Cutting edge: Human Th17 cells are identified as bearing CCR2+CCR5- phenotype

Exploring the mechanisms of cow placental peptides in delaying liver aging based on mitochondrial energy metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

Placenta is a kind of traditional Chinese medicine, known as "Ziheche". The role of cow placental peptides (CPP) in delaying liver aging has been reported, and in-depth exploration of the specific regulatory mechanisms is of great significance for the recycling and utilization of CPP and the development of natural anti-aging drugs.

AIM OF THE STUDY

To investigate the protective effects and mechanisms of CPP on liver aging induced by D-galactose (D-gal) in mice from the perspective of mitochondrial energy metabolism.

METHODS

An aging model was induced in mice using D-gal. The body weight and liver index of mice were measured, followed by staining and electron microscopy to observe liver morphology and aging markers. Reactive oxygen species (ROS) levels and antioxidant-related indicators were assessed, and mitochondrial function was evaluated. Finally, changes and mechanisms in liver transcriptomics and targeted mitochondrial energy metabolomics were analyzed and integrated to elucidate the regulatory pathways through which CPP delays liver aging.

RESULTS

CPP improved liver structural damage, oxidative stress, and mitochondrial dysfunction induced by D-galactose in aging mice. It increased the final body weight and liver index, alleviated hepatocyte swelling and degeneration, enhanced liver antioxidant capacity, and restored normal mitochondrial morphology and function. The combined analysis of targeted mitochondrial energy metabolomics and liver transcriptomics revealed that CPP directly or indirectly regulated mitochondrial energy metabolism and delayed aging by influencing the cAMP signaling pathway, PI3K-Akt signaling pathway, oxidative phosphorylation, and other pathways, thereby modulating related genes and metabolites.

Iguratimod Ameliorates the Severity of Secondary Progressive Multiple Sclerosis in Model Mice by Directly Inhibiting IL-6 Production and Th17 Cell Migration via Mitigation of Glial Inflammation

We previously reported a novel secondary progressive multiple sclerosis (SPMS) model, progressive experimental autoimmune encephalomyelitis (pEAE), in oligodendroglia-specific Cx47-inducible conditional knockout (Cx47 icKO) mice. Based on our prior study showing the efficacy of iguratimod (IGU), an antirheumatic drug, for acute EAE treatment, we aimed to elucidate the effect of IGU on the SPMS animal model. We induced pEAE by immunizing Cx47 icKO mice with myelin oligodendrocyte glycoprotein peptide 35-55. IGU was orally administered from 17 to 50 days post-immunization. We also prepared a primary mixed glial cell culture and measured cytokine levels in the culture supernatant after stimulation with designated cytokines (IL-1α, C1q, TNF-α) and lipopolysaccharide. A migration assay was performed to evaluate the effect of IGU on the migration ability of T cells toward mixed glial cell cultures. IGU treatment ameliorated the clinical signs of pEAE, decreased the demyelinated area, and attenuated glial inflammation on immunohistochemical analysis. Additionally, IGU decreased the intrathecal IL-6 level and infiltrating Th17 cells. The migration assay revealed reduced Th17 cell migration and IL-6 levels in the culture supernatant after IGU treatment. Collectively, IGU successfully mitigated the clinical signs of pEAE by suppressing Th17 migration through inhibition of IL-6 production by proinflammatory-activated glial cells.

GM-CSF-producing CCR2+ CCR6+ Th17 cells are pathogenic in dextran sodium sulfate-induced colitis model in mice

Although excessive immune responses by Th17 cells, a helper T cell subset, are implicated in the pathogenesis of inflammatory bowel disease (IBD), the mechanism by which its localization in an inflamed colon is regulated remains unclear. Chemokines and their receptors are involved in the pathogenesis of IBD, however, the relative significance of each receptor on Th17 cells remains unknown. We generated C-C motif chemokine receptor 2 (CCR2) knockout (KO) and CCR6 KO mice in the syngeneic background using the CRISPR/Cas9 system and found that the phenotypes of experimental colitis worsened in both mutant mice. Surprisingly, the phenotype of colitis in CCR2/CCR6-double knockout (CCR2/6 DKO) mice was opposite to that of the single-deficient mice, with significantly milder experimental colitis (p < .05). The same was true for the symptoms in CCR6 KO mice, but not in wild type mice treated with a CCR2 inhibitor, propagermanium. Colonic CCR2⁺ CCR6⁺ Th17 cells produced a potentially pathogenic cytokine GM-CSF whose levels in the gut were significantly reduced in CCR2/6 DKO mice (p < .05). These results suggest that GM-CSF-producing CCR2⁺ CCR6⁺ Th17 cells are pathogenic and are attracted to the inflamed colon by either CCR2 or CCR6 gradient, which subsequently exacerbates experimental colitis in mice.

Autoimmunity in dry eye disease - An updated review of evidence on effector and memory Th17 cells in disease pathogenicity

The classic Th1/Th2 dogma has been significantly reshaped since the subsequent introduction of several new T helper cell subsets, among which the most intensively investigated during the last decade is the Th17 lineage that demonstrates critical pathogenic roles in autoimmunity and chronic inflammation - including the highly prevalent dry eye disease. In this review, we summarize current concepts of Th17-mediated disruption of ocular surface immune homeostasis that leads to autoimmune inflammatory dry eye disease, by discussing the induction, activation, differentiation, migration, and function of effector Th17 cells in disease development, highlighting the phenotypic and functional plasticity of Th17 lineage throughout the disease initiation, perpetuation and sustention. Furthermore, we emphasize the most recent advance in Th17 memory formation and function in the chronic course of dry eye disease, a major area to be better understood for facilitating the development of effective treatments in a broader field of autoimmune diseases that usually present a chronic course with recurrent episodes of flare in the target tissues or organs.

Absence of CCR2 reduces spontaneous intestinal tumorigenesis in the ApcMin /+ mouse model

The biological activities of chemokine (C-C motif) ligand 2 (CCL2) are mediated via C-C chemokine receptor-2 (CCR2). Increased CCL2 level is associated with metastasis of many cancers. In our study, we investigated the role of the CCL2/CCR2 axis in the development of spontaneous intestinal tumorigenesis using the ApcMin/+ mouse model. Ablation of CCR2 in ApcMin/+ mice significantly increased the overall survival and reduced intestinal tumor burden. Immune cell analysis showed that CCR2-/- ApcMin/+ mice exhibited significant reduction in the myeloid cell population and increased interferon γ (IFN-γ) producing T cells both in spleen and mesenteric lymph nodes compared to ApcMin/+ mice. The CCR2-/- ApcMin/+ tumors showed significantly reduced levels of interleukin (IL)-17 and IL-23 and increased IFN-γ and Granzyme B compared to ApcMin/+ tumors. Transfer of CCR2+/+ ApcMin/+ CD4+ T cells into Rag2-/- mice led to development of colitis phenotype with increased CD4+ T cells hyper proliferation and IL-17 production. In contrast, adoptive transfer of CCR2-/- ApcMin/+ CD4+ T cells into Rag2-/- mice failed to enhance colonic inflammation or IL-17 production. These results a suggest novel additional role for CCR2, where it regulates migration of IL-17 producing cells mediating tumor-promoting inflammation in addition to its role in migration of tumor associated macrophages.

