Control of T-cell activation by CD4+ CD25+ suppressor T cells

Deficiency of forkhead box P3 and cytotoxic T-lymphocyte-associated antigen-4 gene expressions and impaired suppressor function of CD4(+)CD25(+) T cells in patients with autoimmune hepatitis

AIM

Recently, forkhead box P3 (Foxp3), cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), glucocorticoid-induced tumor necrosis factor receptor family-related gene (GITR), and CD28 were identified as the key molecules that control the development and activation of CD4+CD25+ regulatory T cells (T-reg). We investigated the expression pattern of these molecules on T-reg, and investigated the ability of T-reg to produce cytokines in patients with autoimmune hepatitis (AIH).

METHODS

Fifteen patients with AIH and nine healthy patients were included. To determine the frequency of T-reg, a two-color flow cytometry analysis was performed. T-reg were isolated using immunomagnetic beads, and the mRNA levels of Foxp3, CTLA-4, GITR, and CD28 were quantified by real-time polymerase chain reaction (PCR). The ability of T-reg to produce interferon-gamma, interleukin (IL)-10, transforming growth factor-beta, and tumor necrosis factor-alpha after stimulation by OKT3 was evaluated by measuring the levels of mRNA in T-reg by real-time PCR.

RESULTS

The frequency of T-reg was increased in AIH. The mRNA levels of Foxp3 and CTLA-4 were significantly lower in AIH. The ability of T-reg to produce IL-10 was impaired in AIH.

CONCLUSION

We speculate that the inferiority of the Foxp3 and CTLA-4 gene expressions on T-reg results in the impaired suppressor function of T-reg, and eventually in the breakdown of self-tolerance.

Expression of ICOS on human melanoma-infiltrating CD4+CD25highFoxp3+ T regulatory cells: implications and impact on tumor-mediated immune suppression

OBJECTIVE

Interaction of ICOS with its ligand (ICOSL, B7-H2) promotes T cell responses. As CD4+CD25highFoxp3+ naturally occurring T regulatory cells in melanoma patients express ICOS, we investigated the impact of ICOS on naturally occurring T regulatory cell function.

METHODS

Expression of ICOS and T regulatory (Treg) cell markers was determined on CD4+CD25high T cells in PBMC and tumor-infiltrating lymphocytes from melanoma patients (n=10) and PBMC of normal controls (n=10) by multicolor flow cytometry. Suppression mediated by sorted ICOShigh and ICOSlow Treg was assessed in CFSE-based suppression assays with autologous CD4+CD25- responder cells (RC). Transwell inserts separating Treg from RC were used to evaluate suppression mechanisms used by Treg. ICOShigh or ICOSlow Treg were coincubated with RC+/-TCR and IL-2 stimulation. ICOShigh and ICOS- Treg were also expanded under conditions previously shown to induce Tr1 from RC.

RESULTS

Treg in tumor-infiltrating lymphocytes expressed ICOS (mean fluorescence intensity=70+/-10), while Treg in PBMC had low ICOS expression (mean fluorescence intensity=3.5+/-2.5, p<or=0.001). ICOShigh Treg up-regulated Treg markers (p<or=0.0016) and mediated stronger suppression (p<or=0.001) relative to ICOSlow Treg. ICOShigh Treg induced Tr1 cells in nonactivated RC and Th2 cells in preactivated RC. ICOShigh Treg exposed to Tr1 cytokines expressed IL-10 and suppressed RC (92+/-12%) in contrast to ICOSlow Treg, which mediated low suppression (21+/-15%; p<or=0.0028).

CONCLUSION

ICOShigh Treg can induce diverse immune responses in RC, depending on activation signals and cytokines present. ICOShigh Treg induce Tr1 or Th2 cells depending on the activation state of RC. In a "Tr1" cytokine milieu, ICOShigh Treg transit to Tr1.

Functional regulatory T cells accumulate in aged hosts and promote chronic infectious disease reactivation

Declines in immune function are well described in the elderly and are considered to contribute significantly to the disease burden in this population. Regulatory T cells (T(regs)), a CD4(+) T cell subset usually characterized by high CD25 expression, control the intensity of immune responses both in rodents and humans. However, because CD25 expression does not define all T(regs), especially in aged hosts, we characterized T(regs) by the expression of FOXP3, a transcription factor crucial for T(reg) differentiation and function. The proportion of FOXP3(+)CD4(+) T(regs) increased in the blood of the elderly and the lymphoid tissues of aged mice. The expression of functional markers, such as CTLA-4 and GITR, was either preserved or increased on FOXP3(+) T(regs) from aged hosts, depending on the tissue analyzed. In vitro depletion of peripheral T(regs) from elderly humans improves effector T cell responses in most subjects. Importantly, T(regs) from old FoxP3-GFP knock-in mice were suppressive, exhibiting a higher level of suppression per cell than young T(regs). The increased proportion of T(regs) in aged mice was associated with the spontaneous reactivation of chronic Leishmania major infection in old mice, likely because old T(regs) efficiently suppressed the production of IFN-gamma by effector T cells. Finally, in vivo depletion of T(regs) in old mice attenuated disease severity. Accumulation of functional T(regs) in aged hosts could therefore play an important role in the frequent reactivation of chronic infections that occurs in aging. Manipulation of T(reg) numbers and/or activity may be envisioned to enhance the control of infectious diseases in this fragile population.

The influence of IL-2 family cytokines on activation and function of naturally occurring regulatory T cells

IL-2 is essential for CD4+CD25+forkhead box P3+ (FoxP3+) naturally occurring regulatory T cell (Treg) homeostasis and activation. Binding of IL-2 to its receptor leads to phosphorylation of STAT5, and binding of phosphorylated STAT5 to the foxp3 promoter increases foxp3 transcription, resulting in elevated levels of FoxP3 protein in Tregs. Transcriptional regulation by the elevated levels of FoxP3 is thought to be essential for the strong suppressor function seen in activated Tregs. IL-2 belongs to a family cytokines, which all depend on the common gamma-receptor chain (gammac). Given the well-documented effects of IL-2 on Treg function, the effect of other IL-2 family cytokines (IL-7, -15, and -21) on Tregs was examined. We observed that IL-7 and IL-15 induce STAT5 phosphorylation and up-regulation of FoxP3 in Tregs. STAT5 activation correlated with enhanced viability. However, only in the presence of IL-2 did Tregs acquire potent suppressor function. This finding is surprising, as IL-15 as well as IL-2 use the same IL-2R betac and gammac for signaling. In contrast, IL-21 activated STAT3 but did not activate STAT5 and had no effect on Treg viability, activation, or function. We therefore conclude that phosphorylation of STAT5, mediated through the IL-2Rgamma, promotes Treg survival in a resting and activated state. However, activation of STAT5 alone in conjunction with TCR signaling is not sufficient for the induction of potent suppressor function in Tregs, as IL-7 and IL-15 are not capable of inducing potent Treg suppressor function.

