Highly polarized Th17 cells induce EAE via a T-bet independent mechanism

OCA-B promotes autoimmune demyelination through control of stem-like CD4 + T cells

Stem-like T cell populations can selectively contribute to autoimmunity, but the activities that promote and sustain these populations are incompletely understood. Here, we show that T cell-intrinsic loss of the transcription cofactor OCA-B protects mice from experimental autoimmune encephalomyelitis (EAE) while preserving responses to CNS infection. In adoptive transfer EAE models driven by multiple antigen encounters, OCA-B deletion nearly eliminates CNS infiltration, proinflammatory cytokine production and clinical disease. OCA-B-expressing CD4 + T cells within the CNS of mice with EAE comprise a minority of the population but display a memory phenotype and preferentially confer disease. In a relapsing-remitting EAE model, OCA-B T cell deficiency specifically protects mice from relapse. During remission, OCA-B promotes the expression of Tcf7 , Slamf6 , and Sell in proliferating T cell populations. At relapse, OCA-B loss results in both the accumulation of an immunomodulatory CD4 + T cell population expressing Ccr9 and Bach2 , and the loss of pro-inflammatory gene expression from Th17 cells. These results identify OCA-B as a driver of pathogenic stem-like T cells.

Th17 cell promotes apoptosis of IL-23R+ neurons in experimental autoimmune encephalomyelitis

Myelin antigen-reactive Th1 and Th17 cells are critical drivers of central nervous system (CNS) autoimmune inflammation. Transcription factors T-bet and RORγt play a crucial role in the differentiation and function of Th1 and Th17 cells, and impart them a pathogenic role in CNS autoimmune inflammation. Mice deficient in these two factors do not develop experimental autoimmune encephalomyelitis (EAE). While T-bet and RORγt are known to regulate the expression of several cell adhesion and migratory molecules in T cells, their role in supporting Th1 and Th17 trafficking to the CNS is not completely understood. More importantly, once Th1 and Th17 cells reach the CNS, how the function of these transcription factors modulates the local inflammatory response during EAE is unclear. In the present study, we showed that myelin oligodendrocyte glycoprotein 35-55 peptide (MOG35-55)-specific Th1 cells deficient in RORγt could cross the blood-brain barrier (BBB) but failed to induce demyelination, apoptosis of neurons, and EAE. Pathogenic Th17 cell-derived cytokines GM-CSF, TNF-α, IL-17A, and IL-21 significantly increased the surface expression of IL-23R on neuronal cells. Furthermore, we showed that, in EAE, neurons in the brain and spinal cord express IL-23R. IL-23-IL-23R signaling in neuronal cells caused phosphorylation of STAT3 (Ser727 and Tyr705) and induced cleaved caspase 3 and cleaved poly (ADP-ribose) polymerase-1 (PARP-1) molecules in an IL-23R-dependent manner and caused apoptosis. Thus, we provided a mechanism showing that T-bet is required to recruit pathogenic Th17 cells to the CNS and RORγt-mediated inflammatory response to drive the apoptosis of IL-23R+ neurons in the CNS and cause EAE. Understanding detailed molecular mechanisms will help to design better strategies to control neuroinflammation and autoimmunity. ONE SENTENCE SUMMARY: IL-23-IL-23R signaling promotes apoptosis of CNS neurons.

The Exposure to Lead (Pb) Exacerbates Immunological Abnormalities in BTBR T+ Itpr3tf/J Mice through the Regulation of Signaling Pathways Relevant to T Cells

Autism spectrum disorder (ASD) is a common neurodevelopmental illness characterized by abnormal social interactions, communication difficulties, and repetitive and limited behaviors or interests. The BTBR T+ Itpr3tf/J (BTBR) mice have been used extensively to research the ASD-like phenotype. Lead (Pb) is a hazardous chemical linked to organ damage in the human body. It is regarded as one of the most common metal exposure sources and has been connected to the development of neurological abnormalities. We used flow cytometry to investigate the molecular mechanism behind the effect of Pb exposure on subsets of CD4+ T cells in the spleen expressing IFN-γ, T-bet, STAT1, STAT4, IL-9, IRF4, IL-22, AhR, IL-10, and Foxp3. Furthermore, using RT-PCR, we studied the effect of Pb on the expression of numerous genes in brain tissue, including IFN-γ, T-bet, STAT1, STAT4, IL-9, IRF4, IL-22, AhR, IL-10, and Foxp3. Pb exposure increased the population of CD4+IFN-γ+, CD4+T-bet+, CD4+STAT1+, CD4+STAT4+, CD4+IL-9+, CD4+IRF4+, CD4+IL-22+, and CD4+AhR+ cells in BTBR mice. In contrast, CD4+IL-10+ and CD4+Foxp3+ cells were downregulated in the spleen cells of Pb-exposed BTBR mice compared to those treated with vehicle. Furthermore, Pb exposure led to a significant increase in IFN-γ, T-bet, STAT1, STAT4, IL-9, IRF4, IL-22, and AhR mRNA expression in BTBR mice. In contrast, IL-10 and Foxp3 mRNA expression was significantly lower in those treated with the vehicle. Our data suggest that Pb exposure exacerbates immunological dysfunctions associated with ASD. These data imply that Pb exposure may increase the risk of ASD.

Aflatoxin B1 Exposure Aggravates Neurobehavioral Deficits and Immune Dysfunctions of Th1, Th9, Th17, Th22, and T Regulatory Cell-Related Transcription Factor Signaling in the BTBR T+Itpr3tf/J Mouse Model of Autism

Autism spectrum disorder (ASD) is a neurodevelopmental disease characterized by impaired communication, reciprocal social interactions, restricted sociability deficits, and stereotyped behavioral patterns. Environmental factors and genetic susceptibility have been implicated in an increased risk of ASD. Aflatoxin B1 (AFB1) is a typical contaminant of food and feed that causes severe immune dysfunction in humans and animals. Nevertheless, the impact of ASD on behavioral and immunological responses has not been thoroughly examined. To investigate this phenomenon, we subjected BTBR T+Itpr3tf/J (BTBR) mice to AFB1 and evaluated their marble-burying and self-grooming behaviors and their sociability. The exposure to AFB1 resulted in a notable escalation in marble-burying and self-grooming activities while concurrently leading to a decline in social contacts. In addition, we investigated the potential molecular mechanisms that underlie the impact of AFB1 on the production of Th1 (IFN-γ, STAT1, and T-bet), Th9 (IL-9 and IRF4), Th17 (IL-17A, IL-21, RORγT, and STAT3), Th22 (IL-22, AhR, and TNF-α), and T regulatory (Treg) (IL-10, TGF-β1, and FoxP3) cells in the spleen. This was achieved using RT-PCR and Western blot analyses to assess mRNA and protein expression in brain tissue. The exposure to AFB1 resulted in a significant upregulation of various immune-related factors, including IFN-γ, STAT1, T-bet, IL-9, IRF4, IL-17A, IL-21, RORγ, STAT3, IL-22, AhR, and TNF-α in BTBR mice. Conversely, the production of IL-10, TGF-β1, and FoxP3 by CD4+ T cells was observed to be downregulated. Exposure to AFB1 demonstrated a notable rise in Th1/Th9/Th22/Th17 levels and a decrease in mRNA and protein expression of Treg. The results above underscore the significance of AFB1 exposure in intensifying neurobehavioral and immunological abnormalities in BTBR mice, hence indicating the necessity for a more comprehensive investigation into the contribution of AFB1 to the development of ASD.

