IL-33-responsive lineage- CD25+ CD44(hi) lymphoid cells mediate innate type 2 immunity and allergic inflammation in the lungs

Characterization and Quantification of Innate Lymphoid Cell Subsets in Human Lung

BACKGROUND

Innate lymphoid cells (ILC) are a new family of innate immune cells that have emerged as important regulators of tissue homeostasis and inflammation. However, limited data are available concerning the relative abundance and characteristics of ILC in the human lung.

METHODS

The aim of this study was to characterize and enumerate the different ILC subsets in human lung by multi-color flow cytometry.

RESULTS

Within the CD45+ Lin- CD127+ pulmonary ILC population, we identified group 1 (ILC1), group 2 (ILC2) and group 3 (ILC3) innate lymphoid cells using specific surface markers (i.e. IL12Rβ2, CRTH2 and CD117 respectively) and key transcription factors (i.e. T-bet, GATA-3 and RORγT respectively). Based on the presence of NKp44, ILC3 were further subdivided in natural cytotoxicity receptor (NCR)+ and NCR- ILC3. In addition, we demonstrated the production of signature cytokines IFN-γ, IL-5, IL-17A, IL-22 and GM-CSF in the pulmonary ILC population. Interestingly, we observed a tendency to a higher frequency of NCR- ILC3 in lungs of patients with chronic obstructive pulmonary disease (COPD) compared with controls.

CONCLUSIONS

We show that the three main ILC subsets are present in human lung. Importantly, the relative abundance of ILC subsets tended to change in COPD patients in comparison to control individuals.

Innate and Adaptive Immune Response to Fungal Products and Allergens

Exposure to fungi and their products is practically ubiquitous, yet most of this is of little consequence to most healthy individuals. This is because there are a number of elaborate mechanisms to deal with these exposures. Most of these mechanisms are designed to recognize and neutralize such exposures. However, in understanding these mechanisms it has become clear that many of them overlap with our ability to respond to disruptions in tissue function caused by trauma or deterioration. These responses involve the innate and adaptive immune systems usually through the activation of nuclear factor kappa B and the production of cytokines that are considered inflammatory accompanied by other factors that can moderate these reactivities. Depending on different genetic backgrounds and the extent of activation of these mechanisms, various pathologies with resulting symptoms can ensue. Complicating this is the fact that these mechanisms can bias toward type 2 innate and adaptive immune responses. Thus, to understand what we refer to as allergens from fungal sources, we must first understand how they influence these innate mechanisms. In doing so it has become clear that many of the proteins that are described as fungal allergens are essentially homologues of our own proteins that signal or cause tissue disruptions.

Allergic Inflammation in Aspergillus fumigatus-Induced Fungal Asthma

Although fungi are pervasive in many environments, few cause disease in humans. Of these, Aspergillus fumigatus is particularly well suited to be a pathogen of the human lung. Its physical and biological characteristics combine to provide an organism that can cause tremendous morbidity and high mortality if left unchecked. Luckily, that is rarely the case. However, repeated exposure to inhaled A. fumigatus spores often results in an immune response that carries significant immunopathology, exacerbating asthma and changing the structure of the lung with chronic impacts to pulmonary function. This review focuses on the current understanding of the mechanisms that are associated with fungal exposure, sensitization, and infection in asthmatics, as well as the function of various inflammatory cells associated with severe asthma with fungal sensitization.

TCRVγ9 γδ T Cell Response to IL-33: A CD4 T Cell-Dependent Mechanism

The availability of specific stimuli to induce the anticancer cytotoxicity of human TCRVγ9-expressing T lymphocytes has allowed the development of γδ T cell-based cancer immunotherapies. However, the stringent dependence of such strategies on the inherently toxic IL-2 has raised safety concerns for patients, justifying a search for alternative methods for inducing γδ T cell stimulation. IL-33 is a γ-chain receptor-independent cytokine of the IL-1 superfamily that is expressed by endothelial cells from a tumor microenvironment and can sustain Th1 and Th2 immune responses. Therefore, we investigated its ability to support the stimulation of human TCRVγ9(+) γδ T cells. In this study, we report that IL-33 efficiently sustained the in vitro activation of Vγ9 T lymphocytes by synthetic phosphoantigens, zoledronate, and a BTN3A1 Ab in the absence of an exogenous supply of IL-2. IL-33 was as potent as IL-2 in allowing the proliferative amplification of Vγ9 T cells isolated from PBMC following activation by the synthetic phosphoantigen bromohydrin pyrophosphate. IL-33 also induced an identical maturation into TNF-α- and IFN-γ-producing Th1 effector memory cells, and IL-33-stimulated cells showed an equivalent cytotoxicity for various tumor cells in vitro. Finally, we found that the bioactivity of IL-33 on the Vγ9 T cell was indirectly mediated through contact with CD4 T cells and IL-2 production by CD4 T cells and Vγ9 T cells themselves. These data posit IL-33 as an alternative to IL-2 for Vγ9 T cell-based cancer immunotherapies.

Interferon and IL-27 antagonize the function of group 2 innate lymphoid cells and type 2 innate immune responses

Group 2 innate lymphoid cells (ILC2 cells) are type 2 cytokine-producing cells of the innate immune system with important roles in helminth infection and allergic inflammation. Here we found that tissue-resident ILC2 cells proliferated in situ without migrating during inflammatory responses. Both type I and type II interferons and interleukin 27 (IL-27) suppressed ILC2 function in a manner dependent on the transcription factor STAT1. ILC2-mediated lung inflammation was enhanced in the absence of the interferon-γ (IFN-γ) receptor on ILC2 cells in vivo. IFN-γ effectively suppressed the function of tissue-resident ILC2 cells but not that of inflammatory ILC2 cells, and IL-27 suppressed tissue-resident ILC2 cells but not tissue-resident TH2 cells during lung inflammation induced by Alternaria alternata. Our results demonstrate that suppression mediated by interferon and IL-27 is a negative feedback mechanism for ILC2 function in vivo.

IL‑33 and kidney disease (Review)

Interleukin (IL)-33, is a novel member of the IL-1 superfamily, and act as a dual-function molecule as a nuclear factor and cytokine. The expression of IL-33 can be detected in several tissues and cells in humans and in mice. In addition to the conventional secretion approach for cytokines, full-length IL-33 can also be released into the extracellular space following cell damage or mechanical injury. IL-33 mediates its biological effects by interacting with the receptors, suppression of tumorigenicity 2 (ST2) and IL-1 receptor accessory protein, activating intracellular molecules in the nuclear factor-κB and mitogen-activated protein kinase signaling pathways, which drive the production of type 2 cytokines, including IL-4, IL-5 and IL-3, from polarized T helper 2 cells. Increasing evidence indicates that IL-33 is important in chronic kidney disease, and may be involved in the progression of renal fibrosis associated with systemic lupus erythematosus and renal graft damage. In addition, IL-33 contributes to acute kidney injury. In the present review, the biology of IL-33, and the association of IL-33 with kidney diseases are discussed.