IL-10 and natural regulatory T cells: two independent anti-inflammatory mechanisms in herpes simplex virus-induced ocular immunopathology

Two prominent anti-inflammatory mechanisms involved in controlling HSV-1-induced corneal immunopathology (stromal keratitis or SK) are the production of the cytokine IL-10 and the activity of natural regulatory T cells (nTregs). It is not known whether, under in vivo conditions, IL-10 and nTregs influence the corneal pathology independently or in concert. In the current study using wild-type and IL-10(-/-) animals, we have assessed the activity of nTregs in the absence of IL-10 both under in vitro and in vivo conditions. The IL-10(-/-) animals depleted of nTregs before ocular infection showed more severe SK lesions as compared with the undepleted IL-10(-/-) animals. In addition, nTregs purified from naive WT and IL-10(-/-) animals were equally able to suppress the proliferation and the cytokine production from anti-CD3-stimulated CD4(+)CD25(-) T cells in vitro. Furthermore, intracellular cytokine staining results indicated that nonregulatory cells expressing B220 and CD25 markers were the major IL-10-producing cell types in the lymphoid tissues of HSV-infected mice. In contrast, in the infected corneas, cells with the CD11b(+)Gr1(+) phenotype along with a minor population of Foxp3(-)CD4(+) and a few F4/80(+) cells produced IL-10. Our current investigations indicate that at least two independent anti-inflammatory mechanisms are involved in limiting the corneal lesions in SK, both of which may need to be modulated to control SK therapeutically.

Latency-associated peptide identifies a novel CD4+CD25+ regulatory T cell subset with TGFbeta-mediated function and enhanced suppression of experimental autoimmune encephalomyelitis

CD4(+)CD25(+) regulatory T cells (Tregs) are essential for maintaining self-tolerance and immune homeostasis. Here we characterize a novel subset of CD4(+)CD25(+) Tregs that express latency-associated peptide (LAP) on their cell surface (CD4(+)CD25(+)LAP(+) cells). CD4(+)CD25(+)LAP(+) cells express elevated levels of Foxp3 and Treg-associated molecules (CTLA4, glucocorticoid-induced TNFR-related gene), secrete TGFbeta, and express both cell surface TGFbeta and surface receptors for TGFbeta. In vitro, the suppressive function of CD4(+)CD25(+)LAP(+) cells is both cell contact and soluble factor dependent; this contrasts with CD4(+)CD25(+)LAP(-) cells, which are mainly cell contact dependent. In a model of experimental autoimmune encephalomyelitis, CD4(+)CD25(+)LAP(+) cells exhibit more potent suppressive activity than CD4(+)CD25(+)LAP(-) cells, and the suppression is TGFbeta dependent. We further show that CD4(+)CD25(+)LAP(+) cells suppress myelin oligodendrocyte glycoprotein-specific immune responses by inducing Foxp3 and by inhibiting IL-17 production. Our findings demonstrate that CD4(+)CD25(+) Tregs are a heterogeneous population and that the CD4(+)CD25(+) subset that expresses LAP functions in a TGFbeta-dependent manner and has greater in vivo suppressive properties. Our work helps elucidate the ambiguity concerning the role of TGFbeta in CD4(+)CD25(+) Treg-mediated suppression and indicates that LAP is an authentic marker able to identify a TGFbeta-expressing CD4(+)CD25(+) Treg subset.

Effect of house dust mite immunotherapy on transforming growth factor beta1-producing T cells in asthmatic children

BACKGROUND

Recent evidence suggests that regulatory T cells (Treg cells) and immunosuppressive cytokines, such as transforming growth factor BETA1 (TGF-BETA1) and interleukin 10 (IL-10), may have a role in clinically effective allergen specific immunotherapy (SIT).

OBJECTIVE

To evaluate the effect of SIT on the induction of Treg cells in house dust mite-allergic children and on the expression of specific Treg cell markers (cytotoxic T-lymphocyte-associated protein 4 [CTLA-4], IL-10, and TGF-BETA1).

METHODS

In this uncontrolled open-label study, the percentage of peripheral blood CD4+ Treg cells (CD69 CD45RO+CTLA-4+ and CD3+CD4+CD25+FOXP3+) and the expression of molecules associated with their functions (CTLA-4, TGF-BETA1, and IL-10) were analyzed using flow cytometry in 16 children allergic to house dust mites before and at 3 and 12 months of subcutaneous SIT. Clinical variables, such as symptom score, medication requirements, forced expiratory volume in 1 second, peak expiratory flow rate, and serum IgE levels, were also determined. Ten healthy children were included as controls.

RESULTS

All the clinical variables improved during immunotherapy. The percentage of CD4+CD25+CD69-CD45RO+ Treg cells remained unchanged. The percentage of CTLA-4+ -expressing Treg cells transiently increased after 3 months of immunotherapy, whereas the percentage of FOXP3+ Treg cells did not change after 1 year of immunotherapy. Levels of IL-10+ cells transiently decreased after 3 months of immunotherapy. Four children who required inhaled fluticasone propionate administration for significant symptom worsening had no statistically significant increase in TGF-BETA1-secreting T cells at 12 months of SIT, in contrast to 12 children without inhaled corticosteroid treatment.

CONCLUSIONS

The increase in TGF-BETA1-positive T cells only in children without significant symptom worsening requiring inhaled corticosteroid treatment limits the usefulness of TGF-BETA1 in monitoring response to allergen immunotherapy.

Lentivirus-induced immune dysregulation

FIV/HIV infections are associated with an early robust humoral and cellular anti-viral immune response followed by a progressive immune suppression that eventually results in AIDS. Several mechanisms responsible for this immune dysfunction have been proposed including cytokine dysregulation, immunologic anergy and apoptosis, and inappropriate activation of immune regulatory cells. Studies on FIV infection provide evidence for all three. Cytokine alterations include decreases in IL2 and IL12 production and increases in IFNgamma and IL10 in FIV(+) cats compared to normal cats. The elevated IL10:IL12 ratio is associated with the inability of FIV(+) cats to mount a successful immune response to secondary pathogens. Additionally, chronic antigenic (FIV) stimulation results in an increase in the percent of activated T cells expressing B7 and CTLA4 co-stimulatory molecules in infected cats. The expression of these molecules is associated with T cells that are undergoing apoptosis in the lymph nodes. As ligation of CTLA4 by B7 transduces a signal for induction of anergy, one can speculate that the activated T cells are capable of T cell-T cell interactions resulting in anergy and apoptosis. The inability of CD4(+) cells from FIV(+) cats to produce IL2 in response to recall antigens and the gradual loss of CD4(+) cell numbers could be due to B7-CTLA4 interactions. The chronic antigenemia may also lead to activation of CD4(+)CD25(+) T regulatory cells. Treg cells from FIV(+) cats are chronically activated and inhibit the mitogen-induced proliferative response of CD4(+)CD25(-) by down-regulating IL2 production. Although Treg cell activation can be antigen-specific, the suppressor function is not, and thus activated Treg cells would suppress responses to secondary pathogens as well as to FIV. Concomitant with the well-known virus-induced immune suppression is a progressive immune hyper-activation. Evidence for immune hyper-activation includes polyclonal B cell responses, gradual replacement of naïve CD4(+) and CD8(+) T cell phenotypes with activation phenotypes (CD62L(-), B7(+), CTLA4(+)), and the chronic activation of CD4(+)CD25(+) Treg cells. Thus lentivirus infections lead to severe immune dysregulation manifested as both chronic immune suppression and chronic immune activation. FIV infection of cats provides a number of advantages over other lentivirus infections as a model to study this immune dysregulation. It is a natural infection that has existed in balance with the cat's immune system for thousands of years. As such, the natural history and pathogenesis provides an excellent model to study the long-term relationships between AIDS lentivirus and host immune system function/dysregulation.