Systemic cellular immunity and neuroinflammation during acute flare-up in multiple sclerosis and neuromyelitis optica spectrum disorder patients

Twenty-seven treatment-naïve patients with relapsing-remitting multiple sclerosis (MS) and 13 with neuromyelitis optica spectrum disorder (NMOSD) were enrolled during a time of acute flare-up. Common cerebrospinal fluid (CSF) features were increased CD29- and/or CD45RO-positive helper T cells capable of propagating inflammation in the central nervous system (CNS). B cell activation in the CSF was unique to MS, while an increase in CD4⁺CD192 (CCR2)⁺ cells in blood and breakdown of the blood-brain barrier (BBB) characterized NMOSD. Intravenous corticosteroid therapy suppressed neuroinflammation via modulation of cellular immunity in MS, as opposed to restoration of the BBB in NMOSD.

The role of Th17 cells in viral infections

The present review provides an overview of recent advances regarding the function of Th17 cells and their produced cytokines in the progression of viral diseases. Viral infections alone do not lead to virus-induced malignancies, as both genetic and host safety factors are also involved in the occurrence of malignancies. Acquired immune responses, through the differentiation of Th17 cells, form the novel components of the Th17 cell pathway when reacting with viral infections all the way from the beginning to its final stages. As a result, instead of inducing the right immune responses, these events lead to the suppression of the immune system. In fact, the responses from Th17 cells during persistent viral infections causes chronic inflammation through the production of IL-17 and other cytokines which provide a favorable environment for tumor growth and its development. Additionally, during the past decade, these cells have been understood to be involved in tumor progression and metastasis. However, further research is required to understand Th17 cells' immune mechanisms in the vast variety of viral diseases. This review aims to determine the roles and effects of the immune system, especially Th17 cells, in the progression of viral diseases; which can be highly beneficial for the diagnosis and treatment of these infections.

T-bet Expression in Peripheral Th17.0 Cells Is Associated With Pulmonary Function Changes in Sarcoidosis

Background: Interferon-gamma (IFN-γ) is a key mediator of sarcoidosis-related granulomatous inflammation. Previous findings of IFN-γ-producing Th17 cells in bronchoalveolar lavage fluid from sarcoidosis patients invokes the transition of Th17.0 cells to Th17.1 cells in the disease's pathogenesis. Since the T-bet transcription factor is crucial for this transition, the goal of this study was to determine if T-bet expression in Th17.0 cells reflects the extent of granulomatous inflammation in sarcoidosis patients as assessed by clinical outcomes.

Methods: Using a case-control study design, we identified two groups of sarcoidosis subjects (total N = 43) with pulmonary function tests (PFTs) that either (1) changed (increased or decreased) longitudinally or (2) were stable. We used flow cytometry to measure the transcription factors T-bet and RORγt in Th1, Th17.0, and Th17.1 cell subsets defined by CCR6, CCR4 and CXCR3 in blood samples. We compared the percentages of T-bet⁺ cells in RORγt⁺Th17.0 cells (defined as CCR6⁺CCR4⁺CXCR3⁻) based on subjects' PFT group. We also assessed the relationship between the direction of change in PFTs with the changes in %T-bet⁺ frequencies using mixed effects modeling.

Results: We found that T-bet expression in subjects' RORγt⁺Th17.0 cells varied based on clinical outcome. The T-bet⁺ percentage of RORγt⁺Th17.0 cells was higher in the cases (subject group with PFT changes) as compared to controls (stable group) (27 vs. 16%, p = 0.0040). In comparisons before and after subjects' PFT changes, the T-bet⁺ frequency of RORγt⁺Th17.0 cells increased or decreased in the opposite direction of the PFT change. The percentage of these T-bet⁺ cells was also higher in those with greater numbers of involved organs. Serum levels of interferon-γ-induced chemokines, CXCL9, CXCL10, and CXCL11, and whole blood gene expression of IFN-γ-related genes including GBP1, TAP1, and JAK2 were independently positively associated with the T-bet⁺ frequencies of RORγt⁺Th17.0 cells.

Conclusions: These data suggest that expression of T-bet in Th17.0 cells could reflect the extent of granulomatous inflammation in sarcoidosis patients because they represent a transition state leading to the Th17.1 cell phenotype. These findings indicate that Th17 plasticity may be part of the disease paradigm.

Human CCR5high effector memory cells perform CNS parenchymal immune surveillance via GZMK-mediated transendothelial diapedesis

Although the CNS is immune privileged, continuous search for pathogens and tumours by immune cells within the CNS is indispensable. Thus, distinct immune-cell populations also cross the blood-brain barrier independently of inflammation/under homeostatic conditions. It was previously shown that effector memory T cells populate healthy CNS parenchyma in humans and, independently, that CCR5-expressing lymphocytes as well as CCR5 ligands are enriched in the CNS of patients with multiple sclerosis. Apart from the recently described CD8+ CNS tissue-resident memory T cells, we identified a population of CD4+CCR5high effector memory cells as brain parenchyma-surveilling cells. These cells used their high levels of VLA-4 to arrest on scattered VCAM1, their open-conformation LFA-1 to crawl preferentially against the flow in search for sites permissive for extravasation, and their stored granzyme K (GZMK) to induce local ICAM1 aggregation and perform trans-, rather than paracellular diapedesis through unstimulated primary brain microvascular endothelial cells. This study included peripheral blood mononuclear cell samples from 175 healthy donors, 29 patients infected with HIV, with neurological symptoms in terms of cognitive impairment, 73 patients with relapsing-remitting multiple sclerosis in remission, either 1-4 weeks before (n = 29), or 18-60 months after the initiation of natalizumab therapy (n = 44), as well as white matter brain tissue of three patients suffering from epilepsy. We here provide ex vivo evidence that CCR5highGZMK+CD4+ effector memory T cells are involved in CNS immune surveillance during homeostasis, but could also play a role in CNS pathology. Among CD4+ T cells, this subset was found to dominate the CNS of patients without neurological inflammation ex vivo. The reduction in peripheral blood of HIV-positive patients with neurological symptoms correlated to their CD4 count as a measure of disease progression. Their peripheral enrichment in multiple sclerosis patients and specific peripheral entrapment through the CNS infiltration inhibiting drug natalizumab additionally suggests a contribution to CNS autoimmune pathology. Our transcriptome analysis revealed a migratory phenotype sharing many features with tissue-resident memory and Th17.1 cells, most notably the transcription factor eomesodermin. Knowledge on this cell subset should enable future studies to find ways to strengthen the host defence against CNS-resident pathogens and brain tumours or to prevent CNS autoimmunity.