The prostaglandin D₂ receptor CRTH2 regulates accumulation of group 2 innate lymphoid cells in the inflamed lung

Group 2 innate lymphoid cells (ILC2s) promote type 2 cytokine-dependent immunity, inflammation, and tissue repair. Although epithelial cell-derived cytokines regulate ILC2 effector functions, the pathways that control the in vivo migration of ILC2s into inflamed tissues remain poorly understood. Here, we provide the first demonstration that expression of the prostaglandin D2 (PGD2) receptor CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 cells) regulates the in vivo accumulation of ILC2s in the lung. Although a significant proportion of ILC2s isolated from healthy human peripheral blood expressed CRTH2, a smaller proportion of ILC2s isolated from nondiseased human lung expressed CRTH2, suggesting that dynamic regulation of CRTH2 expression might be associated with the migration of ILC2s into tissues. Consistent with this, murine ILC2s expressed CRTH2, migrated toward PGD2 in vitro, and accumulated in the lung in response to PGD2 in vivo. Furthermore, mice deficient in CRTH2 exhibited reduced ILC2 responses and inflammation in a murine model of helminth-induced pulmonary type 2 inflammation. Critically, adoptive transfer of CRTH2-sufficient ILC2s restored pulmonary inflammation in CRTH2-deficient mice. Together, these data identify a role for the PGD2-CRTH2 pathway in regulating the in vivo accumulation of ILC2s and the development of type 2 inflammation in the lung.

The role of IL-33 and mast cells in allergy and inflammation

Interleukin-33 (IL-33) is a member of the interleukin-1 (IL-1) cytokine family. It is preferentially and constitutively expressed in different structural cells such as epithelial cells, endothelial cells, and smooth muscle cells. During necrosis of these cells (after tissue injury or cell damage), the IL-33 that is released may be recognized by different types of immune cells, such as eosinophils, basophils and, especially, mast cells. IL-33 needs the specific receptor ST2 (membrane-bound receptor) and Interleukin-1 receptor accessory protein heterodimer for its binding, which instigates the production of different types of cytokines and chemokines that have crucial roles in the exacerbation of allergic diseases and inflammation. IL-33 and mast cells have been influentially associated to the pathophysiology of allergic diseases and inflammation. IL-33 is a crucial regulator of mast cell functions and might be an attractive therapeutic target for the treatment of allergic and inflammatory diseases. In this review, we summarize the current knowledge regarding the roles of IL-33 and mast cells in the pathogenesis of allergies and inflammation.

The messenger between worlds: the regulation of innate and adaptive type-2 immunity by innate lymphoid cells

Although type-2 immune responses evolved primarily to defend against extracellular helminths, in part through the co-opting of tissue repair and remodeling mechanisms, they are often inappropriately directed towards relatively innocuous allergens resulting in conditions including asthma, allergic rhinitis, food allergy, and atopic dermatitis. The recent discovery of group 2 innate lymphoid cells (ILC2) has increased our understanding of the initiation of these responses and the roles played by CD4(+) T helper (Th) 2 cells in their modulation. This review focuses on the important messenger role of ILC2 in translating epithelial-derived alarmins into downstream adaptive type-2 responses via dendritic cells and T cells, with special emphasis on their roles in allergic disease.

Aspirin-Exacerbated Respiratory Disease Involves a Cysteinyl Leukotriene-Driven IL-33-Mediated Mast Cell Activation Pathway

Aspirin-exacerbated respiratory disease (AERD), a severe eosinophilic inflammatory disorder of the airways, involves overproduction of cysteinyl leukotrienes (cysLTs), activation of airway mast cells (MCs), and bronchoconstriction in response to nonselective cyclooxygenase inhibitors that deplete homeostatic PGE2. The mechanistic basis for MC activation in this disorder is unknown. We now demonstrate that patients with AERD have markedly increased epithelial expression of the alarmin-like cytokine IL-33 in nasal polyps, as compared with polyps from aspirin-tolerant control subjects. The murine model of AERD, generated by dust mite priming of mice lacking microsomal PGE2 synthase (ptges(-/-) mice), shows a similar upregulation of IL-33 protein in the airway epithelium, along with marked eosinophilic bronchovascular inflammation. Deletion of leukotriene C4 synthase, the terminal enzyme needed to generate cysLTs, eliminates the increased IL-33 content of the ptges(-/-) lungs and sharply reduces pulmonary eosinophilia and basal secretion of MC products. Challenges of dust mite-primed ptges(-/-) mice with lysine aspirin induce IL-33-dependent MC activation and bronchoconstriction. Thus, IL-33 is a component of a cysLT-driven innate type 2 immune response that drives pathogenic MC activation and contributes substantially to AERD pathogenesis.

Pulmonary receptor for advanced glycation end-products promotes asthma pathogenesis through IL-33 and accumulation of group 2 innate lymphoid cells

BACKGROUND

Single nucleotide polymorphisms in the human gene for the receptor for advanced glycation end-products (RAGE) are associated with an increased incidence of asthma. RAGE is highly expressed in the lung and has been reported to play a vital role in the pathogenesis of murine models of asthma/allergic airway inflammation (AAI) by promoting expression of the type 2 cytokines IL-5 and IL-13. IL-5 and IL-13 are prominently secreted by group 2 innate lymphoid cells (ILC2s), which are stimulated by the proallergic cytokine IL-33.

OBJECTIVE

We sought to test the hypothesis that pulmonary RAGE is necessary for allergen-induced ILC2 accumulation in the lung.

METHODS

AAI was induced in wild-type and RAGE knockout mice by using IL-33, house dust mite extract, or Alternaria alternata extract. RAGE's lung-specific role in type 2 responses was explored with bone marrow chimeras and induction of gastrointestinal type 2 immune responses.

RESULTS

RAGE was found to drive AAI by promoting IL-33 expression in response to allergen and by coordinating the inflammatory response downstream of IL-33. Absence of RAGE impedes pulmonary accumulation of ILC2s in models of AAI. Bone marrow chimera studies suggest that pulmonary parenchymal, but not hematopoietic, RAGE has a central role in promoting AAI. In contrast to the lung, the absence of RAGE does not affect IL-33-induced ILC2 influx in the spleen, type 2 cytokine production in the peritoneum, or mucus hypersecretion in the gastrointestinal tract.

