Human ILC2s Research Articles

Epigenome analysis links gene regulatory elements in group 2 innate lymphocytes to asthma susceptibility

Group 2 innate lymphoid cells (ILC2s) are major producers of the cytokines driving allergic asthma, and increased ILC2 numbers have been detected in blood and sputum of asthmatic patients. Asthma susceptibility has a strong genetic component, but the underlying mechanisms and whether asthma genetics affect ILC2 biology remain unclear. We sought to study the ILC2 transcriptome and epigenome during airway inflammation (AI) to couple these to genes and genetic variants associated with asthma pathogenesis. Mice harboring a reporter for the key ILC2 transcription factor GATA-3 were subjected to IL-33-driven AI, and ILC2s were isolated from bronchoalveolar lavage fluid and mediastinal lymph nodes. Human ILC2s were purified from peripheral blood and activated invitro. We used RNA sequencing, genome-wide identification of histone-3 lysine-4 dimethylation-marked chromatin, and computational approaches to study the ILC2 transcriptome and epigenome. Activated ILC2s in mice displayed a tissue-specific gene expression signature that emerged from remarkably similar epigenomes. We identified superenhancers implicated in controlling ILC2 identity and asthma-associated genes. More than 300 asthma-associated genetic polymorphisms identified in genome-wide association studies localized to H3K4Me2+ gene regulatory elements in ILC2s. Arefined set of candidate causal asthma-associated variants was uniquely enriched in ILC2, but not TH2 cell, regulatory regions. ILC2s in AI use a flexible epigenome that couples adaptation to new microenvironments with functional plasticity. Importantly, we reveal strong correlations between gene regulatory mechanisms in ILC2s and the genetic basis of asthma, supporting a pathogenic role for ILC2s in patients with allergic asthma.

Potentiating Tissue-Resident Type 2 Innate Lymphoid Cells by IL-33 to Prevent Renal Ischemia-Reperfusion Injury.

The IL-33-type 2 innate lymphoid cell (ILC2) axis has an important role in tissue homeostasis, inflammation, and wound healing. However, the relative importance of this innate immune pathway for immunotherapy against inflammation and tissue damage remains unclear. Here, we show that treatment with recombinant mouse IL-33 prevented renal structural and functional injury and reduced mortality in mice subjected to ischemia-reperfusion injury (IRI). Compared with control-treated IRI mice, IL-33-treated IRI mice had increased levels of IL-4 and IL-13 in serum and kidney and more ILC2, regulatory T cells (Tregs), and anti-inflammatory (M2) macrophages. Depletion of ILC2, but not Tregs, substantially abolished the protective effect of IL-33 on renal IRI. Adoptive transfer of ex vivo-expanded ILC2 prevented renal injury in mice subjected to IRI. This protective effect associated with induction of M2 macrophages in kidney and required ILC2 production of amphiregulin. Treatment of mice with IL-33 or ILC2 after IRI was also renoprotective. Furthermore, in a humanized mouse model of renal IRI, treatment with human IL-33 or transfer of ex vivo-expanded human ILC2 ameliorated renal IRI. This study has uncovered a major protective role of the IL-33-ILC2 axis in renal IRI that could be potentiated as a therapeutic strategy.

Human intrahepatic ILC2 are IL-13positive amphiregulinpositive and their frequency correlates with model of end stage liver disease score.