Regulatory T cells and human disease

The main function of our immune system is to protect us from invading pathogens and microorganisms by destroying infected cells, while minimizing collateral damage to tissues. In order to maintain this balance between immunity and tolerance, current understanding of the immune system attributes a major role to regulatory T cells (Tregs) in controlling both immunity and tolerance. Various subsets of Tregs have been identified based on their expression of cell surface markers, production of cytokines, and mechanisms of action. In brief, naturally occurring thymic-derived CD4+CD25+ Tregs are characterized by constitutive expression of the transcription factor FOXP3, while antigen-induced or adaptive Tregs are mainly identified by expression of immunosuppressive cytokines (interleukin-10 (IL-10) and/or transforming growth factor-beta (TGF-beta)). While Tregs in normal conditions regulate ongoing immune responses and prevent autoimmunity, imbalanced function or number of these Tregs, either enhanced or decreased, might lead, respectively, to decreased immunity (e.g., with tumor development or infections) or autoimmunity (e.g., multiple sclerosis). This review will discuss recent research towards a better understanding of the biology of Tregs, their interaction with other immune effector cells, such as dendritic cells, and possible interventions in human disease.

Advances in type I diabetes associated tolerance mechanisms

Type 1 diabetes (T1D) is an autoimmune disease resulting from the destruction of insulin-producing pancreatic beta cells by autoreactive T cells. The polygenic trait for T1D risk implicates many genes that have an impact on fundamental immunological processes such as central and peripheral tolerance. Several pieces of evidence have suggested that many of the genetic loci that are directly linked to type 1 diabetes susceptibility modulate the generation and/or the activation of autoreactive T-lymphocytes. We and others have proposed a critical role for medullary thymic epithelial cells (mTEC) forming the Hassall's corpuscles in T-cell tolerance. Indeed, mTEC have been found to express promiscuous self-antigens, used directly or through thymic dendritic cells to drive either negative selection of insulin-reacting precursors or their differentiation into naturally occurring regulatory Foxp3+ CD4+ CD25+ T cells. In the periphery, naturally occurring Foxp3+ CD4+ CD25+regulatory T (Treg) cells represent the master cells in dominant peripheral T-cell tolerance. The development and function of Treg cells are ultimately linked to IL-2 and Foxp3 expression. This review addresses recent literature and emerging concepts of central and peripheral T-cell tolerance with regards to T1D.

Foxp3 expression in CD4+ T cells of patients with systemic lupus erythematosus: a comparative phenotypic analysis

OBJECTIVES

The forkhead family transcription factor Foxp3 currently represents the most specific marker molecule for CD4(+)CD25(+) T cells with suppressive/regulatory capacity (Treg) in the mouse. Recent studies in the human system, however, indicate that the expression of Foxp3 can be T cell activation dependent. This tempted us to evaluate the significance of Foxp3 expression under autoimmune conditions with chronic T cell activation in patients with systemic lupus erythematosus (SLE) as compared with healthy controls (HCs).

METHODS

Proportions of peripheral blood CD4(+)Foxp3(+) T cells and CD4(+)CD25(high) T cells were determined in patients with active and inactive SLE as compared with HC by flow cytometry. Comparative analysis of the percentage of CD4(+)Foxp3(+) T cells and of percentage of CD4(+)CD25(high) T cells with clinical disease activity and T cell activation marker molecule expression were performed. Finally, the induction of Foxp3 expression was analysed upon T cell activation in vitro.

RESULTS

Proportions of CD4(+)Foxp3(+) T cells were significantly increased in patients with SLE as compared with HC and a significant correlation was observed between clinical disease activity and proportions of CD4(+)Foxp3(+) T cells. On the other hand, proportions of CD4(+)CD25(high) were decreased in SLE and no correlation with a T cell activation marker expression of was observed. In addition, in vitro activation of T cells induced Foxp3 expression.

CONCLUSIONS

Our data suggest that the expression of Foxp3 on CD4(+) T cells in patients with SLE, at least to some extent, reflects the activation of CD4(+) T cells due to underlying disease activity and does not necessarily indicate a functional regulatory T cell capacity.

The relationship of FOXP3 expression and clinicopathological characteristics in adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma is an aggressive malignant disease associated with regulatory T cells as discussed in some recent reports. We analyzed the expression of FOXP3, a key molecule of regulatory T cells, in adult T-cell leukemia/lymphoma and its association with clinicopathological features. Of 169 adult T-cell leukemia/lymphoma cases examined, 60 (36%) showed FOXP3 expression in lymphoma cells. Morphologically, 22 cases were classified as anaplastic large cell variant and 147 as pleomorphic cell variant. Only 1 (5%) of the anaplastic large cell variant cases and 59/147 (40%) of the pleomorphic cell variant cases expressed FOXP3. Epstein-Barr virus-infected cells were significantly more frequently found in FOXP3(+) cases (23/60; 38%) than in FOXP3(-) cases (12/109; 11%) (P<0.0001). Cytogenetic analysis showed that FOXP3(+) cases had simpler chromosomal abnormalities than FOXP3(-) cases. Clinically, FOXP3(+) and FOXP3(-) cases did not differ significantly in age distribution, clinical stage, lactate dehydrogenase and calcium in serum and overall survival. However, 8 of 34 FOXP3(+) cases suffered a severe infectious state, an indication of immunosuppression, while only 2 of 62 FOXP3(-) cases did so (P<0.005). FOXP3 expression in adult T-cell leukemia/lymphoma thus reflects morphological features and is clinically and pathologically associated with an immunosuppressive state.

Long-chain polyunsaturated fat supplementation in children with low docosahexaenoic acid intakes alters immune phenotypes compared with placebo

OBJECTIVES

The objectives of this study were to assess the effects of long-term supplementation with arachidonic acid (AA; 20:4n-6) and docosahexaenoic acid (DHA; 22:6n-3) on cell phenotypes and cytokine production in children.

PATIENTS AND METHODS

This randomized, double-blind, placebo-controlled trial provided children, (ages 5-7 years; n = 37) who had low intakes of DHA, with a dietary supplement containing AA (20-30 mg daily) and DHA (14-21 mg daily) or a placebo supplement for 7 months. After the supplementation period, a series of stimulants (pokeweed mitogen, phytohemagluttinin, lipopolysaccharide, beta-lactoglobulin, and ibuprofen) was used to stimulate peripheral blood mononuclear cells ex vivo. Antigen expression on T cells (CD25 and CD80), B cells, and macrophages (CD54), as well as cytokine production (interleukin [IL]-4, IL-10, tumor necrosis factor, IL-2, IL-6, and interferon-gamma), were measured using flow cytometry, monoclonal antibodies, and cytometric bead array, respectively.

RESULTS

Mononuclear cells from children provided long-chain polyunsaturated fatty acids (LCPUFAs) had fewer CD8+ cells expressing CD25 and CD80 compared with placebo after exposure to each mitogen. The LCPUFA group also exhibited lower proportions of CD14+ cells after stimulation with beta-lactoglobulin and ibuprofen. The proportion of CD54+ cells was 2-fold higher for the LCPUFA group compared with placebo after exposure to ibuprofen and beta-lactoglobulin (P < 0.05). Each of these immune effects related to the amount of AA and/or DHA in the plasma and erythrocyte phospholipids.

CONCLUSIONS

Alterations in cell phenotypes were evident when children were supplemented with AA and DHA. The results of this study have important implications for immune development and sensitivity to antigens in children.