CONCLUSIONS

For the first time, this study demonstrates that a parenchymal factor, RAGE, mediates lung-specific accumulation of ILC2s.

Interleukin-33 in Tissue Homeostasis, Injury, and Inflammation

Interleukin-33 (IL-33) is a nuclear-associated cytokine of the IL-1 family originally described as a potent inducer of allergic type 2 immunity. IL-33 signals via the receptor ST2, which is highly expressed on group 2 innate lymphoid cells (ILC2s) and T helper 2 (Th2) cells, thus underpinning its association with helminth infection and allergic pathology. Recent studies have revealed ST2 expression on subsets of regulatory T cells, and for a role for IL-33 in tissue homeostasis and repair that suggests previously unrecognized interactions within these cellular networks. IL-33 can participate in pathologic fibrotic reactions, or, in the setting of microbial invasion, can cooperate with inflammatory cytokines to promote responses by cytotoxic NK cells, Th1 cells, and CD8(+) T cells. Here, we highlight the regulation and function of IL-33 and ST2 and review their roles in homeostasis, damage, and inflammation, suggesting a conceptual framework for future studies.

Group 2 innate lymphoid cells in disease

Group 2 innate lymphoid cells (ILC2) are now recognized as an important innate source of type-2 effector cytokines. Although initially associated with mucosal tissues, it is clear that ILC2 are present in diverse anatomical locations. The function of ILC2 at these sites is equally varied, and although ILC2 represent a relatively minor population, they are fundamentally important regulators of innate and adaptive immune processes. As such, there is much interest to understand the role of ILC2 in diseases with a type-2 inflammatory component. This review explores the known roles of ILC2 in disease, and the diseases that show associations or other strong evidence for the involvement of ILC2.

Maintenance of Immune Homeostasis through ILC/T Cell Interactions

Innate lymphoid cells (ILCs) have emerged as a new family of immune cells with crucial functions in innate and adaptive immunity. ILC subsets mirror the cytokine and transcriptional profile of CD4⁺ T helper (T_H) cell subsets. Hence, group 1 (ILC1), group 2 (ILC2), and group 3 (ILC3) ILCs can be distinguished by the production of T_H1, T_H2, and T_H17-type cytokines, respectively. Cytokine release by ILCs not only shapes early innate immunity but can also orchestrate T_H immune responses to microbial or allergen exposure. Recent studies have identified an unexpected effector function of ILCs as antigen presenting cells. Both ILC2s and ILC3s are able to process and present foreign antigens (Ags) via major histocompatibility complex class II, and to induce cognate CD4⁺ T cell responses. In addition, Ag-stimulated T cells promote ILC activation and effector functions indicating a reciprocal interaction between the adaptive and innate immune system. A fundamental puzzle in ILC function is how ILC/T cell interactions promote host protection and prevent autoimmune diseases. Furthermore, the way in which microenvironmental and inflammatory signals determine the outcome of ILC/T cell immune responses in various tissues is not yet understood. This review focuses on recent advances in understanding the mechanisms that coordinate the collaboration between ILCs and T cells under homeostatic and inflammatory conditions. We also discuss the potential roles of T cells and other immune cells to regulate ILC functions and to maintain homeostasis in mucosal tissues.

Deciphering Asthma Biomarkers with Protein Profiling Technology

Asthma is a chronic inflammatory disease of the airways, resulting in bronchial hyperresponsiveness with every allergen exposure. It is now clear that asthma is not a single disease, but rather a multifaceted syndrome that results from a variety of biologic mechanisms. Asthma is further problematic given that the disease consists of many variants, each with its own etiologic and pathophysiologic factors, including different cellular responses and inflammatory phenotypes. These facets make the rapid and accurate diagnosis (not to mention treatments) of asthma extremely difficult. Protein biomarkers can serve as powerful detection tools in both clinical and basic research applications. Recent endeavors from biomedical researchers have developed technical platforms, such as cytokine antibody arrays, that have been employed and used to further the global analysis of asthma biomarker studies. In this review, we discuss potential asthma biomarkers involved in the pathophysiologic process and eventual pathogenesis of asthma, how these biomarkers are being utilized, and how further testing methods might help improve the diagnosis and treatment strain that current asthma patients suffer.

IL-33 promotes an innate immune pathway of intestinal tissue protection dependent on amphiregulin-EGFR interactions

The barrier surfaces of the skin, lung, and intestine are constantly exposed to environmental stimuli that can result in inflammation and tissue damage. Interleukin (IL)-33-dependent group 2 innate lymphoid cells (ILC2s) are enriched at barrier surfaces and have been implicated in promoting inflammation; however, the mechanisms underlying the tissue-protective roles of IL-33 or ILC2s at surfaces such as the intestine remain poorly defined. Here we demonstrate that, following activation with IL-33, expression of the growth factor amphiregulin (AREG) is a dominant functional signature of gut-associated ILC2s. In the context of a murine model of intestinal damage and inflammation, the frequency and number of AREG-expressing ILC2s increases following intestinal injury and genetic disruption of the endogenous AREG-epidermal growth factor receptor (EGFR) pathway exacerbated disease. Administration of exogenous AREG limited intestinal inflammation and decreased disease severity in both lymphocyte-sufficient and lymphocyte-deficient mice, revealing a previously unrecognized innate immune mechanism of intestinal tissue protection. Furthermore, treatment with IL-33 or transfer of ILC2s ameliorated intestinal disease severity in an AREG-dependent manner. Collectively, these data reveal a critical feedback loop in which cytokine cues from damaged epithelia activate innate immune cells to express growth factors essential for ILC-dependent restoration of epithelial barrier function and maintenance of tissue homeostasis.

Transcription Factor Bcl11b Controls Identity and Function of Mature Type 2 Innate Lymphoid Cells

Type 2 innate lymphoid cells (ILC2s) promote anti-helminth responses and contribute to allergies. Here, we report that Bcl11b, previously considered a T-cell-specific transcription factor, acted directly upstream of the key ILC2 transcription factor Gfi1 to maintain its expression in mature ILC2s. Consequently, Bcl11b(-/-) ILC2s downregulated Gata3 and downstream genes, including Il1rl1 (encoding IL-33 receptor), and upregulated Rorc and type 3 ILC (ILC3) genes. Additionally, independent of Gfi1, Bcl11b directly repressed expression of the gene encoding the ILC3 transcription factor Ahr, further contributing to silencing of ILC3 genes in ILC2s. Thus, Bcl11b(-/-) ILC2s lost their functions and gained ILC3 functions, and although they expanded in response to the protease allergen papain, they produced ILC3 but not ILC2 cytokines and caused increased airway infiltration of neutrophils instead of eosinophils. Our results demonstrate that Bcl11b is more than just a T-cell-only transcription factor and establish that Bcl11b sustains mature ILC2 genetic and functional programs and lineage fidelity.