IntroductionInnate lymphoid cells (ILC) have been implicated in the initiation of inflammation and fibrosis in mice. However, ILC have not been characterized in inflamed human liver tissue.MethodsHuman intrahepatic lymphocytes were isolated by mechanical digestion and phenotyped by flow cytometry. Conditioned medium from cultures of primary human biliary epithelial cells, stellate cells, fibroblasts and inflamed human liver tissue was used to model the effects of the inflammatory liver environment of ILC phenotype and function.ResultsAll three ILC subsets were present in the human liver, with the ILC1 (CRTH2negCD117neg) subset constituting around 70% of intrahepatic ILCs. Both NCRpos (NKp44+) and NCRneg ILC3 (CRTH2negCD117pos) subsets were also detected. ILC2 (CRTH2pos) frequency correlated with disease severity measured by model of end stage liver disease (MELD) scoring leading us to study this subset in more detail. ILC2 displayed a tissue resident CD69+ CD161++ phenotype and expressed chemokine receptor CCR6 allowing them to respond to CCL20 secreted by cholangiocytes and stellate cells. ILC2 expressed integrins VLA-5 and VLA-6 and the IL-2 and IL-7 cytokine receptors CD25 and CD127 although IL-2 and IL-7 were barely detectable in inflamed liver tissue. Although biliary epithelial cells secrete IL-33, intrahepatic ILC2 had low expression of the ST2 receptor. Intrahepatic ILC2 secreted the immunoregulatory and repair cytokines IL-13 and amphiregulin.ConclusionsIntrahepatic ILC2 express receptors allowing them to be recruited to bile ducts in inflamed portal tracts. Their frequencies increased with worsening liver function. Their secretion of IL-13 and amphiregulin suggests they may be recruited to promote resolution and repair and thereby they may contribute to ongoing fibrogenesis in liver disease.

CD1a presentation of endogenous antigens by group 2 innate lymphoid cells.

Group 2 innate lymphoid cells (ILC2) are effectors of barrier immunity, with roles in infection, wound healing, and allergy. A proportion of ILC2 express MHCII (major histocompatibility complex II) and are capable of presenting peptide antigens to T cells and amplifying the subsequent adaptive immune response. Recent studies have highlighted the importance of CD1a-reactive T cells in allergy and infection, activated by the presentation of endogenous neolipid antigens and bacterial components. Using a human skin challenge model, we unexpectedly show that human skin-derived ILC2 can express CD1a and are capable of presenting endogenous antigens to T cells. CD1a expression is up-regulated by TSLP (thymic stromal lymphopoietin) at levels observed in the skin of patients with atopic dermatitis, and the response is dependent on PLA2G4A. Furthermore, this pathway is used to sense Staphylococcus aureus by promoting Toll-like receptor-dependent CD1a-reactive T cell responses to endogenous ligands. These findings define a previously unrecognized role for ILC2 in lipid surveillance and identify shared pathways of CD1a- and PLA2G4A-dependent ILC2 inflammation amenable to therapeutic intervention.

Prostaglandin E2 suppresses human group 2 innate lymphoid cell function

BackgroundGroup 2 innate lymphoid cells (ILC2s) are involved in the initial phase of type 2 inflammation and can amplify allergic immune responses by orchestrating other type 2 immune cells. Prostaglandin (PG) E2 is a bioactive lipid that plays protective roles in the lung, particularly during allergic inflammation.ObjectiveWe set out to investigate how PGE2 regulates human ILC2 function.MethodsThe effects of PGE2 on human ILC2 proliferation and intracellular cytokine and transcription factor expression were assessed by means of flow cytometry. Cytokine production was measured by using ELISA, and real-time quantitative PCR was performed to detect PGE2 receptor expression.ResultsPGE2 inhibited GATA-3 expression, as well as production of the type 2 cytokines IL-5 and IL-13, from human tonsillar and blood ILC2s in response to stimulation with a combination of IL-25, IL-33, thymic stromal lymphopoietin, and IL-2. Furthermore, PGE2 downregulated the expression of IL-2 receptor α (CD25). In line with this observation, PGE2 decreased ILC2 proliferation. These effects were mediated by the combined action of E-type prostanoid receptor (EP) 2 and EP4 receptors, which were specifically expressed on ILC2s.ConclusionOur findings reveal that PGE2 limits ILC2 activation and propose that selective EP2 and EP4 receptor agonists might serve as a promising therapeutic approach in treating allergic diseases by suppressing ILC2 function.