Identification and in vitro expansion of functional antigen-specific CD25+ FoxP3+ regulatory T cells in hepatitis C virus infection

CD4(+)CD25(+) regulatory T cells (CD25(+) Tregs) play a key role in immune regulation. Since hepatitis C virus (HCV) persists with increased circulating CD4(+)CD25(+) T cells and virus-specific effector T-cell dysfunction, we asked if CD4(+)CD25(+) T cells in HCV-infected individuals are similar to natural Tregs in uninfected individuals and if they include HCV-specific Tregs using the specific Treg marker FoxP3 at the single-cell level. We report that HCV-infected patients display increased circulating FoxP3(+) Tregs that are phenotypically and functionally indistinguishable from FoxP3(+) Tregs in uninfected subjects. Furthermore, HCV-specific FoxP3(+) Tregs were detected in HCV-seropositive persons with antigen-specific expansion, major histocompatibility complex class II/peptide tetramer binding affinity, and preferential suppression of HCV-specific CD8 T cells. Transforming growth factor beta contributed to antigen-specific Treg expansion in vitro, suggesting that it may contribute to antigen-specific Treg expansion in vivo. Interestingly, FoxP3 expression was also detected in influenza virus-specific CD4 T cells. In conclusion, functionally active and virus-specific FoxP3(+) Tregs are induced in HCV infection, thus providing targeted immune regulation in vivo. Detection of FoxP3 expression in non-HCV-specific CD4 T cells suggests that immune regulation through antigen-specific Treg induction extends beyond HCV.

Regulatory T cell-derived interleukin-10 limits inflammation at environmental interfaces

The regulatory T (Treg) cells restrain immune responses through suppressor-function elaboration that is dependent upon expression of the transcription factor Foxp3. Despite a critical role for Treg cells in maintaining lympho-myeloid homeostasis, it remains unclear whether a single mechanism or multiple mechanisms of Treg cell-mediated suppression are operating in vivo and how redundant such mechanisms might be. Here we addressed these questions by examining the role of the immunomodulatory cytokine IL-10 in Treg cell-mediated suppression. Analyses of mice in which the Treg cell-specific ablation of a conditional IL-10 allele was induced by Cre recombinase knocked into the Foxp3 gene locus showed that although IL-10 production by Treg cells was not required for the control of systemic autoimmunity, it was essential for keeping immune responses in check at environmental interfaces such as the colon and lungs. Our study suggests that Treg cells utilize multiple means to limit immune responses. Furthermore, these mechanisms are likely to be nonredundant, in that a distinct suppressor mechanism most likely plays a prominent and identifiable role at a particular tissue and inflammatory setting.

Microbial products trigger autoimmune ocular inflammation

PURPOSE

Microbial products stimulate the immune system by interacting with Toll-like receptors (TLR) on antigen-presenting cells. This study examined the hypothesis that microbial products, which function as TLR ligands, are playing a major role in triggering pathogenic autoimmunity.

METHODS

An experimental system was developed in which microbial TLR ligands were tested in vivo for their capacity to stimulate naïve CD4 cells specific against hen egg lysozyme (HEL) to become effector cells capable of inducing inflammation in eyes in which HEL is expressed. The ligands' mode of action was analyzed by determining their effects on the proliferation, acquisition of tissue-invading capacity, i.e. elevated CD49d and decreased CD62L expression, and production of interferon-gamma by the HEL-specific cells.

RESULTS

All the 7 tested TLR ligands triggered ocular inflammation in the experimental system used here, with pertussis toxin surpassing all other ligands in its activities. A correlation was found between the capacity of the ligands to trigger pathogenic immunity and to stimulate the proliferation, modification of cell surface and interferon-gamma production by T cells.

CONCLUSIONS

This study provides direct evidence to support the notion that microbial products are capable of triggering pathogenic autoimmunity.

IL-10 and the resolution of infections

Chronic viral infections pose serious health concerns, as secondary complications such as immunodeficiencies and cancers are common. Treating such infections with conventional vaccine approaches has proved to be difficult. Studies in animals and humans suggest that vaccine failure is probably due to exhaustion of antiviral T cell responses, which occurs in a number of chronic infections. Attempts to elucidate the causes of impairment of antiviral immunity have pointed to a role for the immunomodulatory cytokine IL-10 in the ability of viruses to establish persistence. Induction of IL-10 production by the host during chronic infection appears to be one of the viral means to alter the class of the antiviral immune response and induce generalized immune suppression. Recent work by us and others suggests that it is possible to resuscitate antiviral immunity by interfering with the IL-10 signalling pathway. Targeting IL-10 thus constitutes a promising alternative to conventional vaccine strategies which have not proved to be successful in treating chronic infections. In addition, sterile cure may be achieved with minimal side-effects by combining agents that alter the IL-10 signalling pathway with other compounds, such as antiviral drugs or interferon, but also agents neutralizing other crucial elements of T cell exhaustion, such as PD-1.

Cutting edge: mechanism of enhancement of in vivo cytokine effects by anti-cytokine monoclonal antibodies

Inhibitory anti-cytokine mAbs are used to treat cytokine-mediated disorders. Recently, however, S4B6, an anti-IL-2 mAb that blocks IL-2 binding to IL-2Ralpha, a receptor component that enhances affinity but is not required for signaling, was shown to enhance IL-2 agonist effects in vivo. We evaluated how S4B6 enhances IL-2 effects and whether a similar mechanism allows mAbs to IL-4 to enhance IL-4 effects. Induction of T cell proliferation by IL-2/S4B6 complexes did not require complex dissociation and was IL-2Ralpha independent. S4B6 increased IL-2 agonist effects by increasing in vivo half-life, not by focusing IL-2 onto cells through Fc receptors. In contrast to IL-2/S4B6 complexes, anti-IL-4 mAb enhancement of in vivo IL-4 effects required IL-4/anti-IL-4 mAb complex dissociation. Thus, agonist effects observed with high doses of anti-IL-2 mAb are most likely only applicable for mAbs that maintain cytokine half-life without blocking binding to receptor signaling components.

Potent in vivo anti-tumor activity of isolated CD62L(low) lymph node cells sensitized in vivo with tumor lysate-pulsed DC-based vaccines

BACKGROUND

DC are potent APC that can activate both CD4 and CD8 T cells in vitro and in vivo. Although the efficacy of DC-based cancer vaccines is currently being evaluated in clinical trials, the systemic immune suppression in cancer patients negatively impacts the clinical benefit of this therapeutic approach. Therefore, in this study we tested the feasibility and anti-tumor effect of adoptive immunotherapy using in vitro-activated CD62L(low) lymph node cells that were isolated from DC-vaccinated draining lymph nodes (VDLN).

METHODS

DC were prepared from BM cells and loaded with tumor lysate for inoculating into naive mice. Subsequently, the VDLN were removed and CD62L(low) cells in the VDLN population isolated, expanded in vitro by 5-day culture with IL-2 and immobilized anti-CD3 stimulation, then injected into mice with established pulmonary tumors. Eighteen days after treatment, mice were killed in order to enumerate pulmonary tumor nodes.

