Treg cells may regulate interlukin-17 production by modulating TH1 responses in 1,3-β-glucan-induced lung inflammation in mice

1,3-β-glucan is considered a fungal biomarker and exposure to this agent can induce lung inflammation. Complement activation plays an important role in early immune responses to β-glucan. Previous studies showed that T-regulatory cells (T_regs) regulated 1,3-β-glucan-induced lung inflammation by modulating the maintenance of immune homeostasis in the lung. Both interleukin (IL)-17 and T_H17 cells play pivotal roles in inflammation associated with lung disease and share reciprocal developmental pathways with T_regs. However, the effect of T_regs on IL-17 and T_H17 responses in 1,3-β-glucan-induced lung inflammation remains unclear. In this study, mice were exposed to 1,3-β-glucan by intratracheal instillation. To investigate the effects of T_regs on IL-17 and T_H17 cells in the induced lung inflammation, a T_reg-depleted mice model was generated by administration of anti-CD25 mAb. The results indicated that T_reg-depleted mice showed more severe pathological inflammatory changes in lung tissues. T_regs depletion reduced IL-17 expression in these tissues, and increased those of T_H1 cytokines. The expression of IL-17 increased at the early phase of the inflammation response. There were no significant effects of the T_regs on expression of RORγt and IL-6 or the amount of CD4⁺IL-17⁺ cells in the lungs. When taken together, the late phase of the 1,3-β-glucan-induced inflammatory response in the mice was primarily mediated by T_H1 cytokines rather than IL-17. In contrast, the early phase of the inflammatory response might be mediated in part by IL-17 along with activated complement. T_regs might be required for IL-17 expression during the late phase inflammatory response in mice. The increased IL-17 mRNA observed during the 1,3-β-glucan induced inflammatory response were attributed to cells other than T_H17 cells.     

Apical TLR ligation of intestinal epithelial cells drives a Th1-polarized regulatory or inflammatory type effector response in vitro

Intestinal epithelial cells (IEC) separate the mucosal immune system from the external milieu. Under inflammatory conditions, Toll-like receptor (TLR) expression by IEC is increased. In a transwell co-culture model immune modulation by IEC upon TLR ligation was studied. Human IEC (HT-29 and T84) grown on filters were apically or basolaterally exposed to TLR4 or TLR9 ligands and co-cultured with CD3/CD28-activated healthy donor PBMC in the basolateral compartment. TLR4 ligation of IEC (HT-29) enhanced the production of TNF-α and IEC-derived MDC and decreased numbers of Foxp3⁺ regulatory T cells. Neutralization of TSLP abrogated TLR4-induced TNF-α secretion. In contrast, apical TLR9 ligation of IEC (HT-29 and T84) enhanced IFN-γ and IL-10 secretion and increased the number of activated T_h1 cells. The increase in IFN-γ secretion depended on the presence of IEC. Furthermore, CD14 expression on monocytes was reduced coinciding with enhanced intracellular IL-10 and decreased TNF-α production. However, basolateral TLR9 ligand exposure of HT-29 cells resulted in enhanced IFN-γ, IL-6 and TNF-α, while IL-10 secretion remained unaltered. TLR4 and TLR9 ligands reduced IL-13 secretion in presence and absence of apically exposed IEC and enhanced IL-12 secretion in presence of IEC. These data suggest that TLR4 ligation of IEC drives an inflammatory, while apical TLR9 ligation drives a regulatory T_h1 effector immune response in vitro in a polarized manner. IEC may be important modulators of the mucosal effector immune response.     

Interleukin-17A negatively regulates lymphangiogenesis in T helper 17 cell-mediated inflammation

During inflammation lymphatic vessels (LVs) are enlarged and their density is increased to facilitate the migration of activated immune cells and antigens. However, after antigen clearance, the expanded LVs shrink to maintain homeostasis. Here we show that interleukin (IL)-17A, secreted from T helper type 17 (T_H17) cells, is a negative regulator of lymphangiogenesis during the resolution phase of T_H17-mediated immune responses. Moreover, IL-17A suppresses the expression of major lymphatic markers in lymphatic endothelial cells and decreases in vitro LV formation. To investigate the role of IL-17A in vivo, we utilized a cholera toxin-mediated inflammation model and identified inflammation and resolution phases based on the numbers of recruited immune cells. IL-17A, markedly produced by T_H17 cells even after the peak of inflammation, was found to participate in the negative regulation of LV formation. Moreover, blockade of IL-17A resulted in not only increased density of LVs in tissues but also their enhanced function. Taken together, these findings improve the current understanding of the relationship between LVs and inflammatory cytokines in pathologic conditions.     

