (HBV)-carrier mouse model, and found that these mice exhibited an antigen-specific tolerance toward peripheral HBsAg vaccination, showing unenlarged draining lymph node (DLN), lower number of germinal centers (GC), and inactivation of GC B cells and follicular T helper (Tfh) cells. Both in vivo and in vitro immune responses toward HBsAg were suppressed by mononuclear cells from HBV-carrier mice, which were CD4(+) Foxp3(-) type 1 regulatory T (Tr1)-like cells producing IL-10. Using recipient Rag1(-/-) mice, hepatic Tr1-like cells from day 7 of HBV-persistent mice acquired the ability to inhibit anti-HBV immunity 3 d earlier than splenic Tr1-like cells, implying that hepatic Tr1-like cells were generated before those in spleen. Kupffer cell depletion or IL-10 deficiency led to impairment of Tr1-like cell generation, along with breaking HBV persistence. The purified EGFP(+)CD4(+) T cells (containing Tr1-like cells) from HBV-carrier mice trafficked in higher numbers to DLN in recipient mice after HBsAg vaccination, and subsequently inactivated both Tfh cells and GC B cells via secreting IL-10, resulting in impaired GC formation and anti-HB antibody production. Thus, our results indicate Tr1-like cells migrate from the liver to the DLN and inhibit peripheral anti-HBV immunity by negatively regulating GC B cells and Tfh cells.

The dual roles of inflammatory cytokines and chemokines in the regulation of autoimmune diseases and their clinical implications

Cytokines and chemokines are secreted, small cell-signaling protein molecules, whose receptors are expressed on immune cells. These factors play a critical role in immune cell differentiation, migration, and polarization into functional subtypes and in directing their biological functions. Much attention has been devoted to exploring the role of key inflammatory cytokines and promigratory chemokines in autoimmune, autoinflammatory, and allergic diseases, leading to development of therapeutic strategies that are based on their targeted neutralization. Recent studies, including those coming from our groups, show that several major proinflammatory cytokines and chemokines, including IFN-γ, IL-2, CCL2, and CXCL12, may also function as anti-inflammatory mediators and therefore, may have potential as anti-inflammatory drugs. Likewise, major anti-inflammatory mediators, such as TGF-β, may under certain conditions, in combination with other cytokines, exhibit proinflammatory function and direct the polarization of the highly inflammatory CD4(+) Th17 cells. We show here that the biological function of pro- and anti-inflammatory cytokines is dependent on three key parameters: the local concentration of a given cytokine, the stage of disease in which it is administered, and its combination with other cytokines. The therapeutic implications of these findings are discussed, including two very recent studies summarizing clinical trials, in which low-dose administration of IL-2 was used to successfully suppress HCV and GVHD.

Activation of CD4⁺ Foxp3⁺ regulatory T cells proceeds normally in the absence of B cells during EAE

B cells and regulatory T (Treg) cells can both facilitate remission from experimental auto immune encephalomyelitis (EAE), a disease of the central nervous system (CNS) used as a model for multiple sclerosis (MS). Considering that B-cell-depletion therapy (BCDT) is used to treat MS patients, we asked whether Treg-cell activation depended on B cells during EAE. Treg-cell proliferation, accumulation in CNS, and augmentation of suppressive activity in the CNS were normal in B-cell-deficient mice, indicating that B cells are not essential for activation of the protective Treg-cell response and thus provide an independent layer of regulation. This function of B cells involved early suppression of the encephalitogenic CD4(+) T-cell response, which was enhanced in B-cell-deficient mice. CD4(+) T-cell depletion was sufficient to intercept the transition from acute-to-chronic EAE when applied to B-cell-deficient animals that just reached the peak of disease severity. Intriguingly, this treatment did not improve disease when applied later, implying that chronic disability was ultimately maintained independently of pathogenic CD4(+) T cells. Collectively, our data indicate that BCDT is unlikely to impair Treg-cell function, yet it might produce undesirable effects on T-cell-mediated autoimmune pathogenesis.