Activated plasmacytoid dendritic cells regulate type 2 innate lymphoid cell–mediated airway hyperreactivity

Allergic asthma is a prevalent inflammatory disease of the airways caused by dysregulated immune balance in the lungs with incompletely understood pathogenesis. The recently identified type 2 innate lymphoid cells (ILC2s) play significant roles in the pathogenesis of asthma. Although ILC2-activating factors have been identified, the mechanisms that suppress ILC2s remain largely unknown. Plasmacytoid dendritic cells (pDCs) are important in antiviral immunity and in maintaining tolerance to inert antigens. We sought to address the role of pDCs in regulating ILC2 function and ILC2-mediated airway hyperreactivity (AHR) and lung inflammation. We used several murine models, including BDCA-2-diphtheria toxin receptor (DTR) transgenic and IFN-α receptor 1-deficient mice, as well as purified primary ILC2s, to reach our objective. We extended and validated our findings to human ILC2s. We show that activation of pDCs through Toll-like receptor 7/8 suppresses ILC2-mediated AHR and airway inflammation and that depletion of pDCs reverses this suppression. We further show that pDCs suppress cytokine production and the proliferation rate while increasing the apoptosis rate of ILC2s through IFN-α production. Transcriptomic analysis of both human and murine ILC2s confirms the activation of regulatory pathways in ILC2s by IFN-α. Activation of pDCs alleviates AHR and airway inflammation by suppressing ILC2 function and survival. Our findings reveal a novel regulatory pathway in ILC2-mediated pulmonary inflammation with important clinical implications.

Immune checkpoints on innate lymphoid cells.

In this issue of JEM, Taylor et al. (https://doi.org/10.1084/jem.20161653) describe PD-1 as a critical negative regulator of group 2 innate lymphoid cells (ILC-2s). PD-1 intrinsically controls proliferation and cytokine production of both mouse and human ILC-2s. PD-1 signaling inhibits STAT5 phosphorylation and the removal of this brake by knocking down PD-1 expression or by using anti-PD-1 blocking antibodies, translated in vivo into better clearance of helminth worm infection in mice.

Toll-like receptor-7-mediated activation of pDCs suppresses the ILC2-mediated airway hyperreactivity and inflammation through type-I interferon

Abstract Type 2 innate lymphoid cells (ILC2s) are newly identified subset of immune cells that play important roles in the pathogenesis of allergic diseases and asthma. The regulatory mechanisms that control the function and homeostasis of ILC2s are incompletely understood. Plasmacytoid dendritic cells (pDCs) have been previously associated with maintaining respiratory tolerance. To identify a novel mechanism for alleviating ILC2-mediated asthma we investigated impact of pDCs on ILC2s and ILC2-mediated airway hyperreactivity and inflammation. We investigated human and murine ILC2s and used clinically relevant allergen, Alternaria Alternata, as well as IL-33, to activate ILC2s in several mouse models including BDCA-2-DTR transgenic and Interferon alpha receptor-1 deficient mice. We found that activation of pDCS by a Toll-like receptor-7 agonist, R848, suppresses ILC2-mediated AHR and airway inflammation and that depletion of pDCs reverses this suppression. Moreover, we found that pDCs suppress cytokine production and proliferation of ILC2s through the production of interferon alpha. Transcriptome analysis of both human and murine ILC2s confirms the activation of regulatory pathways in ILC2s by interferon alpha. In addition, activation of pDCs alleviates airway hyperreactivity and inflammation by suppressing ILC2’s function and survival. Our findings reveal a novel regulatory pathway in ILC2-mediated pulmonary inflammation with important clinical implications.

The human CD34(−)CD117(+)CD56(−)NKp44(−) population in secondary lymphoid tissue serves as a common progenitor to NK cells and ILC2s

