IL-1-induced Bhlhe40 identifies pathogenic T helper cells in a model of autoimmune neuroinflammation

The pathogenicity of Th17 cells in autoimmune diseases

IL-17-producing T helper (Th17) cells have been implicated in the pathogenesis of many inflammatory and autoimmune diseases. Targeting the effector cytokines IL-17 and GM-CSF secreted by autoimmune Th17 cells has been shown to be effective for the treatment of the diseases. Understanding a molecular basis of Th17 differentiation and effector functions is therefore critical for the regulation of the pathogenicity of tissue Th17 cells in chronic inflammation. Here, we discuss the roles of proinflammatory cytokines and environmental stimuli in the control of Th17 differentiation and chronic tissue inflammation by pathogenic Th17 cells in humans and in mouse models of autoimmune diseases. We also highlight recent advances in the regulation of pathogenic Th17 cells by gut microbiota and immunometabolism in autoimmune arthritis.

Pathogenic function of bystander-activated memory-like CD4+ T cells in autoimmune encephalomyelitis

T cells generate antigen-specific immune responses to their cognate antigen as a hallmark of adaptive immunity. Despite the importance of antigen-specific T cells, here we show that antigen non-related, bystander memory-like CD4⁺ T cells also significantly contribute to autoimmune pathogenesis. Transcriptome analysis demonstrates that interleukin (IL)-1β- and IL-23-prime T cells that express pathogenic T_Η17 signature genes such as RORγt, CCR6, and granulocyte macrophage colony-stimulating factor (GM-CSF). Importantly, when co-transferred with myelin-specific 2D2 TCR-transgenic naive T cells, unrelated OT-II TCR-transgenic memory-like T_H17 cells infiltrate the spinal cord and produce IL-17A, interferon (IFN)-γ, and GM-CSF, increasing the susceptibility of the recipients to experimental autoimmune encephalomyelitis in an IL-1 receptor-dependent manner. In humans, IL-1R1^high memory CD4⁺ T cells are major producers of IL-17A and IFN-γ in response to IL-1β and IL-23. Collectively, our findings reveal the innate-like pathogenic function of antigen non-related memory CD4⁺ T cells, which contributes to the development of autoimmune diseases.

T cells express specific T cell receptors (TCR) to recognise antigens and initiate adaptive immune responses. Here the authors show, in a mouse model of autoimmune encephalomyelitis, that memory-like CD4 T cells expressing unrelated TCR can also infiltrate the spinal cord and contribute to autoimmunity.

Inflammasome activation and Th17 responses

Immune sensing of exogenous molecules from microbes (e.g., pathogen-associated molecular patterns) and nonmicrobial molecules (e.g., asbestos, alum, and silica), as well as endogenous damage-associated molecular patterns (e.g., ATP, uric acid crystals, and amyloid A) activates innate immunity by inducing immune-related genes, including proinflammatory cytokines, which further facilitate the development of adaptive immunity. The roles of transcriptional responses downstream of immune sensing have been widely characterized in informing adaptive immunity; however, few studies focus on the effect of post-translational responses on the modulation of adaptive immune responses. Inflammasomes activated by the previously described endo- and exogenous stimuli autocatalytically induce intracellular pro-caspase-1, which cleaves the inactive precursors of interleukin-1β (IL-1β) and IL-18 into bioactive proinflammatory cytokines. IL-1β and IL-18 not only contribute to the host defense against infections by activating phagocytes, such as monocytes, macrophages, dendritic cells, and neutrophils, but also induce T-helper 17 (Th17)- and Th1-mediated adaptive immune responses. In synergy with IL-6 and IL-23, IL-1β activates IL-1 receptor (IL-1R) signaling to drive the differentiation of IL-17-producing Th17 cells, which not only play critical roles in host protective immunity to infections of bacteria, fungi, and certain viruses but also participate in the pathology of inflammatory disorders and tumorigenesis. Consequently, targeting inflammasomes and IL-1/IL-1R signaling may effectively improve the treatment of Th17-associated disorders, such as autoinflammatory diseases and cancers, thereby providing novel insights into drug development.