Type 1 regulatory T cells (Tr1) in autoimmunity

The ability of IL-10 producing Type 1 regulatory T cells (Tr1) to restrain the activation of effector immune cells during autoimmune responses underscores their essential role in maintaining immune tolerance. While mouse studies have demonstrated that increasing the numbers and/or function of Tr1 cells could improve the course of autoimmune diseases, the inability to generate Tr1 cells in vitro in large numbers has hampered identification of the molecular mechanisms responsible for their differentiation. Interleukin-27 (IL-27), a member of the IL-12 heterodimeric cytokine family, was identified as an important cytokine that suppresses effector T(H)17 cells and promotes the generation of Tr1 cells. Tr1 cells dampen autoimmunity and tissue inflammation partly through their secretion of the immunosuppressive cytokine IL-10. Here we review the molecular mechanisms involved in IL-27-induced Tr1 cell differentiation, with a focus on the role of two transcription factors, the aryl hydrocarbon receptor (AhR) and c-Maf. We also discuss how ligands that bind to AhR and affect the biology of IL-27-induced Tr1 cells can be exploited as a therapeutic approach to alleviate human autoimmune diseases.

Role of differential expression of interferon receptor isoforms on the response of multiple sclerosis patients to therapy with interferon beta

The cytokine interferon (IFN)-β is successfully used in the treatment of multiple sclerosis. However, some patients fail to respond to therapy, probably due to different biological patterns that are of importance in influencing clinical response. A common mechanism involved in the modulation of responsiveness to cytokine is represented by regulation of their receptor expression through autocrine-ligand-mediated loops. Mechanistically, IFN-β exerts its biological effects through interaction with the IFN-α/-β-receptor (IFNAR), which then activates several transcription factors. IFNAR is composed of 2 chains, IFNAR-1 and IFNAR-2, which associate with IFN-β to form a ternary complex. The major ligand-binding subunit is IFNAR-2 and it exists in 3 mRNA splice variants, resulting in 2 transmembrane (IFNAR-2b and IFNAR-2c) isoforms and a soluble (IFNAR-2a) one. On the contrary, from normal cells only one IFNAR-1 isoform, with transcriptional capacity, was identified. In the past decades, considerable information has accumulated pertaining to the downregulation of the IFNAR complex in IFN-treated patients, but only a few studies have investigated the molecular events involved in this phenomenon. The intent of the present review is to place this receptor downregulation in the context of IFN-β therapy and of its clinical and biological outcomes in IFN-β-treated patients.

Immune responses elicited in tertiary lymphoid tissues display distinctive features

During chronic inflammation, immune effectors progressively organize themselves into a functional tertiary lymphoid tissue (TLT) within the targeted organ. TLT has been observed in a wide range of chronic inflammatory conditions but its pathophysiological significance remains unknown. We used the rat aortic interposition model in which a TLT has been evidenced in the adventitia of chronically rejected allografts one month after transplantation. The immune responses elicited in adventitial TLT and those taking place in spleen and draining lymph nodes (LN) were compared in terms of antibody production, T cell activation and repertoire perturbations. The anti-MHC humoral response was more intense and more diverse in TLT. This difference was associated with an increased percentage of activated CD4+ T cells and a symmetric reduction of regulatory T cell subsets. Moreover, TCR repertoire perturbations in TLT were not only increased and different from the common pattern observed in spleen and LN but also “stochastic,” since each recipient displayed a specific pattern. We propose that the abnormal activation of CD4+ T cells promotes the development of an exaggerated pathogenic immune humoral response in TLT. Preliminary findings suggest that this phenomenon i) is due to a defective immune regulation in this non-professional inflammatory-induced lymphoid tissue, and ii) also occurs in human chronically rejected grafts.

The multiple faces of CXCL12 (SDF-1alpha) in the regulation of immunity during health and disease