Abstract The developmental pathways of human innate lymphoid cells (ILCs) have not been fully elucidated. We reported that human natural killer (NK) cells can derive from progenitor cells naturally residing in tonsils. We hypothesized that Group 2 ILCs (ILC2s) also develop in tonsils through a shared pathway. In support of this, ex vivo flow cytometry analyses of enriched human tonsil ILCs revealed a putative pathway of human CD294(+) ILC2 development stemming from a lineage (Lin)(−)CD34(−)CD117(+) population from which non-overlapping CD94(+) NK cells also emerged. Furthermore, when purified tonsil Lin(−)CD34(−)CD117(+) cells were cultured for 28 days with murine OP9 stroma expressing the human Notch ligand, Delta-like 1, in the presence of human interleukin-7 and Flt3 ligand, they produced mutually distinct and functionally mature populations of CD94(+) NK cells and CD294(+) ILC2s. The tonsil Lin(−)CD34(−)CD117(+) population is heterogeneous for CD56 and NKp44. Evaluation of the in vitro lineage differentiation potentials of subsets within the Lin(−)CD34(−)CD117(+) population according to NKp44 and CD56 revealed that NKp44(−)CD56(−) cells gave rise to both NK cells and ILC2s, whereas fractions expressing NKp44 and/or CD56 gave rise to NK cells but only to negligible ILC2s. In fact, the NKp44(−)CD56(−) population gave rise to a significantly higher percentage of ILC2s (7.50 ± 0.6) compared to the NKp44(+)CD56(+/−) populations (1.22 ± 0.4) (n = 5, p < 0.001). These data support a model whereby human NK cells and ILC2s can develop from a common Lin(−)CD34(−)CD117(+)CD56(−)NKp44(−) progenitor in tonsils and that the acquisition of NKp44 and/or CD56 restricts lineage differentiation potential towards the NK cell lineage.

Steroid resistance of airway type 2 innate lymphoid cells from patients with severe asthma: The role of thymic stromal lymphopoietin

Type 2 innate lymphoid cells (ILC2s) represent an important type 2 immune cell. Glucocorticoid regulation of human ILC2s is largely unknown. We sought to assess steroid resistance of human blood and airway ILC2s from asthmatic patients and to examine its mechanism of induction. We studied human blood and lung ILC2s from asthmatic patients and control subjects using flow cytometry and ELISA. Dexamethasone inhibited (P=.04) chemoattractant receptor-homologous molecule expressed on TH2 lymphocytes and type 2 cytokine expression by blood ILC2s stimulated with IL-25 and IL-33. However, it did not do so when ILC2s were stimulated with IL-7 and thymic stromal lymphopoietin (TSLP), 2 ligands of IL-7 receptor α. Unlike blood ILC2s, bronchoalveolar lavage (BAL) fluid ILC2s from asthmatic patients were resistant to dexamethasone. BAL fluid from asthmatic patients had increased TSLP but not IL-7 levels. BAL fluid TSLP levels correlated (r=0.74) with steroid resistance of ILC2s. TSLP was synergistically induced in epithelial cells by IL-13 and human rhinovirus. Mechanistically, dexamethasone upregulated ILC2 expression of IL-7 receptor α, which augmented and sustained signal transducer and activator of transcription (STAT) 5 signaling by TSLP. TSLP induced mitogen-activated protein kinase kinase (MEK), c-Fos, inhibitor of DNA binding 3, phosphorylated signal transducer and activator of transcription (pSTAT) 3, and pSTAT5, molecules linked to steroid resistance. Dexamethasone inhibited c-Fos, inhibitor of DNA binding 3, and pSTAT3 but not pSTAT5 and MEK. The MEK inhibitor trametinib, the Janus kinase-STAT inhibitor tofacitinib, and the STAT5 inhibitor pimozide reversed steroid resistance of BAL ILC2s. Dexamethasone inhibited type 2 cytokine production by blood ILC2s. IL-7 and TSLP abrogated this inhibition and induced steroid resistance of ILC2s in a MEK- and STAT5-dependent manner. BAL fluid ILC2s from asthmatic patients with increased TSLP levels were steroid resistant, which was reversed by clinically available inhibitors of MEK and STAT5.

