Distinct inflammatory signals have physiologically divergent effects on epigenetic regulation of Foxp3 expression and Treg function

Impact of interleukin-6 on T cells in kidney transplant recipients

Interleukin-6 (IL-6), a multifunctional proinflammatory cytokine, plays a key role in T cell activation, survival, and differentiation. Acting as a switch that induces the differentiation of naïve T cells into Th17 cells and inhibits their development into regulatory T cells, IL-6 promotes rejection and abrogates tolerance. Therapies that target IL-6 signaling include antibodies to IL-6 and the IL-6 receptor and inhibitors of janus kinases; several of these therapeutics have demonstrated robust clinical efficacy in autoimmune and inflammatory diseases. Clinical trials of IL-6 inhibition in kidney transplantation have focused primarily on its effects on B cells, plasma cells, and HLA antibodies. In this review, we summarize the impact of IL-6 on T cells in experimental models of transplant and describe the effects of IL-6 inhibition on the T cell compartment in kidney transplant recipients.

Peritoneal Modulators of Endometriosis-Associated Ovarian Cancer

Ovarian cancer is the 4th largest cause of cancer death in women. Approximately 10-15% of women of childbearing age suffer from endometriosis. Endometriosis is defined by the growth and presence of endometrial tissue (lesions) outside of the uterus. The women with endometriosis also have an increased presence of peritoneal fluid (PF) that comprises of inflammatory cells, growth factors, cytokines/chemokines, etc. Epidemiological studies have shown that >3% of women with endometriosis develop ovarian cancer (low-grade serous or endometrioid types). Our hypothesis is that the PF from women with endometriosis induces transformative changes in the ovarian cells, leading to ovarian cancer development. PF from women with and without endometriosis was collected after IRB approval and patient consent. IOSE (human normal ovarian epithelial cells) and TOV-21G cells (human ovarian clear cell carcinoma cell line) were treated with various volumes of PF (no endometriosis or endometriosis) for 48 or 96 h and proliferation measured. Expression levels of epigenetic regulators and FoxP3, an inflammatory tumor suppressor, were determined. A Human Cancer Inflammation and Immunity Crosstalk RT2 Profiler PCR array was used to measure changes in cancer related genes in treated cells. Results showed increased growth of TOV-21G cells treated with PF from women with endometriosis versus without endometriosis and compared to IOSE cells. Endo PF treatment induced EZH2, H3K27me3, and FoxP3. The RT2 PCR array of TOV-21G cells treated with endo PF showed upregulation of various inflammatory genes (TLRs, Myd88, etc.). These studies indicate that PF from women with endometriosis can both proliferate and transform ovarian cells and hence this microenvironment plays a major mechanistic role in the progression of endometriosis to ovarian cancer.

Interleukin-6 blockade with tocilizumab increases Tregs and reduces T effector cytokines in renal graft inflammation: A randomized controlled trial

Interleukin-6 (IL-6) is a proinflammatory cytokine and key regulator of Treg: T effector cell (Teff) balance. We hypothesized that IL-6 blockade with tocilizumab, a monoclonal antibody to IL-6R, would increase Tregs, dampen Teff function, and control graft inflammation. We conducted a randomized controlled clinical trial (2014-2018) of clinically stable kidney transplant recipients on calcineurin inhibitor, mycophenolate mofetil, and prednisone, with subclinical graft inflammation noted on surveillance biopsies during the first year posttransplant. Subjects received tocilizumab (8 mg/kg IV every 4 weeks; 6 doses; n = 16) or no treatment (controls; n = 14) on top of usual maintenance immunosuppression. Kidney biopsies pre- and post-treatment were analyzed using Banff criteria. Blood was analyzed for serum cytokines, Treg frequencies, and T cell effector molecule expression (IFN-γ, IL-17, granzyme B) post-stimulation ex vivo. Tocilizumab-treated subjects were more likely to show improved Banff ti-score (62.5% vs. 21.4%, p = .03), increased Treg frequency (7.1% ± 5.55% vs. 3.6% ± 1.7%, p = .0168), and a blunted Teff cytokine response compared to controls. Changes in Banff i- and t-scores were not significantly different. The treatment was relatively well tolerated with no patient deaths or graft loss. Blockade of IL-6 is a novel and promising treatment option to regulate the T cell alloimmune response in kidney transplant recipients. NCT02108600.

Dissecting the defects in the neonatal CD8+ T-cell response

The neonatal period presents a complex scenario where the threshold of reactivity toward colonizing microbiota, maternal antigens, autoantigens, and pathogens must be carefully moderated and balanced. CD8⁺ T cells are critical for the response against intracellular bacteria and viruses, but this immune compartment maintains altered function relative to adult counterparts because of the unique challenges which infants face. Here, we review our current understanding of the factors which may promote the attenuation and altered function of the neonatal CD8⁺ T-cell response and potential avenues for future study. Specifically, we have focused on the neonatal CD8⁺ T-cell ontogeny, memory formation, TCR structure and repertoire, TCR inhibitory receptors, and the clinical implications of altered neonatal CD8⁺ T-cell function. Special emphasis has been placed on examining the response of preterm neonates relative to term neonates and adults.

mTOR Complex 1 Signaling Regulates the Generation and Function of Central and Effector Foxp3+ Regulatory T Cells

The mechanistic/mammalian target of rapamycin (mTOR) has emerged as a critical integrator of signals from the immune microenvironment capable of regulating T cell activation, differentiation, and function. The precise role of mTOR in the control of regulatory T cell (Treg) differentiation and function is complex. Pharmacologic inhibition and genetic deletion of mTOR promotes the generation of Tregs even under conditions that would normally promote generation of effector T cells. Alternatively, mTOR activity has been observed to be increased in Tregs, and the genetic deletion of the mTOR complex 1 (mTORC1)-scaffold protein Raptor inhibits Treg function. In this study, by employing both pharmacologic inhibitors and genetically altered T cells, we seek to clarify the role of mTOR in Tregs. Our studies demonstrate that inhibition of mTOR during T cell activation promotes the generation of long-lived central Tregs with a memory-like phenotype in mice. Metabolically, these central memory Tregs possess enhanced spare respiratory capacity, similar to CD8⁺ memory cells. Alternatively, the generation of effector Tregs (eTregs) requires mTOR function. Indeed, genetic deletion of Rptor leads to the decreased expression of ICOS and PD-1 on the eTregs. Overall, our studies define a subset of mTORC1^hi eTregs and mTORC1^lo central Tregs.