RANTES-induced invasion of Th17 cells into substantia nigra potentiates dopaminergic cell loss in MPTP mouse model of Parkinson's disease

Although Parkinson's disease (PD) is a progressive neurodegenerative disease, the disease does not progress or persist in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model, the most common animal model of PD. Recently, we have described that supplementation of regulated on activation, normal T cell expressed and secreted (RANTES), a chemokine known to drive infiltration of T cells, induces persistent nigrostriatal pathology in MPTP mouse model. However, which particular T cell subsets are recruited to the substantia nigra (SN) by RANTES is not known. Here, by adoptive transfer of different subset of T cells from tomato red transgenic mice to MPTP-intoxicated immunodeficient Rag1^-/- mice, we describe that invasion of Th17 cells into the SN is stimulated by exogenous RANTES administration. On the other hand, RANTES supplementation remained unable to influence the infiltration of Th1 and Tregs into the SN of MPTP-insulted Rag1^-/- mice. Accordingly, RANTES supplementation increased MPTP-induced TH cell loss in Rag1^-/-mice receiving Th17, but neither Th1 nor Tregs. RANTES-mediated aggravation of nigral TH neurons also paralleled with significant DA loss in striatum and locomotor deficits in MPTP-intoxicated Rag1^-/- mice receiving Th17 cells. Finally, we demonstrate that levels of IL-17 (a Th17-specific cytokine) and RANTES are higher in serum of PD patients than age-matched controls and that RANTES positively correlated with IL-17 in serum of PD patients. Together, these results highlight the importance of RANTES-Th17 pathway in progressive dopaminergic neuronal loss and associated PD pathology.

Imbalance of gut microbiome and intestinal epithelial barrier dysfunction in patients with high blood pressure

Recent evidence indicates a link between gut pathology and microbiome with hypertension (HTN) in animal models. However, whether this association exists in humans is unknown. Thus, our objectives in the present study were to test the hypotheses that high blood pressure (BP) patients have distinct gut microbiomes and that gut-epithelial barrier function markers and microbiome composition could predict systolic BP (SBP). Fecal samples, analyzed by shotgun metagenomics, displayed taxonomic and functional changes, including altered butyrate production between patients with high BP and reference subjects. Significant increases in plasma of intestinal fatty acid binding protein (I-FABP), lipopolysaccharide (LPS), and augmented gut-targetting proinflammatory T helper 17 (Th17) cells in high BP patients demonstrated increased intestinal inflammation and permeability. Zonulin, a gut epithelial tight junction protein regulator, was markedly elevated, further supporting gut barrier dysfunction in high BP. Zonulin strongly correlated with SBP (R2 = 0.5301, P<0.0001). Two models predicting SBP were built using stepwise linear regression analysis of microbiome data and circulating markers of gut health, and validated in a separate cohort by prediction of SBP from zonulin in plasma (R2 = 0.4608, P<0.0001). The mouse model of HTN, chronic angiotensin II (Ang II) infusion, was used to confirm the effects of butyrate and gut barrier function on the cardiovascular system and BP. These results support our conclusion that intestinal barrier dysfunction and microbiome function are linked to HTN in humans. They suggest that manipulation of gut microbiome and its barrier functions could be the new therapeutic and diagnostic avenues for HTN.

Exogenous IL-2 Induces FoxP3+ Th17 Cells In Vivo in Melanoma Patients

Th17 cells represent a distinct subset of CD4 effector T cells with potent pathogenic qualities, capable of directly mediating tumor cell destruction. IL-2 has frequently been shown to have a negative effect on Th17 differentiation while supporting regulatory T-cell (FoxP3CD4, TREG) growth and development in both in vitro models and in vivo animal models. We investigated the effect of in vivo IL-2 on both the Th17 and FoxP3CD4 T-cell compartments in a human model of cancer. High-dose IL-2 (HDIL-2) was administered at a dose of 720,000 IU/kg to patients with melanoma (n=7) and peripheral blood was collected at baseline and at 24, 48, 72, and 96 hours posttreatment. Peripheral blood mononuclear cells (PBMCs) were isolated and subjected to intracellular cytokine and extracellular receptor staining for flow cytometry. We report that HDIL-2 increased both frequencies and absolute numbers of Th17 cells on day 4 of treatment. The administration of HDIL-2 to patients with melanoma increased IL-6 production by peripheral immune cells, a cytokine vital in the downregulation of FoxP3 expression and expansion of the Th17-cell population. Furthermore, we demonstrated that FoxP3CD4 T cells express IL-17 in patients with melanoma undergoing HDIL-2 therapy. Taken together, our findings indicate that HDIL-2 combined with the conditions of malignancy create an immune environment supportive of Th17 differentiation and that expansion of this compartment may occur through the transdifferentiation of IL-17-secreting FoxP3CD4 T cells.

Host and Viral Factors in HIV-Mediated Bystander Apoptosis

Human immunodeficiency virus (HIV) infections lead to a progressive loss of CD4 T cells primarily via the process of apoptosis. With a limited number of infected cells and vastly disproportionate apoptosis in HIV infected patients, it is believed that apoptosis of uninfected bystander cells plays a significant role in this process. Disease progression in HIV infected individuals is highly variable suggesting that both host and viral factors may influence HIV mediated apoptosis. Amongst the viral factors, the role of Envelope (Env) glycoprotein in bystander apoptosis is well documented. Recent evidence on the variability in apoptosis induction by primary patient derived Envs underscores the role of Env glycoprotein in HIV disease. Amongst the host factors, the role of C-C Chemokine Receptor type 5 (CCR5), a coreceptor for HIV Env, is also becoming increasingly evident. Polymorphisms in the CCR5 gene and promoter affect CCR5 cell surface expression and correlate with both apoptosis and CD4 loss. Finally, chronic immune activation in HIV infections induces multiple defects in the immune system and has recently been shown to accelerate HIV Env mediated CD4 apoptosis. Consequently, those factors that affect CCR5 expression and/or immune activation in turn indirectly regulate HIV mediated apoptosis making this phenomenon both complex and multifactorial. This review explores the complex role of various host and viral factors in determining HIV mediated bystander apoptosis.

Modulation of Neuroinflammation in the Central Nervous System: Role of Chemokines and Sphingolipids

Neuroinflammation is a process involved in the pathogenesis of different disorders, both autoimmune, such as neuropsychiatric systemic lupus erythematosus, and degenerative, such as Alzheimer's and Parkinson's disease. In the central nervous system, the local milieu is tightly regulated by different mediators, among which are chemoattractant cytokines, also known as chemokines. These small molecules are able to modulate trafficking of immune cells in the course of nervous system development or in response to tissue damage, and different patterns of chemokine molecule and receptor expression have been described in several neuroinflammatory disorders. In recent years, a number of studies have highlighted a pivotal role of sphingolipids in regulating neuroinflammation. Sphingolipids have different functions, among which are the control of leukocyte egress from lymphonodes into inflamed tissues, the expression of various mediators of inflammation and a direct effect on the cells of the central nervous system as regulators of neuroinflammation. In the future, a better knowledge of these two groups of mediators could provide insight into the pathogenesis of neuroinflammatory disorders and could help develop novel diagnostic tools and therapeutic strategies.

Mechanisms of T cell organotropism

Protective immunity relies upon T cell differentiation and subsequent migration to target tissues. Similarly, immune homeostasis requires the localization of regulatory T cells (Tregs) to the sites where immunity takes place. While naïve T lymphocytes recirculate predominantly in secondary lymphoid tissue, primed T cells and activated Tregs must traffic to the antigen rich non-lymphoid tissue to exert effector and regulatory responses, respectively. Following priming in draining lymph nodes, T cells acquire the 'homing receptors' to facilitate their access to specific tissues and organs. An additional level of topographic specificity is provided by T cells receptor recognition of antigen displayed by the endothelium. Furthermore, co-stimulatory signals (such as those induced by CD28) have been shown not only to regulate T cell activation and differentiation, but also to orchestrate the anatomy of the ensuing T cell response. We here review the molecular mechanisms supporting trafficking of both effector and regulatory T cells to specific antigen-rich tissues.