Chemokines are a group of small, structurally related molecules that regulate the trafficking of various types of leukocytes through interactions with a subset of 7-transmembrane G-protein-coupled receptors. As key chemoattractants of inflammatory leukocytes, chemokines have been marked as potential targets for neutralization in autoimmune diseases. Cancer cells also express chemokines, where they function as survival/growth factors and/or angiogenic factors that promote tumor development and angiogenesis. Accordingly, these functions make them attractive targets for therapy of these diseases. Recently, we reported that one of these chemokines CXCL12 (SDF-1alpha) functions as an anti-inflammatory chemokine during autoimmune inflammatory responses and explored the mechanistic basis of this function. As a pleiotropic chemokine, CXCL12 participates in the regulation of tissue homeostasis, immune surveillance, autoimmunity, and cancer. This chemokine is constitutively expressed in the BM and various tissues, which enables it to regulate the trafficking and localization of immature and maturing leukocytes, including BM stem cells, neutrophils, T cells, and monocytic cells. We have shown recently that CXCL12 increases immunological tolerance in autoimmune diseases by polarizing Tregs and by doing so, restrains the progression of these diseases. This finding suggests a possible use of stabilized rCXCL12 as a potential drug for therapy of these diseases and targeted neutralization of CXCL12 for therapy of cancer diseases. The current review explores the different biological properties of CXCL12 and discusses the implications of CXCL12-based therapies for autoimmunity and cancer diseases.

Antigen-specific CD25- Foxp3- IFN-gamma(high) CD4+ T cells restrain the development of experimental allergic encephalomyelitis by suppressing Th17

The current study identifies within the Th1 subtype two distinct CD4(+) populations: those capable of transferring inflammatory autoimmunity and others that regulate its development by suppressing Th17 in an interferon (IFN)-gamma-dependent manner. These CD4(+)IFN-gamma(high)IL-4(low)IL-10(low)TGF-beta(low)FOXp3(-) cells in fact function as antigen-specific regulatory cells that restrain the development of autoimmunity by increasing the threshold of Th17 activation. We show that development of autoimmune conditions within the central nervous system is dependent on the Fas ligand-mediated apoptosis of these regulatory cells at early stages of disease. We also show that not only is the function of these cells IFN-gamma dependent but also that stable over expression of IFN-gamma in encephalitogenic CD4(+) T cells redirects their biological function to become antigen-specific regulatory cells. This may also explain, in part, the pleiotropic role of IFN-gamma in the regulation of autoimmunity, as previously observed by others.

Naturally occurring and inducible T-regulatory cells modulating immune response in allergic asthma

RATIONALE

T-regulatory cells (Tregs) are potent immunomodulators in allergic asthma.

OBJECTIVES

We evaluated the functional effects of Tregs by adoptively transferring naturally occurring CD4(+)CD25(+) Tregs (NTregs) and CD4(+)CD25(-) inducible Tregs (iTregs) from lung and spleens of green fluorescent protein (GFP)-transgenic Balb/c mice into cockroach-sensitized and -challenged mice.

METHODS

GFP-labeled NTregs and iTregs were adoptively transferred into cockroach-sensitized and -challenged mice. Airway hyperresponsiveness (AHR) to methacholine was examined using a single-chamber, whole-body plethysmograph and invasive tracheostomy.

MEASUREMENTS AND MAIN RESULTS

Adoptive transfer of either NTregs or iTregs from lung or spleen reversed airway inflammation and AHR to methacholine, and the effect lasted for at least 4 weeks. GFP-labeled iTregs up-regulated CD25 and forkhead-winged transcriptional factor box protein 3 and migrated to lymph node and lung. Lung CD4(+)CD25(+) T cells isolated from each group of recipient mice were inducible costimulatory molecule-high and programmed death (PD)-1-positive; however, higher expression of PD-1 was found in the spleen iTregs (S25(-)) and lung iTregs (L25(-)) groups. Higher levels of transforming growth factor-beta and IL-10 mRNA transcripts and bronchoalveolar lavage fluid IL-10 and INF-gamma levels were observed in lung CD4(+)CD25(+) cells from the L25(-) and S25(-) cell-recipient mice than from lung NTregs (L25(+)) and spleen NTregs (S25(+)) cell-recipient mice. Adoptive transfer of either cell type significantly reduced bronchoalveolar lavage fluid IL-4, IL-5, and IL-13 levels.

CONCLUSIONS

Tregs reverse AHR and airway inflammation; however iTregs that differentiated into IL-10-producing CD4(+) type 1 cells in the lung exert their suppressive activity likely by higher levels of transforming growth factor-beta, IL-10, IFN-gamma, and elevated levels of PD-1 compared with NTregs. Hence, PD-1 may be a conduit for reversing AHR by Tregs and a plausible target for treating asthma.