On the role of retinoic acid in virus induced inflammatory response in cornea

Ocular infection with herpes simplex virus (HSV) can result in a chronic immune inflammatory lesion that is a significant cause of human blindness. A key to controlling stromal keratitis (SK) lesion severity is to identify cellular and molecular events responsible for tissue damage and to counteract them. One potentially useful approach to achieve such therapy is Retinoic Acid (RA). Here we show that RA therapy reduces the severity of SK by having inhibitory effects on the T effector subtypes responsible for orchestrating SK. RA also served to stabilize the function of regulatory T cell (Treg) which counteract inflammatory cell activity. The Treg stabilizing effect was demonstrated by in vitro studies where RA was shown to retain Foxp3 expression when exposed to proinflammatory conditions such as IL-12 and IL-6+TGF-β. in vivo studies revealed that RA exerted its stabilizing effects by downregulating IL-6R expression on Treg after HSV-1 infection and this helped to control the progression of SK. Since the therapy was effective when used both early and after the initiation of lesions, it may represent a valuable means of therapy when used alone or along with additional therapies.

CCR6 signaling inhibits suppressor function of induced-Treg during gut inflammation

CCR6 is a G protein-coupled receptor (GPCR) that binds to a specific chemokine, CCL20. The role of CCR6-CCL20 is very well studied in the migration of immune cells, but the non-chemotaxis functions of CCR6 signaling were not known. Here, we show that during gut inflammation, the frequency of Foxp3⁺CD4⁺ T cells (Tregs) reduced in the secondary lymphoid tissues and CCR6⁺ Tregs enhanced the expression of RORγt. The peripheral blood mononuclear cells (PBMCs) of ulcerative colitis (UC) patients showed lower percentages of Foxp3⁺CD4⁺ T cells, as compared to healthy individuals, with CCR6⁺ Tregs showing higher RORγt expression as compared to CCR6^-Tregs. CCL20 inhibited the TGF-β1-induced Treg (iTreg) differentiation and directed them towards the pathogenic Th17-lineage in a CCR6-dependent manner. The iTreg that differentiated in the presence of CCL20 showed lower surface expression of suppressor molecules such as CD39, CD73 and FasL, and had impaired suppressive function. Furthermore, CCR6 signaling induced phosphorylation of Akt, mTOR, and STAT3 molecules in T cells. In conclusion, we have identified a new role of CCR6 signaling in the differentiation of iTregs during inflammation and gut autoimmunity.

Research and therapeutics-traditional and emerging therapies in systemic lupus erythematosus

This review summarizes traditional and emerging therapies for SLE. Evidence suggests that the heterogeneity of SLE is a crucial aspect contributing to the failure of large clinical trials for new targeted therapies. A clearer understanding of the mechanisms driving disease pathogenesis combined with recent advances in medical science are predicted to enable accelerated progress towards improved SLE diagnosis and personalized approaches to treatment.

TGF-beta/atRA-induced Tregs express a selected set of microRNAs involved in the repression of transcripts related to Th17 differentiation

Regulatory T cells (Tregs) are essential regulators of immune tolerance. atRA and TGF-β can inhibit the polarization of naïve T cells into inflammatory Th17 cells, favoring the generation of stable iTregs, however the regulatory mechanisms involved are not fully understood. In this context, the roles of individual microRNAs in Tregs are largely unexplored. Naïve T cells were immunomagnetically isolated from umbilical cord blood and activated with anti-human CD2/CD3/CD28 beads in the presence of IL-2 alone (CD4_Med) or with the addition of TGF-β and atRA (CD4_TGF/atRA). As compared to CD4_Med, the CD4_TGF/atRA condition allowed the generation of highly suppressive CD4⁺CD25^hiCD127⁻FOXP3^hi iTregs. Microarray profiling allowed the identification of a set of microRNAs that are exclusively expressed upon TGF-β/atRA treatment and that are predicted to target a set of transcripts concordantly downregulated. This set of predicted targets were enriched for central components of IL-6/JAK/STAT and AKT-mTOR signaling, whose inhibition is known to play important roles in the generation and function of regulatory lymphocytes. Finally, we show that mimics of exclusively expressed miRs (namely miR-1299 and miR-30a-5p) can reduce the levels of its target transcripts, IL6R and IL6ST (GP130), and increase the percentage of FoxP3⁺ cells among CD4⁺CD25^+/hi cells.

The ST2/IL-33 Axis in Immune Cells during Inflammatory Diseases

Il1rl1 (also known as ST2) is a member of the IL-1 superfamily, and its only known ligand is IL-33. ST2 exists in two forms as splice variants: a soluble form (sST2), which acts as a decoy receptor, sequesters free IL-33, and does not signal, and a membrane-bound form (ST2), which activates the MyD88/NF-κB signaling pathway to enhance mast cell, Th2, regulatory T cell (Treg), and innate lymphoid cell type 2 functions. sST2 levels are increased in patients with active inflammatory bowel disease, acute cardiac and small bowel transplant allograft rejection, colon and gastric cancers, gut mucosal damage during viral infection, pulmonary disease, heart disease, and graft-versus-host disease. Recently, sST2 has been shown to be secreted by intestinal pro-inflammatory T cells during gut inflammation; on the contrary, protective ST2-expressing Tregs are decreased, implicating that ST2/IL-33 signaling may play an important role in intestinal disease. This review will focus on what is known on its signaling during various inflammatory disease states and highlight potential avenues to intervene in ST2/IL-33 signaling as treatment options.

