Quantitative live-cell imaging of secretion activity reveals dynamic immune responses.

Quantification of cytokine secretion has facilitated advances in the field of immunology, yet the dynamic and varied secretion profiles of individual cells, particularly those obtained from limited human samples, remain obscure. Herein, we introduce a technology for quantitative live-cell imaging of secretion activity (qLCI-S) that enables high-throughput and dual-color monitoring of secretion activity at the single-cell level over several days, followed by transcriptome analysis of individual cells based on their phenotype. The efficacy of qLCI-S was demonstrated by visualizing the characteristic temporal pattern of cytokine secretion of group 2 innate lymphoid cells, which constitute less than 0.01% of human peripheral blood mononuclear cells, and by revealing minor subpopulations with enhanced cytokine production. The underlying mechanism of this feature was linked to the gene expression of stimuli receptors. This technology paves the way for exploring gene expression signatures linked to the spatiotemporal dynamic nature of various secretory functions.

Activation of ILC2s through constitutive IFNγ signaling reduction leads to spontaneous pulmonary fibrosis.

Pulmonary fibrosis (PF), a condition characterized by inflammation and collagen deposition in the alveolar interstitium, causes dyspnea and fatal outcomes. Although the bleomycin-induced PF mouse model has improved our understanding of exogenous factor-induced fibrosis, the mechanism governing endogenous factor-induced fibrosis remains unknown. Here, we find that Ifngr1-/-Rag2-/- mice, which lack the critical suppression factor for group 2 innate lymphoid cells (ILC2), develop PF spontaneously. The onset phase of fibrosis includes ILC2 subpopulations with a high Il1rl1 (IL-33 receptor) expression, and fibrosis does not develop in ILC-deficient or IL-33-deficient mice. Although ILC2s are normally localized near bronchioles and blood vessels, ILC2s are increased in fibrotic areas along with IL-33 positive fibroblasts during fibrosis. Co-culture analysis shows that activated-ILC2s directly induce collagen production from fibroblasts. Furthermore, increased IL1RL1 and decreased IFNGR1 expressions are confirmed in ILC2s from individuals with idiopathic PF, highlighting the applicability of Ifngr1-/-Rag2-/- mice as a mouse model for fibrosis research.

Time-dependent cell-state selection identifies transiently expressed genes regulating ILC2 activation.

The decision of whether cells are activated or not is controlled through dynamic intracellular molecular networks. However, the low population of cells during the transition state of activation renders the analysis of the transcriptome of this state technically challenging. To address this issue, we have developed the Time-Dependent Cell-State Selection (TDCSS) technique, which employs live-cell imaging of secretion activity to detect an index of the transition state, followed by the simultaneous recovery of indexed cells for subsequent transcriptome analysis. In this study, we used the TDCSS technique to investigate the transition state of group 2 innate lymphoid cells (ILC2s) activation, which is indexed by the onset of interleukin (IL)-13 secretion. The TDCSS approach allowed us to identify time-dependent genes, including transiently induced genes (TIGs). Our findings of IL4 and MIR155HG as TIGs have shown a regulatory function in ILC2s activation.

RIPK1 blocks T cell senescence mediated by RIPK3 and caspase-8.

Receptor-interacting protein kinase 1 (RIPK1) regulates cell death and inflammation. Here, we show that T cell-specific RIPK1 deficiency in mice leads to the premature senescence of T cells and induces various age-related diseases, resulting in premature death. RIPK1 deficiency causes higher basal activation of mTORC1 (mechanistic target of rapamycin complex 1) that drives enhanced cytokine production, induction of senescence-related genes, and increased activation of caspase-3/7, which are restored by inhibition of mTORC1. Critically, normal aged T cells exhibit similar phenotypes and responses. Mechanistically, a combined deficiency of RIPK3 and caspase-8 inhibition restores the impaired proliferative responses; the elevated activation of Akt, mTORC1, extracellular signal-regulated kinase, and caspase-3/7; and the increased expression of senescence-related genes in RIPK1-deficient CD4 T cells. Last, we revealed that the senescent phenotype of RIPK1-deficient and aged CD4 T cells is restored in the normal tissue environment. Thus, we have clarified the function of RIPK3 and caspase-8 in inducing CD4 T cell senescence, which is modulated by environmental signals.