Increased numbers of activated group 2 innate lymphoid cells in the airways of patients with severe asthma and persistent airway eosinophilia

BACKGROUND

In patients with severe eosinophilic asthma, local maturation rather than systemic recruitment of mature cells might contribute to persistent airway eosinophilia. Group 2 innate lymphoid cells (ILC2s) are a major source of type 2 cytokines (IL-5 and IL-13) and can facilitate eosinophilic inflammatory responses in mouse models of asthma in the absence of CD4+ lymphocytes. This study investigated the potential role of ILC2s in driving chronic airway eosinophilia in patients with severe asthma, despite regular high-dose oral corticosteroid therapy.

METHODS

In a cross-sectional study we enumerated blood and sputum ILC2s (lin(-)CD45(+)127(+)ST2(+)) and levels of intracellular IL-5 and IL-13 in patients with severe asthma (n = 25), patients with steroid-naive mild atopic asthma (n = 19), and nonatopic control subjects (n = 5). Results were compared with numbers of CD4+ lymphocytes, eosinophil lineage-committed progenitors (eosinophilopoietic progenitor cells [EoPs]), and mature eosinophils.

RESULTS

Significantly greater numbers of total and type 2 cytokine-producing ILC2s were detected in blood and sputum of patients with severe asthma compared to mild asthmatics. In contrast, intracellular cytokine expression by CD4 cells and EoPs within the airways did not differ between the asthmatic groups. In patients with severe asthma, although sputum CD4+ cells were more abundant than ILC2s and EoPs, proportionally, ILC2s were the predominant source of type 2 cytokines. In addition, there were significantly greater numbers of sputum IL-5(+)IL-13(+) ILC2s in patients with severe asthma whose airway eosinophilia was greater than 3%, despite normal blood eosinophil numbers (<300/μL).

CONCLUSIONS

Our findings suggest that ILC2s can promote the persistence of airway eosinophilia in patients with severe asthma through uncontrolled localized production of the type 2 cytokines IL-5 and IL-13, despite high-dose oral corticosteroid therapy.

Innate lymphocyte cells in asthma phenotypes

T helper type 2 (T_H2) cells were previously thought to be the main initiating effector cell type in asthma; however, exaggerated T_H2 cell activities alone were insufficient to explain all aspects of asthma. Asthma is a heterogeneous syndrome comprising different phenotypes that are characterized by their different clinical features, treatment responses, and inflammation patterns. The most-studied subgroups of asthma include T_H2-associated early-onset allergic asthma, late-onset persistent eosinophilic asthma, virus-induced asthma, obesity-related asthma, and neutrophilic asthma. The recent discovery of human innate lymphoid cells capable of rapidly producing large amounts of cytokines upon activation and the mouse data pointing to an essential role for these cells in asthma models have emphasized the important role of the innate immune system in asthma and have provided a new means of better understanding asthma mechanisms and differentiating its phenotypes.

Group 2 innate lymphoid cells and asthma

Group 2 innate lymphoid cells (ILC2s) are recently identified cell populations that produce type 2 cytokines such as IL-5 and IL-13 in response to epithelial cell-derived cytokines. Although ILC2s were initially reported to play a key role in the anti-helminth innate immunity, we now have greater interest in their role in asthma and other allergic diseases. In various asthma mouse models, ILC2s provoke eosinophilic inflammation accompanied by airway hyperresponsiveness independent of acquired immunity. Moreover, recent mouse studies show that ILC2s also promote acquired immunity and Th2 polarization, and various cytokines and lipid mediators influence the functions of ILC2s. Although ILC2s have also been identified in humans, studies on the role of human ILC2s in asthma are very limited. Thus far, human studies have shown that there is a slight difference in responsiveness and production of cytokines between mouse and human ILC2s, and it has been suggested that ILC2s are involved in allergic-type asthma and the exacerbation of asthma. In this review, we focus on mouse and human ILC2s, and discuss their role in asthma.

ILC2s and fungal allergy

Innate lymphoid cells (ILCs) have emerged recently as an important component of the immune system and the cell type that regulates mucosal immune responses and tissue homeostasis. Group 2 ILCs (ILC2s), a subset of ILCs, reside in various tissues and are characterized by their capacity to produce type 2 cytokines and tissue growth factors. These ILC2s play an important role in allergic immune responses by linking signals in the atmospheric environment to the immune system. Fungi are one of the major allergens associated with human asthma, and animal and in vitro models using the fungal allergens have provided significant information toward our understanding of the mechanisms of allergic disease. In mouse models of fungus-induced allergic airway inflammation, IL-33, IL-25, and TSLP are released by airway epithelial cells. Lung ILC2s that respond to these cytokines quickly produce a large quantity of type 2 cytokines, resulting in airway eosinophilia, mucus production, and airway hyperreactivity even in the absence of adaptive immune cells. Evidence also suggests that ILC2s interact with conventional immune cells, such as CD4⁺ T cells, and facilitate development of adaptive immune response and persistent airway inflammation. ILC2s are also present in respiratory mucosa in humans. Further investigations into the biology of ILC2s and their roles in the pathophysiology of allergic diseases will provide major conceptual advances in the field and may provide useful information toward development of new therapeutic strategies for patients.

Innate lymphoid cells in the initiation, regulation and resolution of inflammation

A previously unappreciated cell type of the innate immune system, termed innate lymphoid cells (ILCs), has been characterized in mice and humans and found to influence the induction, regulation and resolution of inflammation. ILCs have an important role in these processes in mouse models of infection, inflammation and tissue repair. Further, disease-association studies in defined patient populations have identified significant alterations in ILC responses, suggesting a potential role for these cell populations in human health and disease. In this review we discuss the emerging family of ILCs, the role of ILCs in inflammation, and how current or novel therapeutic strategies could be used to selectively modulate ILC responses and limit chronic inflammatory diseases.

