TH17 cells express ST2 and are controlled by the alarmin IL-33 in the small intestine

T_H17 cells are major drivers of inflammation and involved in several autoimmune diseases. Tissue inflammation is a beneficial host response to infection, but it can also contribute to autoimmunity. The crosstalk between a tissue and the immune system during an inflammatory response is key for preserving tissue integrity and restoring physiological processes. However, how the inflamed tissue regulates the magnitude of an immune response by controlling pro-inflammatory T cells is not well characterized so far. Here we show that T_H17 cells accumulating in the small intestine upon inflammation express the IL-33 receptor (ST2) and intestinal epithelial cells (IEC) are the main source of the alarmin interleukin-33 (IL-33). We show that pro-inflammatory T_H17 cells acquire a regulatory phenotype with immunosuppressive properties in response to IL-33. Absence of ST2 signaling promotes the secretion of pro-inflammatory cytokines by T_H17 cells and dampens the secretion of IL-10. Our results provide new insights into the mechanisms by which IEC, via IL-33/ST2 axis, may control pro-inflammatory T_H17 cells in the small intestine to sustain homeostasis.     

The alarmin functions of high-mobility group box-1 and IL-33 in the pathogenesis of systemic lupus erythematosus

‘Alarmins’ are a group of endogenous proteins or molecules that are released from cells during cellular demise to alert the host innate immune system. Two of them, high-mobility group box-1 (HMGB1) and IL-33 shared many similarities of cellular localization, functions and involvement in various inflammatory diseases including systemic lupus erythematosus (SLE). The expressions of HMGB1 and IL-33, and their corresponding receptors RAGE (receptor for advanced glycation end products) and ST2, respectively, are substantially upregulated in patients with lupus nephritis (LN). This review highlights the emerging roles of alarmin proteins in various pathologies of LN, by focusing on classical HMGB1 and a newly discovered alarmin IL-33.     

IL-33 is a chemoattractant for human Th2 cells

IL-33 is a novel cytokine of the IL-1 family and mediates its biological effect via the receptor ST2, which is selectively expressed on Th2 cells but not Th1 cells. IL-33 drives production of Th2-associated cytokines including IL-5 and IL-13 and thereby promotes defense and pathology in mucosal organs. Cell locomotion is crucial to the induction of an effective immune response. We report here the chemoattraction of Th2 cells by IL-33. Recombinant IL-33 increased the proportion of human Th2 cells, but not Th1 cells, in polarized morphology in vitro and stimulated their subsequent invasion into collagen gels in an IL-33 concentration-dependent manner. Injection of recombinant IL-33 into the footpad of ST2(-/-) mice which had been adoptively transferred with polarized Th2 cells, led to local accumulation of the transferred Th2 cells. These data therefore demonstrate that IL-33 is a selective Th2 chemoattractant associated with the pro-inflammatory property of this novel cytokine.     

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.     

Pathomorphology of the uterus in decreased labor activity

A comprehensive study of the pathomorphology of the corpus, lower segment, and placental bed of the uterus during powerless labor revealed the systematic pattern of uteroplacental complex abnormalities. In powerless labor, tonic uterine tonic component inactivity that develops in the presence of morphofunctional incompetence of the placental bed is determined by inadequate lacunar transformation of venous collectors of the corpus uteri and a forming lower segment. This leads to insufficient blood accumulation in the uterine venous vascular bed and to the development of hypotonic nonproductive birth pangs.     

Special aspects of interleukin-33 and the IL-33 receptor complex

Interleukin-33 (IL-33) is an unconventional member of the IL-1 family: it is a dual function cytokine. Many different cell types, tissue cells and leukocytes, produce IL-33 either constitutively or after stimulation and release it by a poorly defined molecular mechanism. Free IL-33 acts as a classical cytokine by binding to target cells expressing receptors for IL-33 minimally consisting of ST2 and IL-1RAcP. Depending on the target cell type IL-33 will stimulate cell-type specific signal transduction mechanisms and thereby change the biosynthetic profile of the respective cell. In addition, it is stored in the nucleus of cells and may be released after cell stress, death by injury or necrosis, acting as an alarmin by orchestrating a sterile inflammation. Furthermore, IL-33 has intracrine functions in the cell producing it, which are independent of IL-33 receptors. Intracellular IL-33 is predominantly found in the nucleus associated to the chromatin and may exert gene regulatory function by yet poorly defined mechanisms. It is the aim of this review to address two basic biological aspects of the IL-33/IL-33 receptor system. First, to summarize the current understanding of the fate and function of intracellular IL-33, and second, to discuss recent advances in the knowledge of the molecular composition, function and regulation of the IL-33 receptor complex, including initial signaling mechanisms.     