Semaphorin 6D-expressing mesenchymal cells regulate IL-10 production by ILC2s in the lung.

Group 2 innate lymphoid cells (ILC2s) have been implicated in both physiologic tissue remodeling and allergic pathology, yet the niche signaling required for ILC2 properties is poorly understood. Here, we show that an axonal guidance cue semaphorin 6D (Sema6D) plays critical roles in the maintenance of IL-10-producing ILC2s. Sema6d -/- mice exhibit a severe steady-state reduction in ILC2s in peripheral sites such as the lung, visceral adipose tissue, and mesentery. Interestingly, loss of Sema6D results in suppressed alarmin-driven type 2 cytokine production but increased IL-10 production by lung ILC2s both in vitro and in vivo. Consequently, Sema6d -/- mice are resistant to the development of allergic lung inflammation. We further found that lung mesenchymal cells highly express Sema6D, and that niche-derived Sema6D is responsible for these phenotypes through plexin A1. Collectively, these findings suggest that niche-derived Sema6D is implicated in physiological and pathological characteristics of ILC2s.

ILCs and Allergy.

The recent discovery of new innate lymphoid cells (ILCs) has revolutionized the field of allergies. Since most allergic diseases induce a type 2 immune response, Th2 cells, which produce IL-4, IL-5, and IL-13 in an antigen-dependent manner, in addition to basophils and mast cells which are activated by antigen-specific IgE, are thought to play a major role in the pathogenesis. However, since group 2 innate lymphoid cells (ILC2s) produce type 2 cytokines (i.e., IL-2, IL-4, IL-5, IL-6, IL-9, IL-13, GM-CSF, and amphiregulin) in response to various cytokines, including IL-33 in the surrounding environment, the possibility has emerged that there are two types of allergies: allergies induced in an antigen-dependent manner by Th2 cells and allergies induced in an antigen-independent manner by ILC2s. In order to make an impact on the increasing incidence of allergic diseases in the world, it is essential to research and develop new treatments that focus not only on Th2 cells but also on ILC2s. In this chapter, the role of ILCs in allergic diseases, which has rapidly changed with the discovery of ILCs, is discussed, focusing mainly on ILC2s.

Posttranscriptional regulation of ILC2 homeostatic function via tristetraprolin.

Group 2 innate lymphoid cells (ILC2s) are unique in their ability to produce low levels of type 2 cytokines at steady state, and their production capacity is dramatically increased upon stimulation with IL-33. However, it is unknown how constitutive cytokine production is regulated in the steady state. Here, we found that tristetraprolin (TTP/Zfp36), an RNA-binding protein that induces mRNA degradation, was highly expressed in naive ILC2s and was downregulated following IL-33 stimulation. In ILC2s from Zfp36-/- mice, constitutive IL-5 production was elevated owing to the stabilization of its mRNA and resulted in an increased number of eosinophils in the intestine. Luciferase assay demonstrated that TTP directly regulates Il5 mRNA stability, and overexpression of TTP markedly suppressed IL-5 production by ILC2s, even under IL-33 stimulation. Collectively, TTP-mediated posttranscriptional regulation acts as a deterrent of excessive cytokine production in steady-state ILC2s to maintain body homeostasis, and downregulation of TTP may contribute to massive cytokine production under IL-33 stimulation.

The discovery of group 2 innate lymphoid cells has changed the concept of type 2 immune diseases.

Group 2 innate lymphoid cells (ILC2s), discovered in 2010, have been recognized as immune cells with unique functions and their involvement in various diseases has been clarified. Before 2010, the antigen-specific response was a primary focus of immunology research, and immune responses were considered almost equivalent to biological responses to foreign antigens. However, with the emergence of ILC2s, the importance of 'antigen-independent responses' was confirmed, and this concept has permeated basic and clinical research as well as drug development. When ILC2s were discovered, their function in the acute phase of diseases garnered attention because of their rapid and potent type 2 immune response. However, several studies have revealed that the main role of ILC2s is more closely related to the chronicity of diseases, such as allergy and fibrosis, than to the induction of diseases. In this review, we discuss how ILC2 research has affected the concept of 'Taishitsu', a Japanese term describing the overall nature of an individual as determined by the interaction of genetic and acquired predisposition.

Group 2 innate lymphoid cells in bone marrow regulate osteoclastogenesis in a reciprocal manner via RANKL, GM-CSF and IL-13.