Transcriptional regulation of innate lymphoid cell fate

Innate lymphoid cells (ILCs) are a recently described family of lymphoid effector cells that have important roles in immune defence, inflammation and tissue remodelling. It has been proposed that ILCs represent 'innate' homologues of differentiated effector T cells, and they have been categorized into three groups — namely, ILC1s, ILC2s and ILC3s — on the basis of their expression of cytokines and transcription factors that are typically associated with T helper 1 (T(H)1)-, T(H)2- and T(H)17-type immune responses, respectively. Indeed, remarkable similarity is seen between the specific transcription factors required for the development and diversification of different ILC groups and those that drive effector T cell differentiation. The recent identification of dedicated ILC precursors has provided a view of the mechanisms that control this first essential stage of ILC development. Here, we discuss the transcriptional mechanisms that regulate ILC development and diversification into distinct effector subsets with key roles in immunity and tissue homeostasis. We further caution against the current distinction between 'helper' versus 'killer' subsets in the evolving area of ILC nomenclature.

The differential expression of IL-4 and IL-13 and its impact on type-2 immunity

Allergic disease represents a significant global health burden, and disease incidence continues to rise in urban areas of the world. As such, a better understanding of the basic immune mechanisms underlying disease pathology are key to developing therapeutic interventions to both prevent disease onset as well as to ameliorate disease morbidity in those individuals already suffering from a disorder linked to type-2 inflammation. Two factors central to type-2 immunity are interleukin (IL)-4 and IL-13, which have been linked to virtually all major hallmarks associated with type-2 inflammation. Therefore, IL-4 and IL-13 and their regulatory pathways represent ideal targets to suppress disease. Despite sharing many common regulatory pathways and receptors, these cytokines perform very distinct functions during a type-2 immune response. This review summarizes the literature surrounding the function and expression of IL-4 and IL-13 in CD4+ T cells and innate immune cells. It highlights recent findings in vivo regarding the differential expression and non-canonical regulation of IL-4 and IL-13 in various immune cells, which likely play important and underappreciated roles in type-2 immunity.

IL-33 Aggravates DSS-Induced Acute Colitis in Mouse Colon Lamina Propria by Enhancing Th2 Cell Responses

Interleukin- (IL-) 33, a member of the IL-1 cytokine family, is an important modulator of the immune system associated with several immune-mediated diseases. IL-33 was expressed in high level on epithelial cells of intestinal tract. It suggested that IL-33 plays a potential role in inflammatory bowel diseases (IBD). We investigated the role of interleukin- (IL-) 33 in dextran sulphate sodium- (DSS-) induced acute colitis in mice using recombinant mouse IL-33 protein (rIL-33). We found that DSS-induced acute colitis was aggravated by rIL-33 treatment. rIL-33-treated DSS mice showed markedly reduced levels of interferon- (IFN-)γ and IL-17A in their colon lamina propria lymphocytes (LPL), but the levels of Th2 cytokines, such as IL-5 and IL-13, in these cells were significantly increased, compared to DSS mice treated with PBS. Our results suggested that IL-33 stimulated CD4⁺T cells and caused the cell to adopt a Th2-type response but at the same time suppressed Th17 and Th1 cell responses. Therefore, IL-33 may be involved in pathogenesis of DSS-induced acute colitis by promoting Th2 cell response in intestinal mucosa of mice. Modulation of IL-33/ST2 signaling by monoclonal antibody (mAb) could be a novel biological therapy in DSS-induced acute colitis.

Distinct sustained structural and functional effects of interleukin-33 and interleukin-25 on the airways in a murine asthma surrogate

Interleukin-25 (IL-25) and IL-33, which belong to distinct cytokine families, induce and promote T helper type 2 airway inflammation. Both cytokines probably play a role in asthma, but there is a lack of direct evidence to clarify distinctions between their functions and how they might contribute to distinct 'endotypes' of disease. To address this, we made a direct comparison of the effects of IL-25 and IL-33 on airway inflammation and physiology in our established murine asthma surrogate, which involves per-nasal, direct airway challenge. Intranasal challenge with IL-33 or IL-25 induced inflammatory cellular infiltration, collagen deposition, airway smooth muscle hypertrophy, angiogenesis and airway hyper-responsiveness, but neither increased systemic production of IgE or IgG1. Compared with that of IL-25, the IL-33-induced response was characterized by more sustained laying down of extracellular matrix protein, neoangiogenesis, T helper type 2 cytokine expression and elevation of tissue damping. Hence, both IL-25 and IL-33 may contribute significantly and independently to asthma 'endotypes' when considering molecular targets for the treatment of human disease.

Type-2 innate lymphoid cells in human allergic disease

PURPOSE OF REVIEW

Recent decades have seen allergic diseases become endemic in a number of developed countries. Understanding the inflammatory processes that dictate these allergic responses is therefore important.

RECENT FINDINGS

Critical to many allergic responses is the inappropriate release of the type-2 immune-regulatory cytokines: interleukin-4, interleukin-5, interleukin-9, and interleukin-13. The study of these inflammatory mediators has led directly to the development of two new asthma treatments: anti-interleukin-5 and anti-interleukin-13. Until recently, T helper 2 cells were considered to be the major cellular source of type-2 cytokines; however, a paradigm shift occurred with the discovery of a novel population, type-2 innate lymphoid cells (ILC2s), that can produce huge levels of type-2 cytokines and are sufficient to induce allergy in mice. This discovery raises interesting questions about how innate and adaptive type-2 immunity might interact to induce relapsing and remitting episodes of allergy in patients.

SUMMARY

It is essential that alongside the mechanistic investigation using model organisms, the roles of ILC2s in human disease be explored. Here, we discuss how ILC2 traits, discovered in mouse models, have informed research in humans and how newly identified human ILC2 pathways might provide potential therapeutic benefits in the future.

Group 2 innate lymphoid cells in the lung

As the first line of defense, innate immunity plays an important role in protecting the host against pathogens. Innate lymphoid cells (ILCs) are emerging as important effector cells in the innate immune system and the cell type that regulate immune and tissue homeostases. Group 2 ILCs (ILC2s) are a subset of ILCs and are characterized by their capacity to produce large quantities of type 2 cytokines and certain tissue growth factors. In animal models, lung ILC2s are involved in allergic airway inflammation induced by exposure to allergens even in the absence of CD4(+) T cells and are likely responsible for tissue repair and recovery after respiratory virus infection. ILC2s are also identified in various organs in humans, and the numbers are increased in mucosal tissues from patients with allergic disorders. Further investigations of this novel cell type will provide major conceptual advances in our understanding of the mechanisms of asthma and allergic diseases.