Surgical excision of CNS-draining lymph nodes reduces relapse severity in chronic-relapsing experimental autoimmune encephalomyelitis

Despite lack of classical lymphatic vessels in the central nervous system (CNS), cells and antigens do reach the CNS-draining lymph nodes. These lymph nodes are specialized to mediate mucosal immune tolerance, but can also generate T- and B-cell immunity. Their role in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE) therefore remains elusive. We hypothesized that drainage of CNS antigens to the CNS-draining lymph nodes is vital for the recurrent episodes of CNS inflammation. To test this, we surgically removed the superficial cervical lymph nodes, deep cervical lymph nodes, and the lumbar lymph nodes prior to disease induction in three mouse EAE models, representing acute, chronic, and chronic-relapsing EAE. Excision of the CNS-draining lymph nodes in chronic-relapsing EAE reduced and delayed the relapse burden and EAE pathology within the spinal cord, which suggests initiation of CNS antigen-specific immune responses within the CNS-draining lymph nodes. Indeed, superficial cervical lymph nodes from EAE-affected mice demonstrated proliferation against the immunizing peptide, and the deep cervical lymph nodes, lumbar lymph nodes, and spleen demonstrated additional proliferation against other myelin antigen epitopes. This indicates that intermolecular epitope spreading occurs and that CNS antigen-specific immune responses are differentially generated within the different CNS-draining lymphoid organs. Proliferation of splenocytes from lymphadenectomized and sham-operated mice against the immunizing peptide was similar. These data suggest a role for CNS-draining lymph nodes in the induction of detrimental immune responses in EAE relapses, and conclusively demonstrate that the tolerance-inducing capability of cervical lymph nodes is not involved in EAE.

CXCL12 (SDF-1alpha) suppresses ongoing experimental autoimmune encephalomyelitis by selecting antigen-specific regulatory T cells

Experimental autoimmune encephalomyelitis (EAE) is a T cell–mediated autoimmune disease of the central nervous system induced by antigen-specific effector Th17 and Th1 cells. We show that a key chemokine, CXCL12 (stromal cell–derived factor 1α), redirects the polarization of effector Th1 cells into CD4⁺CD25⁻Foxp3⁻interleukin (IL) 10^high antigen-specific regulatory T cells in a CXCR4-dependent manner, and by doing so acts as a regulatory mediator restraining the autoimmune inflammatory process. In an attempt to explore the therapeutic implication of these findings, we have generated a CXCL12-immunoglobulin (Ig) fusion protein that, when administered during ongoing EAE, rapidly suppresses the disease in wild-type but not IL-10–deficient mice. Anti–IL-10 neutralizing antibodies could reverse this suppression. The beneficial effect included selection of antigen-specific T cells that were CD4⁺CD25⁻Foxp3⁻IL-10^high, which could adoptively transfer disease resistance, and suppression of Th17 selection. However, in vitro functional analysis of these cells suggested that, even though CXCL12-Ig–induced tolerance is IL-10 dependent, IL-10–independent mechanisms may also contribute to their regulatory function. Collectively, our results not only demonstrate, for the first time, that a chemokine functions as a regulatory mediator, but also suggest a novel way for treating multiple sclerosis and possibly other inflammatory autoimmune diseases.

The genetics of immunoregulatory T cells

The immune repertoire of normal, healthy individuals contains autoreactive T cells and natural antibodies that, under normal conditions, are controlled, either through central tolerance or by the activity of immunoregulatory T cells to prevent the onset of autoimmune diseases. Over the years, several types of immunoregulatory T cells have been identified. These include natural CD4+CD25+Foxp3+T (Treg) cells and type 1 NKT cells, which develop in the thymus, as well as acquired immunoregulatory T cells, such as type 1 cells (Tr1), Th3 cells, Ts cells and anergic CD4 T cells, which all appear to be products of peripheral immune activation. While little is understood about the genetics of most types of immunoregulatory T cell, detailed information on the genetic control of NKT and Treg cells is now available and may contribute significantly to our understanding of the aetiology of autoimmune disease.