Satb1 regulates the effector program of encephalitogenic tissue Th17 cells in chronic inflammation

The genome organizer, special AT-rich sequence-binding protein-1 (Satb1), plays a pivotal role in the regulation of global gene networks in a cell type-dependent manner and is indispensable for the development of multiple cell types, including mature CD4+ T, CD8+ T, and Foxp3+ regulatory T cells in the thymus. However, it remains unknown how the differentiation and effector program of the Th subsets in the periphery are regulated by Satb1. Here, we demonstrate that Satb1 differentially regulates gene expression profiles in non-pathogenic and pathogenic Th17 cells and promotes the pathogenic effector program of encephalitogenic Th17 cells by regulating GM-CSF via Bhlhe40 and inhibiting PD-1 expression. However, Satb1 is dispensable for the differentiation and non-pathogenic functions of Th17 cells. These results indicate that Satb1 regulates the specific gene expression and function of effector Th17 cells in tissue inflammation.

Transcriptional regulation of CD4+ TH cells that mediate tissue inflammation

Acquired and genetic immunodeficiencies have revealed an indispensable role for CD4⁺ T cells in the induction of protective host immune responses against a myriad of microbial pathogens. Influenced by the cytokines present in the microenvironment, activated CD4⁺ T cells may differentiate into several highly-specialized helper subsets defined by the production of distinct signature cytokines tailored to combat diverse classes of pathogens. The process of specification and differentiation is controlled by networks of core, master, and accessory transcription factors, which ensure that CD4⁺ T helper (T_H ) cell responses mounted against an invading microbe are of the correct specificity and type. However, aberrant activation or inactivation of transcription factors can result in sustained and elevated expression of immune-related genes, leading to chronic activation of CD4⁺ T_H  cells and organ-specific autoimmunity. In this review, we provide an overview of the molecular basis of CD4⁺ T_H  cell differentiation and examine how combinatorial expression of transcription factors, which promotes genetic plasticity of CD4⁺ T_H  cells, can contribute to immunological dysfunction of CD4⁺ T_H responses. We also discuss recent studies which highlight the potential of exploiting the genetic plasticity of CD4⁺ T_H  cells in the treatment of autoimmune and other immune-mediated disorders.

The transcription factor Bhlhe40 is a switch of inflammatory versus antiinflammatory Th1 cell fate determination

The balance between inflammatory IFN-γ and antiinflammatory IL-10 plays a critical role in modulating type 1 immune responses. Yu et al. show that the transcription factor Bhlhe40 serves as a molecular switch between inflammatory and antiinflammatory Th1 cells.

Type 1 T helper (Th1) cells play a critical role in host defense against intracellular pathogens and in autoimmune diseases by producing a key inflammatory cytokine interferon (IFN)–γ; some Th1 cells can also be antiinflammatory through producing IL-10. However, the molecular switch for regulating the differentiation of inflammatory and antiinflammatory Th1 cells is still elusive. Here, we show that Bhlhe40-deficient CD4 Th1 cells produced less IFN-γ but substantially more IL-10 than wild-type Th1 cells both in vitro and in vivo. Bhlhe40-mediated IFN-γ production was independent of transcription factor T-bet regulation. Mice with conditional deletion of Bhlhe40 in T cells succumbed to Toxoplasma gondii infection, and blockade of IL-10 signaling during infection rescued these mice from death. Thus, our results demonstrate that transcription factor Bhlhe40 is a molecular switch for determining the fate of inflammatory and antiinflammatory Th1 cells.

Bhlhe40 is an essential repressor of IL-10 during Mycobacterium tuberculosis infection

The cytokine IL-10 antagonizes pathways that control Mycobacterium tuberculosis (Mtb) infection. Nevertheless, the impact of IL-10 during Mtb infection has been difficult to decipher because loss-of-function studies in animal models have yielded only mild phenotypes. We have discovered that the transcription factor basic helix-loop-helix family member e40 (Bhlhe40) is required to repress Il10 expression during Mtb infection. Loss of Bhlhe40 in mice results in higher Il10 expression, higher bacterial burden, and early susceptibility similar to that observed in mice lacking IFN-γ. Deletion of Il10 in Bhlhe40^-/- mice reverses these phenotypes. Bhlhe40 deletion in T cells or CD11c⁺ cells is sufficient to cause susceptibility to Mtb Bhlhe40 represents the first transcription factor found to be essential during Mtb infection to specifically regulate Il10 expression, revealing the importance of strict control of IL-10 production by innate and adaptive immune cells during infection. Our findings uncover a previously elusive but significant role for IL-10 in Mtb pathogenesis.