Allergens and the airway epithelium response: gateway to allergic sensitization

Allergic sensitization to inhaled antigens is common but poorly understood. Although lung epithelial cells were initially merely regarded as a passive barrier impeding allergen penetrance, we now realize that they recognize allergens through expression of pattern recognition receptors and mount an innate immune response driven by activation of nuclear factor κB. On allergen recognition, epithelial cells release cytokines, such as IL-1, IL-25, IL-33, thymic stromal lymphopoietin, and GM-CSF, and endogenous danger signals, such as high-mobility group box 1, uric acid, and ATP, that activate the dendritic cell network and other innate immune cells, such as basophils and type 2 innate lymphoid cells. Different allergens stimulate different aspects of this general scheme, and common environmental risk factors for sensitization, such as cigarette smoke and diesel particle exposure, do so as well. All of this is influenced by genetic polymorphisms affecting epithelial pattern recognition, barrier function, and cytokine production. Therefore, epithelial cells are crucial in determining the outcome of allergen inhalation.

Cellular mechanisms underlying eosinophilic and neutrophilic airway inflammation in asthma

Asthma is a phenotypically heterogeneous chronic disease of the airways, characterized by either predominant eosinophilic or neutrophilic, or even mixed eosinophilic/neutrophilic inflammatory patterns. Eosinophilic inflammation can be associated with the whole spectrum of asthma severity, ranging from mild-to-moderate to severe uncontrolled disease, whereas neutrophilic inflammation occurs mostly in more severe asthma. Eosinophilic asthma includes either allergic or nonallergic phenotypes underlying immune responses mediated by T helper (Th)2 cell-derived cytokines, whilst neutrophilic asthma is mostly dependent on Th17 cell-induced mechanisms. These immune-inflammatory profiles develop as a consequence of a functional impairment of T regulatory (Treg) lymphocytes, which promotes the activation of dendritic cells directing the differentiation of distinct Th cell subsets. The recent advances in the knowledge of the cellular and molecular mechanisms underlying asthmatic inflammation are contributing to the identification of novel therapeutic targets, potentially suitable for the implementation of future improvements in antiasthma pharmacologic treatments.

Cigarette smoke silences innate lymphoid cell function and facilitates an exacerbated type I interleukin-33-dependent response to infection

Cigarette smoking is a major risk factor for chronic obstructive pulmonary disease and is presumed to be central to the altered responsiveness to recurrent infection in these patients. We examined the effects of smoke priming underlying the exacerbated response to viral infection in mice. Lack of interleukin-33 (IL-33) signaling conferred complete protection during exacerbation and prevented enhanced inflammation and exaggerated weight loss. Mechanistically, smoke was required to upregulate epithelial-derived IL-33 and simultaneously alter the distribution of the IL-33 receptor ST2. Specifically, smoke decreased ST2 expression on group 2 innate lymphoid cells (ILC2s) while elevating ST2 expression on macrophages and natural killer (NK) cells, thus altering IL-33 responsiveness within the lung. Consequently, upon infection and release, increased local IL-33 significantly amplified type I proinflammatory responses via synergistic modulation of macrophage and NK cell function. Therefore, in COPD, smoke alters the lung microenvironment to facilitate an alternative IL-33-dependent exaggerated proinflammatory response to infection, exacerbating disease.

Collaborative interactions between type 2 innate lymphoid cells and antigen-specific CD4+ Th2 cells exacerbate murine allergic airway diseases with prominent eosinophilia

Type-2 innate lymphoid cells (ILC2s) and the acquired CD4(+) Th2 and Th17 cells contribute to the pathogenesis of experimental asthma; however, their roles in Ag-driven exacerbation of chronic murine allergic airway diseases remain elusive. In this study, we report that repeated intranasal rechallenges with only OVA Ag were sufficient to trigger airway hyperresponsiveness, prominent eosinophilic inflammation, and significantly increased serum OVA-specific IgG1 and IgE in rested mice that previously developed murine allergic airway diseases. The recall response to repeated OVA inoculation preferentially triggered a further increase of lung OVA-specific CD4(+) Th2 cells, whereas CD4(+) Th17 and ILC2 cell numbers remained constant. Furthermore, the acquired CD4(+) Th17 cells in Stat6(-/-)/IL-17-GFP mice, or innate ILC2s in CD4(+) T cell-ablated mice, failed to mount an allergic recall response to OVA Ag. After repeated OVA rechallenge or CD4(+) T cell ablation, the increase or loss of CD4(+) Th2 cells resulted in an enhanced or reduced IL-13 production by lung ILC2s in response to IL-25 and IL-33 stimulation, respectively. In return, ILC2s enhanced Ag-mediated proliferation of cocultured CD4(+) Th2 cells and their cytokine production, and promoted eosinophilic airway inflammation and goblet cell hyperplasia driven by adoptively transferred Ag-specific CD4(+) Th2 cells. Thus, these results suggest that an allergic recall response to recurring Ag exposures preferentially triggers an increase of Ag-specific CD4(+) Th2 cells, which facilitates the collaborative interactions between acquired CD4(+) Th2 cells and innate ILC2s to drive the exacerbation of a murine allergic airway diseases with an eosinophilic phenotype.

The immunology of asthma

Asthma is a common disease that affects 300 million people worldwide. Given the large number of eosinophils in the airways of people with mild asthma, and verified by data from murine models, asthma was long considered the hallmark T helper type 2 (TH2) disease of the airways. It is now known that some asthmatic inflammation is neutrophilic, controlled by the TH17 subset of helper T cells, and that some eosinophilic inflammation is controlled by type 2 innate lymphoid cells (ILC2 cells) acting together with basophils. Here we discuss results from in-depth molecular studies of mouse models in light of the results from the first clinical trials targeting key cytokines in humans and describe the extraordinary heterogeneity of asthma.

ICOS:ICOS-ligand interaction is required for type 2 innate lymphoid cell function, homeostasis, and induction of airway hyperreactivity

Allergic asthma is caused by Th2-cell-type cytokines in response to allergen exposure. Type 2 innate lymphoid cells (ILC2s) are a newly identified subset of immune cells that, along with Th2 cells, contribute to the pathogenesis of asthma by producing copious amounts of IL-5 and IL-13, which cause eosinophilia and airway hyperreactivity (AHR), a cardinal feature of asthma. ILC2s express ICOS, a T cell costimulatory molecule with a currently unknown function. Here we showed that a lack of ICOS on murine ILC2s and blocking the ICOS:ICOS-ligand interaction in human ILC2s reduced AHR and lung inflammation. ILC2s expressed both ICOS and ICOS-ligand, and the ICOS:ICOS-ligand interaction promoted cytokine production and survival in ILC2s through STAT5 signaling. Thus, ICOS:ICOS-ligand signaling pathway is critically involved in ILC2 function and homeostasis.