Impact of Immune-Modulatory Drugs on Regulatory T Cell

Immunosuppression strategies that selectively inhibit effector T cells while preserving and even enhancing CD4FOXP3 regulatory T cells (Treg) permit immune self-regulation and may allow minimization of immunosuppression and associated toxicities. Many immunosuppressive drugs were developed before the identity and function of Treg were appreciated. A good understanding of the interactions between Treg and immunosuppressive agents will be valuable to the effective design of more tolerable immunosuppression regimens. This review will discuss preclinical and clinical evidence regarding the influence of current and emerging immunosuppressive drugs on Treg homeostasis, stability, and function as a guideline for the selection and development of Treg-friendly immunosuppressive regimens.

The Gut Microbiota and their Metabolites: Potential Implications for the Host Epigenome

The gut microbiota represents a metabolically active biomass of up to 2 kg in adult humans. Microbiota-derived molecules significantly contribute to the host metabolism. Large amounts of bacterial metabolites are taken up by the host and are subsequently utilized by the human body. For instance, short chain fatty acids produced by the gut microbiota are a major energy source of humans.It is widely accepted that microbiota-derived metabolites are used as fuel for beta-oxidation (short chain fatty acids) and participate in many metabolic processes (vitamins, such as folic acid). Apart from these direct metabolic effects, it also becomes more and more evident that these metabolites can interact with the mammalian epigenetic machinery. By interacting with histones and DNA they may be able to manipulate the host's chromatin state and functionality and hence its physiology and health.In this chapter, we summarize the current knowledge on possible interactions of different bacterial metabolites with the mammalian epigenetic machinery, mostly based on in vitro data. We discuss the putative impact on chromatin marks, for example histone modifications and DNA methylation. Subsequently, we speculate about possible beneficial and adverse consequences for the epigenome, the physiology and health of the host, as well as plausible future applications of this knowledge for in vivo translation to support personal health.

Toll-like receptor 2 activators modulate oral tolerance in mice

BACKGROUND

Toll-like receptor 2 (TLR2) is a widely expressed pattern recognition receptor critical for innate immunity. TLR2 is also a key regulator of mucosal immunity implicated in the development of allergic disease. TLR2 activators are found in many common foods, but the role of TLR2 in oral tolerance and allergic sensitization to foods is not well understood.

OBJECTIVE

The purpose of this study was to evaluate the impacts of TLR2 expression and TLR2 activation on oral tolerance to food antigens in a murine model.

METHODS

Mice were fed ovalbumin (OVA) or peanut butter with or without the addition of low doses of TLR2 activators Pam3 CSK4 or FSL-1. Oral tolerance was assessed by analysing antibody responses after a systemic antigen challenge. OVA-specific Tregs were assessed in the Peyer's patches, mesenteric lymph nodes, and spleen in wild-type and TLR2(-/-) mice. Low-dose Pam3 CSK4 was also tested as an oral adjuvant.

RESULTS

Oral tolerance was successfully induced in both wild-type and TLR2(-/-) recipient mice, with an associated regulatory T-cell response. Oral TLR2 activation, with low-dose Pam3 CSK4 or FSL-1, during oral antigen exposure was found to alter oral tolerance and was associated with the development of substantial IgE and IgA responses to foods upon systemic challenge. Low-dose oral Pam3 CSK4 treatment also selectively enhanced antigen-specific IgA responses to oral antigen exposure.

CONCLUSIONS AND CLINICAL RELEVANCE

TLR2 is not necessary for oral tolerance induction, but oral TLR2 activation modulates humoral IgE and IgA responses during tolerance development. Low-dose Pam3 CSK4 is also an effective oral adjuvant that selectively enhances IgA production. These observations are pertinent to the optimization of oral allergen immunotherapy and oral vaccine development.

Regulatory T cell expressed MyD88 is critical for prolongation of allograft survival

MyD88 signaling directly promotes T-cell survival and is required for optimal T-cell responses to pathogens. To examine the role of T-cell-intrinsic MyD88 signals in transplantation, we studied mice with targeted T-cell-specific MyD88 deletion. Contrary to expectations, we found that these mice were relatively resistant to prolongation of graft survival with anti-CD154 plus rapamycin in a class II-mismatched system. To specifically examine the role of MyD88 in Tregs, we created a Treg-specific MyD88-deficient mouse. Transplant studies in these animals replicated the findings observed with a global T-cell MyD88 knockout. Surprisingly, given the role of MyD88 in conventional T-cell survival, we found no defect in the survival of MyD88-deficient Tregs in vitro or in the transplant recipients and also observed intact cell homing and expression of Treg effector molecules. MyD88-deficient Tregs also fail to protect allogeneic bone marrow transplant recipients from chronic graft-versus-host disease, confirming the observations of defective regulation seen in a solid organ transplant system. Together, our data define MyD88 as having a divergent requirement for cell survival in non-Tregs and Tregs, and a yet-to-be defined survival-independent requirement for Treg function during the response to alloantigen.

