Nick Pitman

Disease-associated functions of IL-33: the new kid in the IL-1 family

Interleukin-33 (IL-33), a newly described member of the IL-1 family, is expressed by many cell types following pro-inflammatory stimulation and is thought to be released on cell lysis. The IL-33 receptor, consisting of ST2 and IL-1 receptor accessory protein, is also widely expressed, particularly by T helper 2 (TH2) cells and mast cells. IL-33 is host-protective against helminth infection and reduces atherosclerosis by promoting TH2-type immune responses. However, IL-33 can also promote the pathogenesis of asthma by expanding TH2 cells and mediate joint inflammation, atopic dermatitis and anaphylaxis by mast cell activation. Thus IL-33 could be a new target for therapeutic intervention across a range of diseases.

IL-33 Amplifies the Polarization of Alternatively Activated Macrophages That Contribute to Airway Inflammation

Alternatively activated macrophages (AAM) play a crucial role in type 2 immunity. Mice deficient in ST2, a receptor for the latest member of the IL-1 family, IL-33, have impaired type 2 immune responses. We therefore reasoned that IL-33/ST2 signaling may be involved in the differentiation and activation of AAM during airway inflammation. We report here that IL-33 changed the quiescent phenotype of alveolar macrophages toward an AAM phenotype that expressed mannose receptor, IL-4Rα, and produced high levels of CCL24 and CCL17 in an IL-13-dependent manner during IL-33-induced airway inflammation. Neutralization of AAM-derived CCL24 led to an amelioration of IL-33-induced eosinophilia in the lungs. Moreover, depletion of alveolar macrophages reduced IL-33-induced airway inflammation. Additionally, the attenuated OVA-induced airway inflammation in ST2−/− mice was associated with a decrease in AAM differentiation. In vitro, IL-33 amplified IL-13-induced polarization of alveolar- and bone marrow-derived macrophage toward an AAM phenotype by increasing the expression of arginase I, Ym1, as well as the production of CCL24 and CCL17. IL-13/IL-4Rα signaling was crucial for IL-33-driven AAM amplification by inducing the expression of ST2L. Finally, we showed that IL-33 was more abundantly expressed in the lung epithelial cells of asthma patients than those from healthy controls, suggesting that IL-33 may be involved in lung macrophage activation in clinical asthma. Taken together, we demonstrate here that IL-33/ST2 plays a significant role in the amplification of AAM polarization and chemokine production which contribute to innate and Ag-induced airway inflammation.

IL-33 exacerbates antigen-induced arthritis by activating mast cells

IL-33, a cytokine of the IL-1 family, is closely associated with type II T cell responses. Here, we report an unexpected proinflammatory role of IL-33 in inflammatory arthritis. IL-33 was expressed in synovial fibroblasts from patients with rheumatoid arthritis (RA). Expression was markedly elevated in vitro by inflammatory cytokines. Mice lacking ST2, the IL-33 receptor α-chain, developed attenuated collagen-induced arthritis (CIA) and reduced ex vivo collagen-specific induction of proinflammatory cytokines (IL-17, TNFα, and IFNγ), and antibody production. Conversely, treatment of wild-type (WT) but not ST2−/− mice with IL-33 exacerbated CIA and elevated production of both proinflammatory cytokines and anti-collagen antibodies. Mast cells expressed high levels of ST2 and responded directly to IL-33 to produce a spectrum of inflammatory cytokines and chemokines in vitro. In vivo, IL-33 treatment exacerbated CIA in ST2−/− mice engrafted with mast cells from WT but not from ST2−/− mice. Disease exacerbation was accompanied by elevated expression levels of proinflammatory cytokines. Our results demonstrate that IL-33 is a critical proinflammatory cytokine for inflammatory joint disease that integrates fibroblast activation with downstream immune activation mainly via an IL-33-driven, mast-cell-dependent pathway. Thus, this IL-1 superfamily member represents a therapeutic target for RA.