RESULTS

DC phagocytosed the tumor lysate efficiently and induced detectable T-cell responses and significant cell expansion in the draining lymph nodes. After induction of maturation by LPS treatment, DC expressed higher levels of CD40, CD86 and MHC class II molecules. When CD62L(low) VDLN cells that had been isolated and expanded in vitro were transferred into tumor-bearing mice, as few as 3 x 10(6) cells were able to cure metastatic pulmonary tumors in vivo.

DISCUSSION

DC-based VDLN T cells are an important source of anti-tumor effector for adoptive immunotherapy. This study provides a novel and an effective protocol using T-cell adoptive immunotherapy for application in cancer patients; therefore, clinical trials based on this protocol may be warranted.

Induction of EBV-latent membrane protein 1-specific MHC class II-restricted T-cell responses against natural killer lymphoma cells

EBV-encoded latent membrane protein 1 (LMP1) has oncogenic potential and is expressed in many EBV-associated malignancies. Although LMP1 is regarded as a potential tumor-associated antigen for immunotherapy and several LMP1-specific MHC class I-restricted CTL epitopes have been reported, little is known regarding MHC class II-restricted CD4 helper T-lymphocyte (HTL) epitopes for LMP1. The goal of the present studies was to determine whether MHC class II-restricted CD4 T-cell responses could be induced against the LMP1 antigen and to evaluate the antitumor effect of these responses. We have combined the use of a predictive MHC class II binding peptide algorithm with in vitro vaccination of CD4 T cells using candidate peptides to identify naturally processed epitopes derived from LMP1 that elicit immune responses against EBV-expressing tumor cells. Peptide LMP1(159-175) was effective in inducing HTL responses that were restricted by HLA-DR9, HLA-DR53, or HLA-DR15, indicating that this peptide behaves as a promiscuous T-cell epitope. Moreover, LMP1(159-175)-reactive HTL clones directly recognized EBV lymphoblastoid B cells, EBV-infected natural killer (NK)/T-lymphoma cells and naturally processed antigen in the form of LMP1+ tumor cell lysates presented by autologous dendritic cells. Because the newly identified epitope LMP1(159-175) overlaps with an HLA-A2-restricted CTL epitope (LMP1(159-167)), this peptide might have the ability to induce simultaneous CTL and HTL responses against LMP1. Overall, our data should be relevant for the design and optimization of T-cell epitope-based immunotherapy against various EBV-associated malignancies, including NK/T cell lymphomas.

T lymphocytes in Sjögren's syndrome: contributors to and regulators of pathophysiology

Sjögren's syndrome is a chronic autoimmune disorder characterized by lymphocytic infiltration and malfunction of the exocrine glands, resulting in dry mouth and eyes. This multigenic and multifunctional disease can present as primary Sjögren's syndrome or secondary to an underlying connective tissue disease. Immune activation subsequent to activation or apoptosis of glandular epithelial cells in genetically predisposed individuals may expose autoantigens, which engage self-perpetuating T cell dependent autoimmune sequelae. The cellular and molecular context of this immune response may drive proinflammatory (Th1 and Th17) and restrain inhibitory (Treg) pathways. Inability to suppress the immune response results in persistent tissue damage and compromised function of salivary and lacrimal glands. Defining the contributions of participating T cells may unravel strategies for therapeutic intervention.

Matured human monocyte-derived dendritic cells (MoDCs) induce expansion of CD4+CD25+FOXP3+ T cells lacking regulatory properties

Naturally occurring CD4(+)CD25(+) T regulatory cells (nTregs) play a key role as suppressors in immune mechanisms that protect against self-destruction. The forkhead box p3 transcription factor (FOXP3) has a central role in the development of nTregs. We show here that co-culture of naïve T cells with flagellin-exposed monocyte-derived dendritic cells (MoDCs) generates CD4(+)CD25(+)FOXP3(+) T cells that transiently express FOXP3 together with CD25 but do not suppress proliferation of CD4(+)CD25(-) T cells. Moreover, purified CD4(+)CD25(+)FOXP3(+) T cells reveal a different proliferation and cytokine production profile from that of nTregs. These data indicate that in the presence of ongoing immune responses a T cell antigenic phenotype superimposable of that of nTregs does not necessarily predict suppressive function and that FOXP3 in humans is not sufficient for development and function of regulatory T cells.

Circulating CD4+ CD25+ regulatory T cells correlate with chronic hepatitis B infection

Circulating CD4+ CD25+ regulatory T cells (Tregs) have been demonstrated to maintain immunotolerance and suppress the antigen-specific or antigen-non-specific T-cell responses, but their role in chronic hepatitis B (CHB) infection in humans has not been well characterized. In this study, we analysed the frequency and phenotypic characteristics of CD4+ CD25+ Tregs in patients of different hepatitis B virus (HBV) infection status, and investigated the effect of Tregs on antiviral immune responses in CHB patients, and the mechanism of this effect. A total of 137 subjects, including 79 CHB patients, 26 asymptomatic HBV carriers (ASCs), 12 acute hepatitis B (AHB) patients and 20 healthy controls, were enrolled in the study. We found that the frequency of CD4+ CD25(high) Tregs in AHB patients was comparable to that in healthy controls, while it was significantly increased in CHB patients. CD4+ CD25+ Tregs produced interleukin (IL)-10 but little or no interferon (IFN)-gamma under anti-CD3 stimulation. In CHB patients, the frequency of CD4+ CD25(high) Tregs positively correlated with serum viral load, and the Tregs were capable of suppressing the proliferation and IFN-gamma production of autologous peripheral blood mononuclear cells (PBMC) mediated by HBV antigen stimulation in vitro. However, combined administration of anti-programmed death-1 (PD-1) and anti-cytotoxic lymphocyte antigen-4 (CTLA-4) monoclonal antibody slightly enhanced the cellular proliferation and significantly increased the IFN-gamma production of PBMC cocultured with Tregs at a ratio of 2:1. Thus, the frequency of circulating CD4+ CD25+ Tregs is increased in patients with CHB, and this may play an important role in viral persistence by modulating virus-specific immune responses.

Lymphocyte subpopulations in human exposure to metals (IUPAC Technical Report)

Numerous species of metal ions cause immunosensitization in humans. Possible approaches to determine those occupational and environmental exposures to metals that result in immunological changes include lymphocyte transformation assay, cytokine profiling, and measurement of lymphocyte subpopulations. In two previous papers, we considered lymphocyte transformation assay [1] and cytokine profiling [2]. Here we review the effects of exposures to metals on lymphocyte subpopulations. Specific consideration is given to beryllium, chromium, cobalt, nickel, palladium and platinum, cadmium, gold, mercury, and lead. Analysis of the scientific literature shows that immunosensitizing metals may have influences on the lymphocyte subset composition, but only in a few instances does exposure to metals cause reproducible shifts of lymphocyte subpopulations. If lymphocyte subpopulations are analyzed, each diagnostic step, including indication, sample handling, analytic procedure, and data interpretation, should adhere to good quality assurance and quality control.

The effects of antibody treatment on regulatory CD4(+)CD25(+) T cells

Current therapeutic antibodies, at least some, possess the capacity to induce immune tolerance in experimental models with allo-grafts or autoimmune diseases. Clinical application of humanized or chimeric antibodies to treat graft rejection or autoimmune diseases is presently underway. It is now becoming clear that immune tolerance can be acquired in some cases due to the action of regulatory T cells (Tregs), especially CD4(+)CD25(+) Tregs. In addition to their inhibition on immune response, some antibodies could promote tolerance induction in organ transplantation and autoimmune diseases essentially through the induction of Tregs. In this manuscript, we review the recent progress on the effects of therapeutic antibodies on the development, phenotypic changes and functions of CD4(+)CD25(+) Tregs.