Contribution of interleukin 17A to the development and regulation of allergic inflammation in a murine allergic rhinitis model

BackgroundInterleukin (IL) 17A, a key cytokine of T_H17 cells, is a well-known proinflammatory cytokine. Despite the important role of T_H17 cells in acute airway inflammation, the role of IL-17A in allergic rhinitis (AR) remains unclear.ObjectiveTo investigate the role of IL-17A in the allergic response in AR.MethodsWild-type BALB/c and IL-17A–deficient mice were immunized intraperitoneally and were challenged intranasally with ovalbumin. Allergic symptom scores, eosinophil infiltration, serum IgE level, and the levels of several cytokines in nasal lavage fluid and splenocyte supernatants were analyzed.ResultsIL-17A levels increased significantly more in ovalbumin-sensitized wild-type mice than in the negative control group. IL-17A–deficient mice showed a significant decrease in allergic symptoms, serum IgE levels, and eosinophil infiltration into the nasal mucosa compared with wild-type mice. IL-17A–deficient mice also showed decreased histamine and cysteinyl leukotriene release. Bone marrow–derived mast cells from IL-17A–deficient mice showed significantly lower degranulation and secretion of tumor necrosis factor α. Moreover, IL-17A deficiency attenuated the IL-5 level in nasal lavage fluid and its production in response to ovalbumin but did not increase interferon γ production and its level in nasal lavage fluid. In addition, secretion of IL-17A from spleen cells induced the expression of proinflammatory cytokine messenger RNA in macrophages. The mean level of proinflammatory cytokines, including tumor necrosis factor α and IL-17, decreased in IL-17A–deficient mice.ConclusionThese results suggest that IL-17A may partly contribute to the development of nasal allergic inflammation in an AR animal model and regulate AR via the activation of proinflammatory cytokines and modulation of T_H2 cytokine.     

Cytokines related to three major types of cell-mediated immunity in short- and long-term exposures to lead compounds

Many investigators have posited on the significant influence of lead on the immune system function. However, available data on this topic are not conclusive. Therefore, a study was undertaken to examine associations between lead exposure and levels of cytokines related to the T-helper (T_H)-1, T_H2, and T_H17 types of immune response in humans. For these analyses, three population groups were examined: the first consisted of male workers exposed to lead for a short period of time (36–44 days); the second included male workers chronically exposed to lead (13?±?10 years); and a control group that was composed of male administrative workers with blood lead levels (BLL)?H1 cells), IL-4, IL-5, IL-13 (related to T_H2 cells), and IL-17A (related to T_H17 cells) did not change after a short-term exposure to lead (compared to baseline). However, the levels of all of these cytokines were significantly higher in workers chronically exposed to lead than in the controls by 82%, 32%, 81%, 22%, 70%, 42%, and 17% (IFNγ, IL-2, IL-12, IL-4, IL-5, IL-13, IL-17A, respectively). From these studies, we conclude that in humans, a short-term exposure to lead does not affect levels of cytokines related to the T_H1-, T_H2-, and T_H17-mediated immune responses, while chronic exposure modifies their levels. Taken together, these modifications do not evidence an ability of lead to promote specifically one type of immune response in an exposed host.     

A novel TH17-type cell is rapidly increased in the liver in response to acetaminophen-induced liver injury: TH17 cells and the innate immune response

Helper T (T_H) cells are an important part of the adaptive immune system. It is hypothesized that one type of helper T-cell, T_H17 cells, play an important role in idiosyncratic drug-induced liver failure, and it was found that interleukin (IL)-17, the signature cytokine of T_H17 cells, was elevated in most patients with idiosyncratic drug-induced liver failure. However, it was also found that IL-17 was elevated in some patients with acetaminophen (APAP)-induced liver failure. It is unlikely that APAP-induced liver failure is mediated by the adaptive immune system, but there are other cells such as macrophages and natural killer (NK) cells that also produce IL-17. Therefore, the phenotype of cells that produce IL-17 was studied in a mouse model of APAP-induced liver toxicity. To the authors’ surprise, it was found that most of the IL-17 producing cells in the liver were T_H17 cells, and they were increased within hours of APAP treatment. This is too fast for a response of the adaptive immune system. These data suggest that T_H17 cells can be part of the innate immune response; however, it is unclear what role they play in the pathogenesis of APAP-induced hepatotoxicity.     