CCR2 defines in vivo development and homing of IL-23-driven GM-CSF-producing Th17 cells

IL-17-producing helper T (Th17) cells are critical for host defense against extracellular pathogens but also drive numerous autoimmune diseases. Th17 cells that differ in their inflammatory potential have been described including IL-10-producing Th17 cells that are weak inducers of inflammation and highly inflammatory, IL-23-driven, GM-CSF/IFNγ-producing Th17 cells. However, their distinct developmental requirements, functions and trafficking mechanisms in vivo remain poorly understood. Here we identify a temporally regulated IL-23-dependent switch from CCR6 to CCR2 usage by developing Th17 cells that is critical for pathogenic Th17 cell-driven inflammation in experimental autoimmune encephalomyelitis (EAE). This switch defines a unique in vivo cell surface signature (CCR6⁻CCR2⁺) of GM-CSF/IFNγ-producing Th17 cells in EAE and experimental persistent extracellular bacterial infection, and in humans. Using this signature, we identify an IL-23/IL-1/IFNγ/TNFα/T-bet/Eomesodermin-driven circuit driving GM-CSF/IFNγ-producing Th17 cell formation in vivo. Thus, our data identify a unique cell surface signature, trafficking mechanism and T-cell intrinsic regulators of GM-CSF/IFNγ-producing Th17 cells.

Little is known regarding migration of Th17 cells that produce distinct cytokines implicated in protection and pathology. Kara et al. show that a switch from CCR6 to CCR2 by Th17 cells defines a signature (CCR6⁻CCR2⁺) of GM-CSF⁺ Th17 cells and drives pathology in a mouse model of autoimmunity.

New Insights about Treg and Th17 Cells in HIV Infection and Disease Progression

Treg and Th17 cell subsets are characterized by the expression of specific transcriptional factors and chemokine receptor as well as by secretion of specific cytokine and chemokines. These subsets are important to the differentiation, expansion, homing capacity, and recruitment of several different immune cell populations to the site of infection. Whereas Treg cells maintain self-tolerance and control the activation and expansion of autoreactive CD4⁺ T effector cells through an anti-inflammatory response, Th17 cells, in an exacerbated unregulated proinflammatory response, can promote autoimmunity. Despite such apparently opposite functions, Th17 and Treg cells share common characteristics, and their differentiation pathways are interconnected. Recent studies have revealed quite intricate relations between Treg and Th17 cells in HIV infection and progression to AIDS. Considering Treg cells, different subsets were already investigated in the context of HIV infection, indicating a fluctuation in the total number and frequency throughout the disease course. This review focuses on the recent findings regarding the role of regulatory T and Th17 cells in the context of HIV infection, highlighting the importance of the balance between these two subsets on disease progression.

Differential roles of resident microglia and infiltrating monocytes in murine CNS autoimmunity

Macrophages can be of dual origin. Most tissue-resident macrophage compartments are generated before birth and subsequently maintain themselves independently from each other locally in healthy tissue. Under inflammatory conditions, these cells can however be complemented by macrophages derived from acute monocyte infiltrates. Due to the lack of suitable experimental systems, differential functional contributions of central nervous system (CNS)-resident microglia and monocyte-derived macrophages (MoMF) to CNS inflammation, such as experimental autoimmune encephalomyelitis (EAE), the mouse model of multiple sclerosis (MS), remain poorly understood. Here, we will review recent progress in this field that suggest distinct roles of microglia and MoMF in disease induction and progression, capitalizing on novel transgenic mouse models. The latter finding could have major implications for the rationale development of therapeutic approaches to the management of brain inflammation and MS therapy.

The role of the Th17 cytokines IL-17 and IL-22 in Rheumatoid Arthritis pathogenesis and developments in cytokine immunotherapy

Over the past few years, the importance of Interleukin (IL)-17 and T helper (Th)17 cells in the pathology of Rheumatoid Arthritis (RA) has become apparent. RA is a systemic autoimmune disease that affects up to 1% of the population worldwide. It is characterized by an inflamed, hyperplastic synovium with pannus formation, leading to bone and cartilage destruction in the joints. By the production of effector cytokines like IL-17 and IL-22, the T helper 17 subset protects the host against bacterial and fungal infections, but it can also promote the development of various autoimmune diseases like RA. Hence, the Th17 pathway recently became a very interesting target in RA treatment. Up to now, several therapies targeting the Th17 cells or its effector cytokines have been tested, or are currently under investigation. This review clarifies the role of Th17 cells and its cytokines in the pathogenesis of RA, and provides an overview of the clinical trials using immunotherapy to target this particular T helper subset or the two main effector cytokines by which the Th17 cells exert their function, IL-17 and IL-22.

Preferential recruitment of Th17 cells to cervical cancer via CCR6-CCL20 pathway

Our previous studies suggest that Th17 cells accumulate within tumor tissues and correlate with recurrence of cervical cancer patients. However, the source of the increased tumor-infiltrating Th17 cells remains poorly understood. We investigated the prevalence, phenotype and trafficking property of Th17 cells in patients with cervical cancer. Our results showed that Th17 cells highly aggregated within tumor tissues in an activated phenotype with markedly increased expression of CCR6. Correspondingly, level of CCL20 in the tumor tissues was significantly higher than that in non-tumor and normal control tissues, and strongly positively associated with Th17 cells. Further, in vitro migration assay showed CCL20 had effective chemotaxis to circulating Th17 cells. In conclusion, Th17 cells are recruited into tumor tissues preferentially through CCR6-CCL20 pathway, which can serve as a novel therapeutic target for cervical cancer.

Estrogen regulates T helper 17 phenotype and localization in experimental autoimmune arthritis

INTRODUCTION

The incidence and progression of many autoimmune diseases are sex-biased, which might be explained by the immunomodulating properties of endocrine hormones. Treatment with estradiol potently inhibits experimental autoimmune arthritis. Interleukin-17-producing T helper cells (Th17) are key players in several autoimmune diseases, particularly in rheumatoid arthritis. The aim of this study was to investigate the effects of estrogen on Th17 cells in experimental arthritis.

METHODS

Ovariectomized DBA/1 mice treated with 17β-estradiol (E2) or placebo were subjected to collagen-induced arthritis (CIA), and arthritis development was assessed. Th17 cells in joints and lymph nodes were studied by flow cytometry. Lymph node Th17 cells were also examined in ovariectomized estrogen receptor α-knockout mice (ERα-/-) and wild-type littermates, treated with E2 or placebo and subjected to antigen-induced arthritis.

RESULTS

E2-treated mice with established CIA showed reduced severity of arthritis and fewer Th17 cells in joints compared with controls. Interestingly, E2-treated mice displayed increased Th17 cells in lymph nodes during the early phase of the disease, dependent on ERα. E2 increased the expression of C-C chemokine receptor 6 (CCR6) on lymph node Th17 cells as well as the expression of the corresponding C-C chemokine ligand 20 (CCL20) within lymph nodes.