Clearance of a persistent picornavirus infection is associated with enhanced pro-apoptotic and cellular immune responses

Long-term persistent viral infections cause substantial morbidity and associated economic losses in human and veterinary contexts. Yet, the mechanisms associated with establishment of persistent infections are poorly elucidated. We investigated immunomodulatory mechanisms associated with clearance versus persistence of foot-and-mouth disease virus (FMDV) in micro-dissected compartments of the bovine nasopharynx by microarray. The use of laser-capture microdissection allowed elucidation of differential gene regulation within distinct anatomic compartments critical to FMDV infection. Analysis of samples from transitional and persistent phases of infection demonstrated significant differences in transcriptome profiles of animals that cleared infection versus those that became persistently infected carriers. Specifically, it was demonstrated that clearance of FMDV from the nasopharyngeal mucosa was associated with upregulation of targets associated with activation of T cell-mediated immunity. Contrastingly, gene regulation in FMDV carriers suggested inhibition of T cell activation and promotion of Th2 polarization. These findings were corroborated by immunofluorescence microscopy which demonstrated relative abundance of CD8⁺ T cells in the nasopharyngeal mucosa in association with clearance of FMDV. The findings presented herein emphasize that a critical balance between Th1 and Th2 -mediated immunity is essential for successful clearance of FMDV infection and should be considered for development of next-generation vaccines and antiviral products.

New Insights into the Role of IL-1β in Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

Multiple sclerosis (MS), and its animal model experimental autoimmune encephalomyelitis, are neuroinflammatory diseases driven by autoreactive pathogenic T_H cells that elicit demyelination and axonal damage. How T_H cells acquire pathogenicity and communicate with myeloid cells and cells of the CNS remain unclear. IL-1β is recognized to play an important role in experimental autoimmune encephalomyelitis (EAE) and perhaps MS. Clinical EAE is significantly attenuated in IL-1R-deficient and IL-1β-deficient mice, and IL-1β is found in the blood, cerebrospinal fluid, and CNS lesions of MS patients. In this article, we focus on new reports that elucidate the cellular sources of IL-1β and its actions during EAE, in both lymphoid tissues and within the CNS. Several immune cell types serve as critical producers of IL-1β during EAE, with this cytokine inducing response in both hematopoietic and nonhematopoietic cells. These findings from the EAE model should inspire efforts toward investigating the therapeutic potential of IL-1 blockade in MS.

Dysregulation of the Cytokine GM-CSF Induces Spontaneous Phagocyte Invasion and Immunopathology in the Central Nervous System

Chronic inflammatory diseases are influenced by dysregulation of cytokines. Among them, granulocyte macrophage colony stimulating factor (GM-CSF) is crucial for the pathogenic function of T cells in preclinical models of autoimmunity. To study the impact of dysregulated GM-CSF expression in vivo, we generated a transgenic mouse line allowing the induction of GM-CSF expression in mature, peripheral helper T (Th) cells. Antigen-independent GM-CSF release led to the invasion of inflammatory myeloid cells into the central nervous system (CNS), which was accompanied by the spontaneous development of severe neurological deficits. CNS-invading phagocytes produced reactive oxygen species and exhibited a distinct genetic signature compared to myeloid cells invading other organs. We propose that the CNS is particularly vulnerable to the attack of monocyte-derived phagocytes and that the effector functions of GM-CSF-expanded myeloid cells are in turn guided by the tissue microenvironment.

Cholesterol Accumulation in Dendritic Cells Links the Inflammasome to Acquired Immunity

Autoimmune diseases such as systemic lupus erythematosus (SLE) are associated with increased cardiovascular disease and reduced plasma high-density lipoprotein (HDL) levels. HDL mediates cholesterol efflux from immune cells via the ATP binding cassette transporters A1 and G1 (ABCA1/G1). The significance of impaired cholesterol efflux pathways in autoimmunity is unknown. We observed that Abca1/g1-deficient mice develop enlarged lymph nodes (LNs) and glomerulonephritis suggestive of SLE. This lupus-like phenotype was recapitulated in mice with knockouts of Abca1/g1 in dendritic cells (DCs), but not in macrophages or T cells. DC-Abca1/g1 deficiency increased LN and splenic CD11b⁺ DCs, which displayed cholesterol accumulation and inflammasome activation, increased cell surface levels of the granulocyte macrophage-colony stimulating factor receptor, and enhanced inflammatory cytokine secretion. Consequently, DC-Abca1/g1 deficiency enhanced T cell activation and T_h1 and T_h17 cell polarization. Nlrp3 inflammasome deficiency diminished the enlarged LNs and enhanced T_h1 cell polarization. These findings identify an essential role of DC cholesterol efflux pathways in maintaining immune tolerance.