Upregulation of Inflammatory Mediators in Peripheral Blood CD40+ Cells in Children with Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a common and severe neurodevelopmental disorder in early childhood, defined as social and communication deficits and repetitive and stereotypic behaviours. The aetiology is unknown in most cases. However, several studies have identified immune dysregulation as potentially promoting ASD. Among the numerous immunological findings in ASD, reports of increased pro-inflammatory markers remain the most consistently observed. C-C chemokine receptor type 1 (CCR1) activation is pro-inflammatory in several neurological disorders. Previous evidence has implied that the expression of chemokine receptors, inflammatory mediators, and transcription factors play a pivotal role in several neuroinflammatory disorders. There have also been reports on the association between increased levels of proinflammatory cytokines and ASD. In this study, we aimed to investigate the possible involvement of CCR1, inflammatory mediators, and transcription factor expression in CD40⁺ cells in ASD compared to typically developing controls (TDC). Flow cytometry analysis was used to determine the levels of CCR1-, IFN-γ-, T-box transcription factor (T-bet-), IL-17A-, retinoid-related orphan receptor gamma t (RORγt-), IL-22- and TNF-α-expressing CD40 cells in PBMCs in children with ASD and the TDC group. We further examined the mRNA and protein expression levels of CCR1 using real-time PCR and western blot analysis. Our results revealed that children with ASD had significantly increased numbers of CD40⁺CCR1⁺, CD40⁺IFN-γ⁺, CD40⁺T-bet⁺, CD40⁺IL-17A⁺, CD40⁺RORγt⁺, CD4⁺IL-22⁺, and CD40⁺TNF-α⁺ cells compared with the TDC group. Furthermore, children with ASD had higher CCR1 mRNA and protein expression levels than those in the TDC group. These results indicate that CCR1, inflammatory mediators, and transcription factors expressed in CD40 cells play vital roles in disease progression.

Murine cytomegalovirus promotes renal allograft inflammation via Th1/17 cells and IL-17A

Human cytomegalovirus (HCMV) infection is associated with renal allograft failure. Allograft damage in animal models is accelerated by CMV-induced T helper 17 (Th17) cell infiltrates. However, the mechanisms whereby CMV promotes Th17 cell-mediated pathological organ inflammation are uncharacterized. Here we demonstrate that murine CMV (MCMV)-induced intragraft Th17 cells have a Th1/17 phenotype co-expressing IFN-γ and/or TNF-α, but only a minority of these cells are MCMV specific. Instead, MCMV promotes intragraft expression of CCL20 and CXCL10, which are associated with recruitment of CCR6⁺ CXCR3⁺ Th17 cells. MCMV also enhances Th17 cell infiltrates after ischemia-reperfusion injury, independent of allogeneic responses. Pharmacologic inhibition of the Th17 cell signature cytokine, IL-17A, ameliorates MCMV-associated allograft damage without increasing intragraft viral loads or reducing MCMV-specific Th1 cell infiltrates. Clinically, HCMV DNAemia is associated with higher serum IL-17A among renal transplant patients with acute rejection, linking HCMV reactivation with Th17 cell cytokine expression. In summary, CMV promotes allograft damage via cytokine-mediated Th1/17 cell recruitment, which may be pharmacologically targeted to mitigate graft injury while preserving antiviral T cell immunity.

Tim-3 on CD4+ T cells is associated with pathology in experimental autoimmune encephalomyelitis of mouse

Experimental autoimmune encephalomyelitis (EAE) is a reliable model to study the pathogenesis of Multiple sclerosis (MS), which is a progressive autoimmune-mediated inflammation of the central nervous system (CNS). Tim-3 is one of the crucial immune checkpoints in immune tolerance. We investigated the impact of Tim3 in EAE by the anti-Tim3 antibody and detected the immune cell and inflammation through flow cytometry and ELISA. In this study we found that CD4 T cells express low levels of Tim-3 in EAE mice. Tim-3 suppression exacerbated the disease progression in EAE mice. Furthermore, the Galectin-9/Tim-3 pathway promoted the apoptosis of CD4 T cells and inhibited the differentiation of Th17 in EAE mice. Our study unravels the anti-inflammatory Galectin-9/Tim-3 pathway in EAE mice and provides a potential therapeutic target for EAE and MS treatment.

Revisiting Traumatic Brain Injury: From Molecular Mechanisms to Therapeutic Interventions

Studying the complex molecular mechanisms involved in traumatic brain injury (TBI) is crucial for developing new therapies for TBI. Current treatments for TBI are primarily focused on patient stabilization and symptom mitigation. However, the field lacks defined therapies to prevent cell death, oxidative stress, and inflammatory cascades which lead to chronic pathology. Little can be done to treat the mechanical damage that occurs during the primary insult of a TBI; however, secondary injury mechanisms, such as inflammation, blood-brain barrier (BBB) breakdown, edema formation, excitotoxicity, oxidative stress, and cell death, can be targeted by therapeutic interventions. Elucidating the many mechanisms underlying secondary injury and studying targets of neuroprotective therapeutic agents is critical for developing new treatments. Therefore, we present a review on the molecular events following TBI from inflammation to programmed cell death and discuss current research and the latest therapeutic strategies to help understand TBI-mediated secondary injury.

Cytokines and Chemokines in the Pathogenesis of Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis is a CD4⁺ T cell-mediated demyelinating disease of the CNS that serves as a model for multiple sclerosis. Cytokines and chemokines shape Th1 and Th17 effector responses as well as regulate migration of leukocytes to the CNS during disease. The CNS cellular infiltrate consists of Ag-specific and nonspecific CD4⁺ and CD8⁺ T cells, neutrophils, B cells, monocytes, macrophages, and dendritic cells. The mechanism of immune-mediated inflammation in experimental autoimmune encephalomyelitis has been extensively studied in an effort to develop therapeutic modalities for multiple sclerosis and, indeed, has provided insight in modern drug discovery. The present Brief Review highlights critical pathogenic aspects of cytokines and chemokines involved in generation of effector T cell responses and migration of inflammatory cells to the CNS. Select cytokines and chemokines are certainly important in the regulatory response, which involves T regulatory, B regulatory, and myeloid-derived suppressor cells. However, that discussion is beyond the scope of this brief review.

Independent and inter-dependent immunoregulatory effects of NCF1 and NOS2 in experimental autoimmune encephalomyelitis

Background

Increasing evidence has suggested that a single nucleotide polymorphism in the Ncf1 gene is associated with experimental autoimmune encephalomyelitis (EAE). However, the mechanisms of NCF1-induced immunoregulatory effects remain poorly understood. In this study, we focus on NCF1 deficiency-mediated effects on EAE in NOS2 dependent and independent ways.