Type 2 innate lymphoid cells disrupt bronchial epithelial barrier integrity by targeting tight junctions through IL-13 in asthmatic patients

Bronchial epithelial barrier leakiness and type 2 innate lymphoid cells (ILC2s) have been separately linked to asthma pathogenesis; however, the influence of ILC2s on the bronchial epithelial barrier has not been investigated previously. We investigated the role of ILC2s in the regulation of bronchial epithelial tight junctions (TJs) and barrier function both in bronchial epithelial cells of asthmatic patients and healthy subjects and general innate lymphoid cell- and ILC2-deficient mice. Cocultures of human ILC2s and bronchial epithelial cells were used to determine transepithelial electrical resistance, paracellular flux, and TJ mRNA and protein expressions. The effect of ILC2s on TJs was examined by using a murine model of IL-33-induced airway inflammation in wild-type, recombination-activating gene 2 (Rag2)-/-, Rag2-/-Il2rg-/-, and Rorasg/sg mice undergoing bone marrow transplantation to analyze the invivo relevance of barrier disruption by ILC2s. ILC2s significantly impaired the epithelial barrier, as demonstrated by reduced transepithelial electrical resistance and increased fluorescein isothiocyanate-dextran permeability in air-liquid interface cultures of human bronchial epithelial cells. This was in parallel to decreased mRNAs and disrupted protein expression of TJ proteins and was restored by neutralization of IL-13. Intranasal administration of recombinant IL-33 to wild-type and Rag2-/- mice lacking T and B cells triggered TJ disruption, whereas Rag2-/-Il2rg-/- and Rorasg/sg mice undergoing bone marrow transplantation that lack ILC2s did not show any barrier leakiness. Direct nasal administration of IL-13 was sufficient to induce deficiency in the TJ barrier in the bronchial epithelium of mice invivo. These data highlight an essential mechanism in asthma pathogenesis by demonstrating that ILC2s are responsible for bronchial epithelial TJ barrier leakiness through IL-13.

β2 integrins rather than β1 integrins mediate Alternaria-induced group 2 innate lymphoid cell trafficking to the lung

Group 2 innate lymphoid cells (ILC2s) expand in the lungs of mice during type 2 inflammation induced by the fungal allergen Alternaria alternata. The increase in ILC2 numbers in the lung has been largely attributed to local proliferation and whether ILC2s migrate from the circulation to the lung after Alternaria exposure is unknown. We examined whether human (lung, lymph node, and blood) and mouse lung ILC2s express β1 and β2 integrin adhesion molecules and whether these integrins are required for trafficking of ILC2s into the lungs of mice. Human and mouse ILC2s were assessed for surface expression of β1 and β2 integrin adhesion molecules by using flow cytometry. The role of β1 and β2 integrins in ILC2 trafficking to the lungs was assessed by invivo blocking of these integrins before airway exposure to Alternaria in mice. Both human and mouse lung ILC2s express high levels of β1 and β2 integrin adhesion receptors. Intranasal administration of Alternaria challenge reduced ILC2 numbers in the bone marrow and concurrently increased blood and lung ILC2 numbers. Invivo blocking of β2 integrins (CD18) significantly reduced ILC2 numbers in the lungs but did not alter ILC2 proliferation, apoptosis, and function. In contrast, invivo blocking of β1 integrins or α4 integrins did not affect lung ILC2 numbers. ILC2 numbers increase in the mouse lung not only through local proliferation but also through trafficking from the circulation into the lung using β2 rather than β1 or α4 integrins.

Cysteinyl leukotriene E4 activates human group 2 innate lymphoid cells and enhances the effect of prostaglandin D2 and epithelial cytokines