Pediatric severe asthma with fungal sensitization is mediated by steroid-resistant IL-33

Background

The mechanism underlying severe asthma with fungal sensitization (SAFS) is unknown. IL-33 is important in fungus-induced asthma exacerbations, but its role in fungal sensitization is unexplored.

Objective

We sought to determine whether fungal sensitization in children with severe therapy-resistant asthma is mediated by IL-33.

Methods

Eighty-two children (median age, 11.7 years; 63% male) with severe therapy-resistant asthma were included. SAFS (n = 38) was defined as specific IgE or skin prick test response positivity to Aspergillus fumigatus, Alternaria alternata, or Cladosporium herbarum. Clinical features and airway immunopathology were assessed. Chronic exposure to house dust mite and A alternata were compared in a neonatal mouse model.

Results

Children with SAFS had earlier symptom onset (0.5 vs 1.5 years, P = .006), higher total IgE levels (637 vs 177 IU/mL, P = .002), and nonfungal inhalant allergen-specific IgE. Significantly more children with SAFS were prescribed maintenance oral steroids (42% vs 14%, P = .02). SAFS was associated with higher airway IL-33 levels. In neonatal mice A alternata exposure induced higher serum IgE levels, pulmonary IL-33 levels, and IL-13⁺ innate lymphoid cell (ILC) and T_H2 cell numbers but similar airway hyperresponsiveness (AHR) compared with those after house dust mite exposure. Lung IL-33 levels, IL-13⁺ ILC numbers, T_H2 cell numbers, IL-13 levels, and AHR remained increased with inhaled budesonide during A alternata exposure, but all features were significantly reduced in ST2^−/− mice lacking a functional receptor for IL-33.

Conclusion

Pediatric SAFS was associated with more oral steroid therapy and higher IL-33 levels. A alternata exposure resulted in increased IL-33–mediated ILC2 numbers, T_H2 cell numbers, and steroid-resistant AHR. IL-33 might be a novel therapeutic target for SAFS.

IL-17 in severe asthma. Where do we stand?

Asthma is a major chronic disease ranging from mild to severe refractory disease and is classified into various clinical phenotypes. Severe asthma is difficult to treat and frequently requires high doses of systemic steroids. In some cases, severe asthma even responds poorly to steroids. Several studies have suggested a central role of IL-17 (also called IL-17A) in severe asthma. Indeed, high levels of IL-17 are found in induced sputum and bronchial biopsies obtained from patients with severe asthma. The recent identification of a steroid-insensitive pathogenic Th17 pathway is therefore of major interest. In addition, IL-17A has been described in multiple aspects of asthma pathogenesis, including structural alterations of epithelial cells and smooth muscle contraction. In this perspective article, we frame the topic of IL-17A effects in severe asthma by reviewing updated information from human studies. We summarize and discuss the implications of IL-17 in the induction of neutrophilic airway inflammation, steroid insensitivity, the epithelial cell profile, and airway remodeling.

At the bench: understanding group 2 innate lymphoid cells in disease

The conventional paradigm of type 2 inflammatory responses is characterized by activation of CD4(+) Th2 cells that produce IL-4, IL-5, and IL-13, resulting in tissue eosinophil infiltration, mucus metaplasia, AHR, and IgE production. However, the recent discovery of ILC2s in mice and humans has brought forth a novel pathway in type 2 immunity that may work independent of, or in concert with, adaptive Th2 responses. ILC2s were described initially as lineage-negative lymphocytes that produce high levels of Th2 cytokines IL-5 and IL-13 in response to IL-25 and IL-33 and promote protection against helminth infections. More recent investigations have identified novel upstream regulators, as well as novel ILC2 products. ILC2s are found in mucosal surfaces, including respiratory tract and skin, and studies from experimental asthma and atopic dermatitis models support a role for ILC2s in promoting type 2 inflammatory responses. There are many unanswered questions about the role of ILC2s in chronic allergic diseases, including how ILC2s or upstream pathways can be targeted for therapy. As ILC2s are not antigen specific and may be activated after exposures to a variety of infectious agents and irritants thought to contribute to respiratory and skin diseases, future strategies to target ILC2 function in human disease may be promising. Our intent is to identify priority areas for ILC2 translational research based on basic research insights.

Crucial and diverse role of the interleukin-33/ST2 axis in infectious diseases

Interleukin-33 (IL-33) has now emerged as a cytokine with diverse and pleiotropic functions in various infectious and inflammatory diseases. IL-33 is expressed by epithelial cells, endothelial cells, fibroblasts, and hepatocytes. The target cells of IL-33 are Th2 cells, basophils, dendritic cells, mast cells, macrophages, NKT cells, and nuocytes, newly discovered natural helper cells/innate lymphoid cells bearing the ST2 receptor. IL-33 has dual functions, both as a traditional cytokine and as a nuclear factor that regulates gene transcription. IL-33 functions as an "alarmin" released following cell death, as a biomarker, and as a vaccine adjuvant, with proinflammatory and protective effects during various infections. The exacerbated or protective role of the IL-33/ST2 axis during different infections is dependent upon the organ involved, type of infectious agent, whether the infection is acute or chronic, the invasiveness of the infectious agent, the host immune compartment, and cellular and cytokine microenvironments. In this review, we focus on recent advances in the understanding of the role of the IL-33/ST2 axis in various viral, bacterial, fungal, helminth, and protozoal infectious diseases gained from animal models and studies in human patients. The functional role of IL-33 and ST2 during experimentally induced infections has been summarized by accumulating the data for IL-33- and ST2-deficient mice or for mice exogenously administered IL-33. In summary, exploring the crucial and diverse roles of the IL-33/ST2 axis during infections may help in the development of therapeutic interventions for a wide range of infectious diseases.

Lung ILC2s link innate and adaptive responses in allergic inflammation

How allergens trigger the T helper 2 (Th2) response that characterizes allergic lung inflammation is not well understood. Epithelium-derived alarmins released after an allergen encounter activate the innate immune system, including group 2 innate lymphoid cells (ILC2s) which produce the type 2 interleukins IL-5 and IL-13. It has been recently shown that ILC2-derived cytokines are responsible not only for the innate responses underlying allergic inflammation but also for the initiation of the adaptive Th2 response. We review the role of lung ILC2s in the development of allergic inflammation and, in the context of recent findings, propose a common pathway wherein ILC2s, activated by the epithelium-derived cytokine IL-33, link the innate and the adaptive responses after allergen encounter in the lung.