Th17 and Th1 responses directed against the immunizing epitope, as opposed to secondary epitopes, dominate the autoimmune repertoire during relapses of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory demyelinating disease with similarities to multiple sclerosis (MS). It has been suggested that relapses of EAE and MS may be associated with, and even driven by, T cells specific for novel epitopes that are primed during the course of tissue destruction in the target organ or in secondary lymphoid tissues. We show, however, that IFNgamma and IL-17 responses against the immunizing epitope remain dominant through out the course of multiphasic EAE. Furthermore, induction of tolerance against a putative secondary epitope did not prevent clinical relapses.

Noncanonical NF-kappaB signaling in dendritic cells is required for indoleamine 2,3-dioxygenase (IDO) induction and immune regulation

Ligation of CD40 on dendritic cells (DCs) induces early production of inflammatory mediators via canonical NF-kappaB signaling, as well as late expression of the anti-inflammatory enzyme indoleamine 2,3-dioxygenase (IDO) via unknown signal transduction. By selective blocking of either the canonical NF-kappaB pathway using the NEMO-binding domain peptide or the noncanonical NF-kappaB pathway by small interfering RNA, we demonstrate that IDO expression requires noncanonical NF-kappaB signaling. Also, noncanonical NF-kappaB signaling down-regulates proinflammatory cytokine production in DCs. In addition, selective activation of the noncanonical NF-kappaB pathway results in noninflammatory DCs that suppress T-cell activation and promote the development of T cells with regulatory properties. These findings reveal an important role of the noncanonical NF-kappaB pathway in the regulation of immunity.

Association between parasite infection and immune responses in multiple sclerosis

OBJECTIVE

To assess whether parasite infection is correlated with a reduced number of exacerbations and altered immune reactivity in multiple sclerosis (MS).

METHODS

A prospective, double-cohort study was performed to assess the clinical course and radiological findings in 12 MS patients presenting associated eosinophilia. All patients presented parasitic infections with positive stool specimens. In all parasite-infected MS patients, the eosinophilia was not present during the 2 previous years. Eosinophil counts were monitored at 3- to 6-month intervals. When counts became elevated, patients were enrolled in the study. Interleukin (IL)-4, IL-10, IL-12, transforming growth factor (TGF)-beta, and interferon-gamma production by myelin basic protein-specific peripheral blood mononuclear cells were studied using enzyme-linked immunospot (ELISPOT). FoxP3 and Smad7 expression were studied by reverse-transcriptase polymerase chain reaction.

RESULTS

During a 4.6-year follow-up period, parasite-infected MS patients showed a significantly lower number of exacerbations, minimal variation in disability scores, as well as fewer magnetic resonance imaging changes when compared with uninfected MS patients. Furthermore, myelin basic protein-specific responses in peripheral blood showed a significant increase in IL-10 and TGF-beta and a decrease in IL-12 and interferon-gamma-secreting cells in infected MS patients compared with noninfected patients. Myelin basic protein-specific T cells cloned from infected subjects were characterized by the absence of IL-2 and IL-4 production, but high IL-10 and/or TGF-beta secretion, showing a cytokine profile similar to the T-cell subsets Tr1 and Th3. Moreover, cloning frequency of CD4+CD25+ FoxP3+ T cells was substantially increased in infected patients compared with uninfected MS subjects. Finally, Smad7 messenger RNA was not detected in T cells from infected MS patients secreting TGF-beta.

INTERPRETATION

Increased production of IL-10 and TGF-beta, together with induction of CD25+CD4+ FoxP3+ T cells, suggests that regulatory T cells induced during parasite infections can alter the course of MS.

Interleukin-10-secreting type 1 regulatory T cells in rodents and humans

Interleukin-10 (IL-10)-secreting T regulatory type 1 (Tr1) cells are defined by their specific cytokine production profile, which includes the secretion of high levels of IL-10 and transforming growth factor-beta(TGF-beta), and by their ability to suppress antigen-specific effector T-cell responses via a cytokine-dependent mechanism. In contrast to the naturally occurring CD4+ CD25+ T regulatory cells (Tregs) that emerge directly from the thymus, Tr1 cells are induced by antigen stimulation via an IL-10-dependent process in vitro and in vivo. Specialized IL-10-producing dendritic cells, such as those in an immature state or those modulated by tolerogenic stimuli, play a key role in this process. We propose to use the term Tr1 cells for all IL-10-producing T-cell populations that are induced by IL-10 and have regulatory activity. The full biological characterization of Tr1 cells has been hampered by the difficulty in generating these cells in vitro and by the lack of specific marker molecules. However, it is clear that Tr1 cells play a key role in regulating adaptive immune responses both in mice and in humans. Further work to delineate the specific molecular signature of Tr1 cells, to determine their relationship with CD4+ CD25+ Tregs, and to elucidate their respective role in maintaining peripheral tolerance is crucial to advance our knowledge on this Treg subset. Furthermore, results from clinical protocols using Tr1 cells to modulate immune responses in vivo in autoimmunity, transplantation, and chronic inflammatory diseases will undoubtedly prove the biological relevance of these cells in immunotolerance.