Central role of ILT3 in the T suppressor cell cascade

CD8+ T suppressor cells differentiate both in vivo and in vitro upon chronic exposure of responding T cells to allogeneic APC. These Ts are allospecific and exhibit their function interacting directly with priming APC which they render tolerogenic. Tolerogenicity of professional and non-professional human APC, such as dendritic cells and endothelial cells, respectively is due to the upregulation of the inhibitory receptors ILT3 and ILT4. ILT3 signals both intracellularly, inhibiting NF-kappaB activation, and transcription of costimulatory molecules, and extracellularly, inducing anergy and regulatory function in T cells with cognate specificity. Both membrane and soluble ILT3 are proteins with potent immunosuppressive activity which are of importance for treatment of rejection, autoimmunity and cancer.

Resistance to apoptosis and expansion of regulatory T cells in relation to the detection of circulating tumor cells in patients with metastatic epithelial cancer

Regulatory T cells may be crucial in the development of T cell tolerance to malignancies and contribute to immune dysfunctions. We investigated the percentage, activity, and onset of apoptosis of T cell subpopulations by multicolor flow cytometry in metastatic epithelial cancer patients compared to normal controls. Furthermore, a possible relationship between the presence of circulating tumor cells detected by immunocytochemistry and immune cell abnormalities was evaluated. Our study demonstrated a significantly elevated proportion of regulatory T cells in cancer patients (p < 0.001). In contrast to all other T cell subpopulations, regulatory T cells showed comparable Annexin V-binding characteristics in patients and normal controls. No relationship between the detection of circulating tumor cells and immune dysfunction was observed. These results indicate that cancer patients have a higher number of regulatory T cells with resistance to apoptotic stimuli partly responsible for immune dysfunctions as often observed in cancer patients.

Hydrodynamic vaccination with DNA encoding an immunologically privileged retinal antigen protects from autoimmunity through induction of regulatory T cells

The eye is an immunologically privileged organ whose Ags serve as targets for experimental autoimmune uveitis (EAU), a model for human uveitis. We used a hydrodynamic i.v. injection of naked DNA to express the uveitogenic retinal Ag interphotoreceptor retinoid-binding protein (IRBP) in the periphery, thus revoking its immune-privileged status. IRBP was expressed in the liver within hours of administration of as little as 10 microg of IRBP-DNA. Vaccinated mice were highly protected from EAU induced by immunization with IRBP for at least 10 wk after vaccination. Protection was partial in a reversal protocol. Mechanistic studies revealed specific hyporesponsiveness to IRBP without immune deviation, no evidence for apoptosis either by the Fas- or Bcl-2-regulated (mitochondrial) pathway and apparent lack of dependence on CD8(+) cells, IL-10, or TGF-beta. In contrast, depletion of CD25(+) cells after vaccination and before challenge markedly abrogated protection. IRBP-specific CD4(+)CD25(high) T cells could be cultured from vaccinated mice and transferred protection to unvaccinated, EAU-challenged recipients. In vitro characterization of these cells revealed that they are Ag specific, anergic, express FoxP3, CTLA-4, and glucocorticoid-induced TNFR, and suppress by contact. Thus, expression of IRBP in the periphery by DNA vaccination results in tolerance that acts at least in part through induction of IRBP-specific, FoxP3(+)CD4(+)CD25(+) regulatory T cells. DNA vaccination may offer a new approach to Ag-specific therapy of uveitis.

Increased frequency of CD4(+)CD25(high) Treg cells inhibit BCG-specific induction of IFN-gamma by CD4(+) T cells from TB patients

Cell-mediated immunity plays a considerable role in the protection against Mycobacterium tuberculosis infection. The immune response to tuberculosis (TB) was dominated by both CD4(+) T cells with the T helper 1 type cytokines and CD8(+) T cells. Recent studies have suggested that the circumstances in which protective or tissue-damaging T cell responses to microbes are affected by the activity of Treg (CD4(+)CD25(high)) cells. In the present study, we demonstrated that the frequencies of CD4(+)CD25(+) and CD4(+)CD25(high) T cells in TB patients were significantly higher compared to normal individuals. These Treg cells expressed CTLA-4 and Foxp3 at protein level and displayed activation and memory phenotypes as assessed by flow cytometric analysis. The frequencies of CD4(+)CD25(high)CTLA-4(+) and CD4(+)CD25(high)Foxp3(+) T cells within the total CD4(+) T cell population were significantly increased in the blood of TB patients compared to healthy donors. Moreover, the expression of GITR on Treg cells was higher in TB patients than in normal donors. The phenotypic analysis demonstrated that CD4(+)CD25(high) Treg expressed higher levels of CD45RO and HLA-DR, and lower levels of CD45RA compared to CD4(+)CD25(low) and CD4(+)CD25(-) T cells. The addition of CD4(+)CD25(high) T cells back to cultures could significantly suppress the antigen-specific production of IFN-gamma induced by BCG-stimulated CD4(+)CD25(-) T cells, suggesting that Treg might play a key role in the control of cellular immune responses in TB infection.

Involvement of cellular death in TRAIL/DR5-dependent suppression induced by CD4(+)CD25(+) regulatory T cells

CD4(+)CD25(+) regulatory T cells (Treg) are potent immunosuppressive cells active in controlling normal pathological immune responses. The mechanisms of this suppression have been investigated under various conditions. In this report, tumor necrosis factor-related apoptosis inducing ligand (TRAIL)/death receptor 5 (DR5) was explored as one of the pivotal factors for the suppression and cytotoxicity induced by CD4(+)CD25(+) Treg. Cell death was involved in the suppression induced by activated CD4(+)CD25(+) Treg in vitro. The induction of CD4(+) T cell death was not mediated by the CD95/CD95L pathway, but rather depended upon the upregulation of TRAIL in the Treg. Blocking the TRAIL/DR5 pathway resulted in a significant reduction of the suppressive activity as well as the cytotoxic effects of Treg in vitro. Activated Treg displayed TRAIL-dependent cytotoxicity against CD4(+) T cells in vivo. The prolonged survival of allogeneic skin grafts induced by Treg was inhibited by DR5-blocking antibodies. Our findings suggest that the TRAIL/DR5 pathway is one of the mechanisms used by Treg to regulate immune responses both in vitro and in vivo.

The role of STAT3 in antigen-IgG inducing regulatory CD4(+)Foxp3(+)T cells

Unraveling the events that control the suppressive function of regulatory T (Treg) cells is extremely important because it will enable investigators to manipulate these cells to inhibit or enhance their functions as necessary. One of the members of the Signal Transducer and Activators of Transcription (STATs) family, STAT3, has emerged as a negative regulator of inflammatory responses. Here, we study the role of STAT3 in Treg cell induction. We found that GAD-IgG-transduced splenocytes induce a CD4(+)Foxp3(+)Treg cell increase in NOD mice. In parallel with the Treg cell increase, an IL-6-STAT3 signal pathway is activated. When STAT3 activation is blocked, GAD-specific tolerance disappears, the percentage of Treg cells decreases and IL-10 secretion is reduced in the splenocytes of NOD mice recipients of GAD-IgG-transduced splenocytes. Our findings indicate that transcription factor STAT3 plays an important role in immune tolerance.