CONCLUSIONS

This is the first study in which the effects of E2 on Th17 cells have been characterized in experimental autoimmune arthritis. We report that E2 treatment results in an increase of Th17 cells in lymph nodes during the early phase of arthritis development, but leads to a decrease of Th17 in joints during established arthritis. Our data suggest that this may be caused by interference with the CCR6-CCL20 pathway, which is important for Th17 cell migration. This study contributes to the understanding of the role of estrogen in the development of autoimmune arthritis and opens up new fields for research concerning the sex bias in autoimmune disease.

Potential Sources and Roles of Adaptive Immunity in Age-Related Macular Degeneration: Shall We Rename AMD into Autoimmune Macular Disease?

Age-related macular degeneration (AMD) is the leading cause of vision loss in the elderly throughout the industrialized world. Its most prominent pathologic features are lesions involving the retinal pigment epithelium (RPE) the Bruch's membrane, the degeneration of photoreceptors, and, in the most aggressive cases, choroidal neovascularization. Genetic associations between the risk of developing AMD and polymorphism within components of the complement system, as well as chemokine receptors expressed on microglial cells and macrophages, have linked retinal degeneration and choroidal neovascularization to innate immunity (inflammation). In addition to inflammation, players of the adaptive immunity including cytokines, chemokines, antibodies, and T cells have been detected in animal models of AMD and in patients suffering from this pathology. These observations suggest that adaptive immunity might play a role in different processes associated with AMD such as RPE atrophy, neovascularization, and retinal degeneration. To this date however, the exact roles (if any) of autoantibodies and T cells in AMD remain unknown. In this review we discuss the potential effects of adaptive immune responses in AMD pathogenesis.

Decidual stromal cells recruit Th17 cells into decidua to promote proliferation and invasion of human trophoblast cells by secreting IL-17

T helper 17 (Th17) cells have both regulatory and protective roles in physiological conditions. The Th17 subset and the cytokine interleukin-17A (IL-17A) have been implicated in the pathogenesis of certain autoimmune diseases, several types of cancer and allograft rejection. However, the role of Th17 cells at the maternal/fetal interface remains unknown. Here, we demonstrate that Th17 cells are present in decidua and are increased in the peripheral blood of 10 clinically normal pregnancies based on intracellular cytokine analysis. Our results suggest a potential role of Th17 cells in sustaining pregnancy in humans. Furthermore, we demonstrate that decidual stromal cells (DSCs) but not trophoblast cells recruit peripheral Th17 cells into the decidua by secreting CCL2. The recruited Th17 cells promote proliferation and invasion and inhibit the apoptosis of human trophoblast cells by secreting IL-17 during the first trimester of pregnancy. These findings indicate a novel role for Th17 cells in controlling the maternal-fetal relationship and placenta development.

Chemokines and chemokine receptors in multiple sclerosis

Multiple sclerosis is an autoimmune disease with classical traits of demyelination, axonal damage, and neurodegeneration. The migration of autoimmune T cells and macrophages from blood to central nervous system as well as the destruction of blood brain barrier are thought to be the major processes in the development of this disease. Chemokines, which are small peptide mediators, can attract pathogenic cells to the sites of inflammation. Each helper T cell subset expresses different chemokine receptors so as to exert their different functions in the pathogenesis of MS. Recently published results have shown that the levels of some chemokines and chemokine receptors are increased in blood and cerebrospinal fluid of MS patients. This review describes the advanced researches on the role of chemokines and chemokine receptors in the development of MS and discusses the potential therapy of this disease targeting the chemokine network.

Th17 Cells Coordinate with Th22 Cells in Maintaining Homeostasis of Intestinal Tissues and both are Depleted in SIV-Infected Macaques

Th17 and Th22 cells are thought to function as innate regulators of mucosal antimicrobial responses, tissue inflammation and mucosal integrity, yet their role in persistent SIV infection is still unclear. Here we compared Th17 and Th22 cells in their phenotype, effector/cytokine function, and frequency in blood and intestinal mucosal tissues, and correlate levels with mucosal damage in SIV-infected rhesus macaques. We found that Th17/Th22 cells share similar features in that both highly produce TNF-α and IL-2 and express CCR5 in intestinal tissues; yet very few show cytotoxic functions, as evidenced by lack of IFN-γ and granzyme B production. Further, Th17/Th22 cells display distinct tissue-specific distributions. Both Th17 and Th22 cells and cytokine secretion were significantly depleted in both blood and intestine in chronically SIV-infected macaques. The frequency of Th17 and Th22 cells in the intestine positively correlated with percentages of intestinal CD4+ T cells and negatively with damage to intestinal mucosa, and plasma viral loads in SIV infection. These findings indicate Th17 and Th22 cells share considerable functions, and may coordinate in innate mucosal immune responses, and their regional loss in the intestine may be associated with local mucosal immune dysfunction in persistent HIV/SIV infection.

Transcriptional profiling reveals molecular signatures associated with HIV permissiveness in Th1Th17 cells and identifies peroxisome proliferator-activated receptor gamma as an intrinsic negative regulator of viral replication

BACKGROUND

We previously demonstrated that primary Th1Th17 cells are highly permissive to HIV-1, whereas Th1 cells are relatively resistant. Molecular mechanisms underlying these differences remain unknown.

RESULTS

Exposure to replication competent and single-round VSV-G pseudotyped HIV strains provide evidence that superior HIV replication in Th1Th17 vs. Th1 cells was regulated by mechanisms located at entry and post-entry levels. Genome-wide transcriptional profiling identified transcripts upregulated (n = 264) and downregulated (n = 235) in Th1Th17 vs. Th1 cells (p-value < 0.05; fold change cut-off 1.3). Gene Set Enrichment Analysis revealed pathways enriched in Th1Th17 (nuclear receptors, trafficking, p38/MAPK, NF-κB, p53/Ras, IL-23) vs. Th1 cells (proteasome, interferon α/β). Differentially expressed genes were classified into biological categories using Gene Ontology. Th1Th17 cells expressed typical Th17 markers (IL-17A/F, IL-22, CCL20, RORC, IL-26, IL-23R, CCR6) and transcripts functionally linked to regulating cell trafficking (CEACAM1, MCAM), activation (CD28, CD40LG, TNFSF13B, TNFSF25, PTPN13, MAP3K4, LTB, CTSH), transcription (PPARγ, RUNX1, ATF5, ARNTL), apoptosis (FASLG), and HIV infection (CXCR6, FURIN). Differential expression of CXCR6, PPARγ, ARNTL, PTPN13, MAP3K4, CTSH, SERPINB6, PTK2, and ISG20 was validated by RT-PCR, flow cytometry and/or confocal microscopy. The nuclear receptor PPARγ was preferentially expressed by Th1Th17 cells. PPARγ RNA interference significantly increased HIV replication at levels post-entry and prior HIV-DNA integration. Finally, the activation of PPARγ pathway via the agonist Rosiglitazone induced the nuclear translocation of PPARγ and a robust inhibition of viral replication.