IL-33 and Airway Inflammation

Interleukin-33 (IL-33) is the 11th member of IL-1 cytokine family which includes IL-1 and IL-18. Unlike IL-1β and IL-18, IL-33 is suggested to function as an alarmin that is released upon endothelial or epithelial cell damage and may not enhance acquired immune responses through activation of inflammasome. ST2, a IL-33 receptor component, is preferentially expressed by T-helper type (Th) 2 cells, mast cells, eosinophils and basophils, compared to Th1 cells, Th17 cells and neutrophils. Thus, IL-33 profoundly enhances allergic inflammation through increased expression of proallergic cytokines and chemokines. Indeed, IL-33 and its receptor genes are recognized as the most susceptible genes for asthma by several recent genomewide association studies. It has also recently been shown that IL-33 plays a crucial role in innate eosinophilic airway inflammation rather than acquired immune responses such as IgE production. As such, IL-33 provides a unique therapeutic way for asthma, i.e., ameliorating innate airway inflammation.     

IL-1, IL-18, and IL-33 families of cytokines

Summary: The interleukin-1 (IL-1), IL-18, and IL-33 families of cytokines are related by mechanism of origin, receptor structure, and signal transduction pathways utilized. All three cytokines are synthesized as precursor molecules and cleaved by the enzyme caspase-1 before or during release from the cell. The NALP-3 inflammasome is of crucial importance in generating active caspase-1. The IL-1 family contains two agonists, IL-1α and IL-1β, a specific inhibitor, IL-1 receptor antagonist (IL-1Ra), and two receptors, the biologically active type IL-1R and inactive type II IL-1R. Both IL-1RI and IL-33R utilize the same interacting accessory protein (IL-1RAcP). The balance between IL-1 and IL-1Ra is important in preventing disease in various organs, and excess production of IL-1 has been implicated in many human diseases. The IL-18 family also contains a specific inhibitor, the IL-18-binding protein (IL-18BP), which binds IL-18 in the fluid phase. The IL-18 receptor is similar to the IL-1 receptor complex, including a single ligand-binding chain and a different interacting accessory protein. IL-18 provides an important link between the innate and adaptive immune responses. Newly described IL-33 binds to the orphan IL-1 family receptor T1/ST2 and stimulates T-helper 2 responses as well as mast cells.     

The biological paths of IL-1 family members IL-18 and IL-33

Cytokines are key mediators of the immune system, and few have been more thoroughly studied than those of the IL-1 family. IL-1α and IL-1β are the founding members and now celebrate 25 years since their cloning. In that time, IL-1-directed research has illuminated many aspects of cytokine biology and innate immunity. The family is now recognized to include 11 total members, including IL-18 and IL-33, which are the topic of this review. These two inflammatory cytokines are expressed broadly, and their actions influence a variety of physiologic responses involved in inflammation and immunity. The purpose of this article is not to provide an exhaustive review of IL-18 and IL-33 but rather, to summarize what is known about their key functions and to provide perspective on their similarities and differences.     

IL-33与免疫细胞的关系

IL-33是IL-1家族的新成员,在炎性刺激后由多种细胞表达IL-33,并且在细胞溶解过程中释放.IL-33的膜表面受体包括ST2和IL-1受体辅佐蛋白,机体广泛表达ST2,尤其是在Th2型细胞和肥大细胞等免疫细胞中.IL-33通过结合免疫细胞膜表面的ST2将活化信号传递到胞内,经过一系列的信号传递,引起IL-5等免疫因子的释放,起到调节免疫应答等功能.     

Paeoniflorin suppresses IL-33 production by macrophages

Abstract

Objective: Interleukin (IL)-33 has been attracting more and more attention as a new member of theIL-1 cytokine family in recent years. However, the underlying mechanisms referred to the regulation of endogenous IL-33 production are not fully illustrated. Paeoniflorin (PF) has been reported to possess multiple pharmacological activities, including anti-inflammation and anti-allergy. In this study, we aimed to investigate the effect of PF on IL-33 production by macrophages and explore the underlying mechanisms.

Methods: In vivo, IL-33 production in mice after lipopolysaccharide (LPS) injection together with PF application was detected by enzyme-linked immunosorbent assay (ELISA). In vitro, MTT, Real-time PCR, ELISA, Calcium (Ca²⁺) imaging and Western blot were used to assess the cytotoxicity of PF, IL-33 expression at mRNA and protein levels, Ca²⁺ influx, protein kinase C (PKC) activity, nuclear factor-kappa B (NF-κB), and mitogen-activated protein kinase (MAPK) activation in LPS-stimulated RAW264.7 macrophages with PF administration.

Results: Our results indicated that PF (5 and 25?mg/kg) significantly reduced the production of TNF-a, IL-1β, and IL-33 in the peritoneal exudate of LPS-treated mice. In vitro assay, upregulation of PF concentration (≥ 20?μM) showed an increased cytotoxicity in RAW264.7 cells during the 24-h cell culture. PF (10?μM) inhibited IL-33 production, Ca²⁺ influx, PKC activity, NF-κB (p65) activation, and P38MAPK phosphorylation in LPS-treated macrophages. Notably, NF-κB inhibitor (BAY 11-7085), P38MAPK inhibitor (SB203580), and Ca²⁺ blocker (NiCl₂) also curbed LPS-induced IL-33 production, respectively.

Conclusions: PF suppresses IL-33 production by macrophages via inhibiting NF-κB and P38MAPK activation associated with the regulation of Ca²⁺ mobilization.     