Induction of immunosuppressive functions of dendritic cellsin vivo by CD4+CD25+ regulatory T cells: Role of B7-H3 expression and antigen presentation

Suppressive functions of CD4+CD25+ regulatory T cells (Treg) are mainly studied by their interaction with conventional T cells. However, there is evidence that Treg also interact with antigen-presenting cells (APC), leading to suppression of APC function in in vitro coculture systems. Studying the in vivo distribution of Treg after injection, we found that Treg are located in direct proximity to dendritic cells (DC) and affect their functional maturation status. After contact to Treg, DC up-regulate the inhibitory B7-H3 molecule and display reduced numbers of MHC-peptide complexes, leading to impaired T cell stimulatory function. When Treg-exposed DC were used to immunize animals against antigens, the DC failed to produce a robust immune response as compared to control DC. Thus, these data indicate that Treg are able to inhibit DC activation and produce an inhibitory phenotype of DC. Accordingly, Treg may recruit DC for the amplification of immunosuppression by restraining their maturation in vivo and inducing an immunosuppressive phenotype of DC.

Different Forms of Helper Tolerance to Carcinoembryonic Antigen: Ignorance and Regulation

PURPOSE

Understanding the mechanisms of immune tolerance to tumor-associated antigens (TAA) is an important step in the design of cancer immunotherapy. The aim was to determine how T helper (Th) cell tolerance is mediated for a prototypic TAA, carcinoembryonic antigen (CEA).

EXPERIMENTAL DESIGN

Peripheral blood mononuclear cells from 50 healthy volunteers were stimulated with CEA, and the type and fine specificity of any Th cell responses were identified. The inhibitory effects of T regulatory (Tr) populations were determined by depleting "natural" CD25(+) Tr cells or neutralizing cytokine produced by the "induced" Tr form.

RESULTS

Proliferative Th cell responses were consistently induced by CEA in 22 of 50 individuals. Responding cells were drawn from the CD45RA(+) "naive" or quiescent population. Depleting the CD25(+) fraction did not enhance CEA responsiveness. However, CEA elicited secretion of the Tr cytokine interleukin-10 (IL-10) in 23 of 50 donors, including 20 of 22 where no proliferation was induced. Neutralizing IL-10 revealed previously unseen proliferation to CEA by CD45RO(+) "memory" Th cells. Epitope maps revealed differences in the fine specificities of Th cells capable of proliferating or secreting IL-10.

CONCLUSIONS

There are at least two major forms of CEA tolerance in different individuals. One is "ignorance," a failure of specific Th cells to respond to antigen presented in vivo. The other, seen when ignorance is lost, is mediated by IL-10-secreting Tr cells that recognize CEA. TAA tolerance, for example to colorectal carcinoma cells expressing CEA, may be overcome by peptide vaccines that exploit the differences in epitopes recognized by effector and Tr responses.

Age-related changes in the occurrence and characteristics of thymic CD4(+) CD25(+) T cells in mice

Natural regulatory CD4(+) CD25(+) T cells play an important role in preventing autoimmunity by maintaining self-tolerance. They express CD25 constitutively and are produced in the thymus as a functionally mature T-cell population. Changes in the potential of these cells to regulate the activity of conventional effector lymphocytes may contribute to an increased susceptibility to infection, cancer and age-associated autoimmune diseases. In this study we demonstrated that the thymi of aged mice are populated by a higher percentage of CD4(+) CD25(+) thymocytes than in young animals. The expression of several surface markers (CD69, CD5, CD28, CTLA-4, CD122, FOXP3), usually used to characterize the phenotype of CD4(+) CD25(+) T regulatory cells, was compared between young and aged mice. We also examined the ability of sorted thymus-deriving regulatory T cells of young and aged BALB/c mice to inhibit the proliferation of lymph node lymphocytes activated in vitro. Natural regulatory T cells isolated from the thymi of young mice suppress the proliferation of responder lymph node cells. We demonstrated that thymus-deriving CD4(+) CD25(+) T cells of old mice maintain their potential to suppress the proliferation of activated responder lymphocytes of young mice. However, their potential to inhibit the proliferation of old responder T cells is abrogated. Differences in the occurrence and activity of CD4(+) CD25(+) thymocytes between young and old animals are discussed in relation to the expression of these surface markers.

Differential engagement of Tim-1 during activation can positively or negatively costimulate T cell expansion and effector function

It has been suggested that T cell immunoglobulin mucin (Tim)-1 expressed on T cells serves to positively costimulate T cell responses. However, crosslinking of Tim-1 by its ligand Tim-4 resulted in either activation or inhibition of T cell responses, thus raising the issue of whether Tim-1 can have a dual function as a costimulator. To resolve this issue, we tested a series of monoclonal antibodies specific for Tim-1 and identified two antibodies that showed opposite functional effects. One anti-Tim-1 antibody increased the frequency of antigen-specific T cells, the production of the proinflammatory cytokines IFN-gamma and IL-17, and the severity of experimental autoimmune encephalomyelitis. In contrast, another anti-Tim-1 antibody inhibited the generation of antigen-specific T cells, production of IFN-gamma and IL-17, and development of autoimmunity, and it caused a strong Th2 response. Both antibodies bound to closely related epitopes in the IgV domain of the Tim-1 molecule, but the activating antibody had an avidity for Tim-1 that was 17 times higher than the inhibitory antibody. Although both anti-Tim-1 antibodies induced CD3 capping, only the activating antibody caused strong cytoskeletal reorganization and motility. These data indicate that Tim-1 regulates T cell responses and that Tim-1 engagement can alter T cell function depending on the affinity/avidity with which it is engaged.

TSLP: an epithelial cell cytokine that regulates T cell differentiation by conditioning dendritic cell maturation

Dendritic cells (DCs) are professional antigen-presenting cells that have the ability to sense infection and tissue stress, sample and present antigen to T lymphocytes, and induce different forms of immunity and tolerance. The functional versatility of DCs depends on their remarkable ability to translate collectively the information from both the invading microbes and their resident tissue microenvironments and then make an appropriate immune response. Recent progress in understanding TLR biology has illuminated the mechanisms by which DCs link innate and adaptive antimicrobial immune responses. However, how tissue microenvironments shape the function of DCs has remained elusive. Recent studies of TSLP (thymic stromal lymphopoietin), an epithelial cell-derived cytokine that strongly activates DCs, provide evidence at a molecular level that epithelial cells/tissue microenvironments directly communicate with DCs. We review recent progress on how TSLP expressed within thymus and peripheral lymphoid and nonlymphoid tissues regulates DC-mediated central tolerance, peripheral T cell homeostasis, and inflammatory Th2 responses.

Heme oxygenase-1, carbon monoxide, and bilirubin induce tolerance in recipients toward islet allografts by modulating T regulatory cells

Heme oxygenase-1 (HO-1) induction in, or carbon monoxide (CO), or bilirubin administration to, donors and/or recipients frequently lead to long-term survival (>100 days) of DBA/2 islets into B6AF1 recipients. We tested here whether similar treatments show value in a stronger immunogenetic combination, i.e., BALB/c to C57BL/6, and attempted to elucidate the mechanism accounting for tolerance. Induction of HO-1, administering CO or bilirubin to the donor, the islets or the recipient, prolonged islet allograft survival to different extents. Combining all the above treatments (the "combined" protocol) led to survival for >100 days and antigen-specific tolerance to 60% of the transplanted grafts. A high level of forkhead box P3 (Foxp3) and transforming growth factor beta (TGF-beta) expression was detected in the long-term surviving grafts. With the combined protocol, significantly more T regulatory cells (Tregs) were observed surrounding islets 7 days following transplantation. No prolongation of graft survival was observed using the combined protocol when CD4+ CD25+ T cells were predepleted from the recipients before transplantation. In conclusion, our combined protocol led to long-term survival and tolerance to islets in the BALB/c to C57BL/6 combination by promoting Foxp3+ Tregs; these cells played a critical role in the induction and maintenance of tolerance in the recipient.