IL-33 Induces Antigen-Specific IL-5+ T Cells and Promotes Allergic-Induced Airway Inflammation Independent of IL-4

Type 2 cytokines (IL-4, IL-5, and IL-13) play a pivotal role in helminthic infection and allergic disorders. CD4(+) T cells which produce type 2 cytokines can be generated via IL-4-dependent and -independent pathways. Although the IL-4-dependent pathway is well documented, factors that drive IL-4-independent Th2 cell differentiation remain obscure. We report here that the new cytokine IL-33, in the presence of Ag, polarizes murine and human naive CD4(+) T cells into a population of T cells which produce mainly IL-5 but not IL-4. This polarization requires IL-1R-related molecule and MyD88 but not IL-4 or STAT6. The IL-33-induced T cell differentiation is also dependent on the phosphorylation of MAPKs and NF-kappaB but not the induction of GATA3 or T-bet. In vivo, ST2(-/-) mice developed attenuated airway inflammation and IL-5 production in a murine model of asthma. Conversely, IL-33 administration induced the IL-5-producing T cells and exacerbated allergen-induced airway inflammation in wild-type as well as IL-4(-/-) mice. Finally, adoptive transfer of IL-33-polarized IL-5(+)IL-4(-)T cells triggered airway inflammation in naive IL-4(-/-) mice. Thus, we demonstrate here that, in the presence of Ag, IL-33 induces IL-5-producing T cells and promotes airway inflammation independent of IL-4.

The cytokine interleukin-33 mediates anaphylactic shock

Anaphylactic shock is characterized by elevated immunoglobulin-E (IgE) antibodies that signal via the high affinity Fcε receptor (FcεRI) to release inflammatory mediators. Here we report that the novel cytokine interleukin-33 (IL-33) potently induces anaphylactic shock in mice and is associated with the symptom in humans. IL-33 is a new member of the IL-1 family and the ligand for the orphan receptor ST2. In humans, the levels of IL-33 are substantially elevated in the blood of atopic patients during anaphylactic shock, and in inflamed skin tissue of atopic dermatitis patients. In murine experimental atopic models, IL-33 induced antigen-independent passive cutaneous and systemic anaphylaxis, in a T cell–independent, mast cell–dependent manner. In vitro, IL-33 directly induced degranulation, strong eicosanoid and cytokine production in IgE-sensitized mast cells. The molecular mechanisms triggering these responses include the activation of phospholipase D1 and sphingosine kinase1 to mediate calcium mobilization, Nuclear factor–κB activation, cytokine and eicosanoid secretion, and degranulation. This report therefore reveals a hitherto unrecognized pathophysiological role of IL-33 and suggests that IL-33 may be a potential therapeutic target for anaphylaxis, a disease of considerable unmet medical need.

Nitric oxide induces CD4+CD25+ Foxp3− regulatory T cells from CD4+CD25− T cells via p53, IL-2, and OX40

The principal aim of the immune system is to establish a balance between defense against pathogens and avoidance of autoimmune disease. This balance is achieved partly through regulatory T cells (Tregs). CD4+CD25+ Tregs are either naturally occurring or induced by antigens and are characterized by the expression of the X-linked forkhead/winged helix transcription factor, Foxp3. Here we report a previously unrecognized subset of CD4+CD25+ Tregs derived from CD4+CD25− T cells induced by nitric oxide (NO). The induction of Tregs (NO-Tregs) is independent of cGMP but depends on p53, IL-2, and OX40. NO-Tregs produced IL-4 and IL-10, but not IL-2, IFNγ, or TGFβ. The cells were GITR+, CD27+, T-betlow, GATA3high, and Foxp3−. NO-Tregs suppressed the proliferation of CD4+CD25− T cells in vitro and attenuated colitis- and collagen-induced arthritis in vivo in an IL-10-dependent manner. NO-Tregs also were induced in vivo in SCID mice adoptively transferred with CD4+CD25− T cells in the presence of LPS and IFNγ, and the induction was completely inhibited by NG-monomethyl-l-arginine, a pan NO synthase inhibitor. Therefore, our findings uncovered a previously unrecognized function of NO via the NO–p53–IL-2–OX40–survivin signaling pathway for T cell differentiation and development.