Reducing IRF-1 to Levels Observed in HESN Subjects Limits HIV Replication, But Not the Extent of Host Immune Activation

Cells from women who are epidemiologically deemed resistant to HIV infection exhibit a 40-60% reduction in endogenous IRF-1 (interferon regulatory factor-1), an essential regulator of host antiviral immunity and the early HIV replication. This study examined the functional consequences of reducing endogenous IRF-1 on HIV-1 replication and immune response to HIV in natural HIV target cells. IRF-1 knockdown was achieved in ex vivo CD4(+) T cells and monocytes with siRNA. IRF-1 level was assessed using flow cytometry, prior to infection with HIV-Bal, HIV-IIIB, or HIV-VSV-G. Transactivation of HIV long terminal repeats was assessed by p24 secretion (ELISA) and Gag expression (reverse transcription-polymerase chain reaction (RT-PCR)). The expression of IRF-1-regulated antiviral genes was quantitated with RT-PCR. A modest 20-40% reduction in endogenous IRF-1 was achieved in >87% of ex vivo-derived peripheral CD4(+) T cells and monocytes, resulted in >90% reduction in the transactivation of the HIV-1 genes (Gag, p24) and, hence, HIV replication. Curiously, these HIV-resistant women demonstrated normal immune responses, nor an increased susceptibility to other infection. Similarly, modest IRF-1 knockdown had limited impact on the magnitude of HIV-1-elicited activation of IRF-1-regulated host immunologic genes but resulted in lessened duration of these responses. These data suggest that early expression of HIV-1 genes requires a higher IRF-1 level, compared to the host antiviral genes. Together, these provide one key mechanism underlying the natural resistance against HIV infection and further suggest that modest IRF-1 reduction could effectively limit productive HIV infection yet remain sufficient to activate a robust but transient immune response.

Immunomodulation of host-protective immune response by regulating Foxp3 expression and Treg function in Leishmania-infected BALB/c mice: critical role of IRF1

Visceral leishmaniasis (VL), caused by a protozoan parasite Leishmania donovani, is still a threat to mankind due to treatment failure, drug resistance and coinfection with HIV. The limitations of first-line drugs have led to the development of new strategies to combat this dreaded disease. Recently, we have shown the immunomodulatory property of Ara-LAM, a TLR2 ligand, against leishmanial pathogenesis. In this study, we have extended our study to the effect of Ara-LAM on regulatory T cells in a murine model of VL. We observed that Ara-LAM-treated infected BALB/c mice showed a strong host-protective Th1 immune response due to reduced IL-10 and TGF-β production, along with marked decrease in CD4(+) CD25(+) Foxp3(+) GITR(+) CTLA4(+) regulatory T cell (Treg) generation and activation. The reduction in Foxp3 expression was due to effective modulation of TGF-β-induced SMAD signaling in Treg cells by Ara-LAM. Moreover, we demonstrated that Ara-LAM-induced IRF1 expression in the Treg cells, which negatively regulated foxp3 gene transcription, resulting in the reduced immunosuppressive activity of Treg cells. Interestingly, irf1 gene knockdown completely abrogated the effect of Ara-LAM on Treg cells. Thus, these findings provide detailed mechanistic insight into Ara-LAM-mediated modulation of Treg cells, which might be helpful in combating VL.

Kaempferol Promotes Transplant Tolerance by Sustaining CD4+FoxP3+ Regulatory T Cells in the Presence of Calcineurin Inhibitor

Calcineurin inhibitor cyclosporine is widely used as an immunosuppressant in clinic. However, mounting evidence has shown that cyclosporine hinders tolerance induction by dampening Tregs. Therefore, it is of paramount importance to overcome this pitfall. Kaempferol was reported to inhibit DC function. Here, we found that kaempferol delayed islet allograft rejection. Combination of kaempferol and low-dose, but not high-dose, of cyclosporine induced allograft tolerance in majority of recipient mice. Although kaempferol plus either dose of cyclosporine largely abrogated proliferation of graft-infiltrating T cells and their CTL activity, both proliferation and CTL activity in mice treated with kaempferol plus low-dose, but not high-dose, cyclosporine reemerged rapidly upon treatment withdrawal. Kaempferol increased CD4+FoxP3+ Tregs both in transplanted mice and in vitro, likely by suppressing DC maturation and their IL-6 expression. Reduction in Tregs by low dose of cyclosporine was reversed by kaempferol. Kaempferol-induced Tregs exhibited both allospecific and non-allospecific suppression. Administering IL-6 abrogated allograft tolerance induced by kaempferol and cyclosporine via diminishing CD4+FoxP3+ Tregs. Thus, for the first time, we demonstrated that kaempferol promotes transplant tolerance in the presence of low dose of cyclosporine, which allows for sufficient Treg generation while minimizing side effects, resulting in much-needed synergy between kaempferol and cyclosporine.

iTreg induced from CD39(+) naive T cells demonstrate enhanced proliferate and suppressive ability

CD4(+)CD25(+)FoxP3(+) regulatory T (Treg) cells which consist of naturally occurring Treg (nTreg) and induced Treg (iTreg) cells are associated with the maintenance of immune homeostasis. Previous studies were focused on their potential to ameliorate graft-versus-host disease (GVHD) in human and mice. CD39 is a surface marker both expressed on CD4(+)CD25(-) T cells and Treg cells. CD39(+) Treg cells demonstrate stronger suppressive ability compared to conventional Treg cells. However, whether the potential of CD39(+) naïve T cells induced Treg cells is different from conventional naïve T cells induced Treg cells in vivo and vitro remains to be inconclusive. Here we demonstrate that CD39(+) iTreg cells show enhanced proliferation and suppressive ability as well as lower inflammatory cytokines compared to CD39(-) iTreg cells. To conclude, our findings demonstrate that CD39(+) iTreg cells acquire high suppressive capacity in vitro and vivo, and this may provide a new insight into Treg cell therapy in GVHD clinical trials.

Specific therapy to regulate inflammation in rheumatoid arthritis: molecular aspects

Rheumatoid arthritis (RA) is a chronic inflammatory disease in which persistent inflammation of synovial tissue results in a progressive functional decline of the joint and premature mortality. TNF inhibitors were the first biological disease-modifying antirheumatic drugs (DMARDs) used to treat RA. Since then, new biological drugs have emerged, such as inhibitors of IL-1, IL-6 and others, with different mechanisms of action that include the depletion of B cells and the inhibition of T-cell costimulation. Recently, RA treatments have incorporated the use of synthetic DMARDs. This review describes the molecular aspects of the mechanisms of action of biological and synthetic DMARDs, discusses the adverse effects and limitations of established therapies and analyses the alternative approaches to RA treatment.