Type I Regulatory T Cells in Autoimmunity and Inflammatory Diseases

Regulatory T cells exert a critical role in controlling autoimmunity and maintaining peripheral tolerance. The best described regulatory T cells are the naturally occurring CD4+CD25+ regulatory T cells, which have been shown to be continuously produced within the thymus. Other T-cell subsets bearing suppressive capacity have been reported, including T-helper-3 cells (Th3) and type 1 regulatory T (Tr1) cells. Tr1 cells have been shown to be induced upon antigen exposure under certain tolerogenic conditions and are characterized by the production of the immunosuppressive cytokines IL-10 and TGF-beta, while Th3 cells preferentially produce TGF-beta upon induction by intestinal tolerance. Recent progress has been made in the characterization of Tr1 cells in terms of isolation and induction, respectively. The present review provides an overview of the presence of Tr1 cells in inflammation, infection and neoplastic disorders. Moreover, the relationship between different regulatory T cell subsets and their transcriptional control is discussed. The recent development of methods allowing the ex vivo expansion of regulatory T cells may be the first step towards a cellular therapy with regulatory T cells to control T-cell-mediated pathology in inflammatory disorders.

IL-10-dependent infectious tolerance after the treatment of experimental allergic encephalomyelitis with redirected CD4+CD25+ T lymphocytes

How small numbers of CD4+CD25+ regulatory T cells suppress autoimmune responses in vivo is unclear. In this report we analyze the immunomodulatory activity of CD4+CD25+ T cells that are antigen-specifically redirected against myelin basic protein (MBP)89-101-specific autoreactive T cells by a MBP89-101-IA(s)-zeta chimeric receptor. We have previously shown that these redirected regulatory T cells are highly potent in treating a model autoimmune disease, experimental allergic encephalomyelitis. We show here that they have only limited effect in vivo on autoreactive T cell proliferation and therefore do not act by deleting or suppressing the expansion of pathologic effector cells. Rather, the redirected CD4+CD25+ T cells divert the pathologic T helper 1 self-specific T cell response to one characterized by high IL-10 and lower IL-4 production. Significantly, when isolated from the inducing CD4+CD25+ regulatory T cells, these self-specific T cells can independently suppress the autoreactive T cell response and experimental allergic encephalomyelitis development in an IL-10-dependent manner. These results provide evidence that CD4+CD25+ regulatory T cells can manipulate the adaptive immune response in vivo through the infectious induction of tolerance, specifically by promoting the formation of antigen-specific, IL-10-secreting regulatory T cells.

Human CD4+ regulatory T cells and activation-induced tolerance

In the past years growing attention has been given to the role of regulatory T (Tr) cells in inducing and monitoring peripheral tolerance. Various subsets of Tr cells have been described based on their surface phenotype and cytokine production. However, presently there are no specific reliable markers for any of the Tr subsets and their classification is based predominantly upon their mode of suppression. In addition, the molecular mechanisms underlying the induction and mode of action of all Tr cell subsets remain to be elucidated. Here we review recent developments regarding human CD4+ Tr cells, their origin, phenotype, antigen specificity and mode of suppression.

Utilizing regulatory T cells to control alloreactivity

Effective resetting of the immune system cannot be achieved by non-specific immunosuppression. Instead, novel strategies aim at harnessing the body's natural tolerance mechanisms to rectify an Ag-specific response without disturbing other immune functions. Fine-tuning of the balance between Ag-specific effector and regulatory T (Tr) cells is a promising strategy that requires detailed understanding of the differentiation and expansion pathways of the relevant Tr cell subsets. Here we review recent developments regarding the control of alloreactivity by induction and expansion of Tr cells. T-cell activation in the presence of tolerogenic APC and cytokines leads to the induction of Tr cells, which can mediate tolerance through cytokine-dependent and/or contact-dependent mechanisms. Better understanding of the mechanisms of immune regulation mediated by Tr cells may enable fine-tuning of specific immune responses and pave the way for novel therapeutic approaches.