Methods

To determine the effects of NCF1 and NOS2 during EAE development, we have established recombinant mouse strains deficient at NCF1 and/or NOS2 in a crossbreeding system. Different strains allow us to examine the entire course of the disease in the Nos2-null mice bearing a Ncf1 gene that encodes a mutated NCF1, deficient in triggering oxidative burst, after immunization with recombinant myelin oligodendrocyte glycoprotein (MOG)_79-96 peptides. The peptide-induced innate and adaptive immune responses were analyzed by flow cytometry.

Results

NCF1-deficient mice developed a reduced susceptibility to EAE, whereas NCF1-NOS2 double-deficient mice developed an enhanced EAE, as compared with NOS2-deficient mice. Flow cytometry analyses show that double deficiencies resulted in an increase of neutrophils in the spleen, accompanied with higher release of interleukin-1β in neutrophils prior to EAE onset. The additional deficiency in NCF1 had no added effect on either interleukin-17 or interferon-γ secretion of T cells during the priming phase.

Conclusions

These studies show that NCF1 and NOS2 interact to regulate peptide-induced EAE.

Biological and clinical significance of T helper 17 cell plasticity

Mature T helper (Th) effector cells originate following antigen recognition by naive T precursors. The maturation process is accompanied by the acquisition of specific effector functions that distinguish at least three different T helper subsets: Th1, Th2 and Th17. In general, maturation of somatic cells is accompanied by terminal differentiation. However, accumulating evidence shows that effector T cells retain a certain degree of plasticity. This is especially true for Th17 cells, which have been shown to converge towards other phenotypes in response to specific microenvironmental pressure. In this review we will discuss the experimental evidence that supports the hypothesis of Th17 plasticity, with particular emphasis on the generation of Th17-derived 'non-classic' Th1 cells, and the molecular networks that control it. Moreover, we will consider why Th17 plasticity is important for host protection, but also why it can have pathogenic functions during chronic inflammation. Regarding the last point, we will discuss a possible role for biological drugs in the control of Th17 plasticity and disease course.

Toll-Like Receptor 4 Promotes Th17 Lymphocyte Infiltration Via CCL25/CCR9 in Pathogenesis of Experimental Autoimmune Encephalomyelitis

Toll-like receptor 4 (TLR4) is a key component in innate immunity and has been linked to central nervous system (CNS) inflammation diseases, such as multiple sclerosis (MS), an inflammatory disorder induced by autoreactive Th17 cells. In our study, we found that TLR4 deficient (TLR4^-/-) mice were inadequate to induce experimental autoimmune encephalomyelitis (EAE), characterized by low clinic score and weight loss, alleviative demyelinating, as well as decreased inflammatory cell infiltration in the spinal cord. In the lesion area of EAE mice, loss of TLR4 down-regulated the secretion of inflammatory cytokines and chemokine CCL25. Furthermore, the expression of CCR9 was decreased and chemotactic migration was attenuated in TLR4^-/- Th17 cells. Our results demonstrate that TLR4 may mediate Th17 infiltration through CCL25/CCR9 signal during pathogenesis of EAE. Graphical Abstract Immunofluorescent staining of RORγt (green) and CCR9 (red) in spinal cords. TLR4 deficiency down-regulates CCR9 expression in infiltrating lymphocytes.

The Diversity of Encephalitogenic CD4+ T Cells in Multiple Sclerosis and Its Animal Models

Autoreactive CD4+ T cells, which target antigens in central nervous system (CNS) myelin, are widely believed to play a critical role in the pathogenesis of multiple sclerosis (MS) in concert with other immune effectors. This theory is supported by data from animal model experiments, genome-wide association studies, and immune profiles of individuals with MS. Furthermore, disease modifying agents that target lymphocytes significantly reduce the rate of MS clinical exacerbations. However, the properties of myelin-reactive CD4+ T cells that are critical for their pathogenic activities are not understood completely. This article reviews the literature on encephalitogenic CD4+ T cells, with an emphasis on T-helper (Th) lineage and cytokine production. An increased understanding of the spectrum of encephalitogenic T cells and how they differ from protective subsets is necessary for the development of the next generation of more effective and safer immunomodulatory therapies customized for individuals with MS and related disorders.

The proportion of peripheral regulatory T cells in patients with Multiple Sclerosis: A meta-analysis

BACKGROUND

Accumulating evidence indicates that regulatory T cells (Tregs) play an important role in the maintenance of immune tolerance. And dysfunction or deficiency of Tregs is thought to be involved in the pathogenesis of Multiple Sclerosis (MS). Nevertheless, previous studies reporting Tregs in patients were controversial due to the different markers adopted to identify Tregs. To clarify the status of Tregs in the pathogenesis of MS patients, we did a meta-analysis of the results published previously to assess the proportion of Tregs in peripheral blood (PB) in patients with MS.

METHODS

We systematically searched Embase, PubMed, Cochrane, Web of Knowledge, FDA.gov, and Clinical Trials.gov for the studies reporting the proportion of Tregs in MS patients. Our main endpoints were the proportion of Tregs among CD4⁺ T cells in PB defined by different markers. We assessed pooled data by using a random-effects model. Our meta-analysis had been registered at International Prospective Register of Systematic Reviews (PROSPERO) (number CRD42017064906).

RESULTS

Of 885 identified studies, a total 16 studies were selected in our analysis. There was no significant difference between MS patients and control subjects in Tregs identified by all Tregs definition methods [-0.07, (-0.46, 0.31, p = 0.706)] and Tregs defined by "CD4⁺ CD25⁺" [0.24, (-0.18, 0.65), p = 0.263]. Compared with control subjects, MS patients had a lower proportion of Tregs defined by "CD4⁺ CD25⁺ FOXP3⁺" [-0.75, (-0.46,0.31), p = 0.001].

CONCLUSION

Under random effect model of meta-analysis, the data showed that the results of Tregs in MS were different according to the definition method; and the proportion of Tregs defined by "CD4⁺ CD25⁺ FOXP3⁺" was decreased in MS. That result demonstrates that FOXP3 may be a vital definition of Tregs, and Tregs defined by stricter definition methods should be involved in the pathogenic mechanisms of MS.

Effective effectors: How T cells access and infiltrate the central nervous system

Several Phase II and III clinical trials have demonstrated that immunotherapy can induce objective responses in otherwise refractory malignancies in tumors outside the central nervous system. In large part, effector T cells mediate much of the antitumor efficacy in these trials, and potent antitumor T cells can be generated through vaccination, immune checkpoint blockade, adoptive transfer, and genetic manipulation. However, activated T cells must still traffic to, infiltrate, and persist within tumor in order to mediate tumor lysis. These requirements for efficacy pose unique challenges for brain tumor immunotherapy, due to specific anatomical barriers and populations of specialized immune cells within the central nervous system that function to constrain immunity. Both autoimmune and infectious diseases of the central nervous system provide a wealth of information on how T cells can successfully migrate to the central nervous system and then engender sustained immune responses. In this review, we will examine the commonalities in the efferent arm of immunity to the brain for autoimmunity, infection, and tumor immunotherapy to identify key factors underlying potent immune responses.