Group 2 innate lymphoid cells (ILC2s) are tissue-resident cells that play different roles in different organs by sensing surrounding environmental factors. Initially, it was thought that ILC2s in bone marrow (BM) are progenitors for systemic ILC2s, which migrate to other organs and acquire effector functions. However, accumulating evidence that ILC2s differentiate in peripheral tissues suggests that BM ILC2s may play a specific role in the BM as a unique effector per se. Here, we demonstrate that BM ILC2s highly express the receptor activator of nuclear factor κB ligand (RANKL), a robust cytokine for osteoclast differentiation and activation, and RANKL expression on ILC2s is up-regulated by interleukin (IL)-2, IL-7 and all-trans retinoic acid (ATRA). BM ILC2s co-cultured with BM-derived monocyte/macrophage lineage cells (BMMs) in the presence of IL-7 induce the differentiation of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts in a RANKL-dependent manner. In contrast, BM ILC2s stimulated with IL-33 down-regulate RANKL expression and convert BMMs differentiation into M2 macrophage-like cells rather than osteoclasts by granulocyte macrophage colony-stimulating factor (GM-CSF) and IL-13 production. Intravital imaging using two-photon microscopy revealed that a depletion of ILC2s prominently impaired in vivo osteoclast activity in an IL-7 plus ATRA-induced bone loss mouse model. These results suggest that ILC2s regulate osteoclast activation and contribute to bone homeostasis in both steady state and IL-33-induced inflammation.

Long-acting muscarinic antagonist regulates group 2 innate lymphoid cell-dependent airway eosinophilic inflammation.

BACKGROUND: Tiotropium bromide, a long-acting muscarinic antagonist, reduces the frequency of exacerbation in patients with moderate to severe asthma, but its underlying mechanism is not clear. Asthma exacerbations are associated with exposure to external stimuli, and group 2 innate lymphoid cells (ILC2s) are considered to be involved in the pathophysiology of asthma exacerbation. We investigated whether tiotropium modulates airway inflammation through ILC2 functions. METHODS: Mice were administered papain intranasally to induce innate-type airway inflammation with or without tiotropium pretreatment, and bronchoalveolar lavage fluids (BALF) and lung tissues were collected. Lung-derived ILC2s and bone marrow-derived basophils were stimulated in vitro with IL-33 in the presence or absence of tiotropium. Muscarinic M3 receptor (M3R) expression on immune cells was assessed by RNA sequence. RESULTS: Papain induced airway eosinophilic inflammation, and tiotropium reduced the numbers of eosinophils in BALF. The concentrations of IL-4, IL-5, and IL-13, and the numbers of ILC2s in BALF were also reduced by tiotropium treatment. However, tiotropium did not affect IL-33-induced IL-5 and IL-13 production from ILC2s, suggesting that tiotropium regulates ILC2s indirectly. Gene-expression analysis showed that basophils predominantly expressed M3R mRNA among murine immune cells. Tiotropium reduced IL-4 production from basophils derived from mouse bone marrow and human basophils after stimulation with IL-33. CONCLUSIONS: These findings suggest that tiotropium attenuates ILC2-dependent airway inflammation by suppressing IL-4 production from basophils and, subsequently, regulating ILC2 activation. The inhibitory effects of long-acting muscarinic antagonists on the innate response may contribute to reducing asthma exacerbation.

Group 2 innate lymphoid cells support hematopoietic recovery under stress conditions.

The cell-cycle status of hematopoietic stem and progenitor cells (HSPCs) becomes activated following chemotherapy-induced stress, promoting bone marrow (BM) regeneration; however, the underlying molecular mechanism remains elusive. Here we show that BM-resident group 2 innate lymphoid cells (ILC2s) support the recovery of HSPCs from 5-fluorouracil (5-FU)-induced stress by secreting granulocyte-macrophage colony-stimulating factor (GM-CSF). Mechanistically, IL-33 released from chemo-sensitive B cell progenitors activates MyD88-mediated secretion of GM-CSF in ILC2, suggesting the existence of a B cell-ILC2 axis for maintaining hematopoietic homeostasis. GM-CSF knockout mice treated with 5-FU showed severe loss of myeloid lineage cells, causing lethality, which was rescued by transferring BM ILC2s from wild-type mice. Further, the adoptive transfer of ILC2s to 5-FU-treated mice accelerates hematopoietic recovery, while the reduction of ILC2s results in the opposite effect. Thus, ILC2s may function by "sensing" the damaged BM spaces and subsequently support hematopoietic recovery under stress conditions.