IL-33 Is Induced by Amyloid-β Stimulation and Regulates Inflammatory Cytokine Production in Retinal Pigment Epithelium Cells

Age-related macular degeneration (AMD) is the predominant cause of irreversible blindness in the elderly population. Despite intensive basic and clinical research, its pathogenesis remains unclear. However, evidence suggests that immunological and inflammatory factors contribute to the pathogenesis of AMD. A newly identified cytokine, IL-33, appears to be an important pro-inflammatory cytokine promoting tissue inflammation. In this study, IL-33 was increased through amyloid-beta_1–40 (Aβ_1–40) stimulation and regulated inflammatory cytokines including IL-6, IL-8, IL-1β, and TNF-α secretion using different signaling pathways in retinal pigment epithelium (RPE) cells. Furthermore, ST2L, the important component of the IL-33 receptor, was significantly increased following recombinant human IL-33 stimulation in RPE cells. These findings suggest that IL-33-mediated inflammatory responses in RPE cells are involved in the pathogenesis of AMD. Greater understanding of the inflammatory effect of IL-33 and its role in RPE cells should aid the development of future clinical therapeutics and enable novel pharmacological approaches towards the prevention of AMD.     

IL-33 links tissue cells, dendritic cells and Th2 cell development in a mouse model of asthma

IL-33 is becoming a central molecule in allergic asthma that addresses various cascades of innate and adaptive immune responses that lead to inflammation in the lung. Its effects are exerted via its heterodimeric receptor that consists of ST2 and the ubiquitously expressed IL-1 receptor accessory protein (ILRAcP). IL-33 integrates both innate and adaptive immunity in a unique fashion via basophils, mast cells, eosinophils, innate lymphoid cells, NK and NKT cells, nuocytes, Th2 lymphocytes and a CD34(pos) precursor cell population. These actions of IL-33 seem to be particularly strong and dominant in models with mucosal inflammation. A study in this issue of the European Journal of Immunology demonstrates that IL-33 acts, in an ST2-dependent manner, as a maturation factor for BM-derived DCs via up-regulation of CD80, CD40 and OX40L. This process is accompanied by the release of pro-inflammatory cytokines, such as IL-6, IL-1β, TNF-α and TARC/CCL17. IL-33-pre-treated DCs were significantly more potent for the generation of allergen-specific Th2-type cells with IL-5 and IL-13 production. Intratracheal administration of OVA-pulsed DCs with IL-33 significantly enhances eosinophil numbers and mucous secretion. In conclusion, IL-33 affects both the development of allergic sensitization and the development of lung inflammation in allergic asthma.     

Is TGFβ as an anti-inflammatory cytokine required for differentiation of inflammatory TH17 cells?

T-Helper 17 (T_H17) cells are a CD4⁺ T_H subset that plays a critical role in the pathophysiology of inflammatory disorders, especially chronic forms. It seems that the derivation of T_H17 cells from their precursors take place in inflammatory microenvironment. The role of transforming growth factor (TGF)-β as an anti-inflammatory cytokine in T_H17 cell differentiation is controversial. To address some of the discrepancies that exist among different studies, this study was undertaken to more clarify the TGFβ role in human T_H17 cell differentiation. Here, CD4⁺ T-cells were isolated from peripheral blood samples and cultured in X-VIVO 15 serum-free medium. Purified cells were then treated with different combinations of polarizing cytokines (interleukin [IL]1-β, -6, and -23, with or without TGFβ), neutralizing anti-interferon (IFN)-γ and anti-IL-4 antibodies and polyclonal stimulators anti-CD3 and -CD28 antibodies, and then analyzed for IL-17, IFNγ, Foxp3, and CD25 expression by flow cytometry and for release of IL-17, -21, -22, and -10 into culture media by ELISA. The effects of selective inhibition of TGFβ signaling pathway on T_H17 cell polarization were also determined by using small molecules SB-431542 and A83-01. The current study found that a combination of pro-inflammatory cytokines, including IL-1β, -6, and -23, but not TGFβ, could be used as a cytokine combination to induce development of human T_H17 cells. It was also shown that TGFβ acted as a negative regulator in this regard and also led to reduced IL-17 and IL-22 production while inducing Foxp3 expression. Indeed, blocking of TGFβ signaling pathways by selective inhibitors up-regulated T_H17 cell differentiation. From the data here, we concluded that TGFβ down-regulates human T_H17 cell differentiation and that a presence of pro-inflammatory cytokines (along with IFNγ and IL-4 neutralizing antibodies) is sufficient for optimal differentiation of human T_H17 cells.     