Experimental Autoimmune Encephalomyelitis (EAE) as Animal Models of Multiple Sclerosis (MS)

Multiple sclerosis (MS) is a multifocal demyelinating disease of the central nervous system (CNS) leading to the progressive destruction of the myelin sheath surrounding axons. It can present with variable clinical and pathological manifestations, which might reflect the involvement of distinct pathogenic processes. Although the mechanisms leading to the development of the disease are not fully understood, numerous evidences indicate that MS is an autoimmune disease, the initiation and progression of which are dependent on an autoimmune response against myelin antigens. In addition, genetic susceptibility and environmental triggers likely contribute to the initiation of the disease. At this time, there is no cure for MS, but several disease-modifying therapies (DMTs) are available to control and slow down disease progression. A good number of these DMTs were identified and tested using animal models of MS referred to as experimental autoimmune encephalomyelitis (EAE). In this review, we will recapitulate the characteristics of EAE models and discuss how they help shed light on MS pathogenesis and help test new treatments for MS patients.

MiR-409-3p and MiR-1896 co-operatively participate in IL-17-induced inflammatory cytokine production in astrocytes and pathogenesis of EAE mice via targeting SOCS3/STAT3 signaling

Th17 cells and interleukin-17 (IL-17) have been found to play an important role in the pathology of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Response to IL-17, reactive astrocytes accompany with immune cells infiltration and axonal damage in MS/EAE. However, the role and the regulatory mechanism of IL-17-activated astrocytes in inflammation and in the EAE process still remain largely unknown. Here, we elucidated that miR-409-3p and miR-1896, as co-upregulated microRNAs in activated astrocytes and in EAE mice, targeted suppressor of cytokine signaling proteins 3 (SOCS3). Overexpression of miR-409-3p or miR-1896 significantly reduced SOCS3 expression and increased phosphorylation of STAT3 as well as induced the inflammatory cytokines production (IL-1β, IL-6, IP-10, MCP-1, and KC), CD4⁺ T cells migration and demyelination, in turn aggravating EAE development. Importantly, the effects of co-overexpression of miR-409-3p and miR-1896 in vitro or in vivo are strongly co-operative. In contrast, simultaneously silenced miR-409-3p and miR-1896 co-operatively ameliorates inflammation and demyelination in the central nervous system of EAE mice. Collectively, our findings highlight that miR-409-3p and miR-1896 co-ordinately promote the production of inflammatory cytokines in reactive astrocytes through the SOCS3/STAT3 pathway and enhance reactive astrocyte-directed chemotaxis of CD4⁺ T cells, leading to aggravate pathogenesis in EAE mice. Co-inhibition of miR-409-3p and miR-1896 may be a therapeutic target for treating MS and neuroinflammation.

TRAIL-Mediated Suppression of T Cell Receptor Signaling Inhibits T Cell Activation and Inflammation in Experimental Autoimmune Encephalomyelitis

Objective

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces cell apoptosis by transducing apoptosis signals after interacting with its receptor (TRAIL-R). Although the actual biological role of TRAIL remains to be elucidated, recent accumulating evidence implies that TRAIL regulates immune responses and immune cell homeostasis via an apoptosis-independent pathway, suggesting a novel immune-regulatory role of TRAIL in autoimmune diseases. The purpose of this study is to address the immune-regulatory role and molecular mechanism of TRAIL in regulating T cell activation in autoimmune diseases.

Design

TRAIL was administered to mice to induce experimental autoimmune encephalomyelitis (EAE), and to evaluate its impact on neuroinflammation and disease activity. The effects of TRAIL on neuroantigen [myelin oligodendrocyte glycoprotein (MOG)_35–55]-activated T cell proliferation and cytokine production were investigated. TRAIL-treated MOG_35–55-activated splenic Th17 cells were further adoptively transferred into Rag1 KO mice to induce passive EAE. Gene expression profiles of CD4⁺ T cells from EAE mice treated with TRAIL were analyzed by RNA sequencing and transcriptome analysis.

Results

TRAIL suppressed autoimmune encephalomyelitis and inhibited T cell reactivity to neuro-antigen in murine EAE, and the effects were dependent on TRAIL-R signaling. Moreover, TRAIL directly inhibited activation of MOG_35–55-activated CD4⁺ T cells, resulting in suppression of neuroinflammation and reduced disease activity in adoptive transfer-induced EAE. Furthermore, TRAIL-R signaling inhibited phosphorylation of proximal T cell receptor (TCR)-associated tyrosine kinases in activated CD4⁺ T cells. Importantly, TRAIL/TRAIL-R interaction downregulated TCR downstream signaling genes in RNA sequencing and transcriptome analysis.

Conclusion

TRAIL/TRAIL-R interaction regulates CD4⁺ T cell activation in autoimmune inflammation and directly suppresses T cell activation via inhibiting TCR signaling, suggesting that TRAIL-R serves as a novel immune checkpoint in T cell responses.

Transcriptional signature of human pro-inflammatory TH17 cells identifies reduced IL10 gene expression in multiple sclerosis

We have previously reported the molecular signature of murine pathogenic T_H17 cells that induce experimental autoimmune encephalomyelitis (EAE) in animals. Here we show that human peripheral blood IFN-γ⁺IL-17⁺ (T_H1/17) and IFN-γ⁻IL-17⁺ (T_H17) CD4⁺ T cells display distinct transcriptional profiles in high-throughput transcription analyses. Compared to T_H17 cells, T_H1/17 cells have gene signatures with marked similarity to mouse pathogenic T_H17 cells. Assessing 15 representative signature genes in patients with multiple sclerosis, we find that T_H1/17 cells have elevated expression of CXCR3 and reduced expression of IFNG, CCL3, CLL4, GZMB, and IL10 compared to healthy controls. Moreover, higher expression of IL10 in T_H17 cells is found in clinically stable vs. active patients. Our results define the molecular signature of human pro-inflammatory T_H17 cells, which can be used to both identify pathogenic T_H17 cells and to measure the effect of treatment on T_H17 cells in human autoimmune diseases.

CD4⁺ T cells secreting interleukin-17 (T_H17) have diverse functions in modulating autoimmune diseases. Here the authors show via transcriptome analyses that a subset of human T_H 17 co-expressing interferon-γ (T_H1/17) has a molecular signature similar to “pathogenic” mouse T_H 17 but distinct from “non-pathogenic” mouse T_H 17.

Levels of peripheral Th17 cells and serum Th17-related cytokines in patients with multiple sclerosis: A meta-analysis

BACKGROUND

Multiple reports have described the proportion of Th17 cells in peripheral blood and serum levels of Th17-related cytokines in patients with multiple sclerosis (MS). To clarify the status of Th17 cells and Th17-related cytokines in MS patients, we did a meta-analysis of the results published previously to assess the levels of peripheral Th17 cells and serum Th17-related cytokines in patients with MS.

METHODS

We searched Embase, PubMed, Cochrane, Web of Knowledge, FDA.gov, and Clinical Trials.gov systematically for studies reporting the proportion of Th17 cells and the serum levels of Th17-related cytokines (IL-17, IL23) in MS patients. Our main endpoints were the proportion of Th17 cells among CD4⁺ T cells in peripheral blood (PB), serum IL-17 levels, and serum IL-23 levels. We assessed pooled data by using a random-effects model. It has been registered at International Prospective Register of Systematic Reviews (PROSPERO) (number CRD42017059113).