Involvement of the IL-1 system in experimental autoimmune encephalomyelitis and multiple sclerosis: Breaking the vicious cycle between IL-1β and GM-CSF

Multiple sclerosis (MS) is an autoimmune disease that affects hundreds of thousands of people worldwide. Given the autoimmune nature of the disease, a large part of the research has focused on autoreactive T and B cells. However, research on the involvement of myeloid cells in the pathophysiology of MS has received a strong and renewed attention over the recent years. Despite the multitude of inflammatory mediators involved in innate immunity, only a select group of cytokines are absolutely critical to the development of CNS autoimmunity, among which is interleukin (IL)-1. While the importance of the IL-1 system in experimental autoimmune encephalomyelitis (EAE) and MS has been recognized for about 20years, it is only recently that we have begun to understand that IL-1 plays multifaceted roles in disease initiation, development, amplification and chronicity. Here, we review the recent findings showing an implication of the IL-1 system in EAE and MS, and introduce a model that highlights how IL-1β and granulocyte-macrophage colony-stimulating factor (GM-CSF) are interacting together to create a vicious feedback cycle of CNS inflammation that ultimately leads to myelin and neuronal damage.

Assessment of Serum Nitrogen Species and Inflammatory Parameters in Relapsing-Remitting Multiple Sclerosis Patients Treated with Different Therapeutic Approaches

The role of nitric oxide and its reactive derivatives (NO _x ) is well known in the pathogenesis of multiple sclerosis, which is an inflammatory disease while NO _x seems to be important in coordinating inflammatory response. The purpose of the present study was to assess serum NO _x as one of the nitrogen species and inflammatory parameters in relapsing-remitting multiple sclerosis patients and to compare the effectiveness of various types of disease-modifying therapies that reduce nitric oxide and inflammatory biomarkers. Elevated NO _x level was observed in patients who received the first-line disease-modifying therapy (interferons beta-1a and beta-1b) in comparison with the subjects treated with the second-line disease-modifying therapy (natalizumab; fingolimod) and healthy controls without significant differences in C-reactive protein and interleukin-1 beta. A negative correlation was observed between serum NO _x level and the duration of multiple sclerosis confirmed in the whole study population and in subjects treated with the first-line agents. Only serum NO _x , concentration could reveal a potential efficacy of disease-modifying therapy with a better reduction in NO _x level due to the second-line agents of disease-modifying therapy.

Macrophage Colony Stimulating Factor Derived from CD4+ T Cells Contributes to Control of a Blood-Borne Infection

Dynamic regulation of leukocyte population size and activation state is crucial for an effective immune response. In malaria, Plasmodium parasites elicit robust host expansion of macrophages and monocytes, but the underlying mechanisms remain unclear. Here we show that myeloid expansion during P. chabaudi infection is dependent upon both CD4+ T cells and the cytokine Macrophage Colony Stimulating Factor (MCSF). Single-cell RNA-Seq analysis on antigen-experienced T cells revealed robust expression of Csf1, the gene encoding MCSF, in a sub-population of CD4+ T cells with distinct transcriptional and surface phenotypes. Selective deletion of Csf1 in CD4+ cells during P. chabaudi infection diminished proliferation and activation of certain myeloid subsets, most notably lymph node-resident CD169+ macrophages, and resulted in increased parasite burden and impaired recovery of infected mice. Depletion of CD169+ macrophages during infection also led to increased parasitemia and significant host mortality, confirming a previously unappreciated role for these cells in control of P. chabaudi. This work establishes the CD4+ T cell as a physiologically relevant source of MCSF in vivo; probes the complexity of the CD4+ T cell response during type 1 infection; and delineates a novel mechanism by which T helper cells regulate myeloid cells to limit growth of a blood-borne intracellular pathogen.

