HTR2A agonists play a therapeutic role by restricting ILC2 activation in papain-induced lung inflammation

Group 2 innate lymphoid cells (ILC2s) are a category of heterogeneous cells that produce the cytokines IL-5 and IL-13, which mediate the type 2 immune response. However, specific drug targets on lung ILC2s have rarely been reported. Previous studies have shown that type 2 cytokines, such as IL-5 and IL-13, are related to depression. Here, we demonstrated the negative correlation between the depression-associated monoamine neurotransmitter serotonin and secretion of the cytokines IL-5 and IL-13 by ILC2s in individuals with depression. Interestingly, serotonin ameliorates papain-induced lung inflammation by suppressing ILC2 activation. Our data showed that the serotonin receptor HTR2A was highly expressed on ILC2s from mouse lungs and human PBMCs. Furthermore, an HTR2A selective agonist (DOI) impaired ILC2 activation and alleviated the type 2 immune response in vivo and in vitro. Mice with ILC2-specific depletion of HTR2A (Il5cre/+·Htr2aflox/flox mice) abolished the DOI-mediated inhibition of ILC2s in a papain-induced mouse model of inflammation. In conclusion, serotonin and DOI could restrict the type 2 lung immune response, indicating a potential treatment strategy for type 2 lung inflammation by targeting HTR2A on ST2+ ILC2s.

Crossing the valley of death: Toward translational research regarding ILC2

Group 2 innate lymphoid cells (ILC2s) are tissue-resident innate lymphoid cells that express the transcription factor GATA3 as a master regulator, which leads to the production of large amounts of type 2 cytokines, such as IL-5 and IL-13. ILC2s are activated by epithelial cell-derived cytokines, including IL-33 and IL-25, and play a key role in parasite expulsion, allergic responses, tissue repair, and metabolism. In the first five years after the discovery of ILC2s, research mainly focused on their function through cytokine receptors. However, in recent years, their regulatory mechanisms through not only cytokine receptors but also lipids, neuropeptides, and hormones have become a hot topic. For ILC2s that do not recognize foreign antigens, receptor expression of such endogenous factors is important, and the diverse expression patterns create the individuality of ILC2s in each organ. By considering the mechanisms of differentiation and regulation of ILC2s and their role in disease while taking into account spatio-temporal information, it is expected that new therapeutic strategies targeting ILC2s will be developed. Herein, we summarize the current understanding of ILC2s in lung homeostasis and pathology and provide valuable insights that will help to guide the future development of therapeutic methods for ILC2-mediated lung diseases.

Neuromedin U Induces Activation of Peripheral Group 2 Innate Lymphoid Cells through the ERK Pathway in Allergic Rhinitis Patients

INTRODUCTION

In allergic diseases, group 2 innate lymphoid cells (ILC2s) play critical roles. Neuromedin U (NMU), a highly conserved multifunctional neuropeptide, is secreted by cholinergic neurons and involved in asthma pathogenesis by amplifying lung inflammation driven by ILC2s. However, the precise effects of NMU on ILC2s in allergic rhinitis (AR) and related diseases remain unclear.

METHODS

A total of 15 patients with persistent AR and 8 healthy controls (HCs) were enrolled in the study. Visual analog scale (VAS) scores are used to assess the severity of clinical symptoms in AR patients. The percentages of ILC2s in peripheral blood mononuclear cells (PBMCs) were enumerated using flow cytometry. The soluble or intracellular cytokines (IL-5 and IL-13) in PBMCs or sorted ILC2s were assessed in response to various stimuli with IL-33, NMU, IL-33 combined with extracellular signal-related kinase (ERK) inhibitor or NMU combined with ERK inhibitor in the presence of IL-2.

RESULTS

We confirmed the proportion of circulating ILC2s was significantly higher in AR patients than in HCs. ILC2s levels were found to be positively related to VAS scores. We also discovered that the release of IL-5 and IL-13 in AR patients' PBMCs stimulated by NMU (p < 0.0001 and p < 0.0001, respectively) or IL-33 (p = 0.002; p = 0.044, respectively) was significantly higher than in HCs. In AR patients, NMU stimulated PBMCs or ILC2s to generate greater inflammatory factors IL-5 and IL-13 compared to IL-33. Furthermore, we observed that NMU-promoted ILC2s activation and proliferation functions were restricted when the ERK pathway was inhibited.