CONCLUSIONS

Thus, transcriptional profiling in Th1Th17 vs. Th1 cells demonstrated that HIV permissiveness is associated with a superior state of cellular activation and limited antiviral properties and identified PPARγ as an intrinsic negative regulator of viral replication. Therefore, triggering PPARγ pathway via non-toxic agonists may contribute to limiting covert HIV replication and disease progression during antiretroviral treatment.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXIX. Update on the extended family of chemokine receptors and introducing a new nomenclature for atypical chemokine receptors

Sixteen years ago, the Nomenclature Committee of the International Union of Pharmacology approved a system for naming human seven-transmembrane (7TM) G protein-coupled chemokine receptors, the large family of leukocyte chemoattractant receptors that regulates immune system development and function, in large part by mediating leukocyte trafficking. This was announced in Pharmacological Reviews in a major overview of the first decade of research in this field [Murphy PM, Baggiolini M, Charo IF, Hébert CA, Horuk R, Matsushima K, Miller LH, Oppenheim JJ, and Power CA (2000) Pharmacol Rev 52:145-176]. Since then, several new receptors have been discovered, and major advances have been made for the others in many areas, including structural biology, signal transduction mechanisms, biology, and pharmacology. New and diverse roles have been identified in infection, immunity, inflammation, development, cancer, and other areas. The first two drugs acting at chemokine receptors have been approved by the U.S. Food and Drug Administration (FDA), maraviroc targeting CCR5 in human immunodeficiency virus (HIV)/AIDS, and plerixafor targeting CXCR4 for stem cell mobilization for transplantation in cancer, and other candidates are now undergoing pivotal clinical trials for diverse disease indications. In addition, a subfamily of atypical chemokine receptors has emerged that may signal through arrestins instead of G proteins to act as chemokine scavengers, and many microbial and invertebrate G protein-coupled chemokine receptors and soluble chemokine-binding proteins have been described. Here, we review this extended family of chemokine receptors and chemokine-binding proteins at the basic, translational, and clinical levels, including an update on drug development. We also introduce a new nomenclature for atypical chemokine receptors with the stem ACKR (atypical chemokine receptor) approved by the Nomenclature Committee of the International Union of Pharmacology and the Human Genome Nomenclature Committee.

Advances in understanding the pathogenesis of autoimmune disorders: focus on chemokines and lymphocyte trafficking

Lymphocyte trafficking is a key step in the pathogenesis of various autoimmune diseases. Recruitment of autoreactive lymphocytes to inflamed tissues is a defining feature of numerous persistent organ-specific autoimmune conditions and various therapies are now used in several of these diseases which appear to specifically block lymphocyte migration. Thus, better understanding of the molecular events involved in homing of autoreactive pathogenic lymphocytes may present novel opportunities for pharmacological intervention in autoimmune diseases, such as multiple sclerosis, rheumatoid arthritis, type-1 diabetes and psoriasis. This review describes recent progress in understanding lymphocyte trafficking in autoimmunity, focusing on the involvement of the chemokine and chemokine receptor superfamily. Possible strategies to improve therapeutics for autoimmune diseases arising from these studies are discussed.

Role of Th17 cells in skin inflammation of allergic contact dermatitis

Extending the classical concept considering an imbalance exclusively of T helper(h) 1 and Th2 cells on the bottom of many inflammatory diseases, Th17 cells were recently described. Today, there is sufficient experimental evidence to classify psoriasis and allergic contact dermatitis (ACD) amongst other inflammatory skin disorders as IL-17 associated diseases. In several human studies, T-cell-clones could be isolated from eczema biopsies, and high IL-17 levels were observed after challenge with allergen. In the last years, the phenotype of these IL-17 releasing T cells was in the focus of discussion. It has been suggested that Th17 could be identified by expression of retinoic acid receptor-related orphan receptor (ROR)C (humans) or RORγt (mice) and IL-17, accompanied by the absence of IFN-γ and IL-22. In cells from skin biopsies, contact allergens elevate IL-17A, IL-23, and RORC within the subset of Th cells. The indications for a participation of Th17 in the development of ACD are supported by data from IL-17 deficient mice with reduced contact hypersensitivity (CHS) reactions that could be restored after transplantation of wild type CD4⁺ T cells. In addition to Th17 cells, subpopulations of CD8⁺ T cells and regulatory T cells are further sources of IL-17 that play important roles in ACD as well. Finally, the results from Th17 cell research allow today identification of different skin diseases by a specific profile of signature cytokines from Th cells that can be used as a future diagnostic tool.

The multiple faces of CCL13 in immunity and inflammation

CCL13/MCP-4, is a CC family chemokine that is chemoattractant for eosinophils, basophils, monocytes, macrophages, immature dendritic cells, and T cells, and its capable of inducing crucial immuno-modulatory responses through its effects on epithelial, muscular and endothelial cells. Similar to other CC chemokines, CCL13 binds to several chemokine receptors (CCR1, CCR2 and CCR3), allowing it to elicit different effects on its target cells. A number of studies have shown that CCL13 is involved in many chronic inflammatory diseases, in which it functions as a pivotal molecule involved in the selective recruitment of cell lineages to the inflamed tissues and their subsequent activation. Based on these studies, we suggest that blocking the actions of CCL13 can serve as a novel strategy for the generation of agents with anti-inflammatory activity. The main goal of this review is to present the current information about CCL13, its gene and protein structure and the roles of this chemokine during innate/adaptive immune responses in inflammatory diseases.

IL-23 induces atopic dermatitis-like inflammation instead of psoriasis-like inflammation in CCR2-deficient mice

Psoriasis is an immune-mediated chronic inflammatory skin disease, characterized by epidermal hyperplasia and infiltration of leukocytes into the dermis and epidermis. IL-23 is expressed in psoriatic skin, and IL-23 injected into the skin of mice produces IL-22-dependent dermal inflammation and acanthosis. The chemokine receptor CCR2 has been implicated in the pathogenesis of several inflammatory diseases, including psoriasis. CCR2-positive cells and the CCR2 ligand, CCL2 are abundant in psoriatic lesions. To examine the requirement of CCR2 in the development of IL-23-induced cutaneous inflammation, we injected the ears of wild-type (WT) and CCR2-deficient (CCR2^−/−) mice with IL-23. CCR2^−/− mice had increased ear swelling and epidermal thickening, which was correlated with increased cutaneous IL-4 levels and increased numbers of eosinophils within the skin. In addition, TSLP, a cytokine known to promote and amplify T helper cell type 2 (Th2) immune responses, was also increased within the inflamed skin of CCR2^−/− mice. Our data suggest that increased levels of TSLP in CCR2^−/− mice may contribute to the propensity of these mice to develop increased Th2-type immune responses.