RESULTS

Of 560 identified studies, a total of 12 studies were selected in our analysis. Compared with control subjects, MS patients had a higher proportion of Th17 cells [1.37, (0.53, 2.21)] in PB, an elevated levels of serum IL-17 [2.48, (1.25, 3.71)] and an increased IL-23 levels in serum [2.29, (0.58, 4.00)].

CONCLUSION

Under random effect model of meta-analysis, the data showed that the proportion of Th17 cells in PB and levels of serum IL-17 and IL-23 increased among MS patients compared to control subjects. This result demonstrated that Th17 cells and Th17-related cytokines may be involved in the pathogenic mechanisms of MS.

White matter damage after traumatic brain injury: A role for damage associated molecular patterns

Traumatic brain injury (TBI) is a leading cause of mortality and long-term morbidity worldwide. Despite decades of pre-clinical investigation, therapeutic strategies focused on acute neuroprotection failed to improve TBI outcomes. This lack of translational success has necessitated a reassessment of the optimal targets for intervention, including a heightened focus on secondary injury mechanisms. Chronic immune activation correlates with progressive neurodegeneration for decades after TBI; however, significant challenges remain in functionally and mechanistically defining immune activation after TBI. In this review, we explore the burgeoning evidence implicating the acute release of damage associated molecular patterns (DAMPs), such as adenosine 5'-triphosphate (ATP), high mobility group box protein 1 (HMGB1), S100 proteins, and hyaluronic acid in the initiation of progressive neurological injury, including white matter loss after TBI. The role that pattern recognition receptors, including toll-like receptor and purinergic receptors, play in progressive neurological injury after TBI is detailed. Finally, we provide support for the notion that resident and infiltrating macrophages are critical cellular targets linking acute DAMP release with adaptive immune responses and chronic injury after TBI. The therapeutic potential of targeting DAMPs and barriers to clinical translational, in the context of TBI patient management, are discussed.

Lineage-Specific Metabolic Properties and Vulnerabilities of T Cells in the Demyelinating Central Nervous System

Multiple sclerosis (MS) is a disease that is characterized by immune-mediated destruction of CNS myelin. Current MS therapies aim to block peripheral immune cells from entering the CNS. Although these treatments limit new inflammatory activity in the CNS, no treatment effectively prevents long-term disease progression and disability accumulation in MS patients. One explanation for this paradox is that current therapies are ineffective at targeting immune responses already present in the CNS. To this end, we sought to understand the metabolic properties of T cells that mediate ongoing inflammation in the demyelinating CNS. Using experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice, a well-studied model of MS, we showed that the CD4⁺ and CD8⁺ T cells that invade the EAE CNS are highly glycolytic. Elevated glycolytic rates in T cells isolated from the EAE CNS correlate with upregulated expression of glycolytic machinery and is essential for inflammatory responses to myelin. Surprisingly, we found that an inhibitor of GAPDH, 3-bromopyruvic acid (3-BrPa), blocks IFN-γ, but not IL-17A, production in immune cells isolated from the EAE CNS. Indeed, in vitro studies confirmed that the production of IFN-γ by differentiated Th1 cells is more sensitive to 3-BrPa than is the production of IL-17A by Th17 cells. Finally, in transfer models of EAE, 3-BrPa robustly attenuates the encephalitogenic potential of EAE-driving immune cells. To our knowledge, these data are among the first to demonstrate the metabolic properties of T cells in the demyelinating CNS in vivo.

Regulation of effector function of CNS autoreactive CD4 T cells through inhibitory receptors and IL-7Rα

Background

Multiple sclerosis (MS) is a chronic CNS autoimmune disease characterized by inflammation, demyelination, and neuronal degeneration, where myelin-specific CD4 T cells play critical roles in the formation of acute MS lesions and disease progression. The suppression of IL-7Rα expression and the upregulation of inhibitory receptors (PD-1, etc.) are essential parts of the cell-intrinsic immunosuppressive program regulating T effector functions to prevent autoimmunity. However, little is known on the factors regulating IL-7Rα/PD-1 balance in myelin-specific CD4 T effector/memory cells during the development of CNS autoimmunity.

Methods

We analyzed the roles of the transcription factor T-bet in regulating the expression of IL-7Rα and inhibitory receptors in myelin-specific CD4 T cells. Furthermore, we compared the effects of different inflammatory cytokines that are crucial for Th1 and Th17 development in regulating the IL-7Rα/PD-1 balance.

Results

We discovered that T-bet suppresses the expression of inhibitory receptors (PD-1 and LAG-3) and promotes IL-7Rα expression in myelin-specific CD4 T cells in vitro and in vivo. As a result, T-bet skews IL-7Rα/PD-1 balance towards IL-7Rα and promotes enhanced effector function. Furthermore, IL-12 enhances IL-7Rα expression in a T-bet independent manner in myelin-specific Th1 cells. Meanwhile, IL-6, the cytokine inducing highly encephalitogenic Th17 differentiation, suppresses PD-1 while upregulating IL-7Rα, skewing IL-7Rα/PD-1 balance towards IL-7Rα, and promoting enhanced effector function. Moreover, blocking IL-7 signaling in myelin-specific CD4 T cells by αIL-7Rα significantly delays experimental autoimmune encephalomyelitis (EAE) onset and reduces disease severity.

Conclusions

T-bet is a major transcription factor regulating IL-7Rα/PD-1 balance in myelin-specific CD4 T cells during EAE development, and there is a positive correlation between several major determinants promoting T cell encephalitogenicity (T-bet, IL-6, IL-12) and an IL-7Rα/PD-1 balance skewed towards IL-7Rα. Furthermore, IL-7 signaling inhibits PD-1 expression in myelin-specific CD4 T cells and blocking IL-7 signaling suppresses T cell encephalitogenicity. Therefore, interference with inhibitory pathways and IL-7Rα expression may suppress the encephalitogenic potential of myelin-specific CD4 T cells and have therapeutic benefits for MS patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0768-3) contains supplementary material, which is available to authorized users.

T-bet promotes the accumulation of encephalitogenic Th17 cells in the CNS

T-bet enhances the encephalitogenicity of myelin-reactive CD4⁺ T cells, however its mechanism of action is unknown. In this study we show that T-bet confers a competitive advantage for the accumulation of IL-23 conditioned Th17 effector cells in the central nervous system (CNS). Impaired migration of T-bet deficient Th17 cells to the CNS is associated with altered expression of adhesion molecules and chemokine receptors on their cell surface. Our data suggest that therapeutic targeting of T-bet in individuals with Th17-mediated autoimmune demyelinating disease may inhibit inflammatory infiltration of the CNS and, hence, clinical exacerbations.