IL-10-producing T regulatory type 1 cells and oral tolerance

Oral tolerance is mediated by multiple mechanisms such as anergy and/or active suppression of antigen-specific effector T cells by T regulatory (Tr) cells. Among the CD4(+) Tr cells, T regulatory type 1 cells (Tr1) have been shown to downmodulate immune responses through production of the immunosuppressive cytokines IL-10 and TGF-beta. Human Tr1 cells can be induced to differentiate in vitro by IL-10 1 IFN-alpha or after stimulation by immature dendritic cells (DCs) or DCs rendered tolerogenic by exposure to immunomodulatory compounds. Murine Tr1 cells can be induced to differentiate in vitro by activating naive CD4(+) T cells in the presence of high doses of IL-10. Several protocols for induction of oral tolerance, including oral administration of the antigen with IL-10, have been shown to induce antigen-specific Tr1 cells that suppress undesired immune responses toward self-antigens, allergens, and food antigens. Overall, these data demonstrate that IL-10-producing Tr1 cells play a central role in the induction of oral as well as systemic tolerance.

Specialization in tolerance: innate CD(4+)CD(25+) versus acquired TR1 and TH3 regulatory T cells

The regulation of immune responses to self-antigens is a complex process that involves maintaining self-tolerance while retaining the capacity to mount robust immune responses against invading microorganisms. Over the past few years, many new insights into this process have been gained, leading to the reemergence of the idea that regulatory T cells (Treg) are key players in immune regulation. These insights have raised fundamental questions concerning the definition of a Treg and what exactly constitutes T-cell-mediated suppression, identification of the signals and the cellular environment that promote the development and differentiation of these cells, and which signals maintain the homeostasis of the immune system. Thus far, the different models where Treg have been characterized cannot fully account for CD(4+)CD(25+) T cells. In this article, the authors propose the coexistence of two specialized types of CD(4+) Treg-innate and acquired-that differ in terms of their development, specificity, mechanisms, and sites of action.

Nasal instillation of gpMBP can exacerbate murine EAE: effect of mucosal priming is an age-dependent phenomenon

Nasal installation or oral feeding of antigens can alter the subsequent immune response in animals and humans. Most mucosal treatments with antigens tend to down-regulate disease, inducing full tolerance or immune deviation; however, priming has also been reported. We evaluated the course of experimental autoimmune encephalomyelitis (EAE) in (SJL x B10.PL)F1 mice after nasal instillation of myelin basic protein. There was a tendency towards exacerbation of subsequent disease in animals if they were nasally exposed to gpMBP during the neonatal period (first week of life), compared to exposure during adulthood. Later, at 11 months of age, this tendency to exacerbate disappeared. Our results suggest that mucosal exposure during early life may regularly modulate the anti-self immune response upwards in individuals genetically predisposed to autoimmune diseases.

Beneficial autoimmunity to proinflammatory mediators restrains the consequences of self-destructive immunity

Therapies that neutralize the function of TNF-alpha suppress rheumatoid arthritis (RA) but not osteoarthritis (OA). We show that patients suffering from RA but not OA have significant levels of autoantibodies directed to TNF-alpha. Thus, the immune system can selectively generate autoimmunity to proinflammatory mediators when such a response is beneficial for the host. A well-defined model of RA was used to elaborate the contribution of beneficial autoimmunity to the regulation of disease. We show that during the disease autoantibody production is elicited against few inflammatory, but not regulatory, mediators. Selective amplification of these beneficial antibodies by targeted DNA vaccines provided protective immunity. Epitope mapping revealed that anti-TNF-alpha immunity is highly restricted and excretes no crossreactivity to other known gene products. Its selective exclusion substantially exacerbated the disease. Administration of anti-TNF-alpha antibodies could then override this aggravation. This substantiates the significance of beneficial autoimmunity in restraining self-destructive immunity.