Imatinib ameliorates neuroinflammation in a rat model of multiple sclerosis by enhancing blood-brain barrier integrity and by modulating the peripheral immune response

Central nervous system (CNS) disorders such as ischemic stroke, multiple sclerosis (MS) or Alzheimeŕs disease are characterized by the loss of blood-brain barrier (BBB) integrity. Here we demonstrate that the small tyrosine kinase inhibitor imatinib enhances BBB integrity in experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis (MS). Treatment was accompanied by decreased CNS inflammation and demyelination and especially reduced T-cell recruitment. This was supported by downregulation of the chemokine receptor (CCR) 2 in CNS and lymph nodes, and by modulation of the peripheral immune response towards an anti-inflammatory phenotype. Interestingly, imatinib ameliorated neuroinflammation, even when the treatment was initiated after the clinical manifestation of the disease. We have previously shown that imatinib reduces BBB disruption and stroke volume after experimentally induced ischemic stroke by targeting platelet-derived growth factor receptor -α (PDGFR-α) signaling. Here we demonstrate that PDGFR-α signaling is a central regulator of BBB integrity during neuroinflammation and therefore imatinib should be considered as a potentially effective treatment for MS.

CCR2(+)CCR5(+) T cells produce matrix metalloproteinase-9 and osteopontin in the pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease of the CNS that is presumably mediated by CD4(+) autoimmune T cells. Although both Th1 and Th17 cells have the potential to cause inflammatory CNS pathology in rodents, the identity of pathogenic T cells remains unclear in human MS. Given that each Th cell subset preferentially expresses specific chemokine receptors, we were interested to know whether T cells defined by a particular chemokine receptor profile play an active role in the pathogenesis of MS. In this article, we report that CCR2(+)CCR5(+) T cells constitute a unique population selectively enriched in the cerebrospinal fluid of MS patients during relapse but not in patients with other neurologic diseases. After polyclonal stimulation, the CCR2(+)CCR5(+) T cells exhibited a distinct ability to produce matrix metalloproteinase-9 and osteopontin, which are involved in the CNS pathology of MS. Furthermore, after TCR stimulation, the CCR2(+)CCR5(+) T cells showed a higher invasive potential across an in vitro blood-brain barrier model compared with other T cells. Of note, the CCR2(+)CCR5(+) T cells from MS patients in relapse are reactive to myelin basic protein, as assessed by production of IFN-γ. We also demonstrated that the CCR6(-), but not the CCR6(+), population within CCR2(+)CCR5(+) T cells was highly enriched in the cerebrospinal fluid during MS relapse (p < 0.0005) and expressed higher levels of IFN-γ and matrix metalloproteinase-9. Taken together, we propose that autoimmune CCR2(+)CCR5(+)CCR6(-) Th1 cells play a crucial role in the pathogenesis of MS.

Comparison of blood and synovial fluid th17 and novel peptidase inhibitor 16 Treg cell subsets in juvenile idiopathic arthritis

OBJECTIVE

Early recognition and treatment of juvenile idiopathic arthritis (JIA) can prevent joint damage and minimize side effects of medication. The balance between proinflammatory and antiinflammatory mechanisms is known to be important in JIA, and we therefore investigated T cell subsets including Th cells, autoaggressive Th17 cells, and regulatory T cells (Treg), including a novel Treg subset in peripheral blood (PB) and synovial fluid (SF) of patients with JIA.

METHODS

Fifty children with JIA were enrolled in our study. Frequency, phenotype, and function of T lymphocytes in PB and SF were characterized using flow cytometry. Migration capabilities of PB and SF cells were compared.

RESULTS

Synovial T cells showed different phenotype and function compared with PB T cells, with an increased proportion of memory T cells, expression of CCR4, CCR5, CXCR3, interleukin 23R, and an increased ratio of Th17 to Treg. Although Treg were increased in SF compared with the PB, we found a significant decrease in the numbers of peptidase inhibitor 16 (PI16)+ Treg in active joints compared with peripheral blood. Coexpression of CCR4 and CCR6 was reduced on PI16+ Treg in PB and SF of patients with JIA compared with healthy children, however the ability of these cells to migrate toward their ligands was unaffected.

CONCLUSION

This is a comprehensive characterization of novel PI16+ Treg and Th17 cells in matched blood and synovial fluid samples of patients with JIA. Despite an increased number of Treg within the inflamed joint, lower numbers of PI16+ Treg but high numbers of Th17 cells might contribute to the inability to control disease.

Chemokine/chemokine receptor interactions contribute to the accumulation of Th17 cells in patients with esophageal squamous cell carcinoma

Chemokine/chemokine receptor interactions play a critical role in lymphocyte infiltration of tumors. Recent studies suggest that Th17 cells accumulate within many types of tumors, although the mechanisms that control this are unclear. We studied the distribution and phenotypic features of Th17 cells chemokine receptors, as well as the mRNA levels of CCL2, CCL17, CCL20, and CCL22 in tumors of patients with esophageal squamous cell carcinoma. We found that Th17 cells accumulated in tumors, and high expressions of CCR4, CCR6 were detected in Th17 cells. Levels of the chemokines CCL17, CCL20, and CCL22 in tumors were significantly higher than in tumor-free tissues, and were positively correlated with the distribution of Th17 cells in tumors. Furthermore, an in vitro migration assay showed that CCL17, CCL20 and CCL22 had chemotactic effects on tumor-derived Th17 cells. In conclusion, the CCR4-CCL17/22 and CCR6-CCL20 axis might play an important role in Th17 cell infiltration of tumors.

Th17 cells: biology, pathogenesis of autoimmune and inflammatory diseases, and therapeutic strategies

Th17 cells that secrete the cytokines IL-17A and IL-17F and express lineage-specific transcription factor RORC (RORγt in mice) represent a distinct lineage of CD4(+) T cells. Transforming growth factor-β and inflammatory cytokines, such as IL-6, IL-21, IL-1β, and IL-23, play central roles in the generation of Th17 cells. Th17 cells are critical for the clearance of extracellular pathogens, including Candida and Klebsiella. However, under certain conditions, these cells and their effector molecules, such as IL-17, IL-21, IL-22, GM-CSF, and CCL20, are associated with the pathogenesis of several autoimmune and inflammatory diseases, such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, psoriasis, inflammatory bowel disease, and allergy and asthma. This review discusses these disease states and the various therapeutic strategies under investigation to target Th17 cells, which include blocking the differentiation and amplification of Th17 cells, inhibiting or neutralizing the cytokines of Th17 cells, and suppressing the transcription factors specific for Th17 cells.

Difference in Th1 and Th17 lymphocyte adhesion to endothelium

T cell subset-specific migration to inflammatory sites is tightly regulated and involves interaction of the T cells with the endothelium. Th17 cells often appear at different inflammatory sites than Th1 cells, or both subsets appear at the same sites but at different times. Differences in T cell subset adhesion to endothelium may contribute to subset-specific migratory behavior, but this possibility has not been well studied. We examined the adhesion of mouse Th17 cells to endothelial adhesion molecules and endothelium under flow in vitro and to microvessels in vivo and we characterized their migratory phenotype by flow cytometry and quantitative RT-PCR. More Th17 than Th1 cells interacted with E-selectin. Fewer Th17 than Th1 cells bound to TNF-α-activated E-selectin-deficient endothelial cells, and intravital microscopy studies demonstrated that Th17 cells engage in more rolling interactions with TNF-α-treated microvessels than Th1 cells in wild-type mice but not in E-selectin-deficient mice. Th17 adhesion to ICAM-1 was dependent on integrin activation by CCL20, the ligand for CCR6, which is highly expressed by Th17 cells. In an air pouch model of inflammation, CCL20 triggered recruitment of Th17 but not Th1 cells. These data provide evidence that E-selectin- and ICAM-1-dependent adhesion of Th17 and Th1 cells with endothelium are quantitatively different.