Tbet or Continued RORγt Expression Is Not Required for Th17-Associated Immunopathology

The discovery of Th17 cell plasticity, in which CD4⁺ IL-17–producing Th17 cells give rise to IL-17/IFN-γ double-producing cells and Th1-like IFNγ⁺ ex-Th17 lymphocytes, has raised questions regarding which of these cell types contribute to immunopathology during inflammatory diseases. In this study, we show using Helicobacter hepaticus-induced intestinal inflammation that IL-17A^Cre– or Rag1^Cre-mediated deletion of Tbx21 has no effect on the generation of IL-17/IFN-γ double-producing cells, but leads to a marked absence of Th1-like IFNγ⁺ ex-Th17 cells. Despite the lack of Th1-like ex-Th17 cells, the degree of H. hepaticus-triggered intestinal inflammation in mice in which Tbx21 was excised in IL-17–producing or Rag1-expressing cells is indistinguishable from that observed in control mice. In stark contrast, using experimental autoimmune encephalomyelitis, we show that IL-17A^Cre–mediated deletion of Tbx21 prevents the conversion of Th17 cells to IL-17A/IFN-γ double-producing cells as well as Th1-like IFN-γ⁺ ex-Th17 cells. However, IL-17A^Cre–mediated deletion of Tbx21 has only limited effects on disease course in this model and is not compensated by Ag-specific Th1 cells. IL-17A^Cre–mediated deletion of Rorc reveals that RORγt is essential for the maintenance of the Th17 cell lineage, but not immunopathology during experimental autoimmune encephalomyelitis. These results show that neither the single Th17 subset, nor its progeny, is solely responsible for immunopathology or autoimmunity.

Effector γδ T Cell Differentiation Relies on Master but Not Auxiliary Th Cell Transcription Factors

γδ T lymphocytes are programmed into distinct IFN-γ-producing CD27(+) (γδ27(+)) and IL-17-producing CD27(-) (γδ27(-)) subsets that play key roles in protective or pathogenic immune responses. Although the signature cytokines are shared with their αβ Th1 (for γδ27(+)) and Th17 (for γδ27(-)) cell counterparts, we dissect in this study similarities and differences in the transcriptional requirements of murine effector γδ27(+), γδ27(-)CCR6(-), and γδ27(-)CCR6(+) γδ T cell subsets and αβ T cells. We found they share dependence on the master transcription factors T-bet and RORγt for IFN-γ and IL-17 production, respectively. However, Eomes is fully dispensable for IFN-γ production by γδ T cells. Furthermore, the Th17 cell auxiliary transcription factors RORα and BATF are not required for IL-17 production by γδ27(-) cell subsets. We also show that γδ27(-) (but not γδ27(+)) cells become polyfunctional upon IL-1β plus IL-23 stimulation, cosecreting IL-17A, IL-17F, IL-22, GM-CSF, and IFN-γ. Collectively, our in vitro and in vivo data firmly establish the molecular segregation between γδ27(+) and γδ27(-) T cell subsets and provide novel insight on the nonoverlapping transcriptional networks that control the differentiation of effector γδ versus αβ T cell subsets.

T-bet Regulates Natural Regulatory T Cell Afferent Lymphatic Migration and Suppressive Function

T-bet is essential for natural regulatory T cells (nTreg) to regulate Th1 inflammation, but whether T-bet controls other Treg functions after entering the inflammatory site is unknown. In an islet allograft model, T-bet(-/-) nTreg, but not induced Treg, failed to prolong graft survival as effectively as wild-type Treg. T-bet(-/-) nTreg had no functional deficiency in vitro but failed to home from the graft to draining lymph nodes (dLN) as efficiently as wild type. T-bet regulated expression of adhesion- and migration-related molecules, influencing nTreg distribution in tissues, so that T-bet(-/-) nTreg remained in the grafts rather than migrating to lymphatics and dLN. In contrast, both wild-type and T-bet(-/-) CD4(+) conventional T cells and induced Treg migrated normally toward afferent lymphatics. T-bet(-/-) nTreg displayed instability in the graft, failing to suppress Ag-specific CD4(+) T cells and prevent their infiltration into the graft and dLN. Thus, T-bet regulates nTreg migration into afferent lymphatics and dLN and consequently their suppressive stability in vivo.

IL-12-polarized Th1 cells produce GM-CSF and induce EAE independent of IL-23

CD4(+) T-helper (Th) cells reactive against myelin antigens mediate the mouse model experimental autoimmune encephalomyelitis (EAE) and have been implicated in the pathogenesis of multiple sclerosis (MS). It is currently debated whether encephalitogenic Th cells are heterogeneous or arise from a single lineage. In the current study, we challenge the dogma that stimulation with the monokine IL-23 is universally required for the acquisition of pathogenic properties by myelin-reactive T cells. We show that IL-12-modulated Th1 cells readily produce IFN-γ and GM-CSF in the CNS of mice and induce a severe form of EAE via an IL-23-independent pathway. Th1-mediated EAE is characterized by monocyte-rich CNS infiltrates, elicits a strong proinflammatory cytokine response in the CNS, and is partially CCR2 dependent. Conversely, IL-23-modulated, stable Th17 cells induce EAE with a relatively mild course via an IL-12-independent pathway. These data provide definitive evidence that autoimmune disease can be driven by distinct CD4(+) T-helper-cell subsets and polarizing factors.

Th17 cells give rise to Th1 cells that are required for the pathogenesis of colitis

Th17 cells reactive to the enteric microbiota are central to the pathogenesis of certain types of inflammatory bowel disease. However, Th17 cells display substantial developmental plasticity, such that some progeny of Th17 cell precursors retain a predominantly IL-17A(+) phenotype, whereas others extinguish IL-17 expression and acquire expression of IFN-γ, giving rise to "Th1-like" cells. It remains unclear what role these subsets play in inflammatory bowel disease. Using a Th17 transfer model of colitis, we found that IFN-γ-deficient Th17 cells retained an IL-17A(+) phenotype and were unable to induce colitis in recipients. Development of disease required the transition of a subset of Th17 precursors to Th1-like cells and was contingent on the expression of both Stat4 and T-bet, but not the IL-12 or IFN-γ receptors. Moreover, Th17 cells could provide "help" for the development of pathogenic Th1 cells from naïve precursors. These results indicate that Th17 cells are potent mediators of colitis pathogenesis by dual mechanisms: by directly transitioning to Th1-like cells and by supporting the development of classic Th1 cells.

Violacein Treatment Modulates Acute and Chronic Inflammation through the Suppression of Cytokine Production and Induction of Regulatory T Cells

Inflammation is a necessary process to control infection. However, exacerbated inflammation, acute or chronic, promotes deleterious effects in the organism. Violacein (viola), a quorum sensing metabolite from the Gram-negative bacterium Chromobacterium violaceum, has been shown to protect mice from malaria and to have beneficial effects on tumors. However, it is not known whether this drug possesses anti-inflammatory activity. In this study, we investigated whether viola administration is able to reduce acute and chronic autoimmune inflammation. For that purpose, C57BL/6 mice were intraperitoneally injected with 1 μg of LPS and were treated with viola (3.5mg/kg) via i.p. at the same time-point. Three hours later, the levels of inflammatory cytokines in the sera and phenotypical characterization of leukocytes were determined. Mice treated with viola presented a significant reduction in the production of inflammatory cytokines compared with untreated mice. Interestingly, although viola is a compound derived from bacteria, it did not induce inflammation upon administration to naïve mice. To test whether viola would protect mice from an autoimmune inflammation, Experimental Autoimmune Encephalomyelitis (EAE)-inflicted mice were given viola i.p. at disease onset, at the 10th day from immunization. Viola-treated mice developed mild EAE disease in contrast with placebo-treated mice. The frequencies of dendritic cells and macrophages were unaltered in EAE mice treated with viola. However, the sole administration of viola augmented the levels of splenic regulatory T cells (CD4+Foxp3+). We also found that adoptive transfer of viola-elicited regulatory T cells significantly reduced EAE. Our study shows, for the first time, that violacein is able to modulate acute and chronic inflammation. Amelioration relied in suppression of cytokine production (in acute inflammation) and stimulation of regulatory T cells (in chronic inflammation). New studies must be conducted in order to assess the possible use of viola in therapeutic approaches in human autoimmune diseases.