Innate immunity in the lung regulates the development of asthma

The lung, while functioning as a gas exchange organ, encounters a large array of environmental factors, including particulate matter, toxins, reactive oxygen species, chemicals, allergens, and infectious microbes. To rapidly respond to and counteract these elements, a number of innate immune mechanisms have evolved that can lead to lung inflammation and asthma, which is the focus of this review. These innate mechanisms include a role for two incompletely understood cell types, invariant natural killer T (iNKT) cells and innate lymphoid cells (ILCs), which together produce a wide range of cytokines, including interleukin-4 (IL-4), IL-5, IL-13, interferon-γ, IL-17, and IL-22, independently of adaptive immunity and conventional antigens. The specific roles of iNKT cells and ILCs in immunity are still being defined, but both cell types appear to play important roles in the lungs, particularly in asthma. As we gain a better understanding of these innate cell types, we will acquire great insight into the mechanisms by which allergic and non-allergic asthma phenotypes develop.

Persistence of asthma requires multiple feedback circuits involving type 2 innate lymphoid cells and IL-33

BACKGROUND

Asthma in a mouse model spontaneously resolves after cessation of allergen exposure. We developed a mouse model in which asthma features persisted for 6 months after cessation of allergen exposure.

OBJECTIVE

We sought to elucidate factors contributing to the persistence of asthma.

METHODS

We used a combination of immunologic, genetic, microarray, and pharmacologic approaches to dissect the mechanism of asthma persistence.

RESULTS

Elimination of T cells though antibody-mediated depletion or lethal irradiation and transplantation of recombination-activating gene (Rag1)(-/-) bone marrow in mice with chronic asthma resulted in resolution of airway inflammation but not airway hyperreactivity or remodeling. Elimination of T cells and type 2 innate lymphoid cells (ILC2s) through lethal irradiation and transplantation of Rag2(-/-)γc(-/-) bone marrow or blockade of IL-33 resulted in resolution of airway inflammation and hyperreactivity. Persistence of asthma required multiple interconnected feedback and feed-forward circuits between ILC2s and epithelial cells. Epithelial IL-33 induced ILC2s, a rich source of IL-13. The latter directly induced epithelial IL-33, establishing a positive feedback circuit. IL-33 autoinduced, generating another feedback circuit. IL-13 upregulated IL-33 receptors and facilitated IL-33 autoinduction, thus establishing a feed-forward circuit. Elimination of any component of these circuits resulted in resolution of chronic asthma. In agreement with the foregoing, IL-33 and ILC2 levels were increased in the airways of asthmatic patients. IL-33 levels correlated with disease severity.

CONCLUSIONS

We present a critical network of feedback and feed-forward interactions between epithelial cells and ILC2s involved in maintaining chronic asthma. Although T cells contributed to the severity of chronic asthma, they were redundant in maintaining airway hyperreactivity and remodeling.

Group 2 innate lymphoid cells in health and disease

Group 2 innate lymphoid cells (ILC2s) play critical roles in anti-helminth immunity, airway epithelial repair, and metabolic homeostasis. Recently, these cells have also emerged as key players in the development of allergic inflammation at multiple barrier surfaces. ILC2s arise from common lymphoid progenitors in the bone marrow, are dependent on the transcription factors RORα, GATA3, and TCF-1, and produce the type 2 cytokines interleukin (IL)-4, IL-5, IL-9, and/or IL-13. The epithelial cell-derived cytokines IL-25, IL-33, and TSLP regulate the activation and effector functions of ILC2s, and recent studies suggest that their responsiveness to these cytokines and other factors may depend on their tissue environment. In this review, we focus on recent advances in our understanding of the various factors that regulate ILC2 function in the context of immunity, inflammation, and tissue repair across multiple organ systems.

Group 2 innate lymphoid cells: new players in human allergic diseases

Allergic diseases are characterized by tissue eosinophilia, mucus secretion, IgE production, and activation of mast cells and TH2 cells. Production of TH2 cytokines including IL-4, IL-5, IL-9, and IL-13 has mainly been attributed to CD4+T(H)2 cells. However, the recent discovery of group 2 innate lymphoid cells (ILC2s) in humans and findings from experimental disease models have challenged conventional concepts associated with the contribution of specific cells to type 2 inflammation in allergic diseases. ILC2s produce high levels of T(H)2 cytokines and have been detected in human lung tissue, peripheral blood, the gastrointestinal tract, skin, and sinonasal tissue, suggesting that ILC2s could contribute to chronic rhinosinusitis, asthma, atopic dermatitis, and gastrointestinal allergic disease. Moreover, depletion of ILC2s in animal models suggests a role for these cells in atopic dermatitis and asthma. This review will focus on the role of ILC2s in human allergy and asthma and provide a mechanistic insight from animal models.

Generation of potent mouse monoclonal antibodies to self-proteins using T-cell epitope "tags"

Immunization of mice or rats with a "non-self" protein is a commonly used method to obtain monoclonal antibodies, and relies on the immune system's ability to recognize the immunogen as foreign. Immunization of an antigen with 100% identity to the endogenous protein, however, will not elicit a robust immune response. To develop antibodies to mouse proteins, we focused on the potential for breaking such immune tolerance by genetically fusing two independent T-cell epitope-containing sequences (from tetanus toxin (TT) and diphtheria toxin fragment A (DTA)) to a mouse protein, mouse ST2 (mST2). Wild-type CD1 mice were immunized with three mST2 tagged proteins (Fc, TT and DTA) and the specific serum response was determined. Only in mice immunized with the T-cell epitope-containing antigens were specific mST2 serum responses detected; hybridomas generated from these mice secreted highly sequence-diverse IgGs that were capable of binding mST2 and inhibiting the interaction of mST2 with its ligand, mouse interleukin (IL)-33 (mIL-33). Of the hundreds of antibodies profiled, we identified five potent antibodies that were able to inhibit IL-33 induced IL-6 release in a mast cell assay; notably one such antibody was sufficiently potent to suppress IL-5 release and eosinophilia infiltration in an Alternaria alternata challenge mouse model of asthma. This study demonstrated, for the first time, that T-cell epitope-containing tags have the ability to break tolerance in wild-type mice to 100% conserved proteins, and it provides a compelling argument for the broader use of this approach to generate antibodies against any mouse protein or conserved ortholog.