Microbial translocation across the GI tract

The lumen of the gastrointestinal (GI) tract is home to an enormous quantity of different bacterial species, our microbiota, that thrive in an often symbiotic relationship with the host. Given that the healthy host must regulate contact between the microbiota and its immune system to avoid overwhelming systemic immune activation, humans have evolved several mechanisms to attenuate systemic microbial translocation (MT) and its consequences. However, several diseases are associated with the failure of one or more of these mechanisms, with consequent immune activation and deleterious effects on health. Here, we discuss the mechanisms underlying MT, diseases associated with MT, and therapeutic interventions that aim to decrease it.

Th17 cell, the new player of neuroinflammatory process in multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease characterized by recurrent episodes of demyelination and axonal lesion mediated by CD4(+) T cells with a proinflammatory Th1 and Th17 phenotype, macrophages, and soluble inflammatory mediators. Identification of Th17 cells led to breaking the dichotomy of Th1/Th2 axis in immunopathogenesis of autoimmune diseases such as MS, and its experimental model, experimental autoimmune encephalomyelitis (EAE). Th17 cells are characterized by expression of retinoic acid-related orphan receptor (ROR)γt and signal transducer and activator of transcription 3 (STAT3) factors. Th17-produced cytokine profile including interleukin (IL)-17, IL-6, IL-21, IL-22, IL-23 and tumour necrosis factor (TNF)-α, which have proinflammatory functions, suggests it as an important factor in immunopathogenesis of MS, because the main feature of MS pathophysiology is the neuroinflammatory reaction. The blood brain barrier (BBB) disruption is an early and central event in MS pathogenesis. Autoreactive Th17 cells can migrate through the BBB by the production of cytokines such as IL-17 and IL-22, which disrupt tight junction proteins in the central nervous system (CNS) endothelial cells. Consistent with this observation and regarding the wide range production of proinflammatory cytokines and chemokines by Th17 cells, it is expected that Th17 cell to be as a potent pathogenic factor in disease immunopathophysiology. Th17-mediated inflammation is characterized by neutrophil recruitment into the CNS and neurons killing. However, the majority of our knowledge about the role of Th17 in MS pathogenesis is resulted in investigation into EAE animal models. In this review, we intend to focus on the newest information regarding the precise role of Th17 cells in immunopathogenesis of MS, and its animal model, EAE.

Treatment of neuromyelitis optica: current debate

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease that largely affects optic nerves and spinal cord. Recent studies have identified an elevation of serum anti-aquaporin 4 antibody as a hallmark of NMO. Typical cases of NMO significantly differ from multiple sclerosis (MS) in immunological markers, histopathology, and responses to therapy. In fact, plasma exchange may be more efficacious for NMO than MS, whereas interferon-ß is recommended for MS but not for NMO. An emerging idea that pathogenesis of NMO may involve an interaction of the newly identified helper T cell subset, Th17, with B cells offers potential targets of therapy.

IL-9 is important for T-cell activation and differentiation in autoimmune inflammation of the central nervous system

Experimental autoimmune encephalomyelitis (EAE) is generally believed to be an autoimmune disease of the central nervous system (CNS) caused by myelin-specific Th1 and/or Th17 effector cells. The underlying cellular and molecular mechanisms, however, are not fully understood. Using mice deficient in IL-9 (IL-9(-/-) ), we showed that IL-9 plays a critical role in EAE. Specifically, IL-9(-/-) mice developed significantly less severe EAE than their WT counterparts following both immunization with myelin proteolipid protein (PLP)(180-199) peptide in the presence of Complete Freund's Adjuvant (CFA), and adoptive transfer of PLP(180-199) peptide-specific effector T cells from WT littermates. EAE-resistant IL-9(-/-) mice exhibited considerably fewer infiltrating immune cells in the CNS, with lower levels of IL-17 and IFN-γ expression, than their WT littermates. Further studies revealed that null mutation of the IL-9 gene resulted in significantly lower levels of PLP(180-199) peptide-specific IL-17 and IFN-γ production. Moreover, IL-9(-/-) memory/activated T cells exhibited decreased C-C chemokine receptors (CCR)2, CCR5, and CCR6 expression. Interestingly, IL-10 was significantly increased in IL-9(-/-) mice compared with WT littermates. Importantly, we found that IL-9-mediated Th17-cell differentiation triggers complex STAT signaling pathways.

Human tumor-infiltrating Th17 cells have the capacity to differentiate into IFN-γ+ and FOXP3+ T cells with potent suppressive function

Accumulating evidence suggests that Th17 cells and Tregs may exhibit development plasticity and that CD4(+) Tregs can differentiate into IL-17-producing T cells; however, whether Th17 cells can reciprocally convert into Tregs has not been described. In this study, we generated Th17 clones from tumor-infiltrating T lymphocytes (TILs). We showed that Th17 clones generated from TILs can differentiate into IFN-γ-producing and FOXP3(+) cells after in vitro stimulation with OKT3 and allogeneic peripheral blood mononuclear cells. We further demonstrated that T-cell receptor (TCR) engagement was responsible for this conversion, and that this differentiation was due to the epigenetic modification and reprogramming of gene expression profiles, including lineage-specific transcriptional factor and cytokine genes. In addition to expressing IFN-γ and FOXP3, we showed that these differentiated Th17 clones mediated potent suppressive function after repetitive stimulation with OKT3, suggesting that these Th17 clones had differentiated into functional Tregs. We further demonstrated that the Th17-derived Tregs, unlike naturally occurring CD4(+) CD25(+) Tregs, did not reconvert back into Th17 cells even under Th17-biasing cytokine conditions. These results provide the critical evidence that human tumor-infiltrating Th17 cells can differentiate into Tregs and indicate a substantial developmental plasticity of Th17 cells.

Th17 cells in natural SIV hosts

PURPOSE OF REVIEW

To summarize our current understanding of the regulation of Th17 cells in pathogenic and nonpathogenic lentiviral infections.

RECENT FINDINGS

It has been shown that Th17 cells, a recently identified T helper-cell subset deemed critical for antimicrobial mucosal immunity, are preferentially depleted in the gastrointestinal tracts of human immunodeficiency virus (HIV)-infected humans and simian immunodeficiency virus (SIV)-infected rhesus and pigtailed (PTMs) macaques. In contrast, Th17 cells are preserved at healthy levels in monkey species that are natural hosts for SIV, such as sooty mangabeys or African green monkeys (AGMs), which maintain mucosal immunity and remain AIDS free. These findings suggest that preservation of Th17 cells (or lack thereof) may be central in determining the pathogenic or nonpathogenic outcome of HIV/SIV infection.

SUMMARY

A preferential depletion of mucosal Th17 cells is a feature that distinguishes pathogenic HIV infection of humans from nonprogressive SIV infection of sooty mangabeys and AGMs. The exact mechanism accounting for this different phenotype is still unclear. To understand how natural hosts for SIV preserve Th17 cells and mucosal immunity might be central to the development of therapeutic interventions aimed at improving mucosal immunity in HIV-infected individuals.