Innate immunity in solid organ transplantation: an update and therapeutic opportunities

Innate immunity is increasingly recognized as a major player in transplantation. In addition to its role in inflammation in the early post-transplant period, innate immunity shapes the differentiation of cells of adaptive immunity, with a capacity to promote either rejection or tolerance. Emerging data indicate that innate allorecognition, a characteristic previously limited to lymphocytes, is involved in allograft rejection. This review briefly summarizes the physiology of each component of the innate immune system in the context of transplantation and presents the current or promising therapeutic applications, such as cellular, anticomplement and anticytokine therapies.

Effect of chorioamnionitis on regulatory T cells in moderate/late preterm neonates

Regulatory T-cells (Treg) have a protective role for the control of immune activation and tissue damage. The effects of chorioamnionitis (chorio) on Treg in moderate/late preterm newborns are not known. We hypothesized that infants exposed to chorio would have decreased Treg frequency and/or function. We isolated mononuclear cells from adult peripheral blood and cord blood from term and moderate/late preterm infants who were classified for severity of chorio exposure. Mononuclear cells were analyzed by flow cytometry for Treg frequency and phenotype. Treg suppression of activation of conventional T-cells (Tcon) was also quantified. Treg frequencies were similar in all groups of neonates, but lower than that found in adults. Newborn Treg had a naïve phenotype, with decreased levels of CD45RO, HLA-DR, CD39 and TIGIT compared to adult Treg and chorio did not affect the phenotype. Treg from preterm newborns exposed to severe chorio had higher expression of Ki67 compared to the other groups. Treg from preterm newborns were less suppressive than Treg from adults or term, and the level of suppression was reduced with severe chorio. Relative to term, Treg frequency and phenotype were not affected by prematurity and chorio but their functionality was decreased. Lower Treg activity may contribute to inflammation in newborns that is often associated with chorioamnionitis.

Engagement of Toll-like receptor 2 enhances interleukin (IL)-17(+) autoreactive T cell responses via p38 mitogen-activated protein kinase signalling in dendritic cells

Functional analysis of single Toll-like receptors (TLRs) in vivo is necessary to understand how they shape the ocular inflammation involved in uveitis. In this study we explored the role and mechanisms of TLR-2 agonists on the autoreactive T helper type 17 (Th17) response in experimental autoimmune uveitis (EAU). Treatment by peptidoglycan (PGN), a specific TLR-2 agonist, remarkably increased mRNA levels of Th17-lineage genes interleukin (IL)-17A, IL-21 and RAR-related orphan receptor (ROR)γt and promoted antigen-specific Th17 response in EAU mice. A mixture of PGN and interphotoreceptor retinoid-binding protein peptide (IRBP161-180 ) could effectively induce EAU in the absence of complete Freund's adjuvant (CFA). PGN treatment also enhanced the pathogenic activities of activated antigen-specific Th17 cells in vivo. PGN significantly increased the production of IL-1β, IL-6 and IL-23 of dendritic cells (DCs) and enhanced their ability to promote IL-17(+) uveitogenic T cells. Enhanced immunostimulatory activities of PGN-DCs depend upon p38 activation. Inhibition of p38 mitogen-activated protein kinase (MAPK) activity dramatically decreased IL-17 gene expression and antigen-specific Th17 responses stimulated by PGN-DCs. Our findings suggest that PGN treatment dramatically promotes the IL-17(+) uveitogenic T cell responses via enhancing the immunostimulatory activities of DCs. This effect may be mediated, at least in part, by activation of the p38 signalling pathway in DCs.

Treg functional stability and its responsiveness to the microenvironment

Regulatory T cells (Tregs) prevent autoimmunity and tissue damage resulting from excessive or unnecessary immune activation through their suppressive function. While their importance for proper immune control is undeniable, the stability of the Treg lineage has recently become a controversial topic. Many reports have shown dramatic loss of the signature Treg transcription factor Forkhead box protein 3 (Foxp3) and Treg function under various inflammatory conditions. Other recent studies demonstrate that most Tregs are extremely resilient in their expression of Foxp3 and the retention of suppressive function. While this debate is unlikely to be settled in the immediate future, improved understanding of the considerable heterogeneity within the Foxp3(+) Treg population and how Treg subsets respond to ranging environmental cues may be keys to reconciliation. In this review, we discuss the diverse mechanisms responsible for the observed stability or instability of Foxp3(+) Treg identity and function. These include transcriptional and epigenetic programs, transcript targeting, and posttranslational modifications that appear responsive to numerous elements of the microenvironment. These mechanisms for Treg functional modulation add to the discussion of Treg stability.

Toll-like receptor 2 as a regulator of oral tolerance in the gastrointestinal tract

Food allergy, other adverse immune responses to foods, inflammatory bowel disease, and eosinophilic esophagitis have become increasingly common in the last 30 years. It has been proposed in the "hygiene hypothesis" that dysregulated immune responses to environmental microbial stimuli may modify the balance between tolerance and sensitization in some patients. Of the pattern recognition receptors that respond to microbial signals, toll-like receptors (TLRs) represent the most investigated group. The relationship between allergy and TLR activation is currently at the frontier of immunology research. Although TLR2 is abundant in the mucosal environment, little is known about the complex relationship between bystander TLR2 activation by the commensal microflora and the processing of oral antigens. This review focuses on recent advances in our understanding of the relationship between TLR2 and oral tolerance, with an emphasis on regulatory T cells, eosinophils, B cells, IgA, intestinal regulation, and commensal microbes.