Is T-bet a potential therapeutic target in multiple sclerosis?

Treatments for multiple sclerosis (MS) have changed over the past years as our understanding of immunology and neuroscience has evolved. Experimental autoimmune encephalomyelitis (EAE) continues to remain the major model for MS and has been a major vehicle in the development of new therapeutic targets for MS, including new agents such as natalizumab, fingolimod, and dimethyl fumarate. As progress in the molecular understanding of immunology continues, many observations in EAE are pursued with the ultimate goal of defining the pathophysiology of MS and development of innovative treatments for the disease. Although many consider MS to be a T cell-mediated autoimmune disease directed against myelin antigens, the exact cause of the disease is still unknown. For many years, it was thought that myelin-specific T cells that secreted interferon-γ and were proinflammatory were the major T cell subset that mediated the disease, but recent studies on the cytokine phenotype of pathogenic T cells in EAE and MS have opened debate on this issue. Work over the past several years suggests that the transcription factor T-bet appears to be an important factor in T cell encephalitogenicity; however, recent data suggest that it is also dispensable in certain situations, particularly for Th17 cells. Understanding the molecular mechanisms responsible for T cell encephalitogenicity in MS and other autoimmune diseases will be essential in the development of specific therapies for these inflammatory diseases.

Interaction of astrocytes and T cells in physiological and pathological conditions

The central nervous system (CNS) has long been recognized as a site of 'immune privilege' because of the existence of the blood brain barrier (BBB) which presumably isolates CNS from the peripheral immunosurveillance. Different from the peripheral organs, CNS is unique in response to all forms of CNS injury and disease which is mainly mediated by resident microglia and astrocyte. There is increasing evidence that immune cells are not only involved in neuroinflammation process but also the maintenance of CNS homeostasis. T cells, an important immune cell population, are involved in the pathogenesis of some neurological diseases by inducing either innate or adaptive immune responses. Astrocytes, which are the most abundant cell type in the CNS, maintain the integrity of BBB and actively participate in the initiation and progression of neurological diseases. Surprisingly, how astrocytes and T cells interact and the consequences of their interaction are not clear. In this review we briefly summarized T cells diversity and astrocyte function. Then, we examined the evidence for the astrocytes and T cells interaction under physiological and pathological conditions including ischemic stroke, multiple sclerosis, viral infection, and Alzheimer's disease. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

T-bet Expression by Foxp3(+) T Regulatory Cells is Not Essential for Their Suppressive Function in CNS Autoimmune Disease or Colitis

Accumulation of T regulatory (Treg) cells within the central nervous system (CNS) during experimental autoimmune encephalomyelitis (EAE) is essential for the resolution of disease. CNS Treg cells have been shown to uniformly express the Th1-associated molecules, T-bet and CXCR3. Here, we report that the expression of T-bet is not required for the function of these Treg within the CNS. Using mice that lacked T-bet expression specifically within the Treg compartment, we demonstrate that there was no deficit in Treg recruitment into the CNS during EAE and no difference in the resolution of disease compared to control mice. T-bet deficiency did not impact on the in vitro suppressive capacity of Treg. Transfer of T-bet-deficient Treg was able to suppress clinical signs of either EAE or colitis. These observations demonstrate that, although Treg can acquire characteristics associated with pathogenic T effector cells, this process is not necessarily required for their suppressive capacity and the resolution of autoimmune inflammation.

Helicobacter pylori infection reduces disease severity in an experimental model of multiple sclerosis

Recent research has demonstrated that infection with the bacterial pathogen Helicobacter pylori is less common amongst patients with multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system (CNS). We aimed to compare the prevalence of H. pylori amongst MS patients and healthy controls, and also investigated the impact of this infection on an animal model for MS, experimental autoimmune encephalomyelitis (EAE). The H. pylori status of 71 MS patients and 42 healthy controls was determined by serology. Groups of C57BL/6 mice were infected with H. pylori, or given diluent alone as a placebo, prior to inducing EAE. Clinical scores were assessed for all mice, and spleens and spinal cord tissue were harvested. CD4⁺ T cell subsets were quantified by flow cytometry, and T cell proliferation assays were performed. In MS patients the seroprevalence of H. pylori was half that of healthy controls (p = 0.018). Over three independent experiments, prior H. pylori infection had a moderate effect in reducing the severity of EAE (p = 0.012). In line with this, the antigen-specific T cell proliferative responses of infected animals were significantly reduced (p = 0.001), and there was a fourfold reduction in the number of CD4⁺ cells in the CNS. CD4⁺ populations in both the CNS and the spleens of infected mice also contained greatly reduced proportions of IFNγ⁺, IL-17⁺, T-bet⁺, and RORγt⁺ cells, but the proportions of Foxp3⁺ cells were equivalent. There were no differences in the frequency of splenic CD4⁺cells expressing markers of apoptosis between infected and uninfected animals. H. pylori was less prevalent amongst MS patients. In mice, the infection exerted some protection against EAE, inhibiting both Th1 and Th17 responses. This could not be explained by the presence of increased numbers of Foxp3⁺ regulatory T cells, or T cell apoptosis. This is the first direct experimental evidence showing that H. pylori may provide protection against inflammatory demyelination in the CNS.

Impact of suppressing retinoic acid-related orphan receptor gamma t (ROR)γt in ameliorating central nervous system autoimmunity

Multiple sclerosis (MS) is an immune-mediated chronic central nervous system (CNS) disease affecting more than 400 000 people in the United States. Myelin-reactive CD4 T cells play critical roles in the formation of acute inflammatory lesions and disease progression in MS and experimental autoimmune encephalomyelitis (EAE), a well-defined mouse model for MS. Current MS therapies are only partially effective, making it necessary to develop more effective therapies that specifically target pathogenic myelin-specific CD4 T cells for MS treatment. While suppressing T-bet, the key transcription factor in T helper type 1 (Th1) cells, has been demonstrated to be beneficial in prevention and treatment of EAE, the therapeutic potential of retinoic acid-related orphan receptor gamma t (ROR)γt, the key transcription factor for Th17 cells, has not been well-characterized. In this study, we characterized the correlation between RORγt expression and other factors affecting T cell encephalitogenicity and evaluated the therapeutic potential of targeting RORγt by siRNA inhibition of RORγt. Our data showed that RORγt expression correlates with interleukin (IL)-17 production, but not with the encephalitogenicity of myelin-specific CD4 T cells. IL-23, a cytokine that enhances encephalitogenicity, does not enhance RORγt expression significantly. Additionally, granulocyte-macrophage colony-stimulating factor (GM-CSF) levels, which correlate with the encephalitogenicity of different myelin-specific CD4 T cell populations, do not correlate with RORγt. More importantly, inhibiting RORγt expression in myelin-specific CD4 T cells with an siRNA does not reduce disease severity significantly in adoptively transferred EAE. Thus, RORγt is unlikely to be a more effective therapeutic target for ameliorating pathogenicity of encephalitogenic CD4 T cells.