CONCLUSION

NMU effectively activated ILC2s in AR patients to produce Th2-type cytokines, and this activation can be prevented by ERK pathway inhibitors. Our findings shed new light on the neuro-immune mechanism of AR and offer new insights into its prevention and treatment.

[Role of type 2 innate lymphoid cells in helminth infections: a review]

Helminth infections may trigger host innate and adaptive immune responses. Group 2 innate lymphoid cells (ILC2) are an important factor involved in type 2 immune responses, and produce a large number of T helper 2 cell (Th2) cytokines following stimulation by interleukin (IL)-25, IL-33 and thymic stromal lymphopoietin (TSLP), which play a critical role in parasite clearance and tissue repair. Following helminth infections, autocrine factors, mast cells, enteric nervous system and Th2 cells have been recently found to be involved in regulation of ILC2. Unraveling the role of ILC2 in immune response against helminth infections is of great value for basic research and drug development. This review summarizes the research progress on ILC2 and its role in helminth infections.

TLR3-driven IFN-β antagonizes STAT5-activating cytokines and suppresses innate type 2 response in the lung

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) are involved in type 2 immune responses in mucosal organs and are associated with various allergic diseases in humans. Studies are needed to understand the molecules and pathways that control ILC2s.

OBJECTIVE

The aims of this study were to develop a mouse model that limits the innate type 2 immune response in the lung and to investigate the immunologic mechanisms involved in regulation of lung ILC2s.

METHODS

Naive BALB/c mice were administered various Toll-like receptor agonists and exposed intranasally to the fungal allergen Alternaria alternata. The mechanisms were investigated using gene knockout mice as well as cultures of lung cells and isolated lung ILC2s.

RESULTS

Polyinosinic-polycytidylic acid, or poly (I:C), effectively inhibited innate type 2 response to A alternata. Poly (I:C) promoted production of IFNα, -β, and -γ, and its inhibitory effects were dependent on the IFN-α/β receptor pathway. IFN-β was 100 times more potent than IFN-α at inhibiting type 2 cytokine production by lung ILC2s. Signal transducer and activator of transcription 5 (STAT5)-activating cytokines, including IL-2, IL-7, and thymic stromal lymphopoietin, but not IL-33, promoted survival and proliferation of lung ILC2s in vitro, while IFN-β blocked these effects. Expression of the transcription factor GATA3, which is critical for differentiation and maintenance of ILC2s, was inhibited by IFN-β.

CONCLUSIONS

IFN-β blocks the effects of STAT5-activating cytokines on lung ILC2s and inhibits their survival and effector functions. Administration of IFN-β may provide a new strategy to treat diseases involving ILC2s.

Anti-inflammatory roles of interleukin-35 in the pathogenesis of Japanese cedar pollinosis

Background

Interleukin (IL)-35 has been recently identified as an anti-inflammatory cytokine in allergic inflammation. However, its biological role in the pathogenesis of allergic rhinitis has not been fully elucidated.

Objective

The purpose of this study was to investigate the anti-inflammatory activity of IL-35 in the pathogenesis of allergic rhinitis in patients with Japanese cedar pollinosis (JCP).

Methods

Peripheral blood mononuclear cells were collected from healthy controls and JCP patients during the off-season for pollen. Peripheral blood mononuclear cells were incubated with Cry j 1, a major allergen of Japanese cedar pollen and production of IL-5, IL-13, and IL-35 were measured by enzyme-linked immunosorbent assay. Th2 (CD4⁺ST2⁺) cells and group 2 innate lymphoid cells were isolated from peripheral blood mononuclear cells of JCP patients, and the inhibitory effects of IL-35 on cell differentiation, proliferation and mRNA expression of IL-5, IL-13, and GATA3 were examined. B cells were also isolated and the effects of IL-35 on total IgE production were examined.

Results

Cry j 1-induced production of IL-5 and IL-13 was significantly increased in peripheral blood mononuclear cells from JCP patients, whereas Cry j 1-induced IL-35 production was significantly decreased compared with healthy controls. IL-35 significantly inhibited Th2 cell differentiation, group 2 innate lymphoid cell proliferation, and mRNA expression of IL-5, IL-13, and GATA3 in Th2 cells and group 2 innate lymphoid cells. IL-35 also inhibited IgE production from B cells.

Conclusion

IL-35 is an important anti-inflammatory cytokine in JCP, and its biological roles include the downregulation of Th2 cells and group 2 innate lymphoid cells, and the inhibition of IgE production from B cells. These findings demonstrate that IL-35 may have the potential to exert anti-allergic effects for the treatment of allergic rhinitis.