A neuro-immune model of Myalgic Encephalomyelitis/Chronic fatigue syndrome

This paper proposes a neuro-immune model for Myalgic Encephalomyelitis/Chronic fatigue syndrome (ME/CFS). A wide range of immunological and neurological abnormalities have been reported in people suffering from ME/CFS. They include abnormalities in proinflammatory cytokines, raised production of nuclear factor-κB, mitochondrial dysfunctions, autoimmune responses, autonomic disturbances and brain pathology. Raised levels of oxidative and nitrosative stress (O&NS), together with reduced levels of antioxidants are indicative of an immuno-inflammatory pathology. A number of different pathogens have been reported either as triggering or maintaining factors. Our model proposes that initial infection and immune activation caused by a number of possible pathogens leads to a state of chronic peripheral immune activation driven by activated O&NS pathways that lead to progressive damage of self epitopes even when the initial infection has been cleared. Subsequent activation of autoreactive T cells conspiring with O&NS pathways cause further damage and provoke chronic activation of immuno-inflammatory pathways. The subsequent upregulation of proinflammatory compounds may activate microglia via the vagus nerve. Elevated proinflammatory cytokines together with raised O&NS conspire to produce mitochondrial damage. The subsequent ATP deficit together with inflammation and O&NS are responsible for the landmark symptoms of ME/CFS, including post-exertional malaise. Raised levels of O&NS subsequently cause progressive elevation of autoimmune activity facilitated by molecular mimicry, bystander activation or epitope spreading. These processes provoke central nervous system (CNS) activation in an attempt to restore immune homeostatsis. This model proposes that the antagonistic activities of the CNS response to peripheral inflammation, O&NS and chronic immune activation are responsible for the remitting-relapsing nature of ME/CFS. Leads for future research are suggested based on this neuro-immune model.

The innate immune system and transplantation

The sensitive and broadly reactive character of the innate immune system makes it liable to activation by stress factors other than infection. Thermal and metabolic stresses experienced during the transplantation procedure are sufficient to trigger the innate immune response and also augment adaptive immunity in the presence of foreign antigen on the donor organ. The resulting inflammatory and immune reactions combine to form a potent effector response that can lead to graft rejection. Here we examine the evidence that the complement and toll-like receptor systems are central to these pathways of injury and present a formidable barrier to transplantation. We review extensive information about the effector mechanisms that are mediated by these pathways, and bring together what is known about the damage-associated molecular patterns that initiate this sequence of events. Finally, we refer to two ongoing therapeutic trials that are evaluating the validity of these concepts in man.

Interrelationship of dendritic cells, type 1 interferon system, regulatory T cells and toll-like receptors and their role in lichen planus and lupus erythematosus -- a literature review

There is evidence that the activation of some receptors of the toll-like family (TLRs) of the innate immune system, and also changes in expression levels of forkhead box p3 (Foxp3) protein, which is found in regulatory T cells (Tregs), could be involved in the development of autoimmunity. We present here a literature review focusing on the interrelationship of dendritic cells, TLRs, Tregs and type 1 interferon in autoimmune diseases, with special interest in lichen planus and lupus erythematosus. Understanding the specific role of each of these factors would help elucidate the obscure aetiology of such diseases and open new perspectives for their management and treatment.

The plasticity and stability of regulatory T cells

Regulatory T (TReg) cells are crucial for the prevention of fatal autoimmunity in mice and humans. Forkhead box P3 (FOXP3)(+) TReg cells are produced in the thymus and are also generated from conventional CD4(+) T cells in peripheral sites. It has been suggested that FOXP3(+) TReg cells might become unstable under certain inflammatory conditions and might adopt a phenotype that is more characteristic of effector CD4(+) T cells. These suggestions have caused considerable debate in the field and have important implications for the therapeutic use of TReg cells. In this article, Nature Reviews Immunology asks several experts for their views on the plasticity and stability of TReg cells.

PLG scaffold delivered antigen-specific regulatory T cells induce systemic tolerance in autoimmune diabetes

Islet transplantation is a promising treatment for human type 1 diabetes mellitus. Transplantation requires systemic immunosuppression, which has numerous deleterious side effects. Islet antigen-specific regulatory T cells (Tregs) have been shown to protect islet grafts from autoimmune destruction in the nonobese diabetic (NOD) model when co-localized in the kidney capsule. An extra-hepatic transplant site was established by transplanting islet-loaded microporous poly (lactide-co-glycolide) (PLG) scaffolds into abdominal fat. This study examined an autoimmune transplantation model and determined whether co-localized Tregs could protect islet grafts in an extra-hepatic and extra-renal transplant site. Normoglycemia was restored, and co-transplanted Tregs extended graft survival, including several instances of indefinite protection. Transplanted Tregs were replaced by recipient-derived Tregs over time, indicating that islet antigen-specific Tregs induce tolerance to islet grafts through host-derived Tregs. Thus, Tregs provided protection against a diverse repertoire of autoreactive T-cell-receptor specificities mediating diabetes in the NOD model, possibly through a phenomenon previously described as infectious tolerance. Interestingly, the infiltration by Tregs protected a second islet transplant, indicating systemic tolerance to islet antigens. In summary, PLG scaffolds can serve as an alternative delivery system for islet transplantation that allows for the co-localization of immunomodulatory cells within islet grafts and induces long-term graft survival in an autoimmune diabetes model. This method of co-localizing immunomodulatory cells with islets in a clinically translatable transplant site to affect the immune system on a local and systemic level has potential therapeutic implications for human islet transplantation.

Role of miRNAs in CD4 T cell plasticity during inflammation and tolerance

Gene expression is tightly regulated in a tuneable, cell-specific and time-dependent manner. Recent advancement in epigenetics and non-coding RNA (ncRNA) revolutionized the concept of gene regulation. In order to regulate the transcription, ncRNA can promptly response to the extracellular signals as compared to transcription factors present in the cells. microRNAs (miRNAs) are ncRNA (~22 bp) encoded in the genome, and present as intergenic or oriented antisense to neighboring genes. The strategic location of miRNA in coding genes helps in the coupled regulation of its expression with host genes. miRNA together with complex machinery called RNA-induced silencing complex (RISC) interacts with target mRNA and degrade the mRNA or inhibits the translation. CD4 T cells play an important role in the generation and maintenance of inflammation and tolerance. Cytokines and chemokines present in the inflamed microenvironment controls the differentiation and function of various subsets of CD4 T cells [Th1, Th2, Th17, and regulatory CD4 T cells (Tregs)]. Recent studies suggest that miRNAs play an important role in the development and function of all subsets of CD4 T cells. In current review, we focused on how various miRNAs are regulated by cell's extrinsic and intrinsic signaling, and how miRNAs affect the transdifferentiation of subsets of CD4 T cell and controls their plasticity during inflammation and tolerance.