BackgroundGroup 2 innate lymphoid cells (ILC2s) are a potential innate source of type 2 cytokines in the pathogenesis of allergic conditions. Epithelial cytokines (IL-33, IL-25, and thymic stromal lymphopoietin [TSLP]) and mast cell mediators (prostaglandin D2 [PGD2]) are critical activators of ILC2s. Cysteinyl leukotrienes (cysLTs), including leukotriene (LT) C4, LTD4, and LTE4, are metabolites of arachidonic acid and mediate inflammatory responses. Their role in human ILC2s is still poorly understood.ObjectivesWe sought to determine the role of cysLTs and their relationship with other ILC2 stimulators in the activation of human ILC2s.MethodsFor ex vivo studies, fresh blood from patients with atopic dermatitis and healthy control subjects was analyzed with flow cytometry. For in vitro studies, ILC2s were isolated and cultured. The effects of cysLTs, PGD2, IL-33, IL-25, TSLP, and IL-2 alone or in combination on ILC2s were defined by using chemotaxis, apoptosis, ELISA, Luminex, quantitative RT-PCR, and flow cytometric assays. The effect of endogenous cysLTs was assessed by using human mast cell supernatants.ResultsHuman ILC2s expressed the LT receptor CysLT1, levels of which were increased in atopic subjects. CysLTs, particularly LTE4, induced migration, reduced apoptosis, and promoted cytokine production in human ILC2s in vitro. LTE4 enhanced the effect of PGD2, IL-25, IL-33, and TSLP, resulting in increased production of type 2 and other proinflammatory cytokines. The effect of LTE4 was inhibited by montelukast, a CysLT1 antagonist. Interestingly, addition of IL-2 to LTE4 and epithelial cytokines significantly amplified ILC2 activation and upregulated expression of the receptors for IL-33 and IL-25.ConclusionCysLTs, particularly LTE4, are important contributors to the triggering of human ILC2s in inflammatory responses, particularly when combined with other ILC2 activators.

Protein kinase Cθ controls type 2 innate lymphoid cell and TH2 responses to house dust mite allergen

Protein kinase C (PKC) θ, a serine/threonine kinase, is involved in TH2 cell activation and proliferation. Type 2 innate lymphoid cells (ILC2s) resemble TH2 cells and produce the TH2 cytokines IL-5 and IL-13 but lack antigen-specific receptors. The mechanism by which PKC-θ drives innate immune cells to instruct TH2 responses in patients with allergic lung inflammation remains unknown. We hypothesized that PKC-θ contributes to ILC2 activation and might be necessary for ILC2s to instruct the TH2 response. PRKCQ gene expression was assessed in innate lymphoid cell subsets purified from human PBMCs and mouse lung ILC2s. ILC2 activation and eosinophil recruitment, TH2-related cytokine and chemokine production, lung histopathology, interferon regulatory factor 4 (IRF4) mRNA expression, and nuclear factor of activated T cells (NFAT1) protein expression were determined. Adoptive transfer of ILC2s from wild-type mice was performed in wild-type and PKC-θ-deficient (PKC-θ-/-) mice. Here we report that PKC-θ is expressed in both human and mouse ILC2s. Mice lacking PKC-θ had reduced ILC2 numbers, TH2 cell numbers and activation, airway hyperresponsiveness, and expression of the transcription factors IRF4 and NFAT1. Importantly, adoptive transfer of ILC2s restored eosinophil influx and IL-4, IL-5 and IL-13 production in lung tissue, as well as TH2 cell activation. The pharmacologic PKC-θ inhibitor (Compound 20) administered during allergen challenge reduced ILC2 numbers and activation, as well as airway inflammation and IRF4 and NFAT1 expression. Therefore our findings identify PKC-θ as a critical factor for ILC2 activation that contributes to TH2 cell differentiation, which is associated with IRF4 and NFAT1 expression in allergic lung inflammation.

Type 2 innate lymphoid cell suppression by regulatory T cells attenuates airway hyperreactivity and requires inducible T-cell costimulator–inducible T-cell costimulator ligand interaction

Atopic diseases, including asthma, exacerbate type 2 immune responses and involve a number of immune cell types, including regulatory T (Treg) cells and the emerging type 2 innate lymphoid cells (ILC2s). Although ILC2s are potent producers of type 2 cytokines, the regulation of ILC2 activation and function is not well understood. In the present study, for the first time, we evaluate how Treg cells interact with pulmonary ILC2s and control their function. ILC2s and Treg cells were evaluated by using invitro suppression assays, cell-contact assays, and gene expression panels. Also, human ILC2s and Treg cells were adoptively transferred into NOD SCID γC-deficient mice, which were given isotype or anti-inducible T-cell costimulator ligand (ICOSL) antibodies and then challenged with IL-33 and assessed for airway hyperreactivity. We show that induced Treg cells, but not natural Treg cells, effectively suppress the production of the ILC2-driven proinflammatory cytokines IL-5 and IL-13 both invitro and invivo. Mechanistically, our data reveal the necessity of inducible T-cell costimulator (ICOS)-ICOS ligand cell contact for Treg cell-mediated ILC2 suppression alongside the suppressive cytokines TGF-β and IL-10. Using a translational approach, we then demonstrate that human induced Treg cells suppress syngeneic human ILC2s through ICOSL to control airway inflammation in a humanized ILC2 mouse model. These findings suggest that peripheral expansion of induced Treg cells can serve as a promising therapeutic target against ILC2-dependent asthma.