Activated IL-1RI Signaling Pathway Induces Th17 Cell Differentiation via Interferon Regulatory Factor 4 Signaling in Patients with Relapsing-Remitting Multiple Sclerosis

IL-1β plays a crucial role in the differentiation of human Th17 cells. We report here that IL-1RI expression is significantly increased in both naive and memory CD4⁺ T cells derived from relapsing-remitting multiple sclerosis (RR MS) patients in comparison to healthy controls. Interleukin 1 receptor (IL-1R)I expression is upregulated in the in vitro-differentiated Th17 cells from RR MS patients in comparison to the Th1 and Th2 cell subsets, indicating the role of IL-1R signaling in the Th17 cell differentiation in RR MS. When IL-1RI gene expression was silenced using siRNA, human naive CD4⁺ T cells cultured in the presence of Th17-polarizing cytokines had a significantly decreased expression of interleukin regulatory factor 4 (IRF4), RORc, IL-17A, IL-17F, IL-21, IL-22, and IL-23R genes, confirming that IL-1RI signaling induces Th17 cell differentiation. Since IL-1R gene expression silencing inhibited IRF4 expression and Th17 differentiation, and IRF4 gene expression silencing inhibited Th17 cell differentiation, our results indicate that IL-1RI induces human Th17 cell differentiation in an IRF4-dependant manner. Our study has identified that IL-1RI-mediated signaling pathway is constitutively activated, leading to an increased Th17 cell differentiation in IRF4-dependent manner in patients with RR MS.

IL-1 signaling is critical for expansion but not generation of autoreactive GM-CSF+ Th17 cells

Interleukin-1 (IL-1) is implicated in numerous pathologies, including multiple sclerosis and its animal model experimental autoimmune encephalomyelitis (EAE). However, the exact mechanism by which IL-1 is involved in the generation of pathogenic T cells and in disease development remains largely unknown. We found that following EAE induction, pertussis toxin administration leads to IL-1 receptor type 1 (IL-1R1)-dependent IL-1β expression by myeloid cells in the draining lymph nodes. This myeloid-derived IL-1β did not vitally contribute to the generation and plasticity of Th17 cells, but rather promoted the expansion of a GM-CSF⁺ Th17 cell subset, thereby enhancing its encephalitogenic potential. Lack of expansion of GM-CSF-producing Th17 cells led to ameliorated disease in mice deficient for IL-1R1 specifically in T cells. Importantly, pathogenicity of IL-1R1-deficient T cells was fully restored by IL-23 polarization and expansion in vitro Therefore, our data demonstrate that IL-1 functions as a mitogenic mediator of encephalitogenic Th17 cells rather than qualitative inducer of their generation.

Anti-CD48 Monoclonal Antibody Attenuates Experimental Autoimmune Encephalomyelitis by Limiting the Number of Pathogenic CD4+ T Cells

CD48 (SLAMF2) is an adhesion and costimulatory molecule constitutively expressed on hematopoietic cells. Polymorphisms in CD48 have been linked to susceptibility to multiple sclerosis (MS), and altered expression of the structurally related protein CD58 (LFA-3) is associated with disease remission in MS. We examined CD48 expression and function in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. We found that a subpopulation of CD4⁺ T cells highly upregulated CD48 expression during EAE and were enriched for pathogenic CD4⁺ T cells. These CD48⁺⁺CD4⁺ T cells were predominantly CD44⁺ and Ki67⁺, included producers of IL-17A, GM-CSF, and IFN-γ, and were most of the CD4⁺ T cells in the CNS. Administration of anti-CD48 mAb during EAE attenuated clinical disease, limited accumulation of lymphocytes in the CNS, and reduced the number of pathogenic cytokine-secreting CD4⁺ T cells in the spleen at early time points. These therapeutic effects required CD48 expression on CD4⁺ T cells but not on APCs. Additionally, the effects of anti-CD48 were partially dependent on FcγRs, as anti-CD48 did not ameliorate EAE or reduce the number of cytokine-producing effector CD4⁺ T cells in Fcεr1γ^-/- mice or in wild-type mice receiving anti-CD16/CD32 mAb. Our data suggest that anti-CD48 mAb exerts its therapeutic effects by both limiting CD4⁺ T cell proliferation and preferentially eliminating pathogenic CD48⁺⁺CD4⁺ T cells during EAE. Our findings indicate that high CD48 expression is a feature of pathogenic CD4⁺ T cells during EAE and point to CD48 as a potential target for immunotherapy.