A Dual Altered Peptide Ligand Inhibits Myasthenia Gravis Associated Responses by Inducing Phosphorylated Extracellular-regulated Kinase 1,2 that Upregulates CD4+CD25+Foxp3+Cells

Myasthenia gravis (MG) and its animal model experimental autoimmune MG (EAMG), are T-cell dependent, antibody-mediated autoimmune disorders. A dual altered peptide ligand (APL) composed of the tandemly arranged two single amino acids analogs of two myasthenogenic peptides, p195-212 and p259-271, was demonstrated to downregulate, in vitro and in vivo, MG-associated autoimmune responses. Upregulation of regulatory CD4(+)CD25(+) cells plays a key role in the mechanism of action of the dual APL. The objectives of the present study were to address the involvement of extracellular-regulated kinase (ERK)1,2 in the mechanisms by which the dual APL-induced CD4(+)CD25(+) cells suppress MG-associated autoimmune responses. We demonstrate here that administration of the dual APL increased activated ERK1,2 in the CD4(+)CD25(+)-enriched population. Further, inhibition of ERK1,2 by its inhibitor, U0126, in dual APL-induced CD4(+)CD25(+) cells, abrogated their ability to suppress interferon (IFN)-gamma secretion by lymph node (LN) cells of mice that were immunized with the myasthenogenic peptide. Moreover, inhibition of ERK1,2 in the dual APL-induced regulatory CD4(+)CD25(+) cells, resulted in downregulation of the forkhead box p3 (Foxp3) gene and protein expression levels, as well as in the downregulation of CD4(+)CD25(+) development, suggesting that the active suppression exerted by the dual APL via CD4(+)CD25(+) cells depends on ERK1,2 activity.

Human CD4+CD25+ regulatory T cells: proteome analysis identifies galectin-10 as a novel marker essential for their anergy and suppressive function

CD4(+)CD25(+)Foxp3(+) regulatory T cells (CD25(+) Treg cells) direct the maintenance of immunological self-tolerance by active suppression of autoaggressive T-cell populations. However, the molecules mediating the anergic state and regulatory function of CD25(+) Treg cells are still elusive. Using differential proteomics, we identified galectin-10, a member of the lectin family, as constitutively expressed in human CD25(+) Treg cells, while they are nearly absent in resting and activated CD4(+) T cells. These data were confirmed on the mRNA and protein levels. Single-cell staining and flow cytometry showed a strictly intracellular expression of galectin-10 in CD25(+) Treg cells. Specific inhibition of galectin-10 restored the proliferative capacity of CD25(+) Treg cells and abrogated their suppressive function. Notably, first identified here as expressed in human T lymphocytes, galectin-10 is essential for the functional properties of CD25(+) Treg cells.

Reversal of tumor-mediated immunosuppression

Therapeutic cancer vaccines, one form of active immunotherapy, have long been under investigation; consequently, several vaccine-based strategies have now moved from the bench to the clinical arena. Despite their tremendous promise, current vaccine strategies have shown only limited success in clinical settings, even in renal cell carcinoma (RCC), a prototypical malignancy for the application of immunotherapy. There is ample evidence that, especially in RCC, multiple immunosuppressive mechanisms exist that considerably dampen antitumor responses and weaken the activity of current immunotherapeutic regimens. Therefore, it will be necessary to reverse tumor-mediated immunosuppression before immunotherapies can successfully be applied. Recent insights into the nature and characteristics of the regulatory elements of the immune system have provided new opportunities to enhance vaccine-mediated antitumor immunity and, thereby, increase the chance for improving patient outcome. These new insights represent important considerations for the future design and application of more effective cancer vaccines against RCC and other cancers.

Potential use of IL-2/anti-IL-2 antibody immune complexes for the treatment of cancer and autoimmune disease

Initially discovered as a potent T cell proliferation factor, IL-2 was soon used for cancer immunotherapy, especially for metastatic melanoma and renal cell carcinoma; however, the severe side effects of IL-2 therapy, plus the negative role of IL-2 in maintaining of CD4+ CD25+ T regulatory cells (Tregs), has somewhat dampened enthusiasm for using IL-2 in immunotherapy. This opinion article discusses the possibility of combining IL-2 with certain anti-IL-2 antibodies for reducing the dose of IL-2 needed and preferentially stimulating effector T cells, but not Tregs, an approach that might provide an improved strategy for anticancer immunotherapy. Alternatively, complexes of IL-2 with other anti-IL-2 antibodies can selectively stimulate Tregs and could, therefore, be useful for treating autoimmune diseases.

A CFSE based assay for measuring CD4+CD25+ regulatory T cell mediated suppression of auto-antigen specific and polyclonal T cell responses

CD4(+)CD25(+) regulatory T cells (Tregs) are considered to play a key role as suppressors of immune mediated reactions. The analysis of Treg function in patients with autoimmune, allergic or oncogenic diseases has emerged over the past years. In the present study we describe a CFSE based protocol to measure Treg mediated suppression of CD4(+) T cells. Measuring Treg suppressive capacity towards proliferation of anti-CD3 Ab stimulated CD4(+)CD25(-) T cells in coculture experiments by means of a CFSE based and a classical [(3)H]thymidine incorporation assay gave similar results, provided that CD4(+)CD25(+) T cells were anergic. However, when CD4(+)CD25(+) T cells proliferated upon mitogenic stimulation, data obtained by the CFSE assay allowed the detection of a significant Treg suppression whereas this was clearly underestimated using the [(3)H]thymidine assay. In addition, an indirect CFSE based method was developed to analyze antigen specific responses of total CD4(+) T cells and Treg depleted CD4(+) T cells (i.e. CD4(+)CD25(-) T cells). Our results indicate that, in healthy individuals, CD4(+) T cell responses against the multiple sclerosis (MS) auto-antigens, myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG), were increased in Treg depleted CD4(+) T cells as compared to total CD4(+) T cells. Our initial data suggest that Tregs in MS patients show an impaired suppression of myelin reactive T cells when compared to healthy controls. Moreover, this experimental setup permits the measurement of cytokine production of the antigen proliferated CFSE(low) T cells by additional flow cytometric analyses. In conclusion, the described CFSE based Treg suppression assay is a valuable tool to study suppressor T cells in (auto)immune disorders.

An eye's view of T regulatory cells

T regulatory (Treg) cells have been studied for more than 30 years. Recently, changing technology and attitudes have led to new interest in T cell regulation of the immune responses. The eye is an immune-privileged site with unique mechanisms for the prevention of damaging immune inflammation. The eye fashions its Treg cells in novel ways to prevent immune inflammation locally and systemically. The purpose of this mini-review is to condense and summarize reports of Treg cells dependent on the eye in the context of the Treg literature in general.