IL-33-activated dendritic cells are critical for allergic airway inflammation

IL-33, a new member of the IL-1 family cytokine, is involved in Th2-type responses in a wide range of diseases and signals through the ST2 receptor expressed on many immune cells. Since the effects of IL-33 on DCs remain controversial, we investigated the ability of IL-33 to modulate DC functions in vitro and in vivo. Here, we report that IL-33 activates myeloid DCs to produce IL-6, IL-1b, TNF, CCL17 and to express high levels of CD40, CD80 OX40L and CCR7. Importantly, IL-33-activated DCs prime naive lymphocytes to produce the Th2 cytokines IL-5 and IL-13, but not IL-4. In vivo, IL-33 exposure induces DC recruitment and activation in the lung. Using an OVA-induced allergic lung inflammation model, we demonstrate that the reduced airway inflammation in ST2-deficient mice correlates with the failure in DC activation and migration to the draining LN. Finally, we show that adoptive transfer of IL-33-activated DCs exacerbates lung inflammation in a DC-driven model of allergic airway inflammation. These data demonstrate for the first time that IL-33 activates DCs during antigen presentation and thereby drives a Th2-type response in allergic lung inflammation.     

IL-10-producing regulatory B cells induced by IL-33 (BregIL-33) effectively attenuate mucosal inflammatory responses in the gut

Regulatory B cells (Breg) have attracted increasing attention for their roles in maintaining peripheral tolerance. Interleukin 33 (IL-33) is a recently identified IL-1 family member, which leads a double-life with both pro- and anti-inflammatory properties. We report here that peritoneal injection of IL-33 exacerbated inflammatory bowel disease in IL-10-deficient (IL-10^−/−) mice, whereas IL-33-treated IL-10-sufficient (wild type) mice were protected from the disease induction. A phenotypically unconventional subset(s) (CD19⁺CD25⁺CD1d^hiIgM^hiCD5^-CD23^-Tim-1^-) of IL-10 producing Breg-like cells (Breg^IL-33) was identified responsible for the protection. We demonstrated further that Breg^IL-33 isolated from these mice could suppress immune effector cell expansion and functions and, upon adoptive transfer, effectively blocked the development of spontaneous colitis in IL-10^−/− mice. Our findings indicate an essential protective role, hence therapeutic potential, of Breg^IL-33 against mucosal inflammatory disorders in the gut.     

Development of an interleukin (IL)-33 sandwich ELISA kit specific for mature IL-33

Interleukin (IL)-33 is an inflammatory cytokine and belongs to the IL-1 family of cytokines. There are eleven members of the IL-1 family of cytokines and all have important roles in host defense against infections. Their levels are increased during infection and in various auto-inflammatory diseases. IL-33 is also associated with autoimmune diseases such as asthma, atopic dermatitis, rheumatoid arthritis, and atherosclerosis. IL-33 receptors consist of IL-1R4 and IL-1R3 to induce both Th1 and Th2 type immune response. Here we present the development of monoclonal antibodies (mAbs) against human mature IL-33. Recombinant human mature IL-33 protein was expressed in E. coli and purified by multi-step affinity chromatography. The human IL-33 activity was examined in HMC-1 and Raw 264.7 cells. Mice were immunized with the biologically active mature IL-33 to generate mAb against IL-33. The anti-IL-33 mAb (clone/4) was used as a capture antibody for a sandwich enzyme-linked immunosorbent assay (ELISA). This assay detects mature IL-33 with a high sensitivity (80 pg/mL) but does not recognize the biologically inactive precursor IL-33. This article describes the methods for a newly developed IL-33 ELISA kit that is specific for mature IL-33 and may be used to analyze bioactive mature IL-33 in various immunological diseases.     

Measurement of interleukin-33 (IL-33) and IL-33 receptors (sST2 and ST2L) in patients with rheumatoid arthritis

The interleukin-33 (IL-33)/ST2 pathway has emerged as an intercellular signaling system that participates in antigen-allergen response, autoimmunity and fibrosis. It has been suggested that IL-33/ST2 signaling has been involved in the pathogenesis of rheumatoid arthritis (RA), because IL-33 and its receptor have been specifically mapped to RA synovium. The aim of this study was to determine the levels of IL-33 and sST2 in sera and synovial fluids in patients with RA. The serum level of IL-33 was significantly higher in patients with RA (294.9 ± 464.0 pg/mL) than in healthy controls (96.0 ± 236.9 pg/mL, P = 0.002). The synovial fluid level of IL-33 was significantly higher in RA patients than in osteoarthritis patients. The level of serum sST2 was higher in RA patients than in healthy controls (P = 0.042). A significant relationship was found between the levels of IL-33 and IL-1β (r = 0.311, P = 0.005), and IL-33 and IL-6 (r = 0.264, P = 0.017) in 81 RA patients. The levels of IL-33, sST2 and C-reactive protein decreased after conventional disease-modifying antirheumatic drugs treatment in 10 patients with treatment-na?ve RA. Conclusively, IL-33 is involved in the pathogenesis of RA and may reflect the degree of inflammation in patients with RA.