Human circulating group 2 innate lymphoid cells can express CD154 and promote IgE production

Protection against helminths consists of adaptive responses by TH2 cells and innate responses by group 2 innate lymphoid cells (ILC2s), with these latter being well characterized in mice but less so in human subjects. We sought to characterize human circulating ILC2s and compare their functional profile with that of autologous TH2 cells. Circulating ILC2s and TH2 cells were isolated by means of fluorescence-activated cell sorting and magnetic cell sorting and expanded invitro. ILC2s were then stimulated with phorbol 12-myristate 13-acetate plus ionomycin, IL-25 plus IL-33 (IL-25/IL-33), or a mixture of Toll-like receptor ligands to evaluate their ability to produce cytokines, express CD154, and induce IgE production by autologous Bcells. Cytokines and transcription factor gene methylation were assessed. ILC2s expressed GATA-3, retinoic acid orphan receptor (RORC) 2, and RORα; were able to produce IL-5, IL-13, and IL-4; and, accordingly, were characterized by demethylation of IL4, IL13, IL5, GATA3, and RORC2, whereas the IFNG, IFNG promoter, and TBX21 regions of interest were methylated. ILC2s expressed TLR1, TLR4, and TLR6, and TLR stimulation induced IL-5 and IL-13 production. Moreover, ILC2s expressed CD154 in response to phorbol 12-myristate 13-acetate plus ionomycin, IL-25/IL-33, or a mixture of TLR ligands. Stimulated ILC2s also induced IgM, IgG, IgA, and IgE production by Bcells. Finally, circulating ILC2s from atopic patients were not different in numbers and frequency but expressed higher IL-4 levels than those from nonatopic subjects. This study provides the first evidence that human ILC2s can express CD154 and stimulate the production of IgE by B lymphocytes through IL-25/IL-33 stimulation or TLR triggering.

Erratum: Inflammatory triggers associated with exacerbations of COPD orchestrate plasticity of group 2 innate lymphoid cells in the lungs.

Innate lymphoid cells (ILCs) are critical mediators of mucosal immunity, and group 1 ILCs (ILC1 cells) and group 3 ILCs (ILC3 cells) have been shown to be functionally plastic. Here we found that group 2 ILCs (ILC2 cells) also exhibited phenotypic plasticity in response to infectious or noxious agents, characterized by substantially lower expression of the transcription factor GATA-3 and a concomitant switch to being ILC1 cells that produced interferon-γ (IFN-γ). Interleukin 12 (IL-12) and IL-18 regulated this conversion, and during viral infection, ILC2 cells clustered within inflamed areas and acquired an ILC1-like phenotype. Mechanistically, these ILC1 cells augmented virus-induced inflammation in a manner dependent on the transcription factor T-bet. Notably, IL-12 converted human ILC2 cells into ILC1 cells, and the frequency of ILC1 cells in patients with chronic obstructive pulmonary disease (COPD) correlated with disease severity and susceptibility to exacerbations. Thus, functional plasticity of ILC2 cells exacerbates anti-viral immunity, which may have adverse consequences in respiratory diseases such as COPD.