Induction of antigen-specific human T suppressor cells by membrane and soluble ILT3

Antigen-specific CD8 suppressor T cells (CD8(+) Ts) are adaptive regulatory T cells that are induced in vivo and in vitro by chronic antigenic stimulation of human T cells. CD8(+) Ts induce the upregulation of the inhibitory receptors ILT3 and ILT4 on monocytes and dendritic cells rendering these antigen presenting cells (APCs) tolerogenic. Tolerogenic APCs induce CD4(+) T helper anergy and elicit the differentiation of CD4(+) and CD8(+) T regulatory/suppressor cells. Overexpression of membrane ILT3 in APC results in inhibition of NF-κB activation, transcription of inflammatory cytokines and costimulatory molecules. Soluble ILT3-Fc which contains only the extracellular, Ig-like domain linked to mutated IgG1 Fc, is strongly immunosuppressive. ILT3-Fc, induces the differentiation of human CD8(+) Ts which inhibit CD4(+) Th and CD8(+) CTL effector function both in vitro and in vivo. The acquisition of Ts' function by primed CD8(+) T cells treated with ILT3-Fc was demonstrated to be the effect of the significant upregulation of BCL6, a transcriptional repressor of IL-2, IFN-gamma, IL-5 and granzyme B. The upregulated expression of BCL6, SOCS1 and DUSP10 is integral to the signature of ILT3-Fc-induced CD8(+) Ts. These genes are known inhibitors of cytokine production and TCR signaling and are targeted by miRNAs which are suppressed by ILT3-Fc. ILT3-Fc induces tolerance to allogeneic human islets and reverses rejection after its onset in a humanized NOD/SCID mouse model. Based on these findings we postulate that ILT3-Fc may become an important new agent for treatment of autoimmunity and transplant rejection.

Intratumor OX40 stimulation inhibits IRF1 expression and IL-10 production by Treg cells while enhancing CD40L expression by effector memory T cells

Treg cells maintain the tumor microenvironment in an immunosuppressive state preventing an effective anti-tumor immune response. A possible strategy to overcome Treg-cell suppression focuses on OX40, a costimulatory molecule expressed constitutively by Treg cells while being induced in activated effector T cells. OX40 stimulation, by the agonist mAb OX86, inhibits Treg-cell suppression and boosts effector T-cell activation. Here we uncover the mechanisms underlying the therapeutic activity of OX86 treatment dissecting its distinct effects on Treg and on effector memory T (Tem) cells, the most abundant CD4+ populations strongly expressing OX40 at the tumor site. In response to OX86, tumor-infiltrating Treg cells produced significantly less interleukin 10 (IL-10), possibly in relation to a decrease in the transcription factor interferon regulatory factor 1 (IRF1). Tem cells responded to OX86 by upregulating surface CD40L expression, providing a licensing signal to DCs. The CD40L/CD40 axis was required for Tem-cell-mediated in vitro DC maturation and in vivo DC migration. Accordingly, OX86 treatment was no longer therapeutic in CD40 KO mice. In conclusion, following OX40 stimulation, blockade of Treg-cell suppression and enhancement of the Tem-cell adjuvant effect both concurred to free DCs from immunosuppression and activate the immune response against the tumor.

Toll-like receptors in transplantation: sensing and reacting to injury

Toll-like receptors (TLRs) are a family of transmembrane proteins that have a major role in pathogen-induced inflammation and orchestrating an organism's defense against infection. Data are emerging that the TLRs play an important role as a first response to tissue injury linking the innate with the adaptive immune system. The recognition that TLRs are expressed on nonimmune cells including renal and liver cells, and that endogenous, cell-derived ligands (damage-associated molecular patterns) can signal through specific TLRs has expanded the understanding of how these receptors impact a variety of diseases. This review focuses on recent findings elucidating the ability of TLRs to affect transplant outcomes. Specifically, observations demonstrating the link between endogenous TLR ligands and IR injury, how this can affect alloimmunity and transplant tolerance, and therapeutic implications will be discussed.

FOXJ2 expression in rat spinal cord after injury and its role in inflammation

Foxj2 (forkhead box J2), a novel member of the forkhead/HNF3 family, binds DNA with a dual sequence specificity. It may play a role in maintenance and survival of developing and adult neurons. However, its expression and function in the central nervous system lesion are still unclear. In this study, we performed a spinal cord injury (SCI) model in adult Sprague-Dawley rats and investigated the dynamic changes of Foxj2 expression in the spinal cord. Western blot analysis revealed that Foxj2 was present in normal spinal cord. It gradually increased, reached a peak at day 5 after SCI, and then declined during the following days. Double immunofluorescence staining revealed wide expression of Foxj2, which is detected in neurons and astrocytes. After injury, Foxj2 expression was increased predominantly in astrocytes, which highly expressed proliferating cell nuclear antigen, a marker for proliferating cells. And knockdown of Foxj2 in cultured primary astrocytes by siRNA showed that Foxj2 played an important role in lipopolysaccharide-induced inflammatory responses. These results suggested that Foxj2 may be involved in the pathophysiology of SCI, and further research is needed to have a good understanding of its function and mechanism.