Sex differences in group 2 innate lymphoid cell-dominant allergic airway inflammation

There were gender differences in the prevalence and severity of allergic diseases. Group 2 innate lymphoid cells (ILC2s) were recently reported to play a critical role in allergic diseases. We investigated the sex-dependent differences in ILC2-dominant allergic airway inflammation model using T\B cell-deficient mice, and determined the gender differences of ILC2 levels in patients with asthma and allergic rhinitis. Female mice exhibited higher levels of inflammatory infiltration and large production of IL-5 and IL-13, especially for ILC2 levels compared to male mice with the induction of IL-33. However, no significant differences were found for the levels of circulating ILC2s between the genders of patients. The treatment of testosterone significantly decreased the intracellular type 2 cytokines in ILC2s and the proliferation of pure ILC2s in response to epithelial cytokines. Our study suggested the sex differences and the involvement of androgen on ILC2s in allergic diseases.

Salidroside suppresses group 2 innate lymphoid cell-mediated allergic airway inflammation by targeting IL-33/ST2 axis

Salidroside, an active component extracted from Rhodiola rosea, has been reported to inhibit allergic asthma. However, its mechanism has not been fully elucidated. Group 2 innate lymphoid cells (ILC2s) accumulate in the lung and cooperate with other cells to drive type 2 inflammation stimulated by inhaled allergens. The study aims to explore the suppressive effect of salidroside on ILC2s and IL-33/IL-33R (ST2) axis in allergic airway inflammation. The ovalbumin (OVA)-sensitized/challenged mice were established. Airway eosinophil recruitment, increased total IgE in the serum and type 2 cytokines IL-4, IL-5, and IL-13 in the bronchoalveolar lavage fluids and lung tissues were identified in the OVA-induced mice model, all of which were inhibited by pretreatment with different doses of salidroside. Moreover, salidroside suppressed lung total ILC2 and ST2-expressing ILC2 accumulation, lung IL-33 and ST2 expressions in mice. In vitro, OVA could induce IL-33 expression in BEAS-2B cells, which was also effectively inhibited by salidroside. This study firstly reveals salidroside as a potential therapeutic drug for allergic asthma by inhibiting ILC2-mediated airway inflammation via targeting IL-33/ST2 axis.

Activations of group 2 innate lymphoid cells depend on endotypes of chronic rhinosinusitis

OBJECTIVE

Chronic rhinosinusitis (CRS) is a complicated disease with several variants caused by different cellular and molecular mechanisms. The characterization of this heterogeneity supports the definition that the disease consists of many endotypes, such as eosinophilic and neutrophilic CRS, and so on. This study aimed to explore group 2 innate lymphoid cells (ILC2s) in neutrophilic CRS without nasal polyps (CRSsNP) and with nasal polyps (CRSwNP), and evaluate ILC2s across characteristics of the disease.

METHODS

Nasal biopsy samples were obtained from normal subjects or subjects with CRSsNP or CRSwNP during surgery. ILC2s were sorted and purified as CD45⁺Lin^-CD127⁺CD4^-CD8^-CRTH2⁺CD161⁺ cells through flow cytometry, and were compared among three groups of subjects. Then, these samples were cultured in vitro, and inflammatory factors were assessed in tissue cultures. After that, human recombinant (rm) interleukin (IL)-33 or IL-17 were administered into the cultures, and we again examined relevant inflammatory substances.

RESULTS

ILC2s were upregulated in neutrophilic CRSsNP and CRSwNP patients, and there were no statistical differences between them. Eosinophil cation protein (ECP), myeloperoxidase (MPO), IL-25, IL-33, IL-5, IL-13, interferon (IFN)-γ and IL-17 were increased in the cultures, however, only concentrations of MPO, IFN-γ and IL-17 were enhanced in CRSwNP tissues compared to CRSsNP ones. After administration of rmIL-33, ECP, IL-5 and IL-13 were all increased in tissues from CRSsNP and CRSwNP patients, however, there were no significant differences between them. Finally, we evaluated concentrations of several above inflammatory factors after the treatment of rmIL-17, and found that MPO and IFN-γ were enhanced in these two phenotypes of patients, and were elevated significantly in CRSwNP tissue cultures.

CONCLUSION

These findings show that ILC2s might be inactivated in neutrophilic CRSsNP and CRSwNP based on this pilot study.

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

BACKGROUND

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.

OBJECTIVE

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.

METHODS

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 in vivo blocking of these integrins before airway exposure to Alternaria in mice.