IL-33/ST2 as a potential target for tumor immunotherapy

IL-33, a member of the IL-1 family, was initially reported to be expressed constitutively in the nucleus of tissue-lining and structural cells. However, upon tissue damage or injury, IL-33 can be released quickly to bind with its cognate receptor ST2 in response to wound healing and inflammation and act as a DAMP. As a key regulator of Th2 responses, IL-33/ST2 signal is primarily associated with immunity and immune-related disorders. In recent years, IL-33/ST2 signaling pathway has been reported to promote the development of cancer and remodel the tumor microenvironment by expanding immune suppressive cells such as myeloid-derived suppressor cells or regulatory T cells. However, its role remains controversial in some tumor settings. IL-33 could also promote effective infiltration of immune cells such as CD8⁺ T and NK cells, which act as antitumor. These dual effects may limit the clinical application to target this cytokine axis. Therefore, more comprehensive exploration and deeper understanding of IL-33 are required. In this review, we summarized the IL-33/ST2 axis versatile roles in the tumor microenvironment with a focus on the IL-33-target immune cells and downstream signaling pathways. We also discuss how the IL-33/ST2 axis could be used as a potential therapeutic target for cancer immunotherapy.     

Prostaglandin E Receptor Subtypes EP2 and EP4 Promote TH1 Cell Differentiation and TH17 Cell Expansion Through Different Signaling Modules

It is well known that prostaglandin (PG) E₂ exerts T cell suppression in vitro through elevating cAMP by its receptors, EP2 and EP4. However, such an action is rarely detected in vivo, leaving PGE₂-mediated immunosuppression an enigma. Here we show that under strong TCR stimulation, PGE₂ facilitates T helper-1 (T_H-1) differentiation through activation of phosphatidylinositol-3-kinase (PI3K) by EP2 and EP4. The PGE₂-EP4 signaling is also required for IL-23 production by activated dendritic cells (DCs), and the PGE2-EP2/EP4 signaling amplifies IL-23-mediated T_H-17 cell expansion. Administration of an EP4-selective antagonist in vivo to mice subjected to experimental allergic encephalomyelitis (EAE) decreases accumulation of both T_H-1 and T_H-17 cells in regional lymph nodes, and suppresses the disease progression. These results suggest PGE₂ promotes immune inflammation through T_H-1 differentiation and T_H-17 expansion and the EP4 antagonism is therapeutically useful for various immune diseases.

     

Modeling TH2 responses and airway inflammation to understand fundamental mechanisms regulating the pathogenesis of asthma

In this review, we highlight experiments conducted in our laboratories that have elucidated functional roles for CD4⁺ T-helper type-2 lymphocytes (T_H2 cells), their associated cytokines, and eosinophils in the regulation of hallmark features of allergic asthma. Notably, we consider the complexity of type-2 responses and studies that have explored integrated signaling among classical T_H2 cytokines (IL-4, IL-5, and IL-13), which together with CCL11 (eotaxin-1) regulate critical aspects of eosinophil recruitment, allergic inflammation, and airway hyper-responsiveness (AHR). Among our most important findings, we have provided evidence that the initiation of T_H2 responses is regulated by airway epithelial cell-derived factors, including TRAIL and MID1, which promote T_H2 cell development via STAT6-dependent pathways. Further, we highlight studies demonstrating that microRNAs are key regulators of allergic inflammation and potential targets for anti-inflammatory therapy. On the background of T_H2 inflammation, we have demonstrated that innate immune cells (notably, airway macrophages) play essential roles in the generation of steroid-resistant inflammation and AHR secondary to allergen- and pathogen-induced exacerbations. Our work clearly indicates that understanding the diversity and spatiotemporal role of the inflammatory response and its interactions with resident airway cells is critical to advancing knowledge on asthma pathogenesis and the development of new therapeutic approaches.     