Nature and nurture in Foxp3(+) regulatory T cell development, stability, and function

Foxp3(+) regulatory T lymphocytes (Treg) are critical homeostatic regulators of immune and inflammatory responses. Their absence leads to fulminant multiorgan autoimmunity. This review explores recent studies that have altered our emerging view of the development, stability, and plasticity of these cells. Treg appear not to be a single entity, but a family of immunomodulatory cell types with shared capabilities. On a first level, Treg may alternatively form in response to developmental cues in the thymus as a distinct lineage of CD4(+) T cells or adaptively, in response to environmental cues received by mature conventional CD4(+) T lymphocytes. These 2 populations bear distinct specificity, stability, and genetic profiles and are differentially used in immune responses. Secondarily, in a manner analogous to the generation of T helper (Th)-1, Th2, and other T cell subsets, Treg may further specialize, adapting to the needs of their immunologic surroundings. Treg therefore comprise developmentally distinct, functionally overlapping cell populations that are uniquely designed to preserve immunologic homeostasis. They combine an impressive degree of both stability and adaptability.

Current status of immunomodulatory and cellular therapies in preclinical and clinical islet transplantation

Clinical islet transplantation is a β-cell replacement strategy that represents a possible definitive intervention for patients with type 1 diabetes, offering substantial benefits in terms of lowering daily insulin requirements and reducing incidences of debilitating hypoglycemic episodes and unawareness. Despite impressive advances in this field, a limiting supply of islets, inadequate means for preventing islet rejection, and the deleterious diabetogenic and nephrotoxic side effects associated with chronic immunosuppressive therapy preclude its wide-spread applicability. Islet transplantation however allows a window of opportunity for attempting various therapeutic manipulations of islets prior to transplantation aimed at achieving superior transplant outcomes. In this paper, we will focus on the current status of various immunosuppressive and cellular therapies that promote graft function and survival in preclinical and clinical islet transplantation with special emphasis on the tolerance-inducing capacity of regulatory T cells as well as the β-cells regenerative capacity of stem cells.

Immunobiology of transplantation: impact on targets for large and small molecules

Organ transplantation is the preferred method of treatment for many forms of end-stage organ failure. However, immunosuppressive drugs that are used to avoid rejection can result in numerous undesirable effects (infection, malignancy, hypertension, diabetes, and accelerated arteriosclerosis). Moreover, they are not effective at preventing chronic rejection resulting in late graft loss. This review summarizes the fundamental concepts underlying the rejection of solid-organ allografts with the aim of highlighting potential new targets for therapeutics. Future improvement will depend on new therapeutic moieties, including biologics, to target various pathways of both the innate and adaptive arms of immunity. Results from some of the most recent clinical trials in transplantation and emerging new therapies are also discussed.

Therapeutic targeting of B7-H1 in breast cancer

INTRODUCTION

Breast cancer is the most common form of malignancy occurring in women worldwide. B7-H1 is a co-inhibitory molecule expressed by several types of tumors, including breast cancer. The aberrant expression of B7-H1 in breast cancer cells has been determined, its role in recruiting regulatory T cells into the tumor microenvironment has been elucidated and a strong link to B7-H1 induction in highly proliferative breast cancer has been provided. It has also been demonstrated that doxorubicin, a drug commonly used for breast cancer treatment, downregulates the cell surface expression of B7-H1 and upregulates its nuclear expression, which therefore suggests an anti-apoptotic role of B7-H1 in breast cancer.

AREAS COVERED

This review illustrates the various factors involved in the induction of B7-H1 and its role in immune evasion and chemoresistance. It also provides potential therapeutic strategies for targeting B7-H1 in breast cancer.

EXPERT OPINION

B7-H1 should be considered as a potential therapeutic target for breast cancer. Indeed, there is increasing evidence for the potential efficacy of B7-H1 blockade in the prevention of immune evasion by cancer cells. Additionally, B7-H1 targeting can be used in conjunction with other therapeutic modalities for improved efficacy and reduced toxicity. We expect that B7-H1 blockade in combination with other therapeutics will be a prime therapeutic strategy in the future.

Permanent protection of PLG scaffold transplanted allogeneic islet grafts in diabetic mice treated with ECDI-fixed donor splenocyte infusions

Allogeneic islet cell transplantation is a promising treatment for human type 1 diabetes. Currently, human islets are transplanted via intra-portal infusions. While successful, it leads to significant early islet attrition from instant blood-mediated inflammatory reaction. An extra-hepatic site was established by transplanting islet-loaded microporous poly(lactide-co-glycolide) (PLG) scaffolds into the epididymal fat pad in syngeneic islet transplant models. This study examined this technology in allogeneic islet transplantation and determined whether transplant tolerance could be effectively induced to protect PLG scaffold transplanted allogeneic islets. The efficacy of an established tolerance induction strategy using donor splenocytes treated with ethylcarbodiimide(ECDI) was tested. ECDI-fixed donor splenocytes were infused 7 days before and 1 day after islet transplantation. Immediate normoglycemia was restored, and treated mice maintained indefinite normoglycemia whereas untreated mice rejected islet grafts within 20 days of transplantation. Interestingly, efficacy of tolerance induction was superior in PLG scaffold compared with intra-portal transplanted islets. Protection of PLG scaffold islet allografts was associated with several mechanisms of immune regulation. In summary, PLG scaffolds can serve as an alternative delivery system for islet transplantation that does not impair tolerance induction. This approach of combining tolerance induction with scaffold islet transplantation has potential therapeutic implications for human islet transplantation.

The dual role of the X-linked FoxP3 gene in human cancers

The FoxP3 (forkhead box P3) gene is an X-linked gene that is submitted to inactivation. It is an essential transcription factor in CD4(+)CD25(+)FoxP3 regulatory T cells, which are therapeutic targets in disseminated cutaneous melanoma. Moreover, FoxP3 is an important tumor suppressor gene in carcinomas and has putative cancer suppressor gene function in cutaneous melanoma as well. Therefore understanding the structure and function of the FoxP3 gene is crucial to gaining insight into the biology of melanoma to better develop immunotherapeutics and future therapeutic strategies.