Cellular Plasticity of CD4+ T Cells in the Intestine

Barrier sites such as the gastrointestinal tract are in constant contact with the environment, which contains both beneficial and harmful components. The immune system at the epithelia must make the distinction between these components to balance tolerance, protection, and immunopathology. This is achieved via multifaceted immune recognition, highly organized lymphoid structures, and the interaction of many types of immune cells. The adaptive immune response in the gut is orchestrated by CD4⁺ helper T (Th) cells, which are integral to gut immunity. In recent years, it has become apparent that the functional identity of these Th cells is not as fixed as initially thought. Plasticity in differentiated T cell subsets has now been firmly established, in both health and disease. The gut, in particular, utilizes CD4⁺ T cell plasticity to mold CD4⁺ T cell phenotypes to maintain its finely poised balance of tolerance and inflammation and to encourage biodiversity within the enteric microbiome. In this review, we will discuss intestinal helper T cell plasticity and our current understanding of its mechanisms, including our growing knowledge of an evolutionarily ancient symbiosis between microbiota and malleable CD4⁺ T cell effectors.

miR-20b suppresses Th17 differentiation and the pathogenesis of experimental autoimmune encephalomyelitis by targeting RORγt and STAT3

The differentiation and function of IL-17-producing Th17 cells are tightly regulated by specific transcription factors and cytokines, which are the key participants in the pathogenesis of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). Although specific miRNAs have been shown to be involved in the development of MS and EAE, the potential role of miRNAs in the context of Th17-driven autoimmunity is just beginning to be clarified. miR-20b has been reported as a downregulated miRNA in blood cells of MS patients. In this report, it was further studied in greater detail because we found it was significantly downregulated during EAE, and, in the in vitro differentiation model, Th17 cells had lower expression of miR-20b than did Th1, Th2, or inducible T regulatory cells. Ectopic expression of miR-20b repressed Th17 differentiation in vitro. Using lentiviral vectors for miR-20b overexpression in vivo, we demonstrated that overexpression of miR-20b led to decreased Th17 cells and reduced severity of EAE. Furthermore, we also identified both RAR-related orphan receptor γt and STAT3 as potential targets of miR-20b. Finally, we confirmed that the mild disease severity and low number of Th17 cells in LV-miR-20b-infected mice were largely reversed by coinfection of these mice with lentivirus-expressing RAR-related orphan receptor γt or STAT3 3'-untranslated regions. Taken together, our results contribute to the importance of miRNAs in Th17 differentiation and pathogenesis of MS and EAE.

IFNγ inhibits Th17 differentiation and function via Tbet-dependent and Tbet-independent mechanisms

The transcription factor Tbet is critical for the differentiation of Th1 CD4 T cells and is associated with the induction of multiple autoimmune diseases, including experimental autoimmune encephalomyelitis (EAE). Herein, we demonstrate that Tbet suppresses IL-17A and Th17 differentiation both in vitro and in vivo in a cell-intrinsic manner, and that in fact, Tbet is not necessary for EAE induction. Moreover, we find that IFNγ inhibits the production of IL-17A and IL-17F in a STAT1-dependent, Tbet-independent manner. These findings illustrate multiple mechanisms utilized by developing Th1 cells to silence the Th17 program.

Molecular Mechanisms of Differentiation of Murine Pro-Inflammatory γδ T Cell Subsets

γδ T cells are unconventional innate-like lymphocytes that actively participate in protective immunity against tumors and infectious organisms including bacteria, viruses, and parasites. However, γδ T cells are also involved in the development of inflammatory and autoimmune diseases. γδ T cells are functionally characterized by very rapid production of pro-inflammatory cytokines, while also impacting on (slower but long-lasting) adaptive immune responses. This makes it crucial to understand the molecular mechanisms that regulate γδ T cell effector functions. Although they share many similarities with αβ T cells, our knowledge of the molecular pathways that control effector functions in γδ T cells still lags significantly behind. In this review, we focus on the segregation of interferon-γ versus interleukin-17 production in murine thymic-derived γδ T cell subsets defined by CD27 and CCR6 expression levels. We summarize the most recent studies that disclose the specific epigenetic and transcriptional mechanisms that govern the stability or plasticity of discrete pro-inflammatory γδ T cell subsets, whose manipulation may be valuable for regulating (auto)immune responses.

Identity crisis of Th17 cells: many forms, many functions, many questions

Th17 cells are a subset of CD4(+) effector T cells characterized by expression of the IL-17-family cytokines, IL-17A and IL-17F. Since their discovery nearly a decade ago, Th17 cells have been implicated in the regulation of dozens of immune-mediated inflammatory diseases and cancer. However, attempts to clarify the development and function of Th17 cells in human health and disease have generated as many questions as answers. On one hand, cytokine expression in Th17 cells appears to be remarkably dynamic and is subject to extensive regulation (both positive and negative) in tissue microenvironments. On the other hand, accumulating evidence suggests that the human Th17 subset is a heterogeneous population composed of several distinct pro- and anti-inflammatory subsets. Clearly, Th17 cells as originally conceived no longer neatly fit the long-standing paradigm of stable and irrepressible effector T cell function. Here we review current concepts surrounding human Th17 cells, with an emphasis on their plasticity, heterogeneity, and their many, tissue-specific functions. In spite of the challenges ahead, a comprehensive understanding of Th17 cells and their relationship to human disease is key to ongoing efforts to develop safer and more selective anti-inflammatory medicines.

T-bet or not T-bet: taking the last bow on the autoimmunity stage

The search for the encephalitogenic factor driving pathogenic T cells in autoimmune diseases such as rheumatoid arthritis, multiple sclerosis (MS), and psoriasis has proven to be a long and difficult mission, which is not yet completed. In this issue of the European Journal of Immunology, the importance of the transcription factor T-bet, previously shown to be essential for the induction of autoimmune disease in mice, is challenged. Two independent groups, O'Connor et al. [Eur. J. Immunol. 2013. 43:2818-2823] report] and Grifka-Walk et al. [Eur. J. Immunol. 2013. 43:2824-2831], report that T-bet is not mandatory for T cells to cause experimental autoimmune encephalomyelitis (EAE), which serves as a paradigmatic T-cell-mediated autoimmune disease. Both groups found that T-bet KO mice were fully susceptible to develop EAE, both after immunization with self-antigen and after adoptive transfer of IL-23-polarized autoaggressive T cells. T-bet deficiency mediated the loss of IFN-γ expression but retained or even enhanced GM-CSF and IL-17 production by central nervous system (CNS)-infiltrating T cells. These findings indicate that we have lost the last transcriptional regulator previously held to be required for the generation of autoimmune pathogenic T cells.