IL-21 and IL-21 receptor in the immunopathogenesis of multiple sclerosis

Cytokines are considered important factors in the modulation of various immune responses. Among them, interleukin (IL)-21 is one of the major immune modulators, adjusting various immune responses by affecting various immune cells. It has been suggested that IL-21 may enhance autoimmunity through different mechanisms, such as development and activation of helper T (T_H)-17 and follicular helper T (T_FH) cells, activation of natural killer (NK) cells, enhancing B-cell differentiation and antibody secretion and suppression of regulatory T (T_reg) cells. Moreover, IL-21 has also been suggested to be an inducer of autoimmunity when following treatment of MS patients with some therapeutics such as alemtuzumab. This review will seek to clarify the precise role of IL-21/IL-21R in the pathogenesis of MS and, in its animal model, experimental autoimmune encephalomyelitis (EAE).     

Involvement of brain-derived neurotrophic factor (BDNF) in MP4-induced autoimmune encephalomyelitis

The role of brain-derived neurotrophic factor (BDNF) in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE) is still unclear. Here we investigate the clinical course, CNS histopathology and peripheral antigen-specific immunity in MP4-induced EAE of BDNF (−/+) mice. We demonstrate that these mice displayed less severe disease compared to BDNF (+/+) mice, reflected by decreased inflammation and demyelination. In correspondence to diminished frequencies of T and B cells in CNS infiltrates, the peripheral MP4-specific T_H1/T_H17 response was attenuated in BDNF (−/+), but not in wild-type animals. In contrast, immunization with ovalbumin triggered similar frequencies of IFN-γ- and IL-17-secreting T cells in both groups. The cytokine secretion and proliferative activity upon mitogen stimulation did not reveal any global defect of T cell function in BDNF (−/+) mice. By influencing the antigen-specific immune response in autoimmune encephalomyelitis, BDNF may support and maintain the disease in ways that go beyond its alleged neuroprotective role.     

Interleukin-33 (IL-33): A nuclear cytokine from the IL-1 family

Interleukin-33 (IL-33) is a tissue-derived nuclear cytokine from the IL-1 family abundantly expressed in endothelial cells, epithelial cells and fibroblast-like cells, both during homeostasis and inflammation. It functions as an alarm signal (alarmin) released upon cell injury or tissue damage to alert immune cells expressing the ST2 receptor (IL-1RL1). The major targets of IL-33 in vivo are tissue-resident immune cells such as mast cells, group 2 innate lymphoid cells (ILC2s) and regulatory T cells (Tregs). Other cellular targets include T helper 2 (Th2) cells, eosinophils, basophils, dendritic cells, Th1 cells, CD8⁺ T cells, NK cells, iNKT cells, B cells, neutrophils and macrophages. IL-33 is thus emerging as a crucial immune modulator with pleiotropic activities in type-2, type-1 and regulatory immune responses, and important roles in allergic, fibrotic, infectious, and chronic inflammatory diseases. The critical function of IL-33/ST2 signaling in allergic inflammation is illustrated by the fact that IL33 and IL1RL1 are among the most highly replicated susceptibility loci for asthma. In this review, we highlight 15 years of discoveries on IL-33 protein, including its molecular characteristics, nuclear localization, bioactive forms, cellular sources, mechanisms of release and regulation by proteases. Importantly, we emphasize data that have been validated using IL-33-deficient cells.     

Prostaglandin E Receptor Subtypes EP2 and EP4 Promote T<Subscript>H</Subscript>1 Cell Differentiation and T<Subscript>H</Subscript>17 Cell Expansion Through Different Signaling Modules

It is well known that prostaglandin (PG) E₂ exerts T cell suppression in vitro through elevating cAMP by its receptors, EP2 and EP4. However, such an action is rarely detected in vivo, leaving PGE₂-mediated immunosuppression an enigma. Here we show that under strong TCR stimulation, PGE₂ facilitates T helper-1 (T_H-1) differentiation through activation of phosphatidylinositol-3-kinase (PI3K) by EP2 and EP4. The PGE₂-EP4 signaling is also required for IL-23 production by activated dendritic cells (DCs), and the PGE2-EP2/EP4 signaling amplifies IL-23-mediated T_H-17 cell expansion. Administration of an EP4-selective antagonist in vivo to mice subjected to experimental allergic encephalomyelitis (EAE) decreases accumulation of both T_H-1 and T_H-17 cells in regional lymph nodes, and suppresses the disease progression. These results suggest PGE₂ promotes immune inflammation through T_H-1 differentiation and T_H-17 expansion and the EP4 antagonism is therapeutically useful for various immune diseases.