A TLR2 ligand suppresses inflammation by modulation of chemokine receptors and redirection of leukocyte migration

Toll-like receptors orchestrate rapid local protective innate-immune responses to invading pathogens and optimize leukocyte priming of subsequent adaptive responses. Paradoxically, systemic excess of the TLR2 ligand, bacterial lipoprotein (BLP), suppresses peripheral inflammatory responses. Here, we demonstrate that this phenomenon is regulated via the TLR2-dependent, cell-autonomous down-regulation of inflammatory chemokine receptor expression on a variety of leukocyte subsets. Remarkably, BLP mediated no effect on constitutive chemokine receptor expression. By tracking adoptively transferred wild-type and TLR2(-/-) leukocytes in vivo, we observed that BLP mediated chemokine receptor switching directed leukocytes away from inflamed sites toward secondary lymphoid organs. These data highlight a novel role for TLR ligands, such as BLP, in regulating leukocyte retention and migration away from innate immune lesions via discrete constitutive and inflammatory chemokine receptor regulation.

Collagen-induced arthritis is not impaired in mast cell-deficient mice

Mast cells are recognised as important effectors in allergic disease. However, it is increasingly clear that mast cells may fulfil more diverse roles within the immune system and may be pathogenic in a number of diseases not typically associated with T-helper type 2 immune responses.1 Indeed, studies have described the presence of degranulated mast cells within inflamed rheumatoid arthritis (RA) synovium and as such implicate mast cells as potential mediators in the pathogenesis of RA.2 Consistent with these observations, the severity of arthritis, induced by antibody transfer, is reduced in mast cell-deficient strains of mice, W/Wv and Sl/Sld, and can be restored by adoptive transfer of mast cells.3 4 Murine collagen-induced arthritis is a well-characterised model of RA that combines adaptive and innate immune effector components. When complete Freunds adjuvant/collagen …

IL-33 is sufficient to induce eosinophilic airway inflammation, and exacerbates established inflammation, through increased ST2 dependent local Th2 cytokine and chemokine production

Introduction: The key pathological features of asthma are eosinophilic airway inflammation, mucus hypersecretion and airway remodelling, mediated by Th2 cytokines (IL-4, IL-5, IL-13). IL-4 or IL-13 administered directly to the airways are sufficient to induce these pathological features independent of antigen (Grunig G et al, Science 1998; Wills-Karp et al, Science 1998). IL-33 is a novel cytokine which binds to the orphan ST2 receptor and induces Th2 cytokine expression (Schmitz et al, Immunity 2005). We hypothesised that IL-33 would be sufficient to induce eosinophilic airway inflammation, and may exacerbate antigen-specific allergic airway inflammation. Methods: The antigen-independent effect of IL-33 was assessed by administering PBS ± recombinant (r)IL-33 intranasally (i.n.) to BALB/c mice for 7 consecutive days. Bronchoalveolar lavage (BAL) was performed 24 h later. Differential cell counts were performed on cytopreps, and the concentration of BAL cytokines and chemokines determined by ELISA. Lungs were obtained for histological assessment. Allergic airway inflammation was induced in BALB/c mice by intraperitoneal (i.p.) sensitisation with ovalbumin (OVA) and alum on day 1, followed by i.n. challenge on days 9 and 11 with OVA ± rIL-33. Mice were analysed as above, and ST2 gene knockout mice were used to demonstrate the specificity of action of rIL-33. Results: rIL-33 induced marked eosinophilic inflammation (fig A). BAL eosinophils (data not shown), cytokines (IL-5 and IL-13, but not IL-4) and chemokines (eotaxin-1, eotaxin-2 and TARC) were increased (table). Airway challenge with OVA following sensitisation induced eosinophilic inflammation, which was increased markedly by rIL-33 (fig B), as were BAL eosinophils, cytokines and chemokines (table). IL-33 had no effect in ST2KO mice in either model. Conclusions: rIL-33 in the absence of antigen induced airway pathology very similar to that of experimental asthma. This was mediated by local induction of Th2 associated cytokines and chemokines, with the exception of IL-4, and was dependent on ST2 expression. In addition, IL-33 exacerbated allergic airway inflammation by a similar mechanism. Thus IL-33/ST2 represents an important mechanism of IL-4-independent airway inflammation, and represents a novel target for therapeutic intervention during both the initiation and maintenance phases of allergic asthma.