Lipid mediators as regulators of human ILC2 function in allergic diseases

Group 2 innate lymphoid cells (ILC2) are specialized in type 2 immunity. ILC2 are activated early in immune responses and, despite their low abundance, are able to initiate and amplify allergic inflammation by orchestrating other type 2 immune cells. Based on recent discoveries, the spectrum of ILC2 regulating factors has been extended. It is now well established that not only epithelial cell-derived innate cytokines, but also bioactive lipids can regulate ILC2 activity and accumulation. Additionally, ILC2 appear to be susceptible to changes in the cytokine milieu and can acquire an ILC1-like phenotype due to a high degree of cellular plasticity. As ILC2 are fundamentally involved in the pathogenesis of type 2 diseases, they represent a promising therapeutic target for allergic airway and skin diseases.In this review we summarize the current knowledge about ILC2 biology in the allergy context, with a particular focus on the emerging role of lipid mediators in regulating ILC2 function.

Fast and efficient enrichment of functional ILC2 from human whole blood

Abstract Group 2 innate lymphoid cells (ILC2) are a functionally distinct subset of recently identified immune cells with important roles in type-2 immunopathologies such as allergies, asthma, helminth infections and other metabolic diseases. Studying these rare cells is challenging due to a lack of specific surface markers, and currently multicolor flow cytometric analysis and cell sorting are the only methods to characterize and isolate ILC2s. However, the scarcity of these cells makes flow cytometry time-consuming, expensive and often results in low purities and recoveries. Thus, better approaches for effective identification and isolation are essential to further understanding of ILC2 biology and function. We have developed a rapid and efficient method for enrichment of human ILC2 from whole blood. In brief, non-ILC2 cells in whole blood were crosslinked to red blood cells already present in the sample using RosetteSep™. The sample was then layered over Lymphoprep in a SepMate™ tube, spun at 1200 x g for 10 minutes (min), and the untouched, desired cells simply poured off. Cells were washed once and were then ready for subsequent analysis. Starting with only 0.01 – 0.07% in whole blood, ILC2 were enriched 350 ± 220 fold to 8.2 ± 6.8% in 35 min (means ± SD, n=17). Subsequent cell sorting from these pre-enriched samples was faster and yielded higher purity ILC2 than sorting from non-enriched controls (n=3, p<0.05 paired t test). Sorted ILC2, both pre-enriched and non-enriched controls, were cultured and stimulated, and secreted similar high levels of IL-13 as assessed by ELISA, indicating that these cells are functional. In summary, ILC2 pre-enrichment improves sorting efficiency, increases ILC2 purity, and maintains ILC2 functionality.

Immunomagnetic enrichment of human ILC2 cells from peripheral blood leukopak

Abstract Group 2 innate lymphoid cells (ILC2s) are essential for airway tissue repair, protection against helminth infection, metabolic homeostasis, and the development of allergic airway diseases. They are widely distributed throughout the human body in lung, intestine, palatine tonsils, skin and peripheral blood, but are extremely rare within a given tissue. In healthy individuals, ILC2s comprise 0.01–0.04% of leukocytes in the peripheral blood. Currently, flow cytometric cell (FACS) sorting is the only method to purify ILC2s, which is time-consuming due to their low frequency. We have adapted EasySep™ to pre-enrich ILC2s from peripheral blood leukopaks, and thereby shorten subsequent FACS analysis and sorting times. Non-ILC2 cells in an unprocessed leukopak were immunomagnetically labeled using a cocktail of antibody complexes and magnetic particles. The sample was then placed in a magnet for 10 minutes, the labeled cells were retained, and the unlabeled cells, containing the ILC2 population, were recovered. ILC2s were enriched from 5 x108unprocessed cells in 30 minutes. Enriched cells were counted and evaluated by FACS. ILC2s, defined as lineage negative (CD1a− CD3− CD11c− CD14− CD19− CD34− CD123− TCRαβ− TCRγδ− BDCA2− FcɛR1−), CRTH2+ CD161+CD127+, were enriched 268±167 fold, with 74± 34% recovery (means ± SD, n=7). EasySep™ pre-enrichment of ILC2s reduced subsequent FACS analysis and sorting time compared to non-enriched samples. Importantly, ILC2s enriched with EasySep™ were functional, as shown by production of the type 2 cytokine IL-13 upon stimulation with IL-33 and IL-2. Overall, EasySep™ is a simple and rapid method to pre-enrich ILC2s from leukopak for subsequent FACS analysis or sorting and functional analyses.