RESULTS

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. In vivo blocking of β₂ integrins (CD18) significantly reduced ILC2 numbers in the lungs but did not alter ILC2 proliferation, apoptosis, and function. In contrast, in vivo blocking of β₁ integrins or α₄ integrins did not affect lung ILC2 numbers.

CONCLUSION

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

Background

Group 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.

Objectives

We sought to determine the role of cysLTs and their relationship with other ILC2 stimulators in the activation of human ILC2s.

Methods

For 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.

Results

Human 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.

Conclusion

CysLTs, particularly LTE₄, are important contributors to the triggering of human ILC2s in inflammatory responses, particularly when combined with other ILC2 activators.

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

BACKGROUND

Protection against helminths consists of adaptive responses by T_H2 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.

OBJECTIVE

We sought to characterize human circulating ILC2s and compare their functional profile with that of autologous T_H2 cells.

METHODS

Circulating ILC2s and T_H2 cells were isolated by means of fluorescence-activated cell sorting and magnetic cell sorting and expanded in vitro. 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 B cells. Cytokines and transcription factor gene methylation were assessed.

RESULTS

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 B cells. Finally, circulating ILC2s from atopic patients were not different in numbers and frequency but expressed higher IL-4 levels than those from nonatopic subjects.

CONCLUSION

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.

ICOS promotes group 2 innate lymphoid cell activation in lungs

Group 2 innate lymphoid cells (ILC2s) are newly identified, potent producers of type 2 cytokines, such as IL-5 and IL-13, and contribute to the development of allergic lung inflammation induced by cysteine proteases. Although it has been shown that inducible costimulator (ICOS), a costimulatory molecule, is expressed on ILC2s, the role of ICOS in ILC2 responses is largely unknown. In the present study, we investigated whether the interaction of ICOS with its ligand B7-related protein-1 (B7RP-1) can promote ILC2 activation. Cytokine production in ILC2s purified from mouse lungs was significantly increased by coculture with B7RP-1-transfected cells, and increased cytokine production was inhibited by monoclonal antibody-mediated blocking of the ICOS/B7RP-1 interaction. ILC2 expansion and eosinophil influx induced by papain, a cysteine protease antigen, in mouse lungs were significantly abrogated by blocking the ICOS/B7RP-1 interaction. Dendritic cells (DCs) in the lungs expressed B7RP-1 and the number of DCs markedly increased with papain administration. B7RP-1 expression on lung DCs was reduced after papain administration. This downregulation of B7RP-1 expression may be an indication of ICOS/B7RP-1 binding. These results indicate that ILC2s might interact with B7RP-1-expressing DCs in allergic inflammatory lung, and ICOS signaling can positively regulate the protease allergen-induced ILC2 activation followed by eosinophil infiltration into the lungs.

Prostaglandin D2 activates group 2 innate lymphoid cells through chemoattractant receptor-homologous molecule expressed on TH2 cells

Background

Activation of the group 2 innate lymphoid cell (ILC2) population leads to production of the classical type 2 cytokines, thus promoting type 2 immunity. Chemoattractant receptor-homologous molecule expressed on T_H2 cells (CRTH2), a receptor for prostaglandin D₂ (PGD₂), is expressed by human ILC2s. However, the function of CRTH2 in these cells is unclear.

Objectives

We sought to determine the role of PGD₂ and CRTH2 in human ILC2s and compare it with that of the established ILC2 activators IL-25 and IL-33.

Methods

The effects of PGD₂, IL-25, and IL-33 on the cell migration, cytokine production, gene regulation, and receptor expression of ILC2s were measured with chemotaxis, ELISA, Luminex, flow cytometry, quantitative RT-PCR, and QuantiGene assays. The effects of PGD₂ under physiologic conditions were evaluated by using the supernatant from activated mast cells.

Results

PGD₂ binding to CRTH2 induced ILC2 migration and production of type 2 cytokines and many other cytokines. ILC2 activation through CRTH2 also upregulated the expression of IL-33 and IL-25 receptor subunits (ST2 and IL-17RA). The effects of PGD₂ on ILC2s could be mimicked by the supernatant from activated human mast cells and inhibited by a CRTH2 antagonist.

Conclusions

PGD₂ is an important and potent activator of ILC2s through CRTH2 mediating strong proallergic inflammatory responses. Through IgE-mediated mast cell degranulation, these innate cells can also contribute to adaptive type 2 immunity; thus CRTH2 bridges the innate and adaptive pathways in human ILC2s.