Profibrotic function of pulmonary group 2 innate lymphoid cells is controlled by regnase-1.

Regnase-1 is an RNase critical for post-transcriptional control of pulmonary immune homeostasis in mice by degrading immune-related mRNAs. However, little is known about the cell types Regnase-1 controls in the lung, and its relevance to human pulmonary diseases.Regnase-1-dependent changes in lung immune cell types were examined by a competitive bone marrow transfer mouse model, and group 2 innate lymphoid cells (ILC2s) were identified. Then the associations between Regnase-1 in ILC2s and human diseases were investigated by transcriptome analysis and a bleomycin-induced pulmonary fibrosis mouse model. The clinical significance of Regnase-1 in ILC2s was further assessed using patient-derived cells.Regnase-1-deficiency resulted in the spontaneous proliferation and activation of ILC2s in the lung. Intriguingly, genes associated with pulmonary fibrosis were highly upregulated in Regnase-1-deficient ILC2s compared with wild-type, and supplementation of Regnase-1-deficient ILC2s augmented bleomycin-induced pulmonary fibrosis in mice. Regnase-1 suppresses mRNAs encoding transcription factors Gata3 and Egr1, which are potent to regulate fibrosis-associated genes. Clinically, Regnase-1 protein levels in ILC2 negatively correlated with the ILC2 population in bronchoalveolar lavage fluid. Furthermore, idiopathic pulmonary fibrosis (IPF) patients with ILC2s >1500 cells·mL-1 peripheral blood exhibited poorer prognosis than patients with lower numbers, implying the contribution of Regnase-1 in ILC2s for the progression of IPF.Collectively, Regnase-1 was identified as a critical post-transcriptional regulator of the profibrotic function of ILC2s both in mouse and human, suggesting that Regnase-1 may be a novel therapeutic target for IPF.

Bacteria-Induced Group 2 Innate Lymphoid Cells in the Stomach Provide Immune Protection through Induction of IgA.

The intestinal microbiota shapes and directs immune development locally and systemically, but little is known about whether commensal microbes in the stomach can impact their immunological microenvironment. Here, we report that group 2 innate lymphoid cells (ILC2s) were the predominant ILC subset in the stomach and show that their homeostasis and effector functions were regulated by local commensal communities. Microbes elicited interleukin-7 (IL-7) and IL-33 production in the stomach, which in turn triggered the propagation and activation of ILC2. Stomach ILC2s were also rapidly induced following infection with Helicobacter pylori. ILC2-derived IL-5 resulted in the production of IgA, which coated stomach bacteria in both specific pathogen-free (SPF) and H. pylori-infected mice. Our study thus identifies ILC2-dependent IgA response that is regulated by the commensal microbiota, which is implicated in stomach protection by eliminating IgA-coated bacteria including pathogenic H. pylori.

Effects of BMP7 produced by group 2 innate lymphoid cells on adipogenesis.

Group 2 innate lymphoid cells (ILC2s) are type 2 cytokine-producing cells that have important roles in helminth infection and allergic inflammation. ILC2s are tissue-resident cells, and their phenotypes and roles are regulated by tissue-specific environmental factors. While the role of ILC2s in the lung, intestine and bone marrow has been elucidated in many studies, their role in adipose tissues is still unclear. Here, we report on the role of ILC2-derived bone morphogenetic protein 7 (BMP7) in adipocyte differentiation and lipid accumulation. Co-culture of fat-derived ILC2s with pluripotent mesenchymal C3H10T1/2 cells and committed white preadipocyte 3T3-L1 cells resulted in their differentiation to adipocytes and induced lipid accumulation. Co-culture experiments using BMP7-deficient ILC2s revealed that BMP7, produced by ILC2s, induces differentiation into brown adipocytes. Our results demonstrate that BMP7, produced by ILC2s, affects adipocyte differentiation, particularly in brown adipocytes.

Tumor-Derived Lactic Acid Contributes to the Paucity of Intratumoral ILC2s.

Group 2 innate lymphoid cells (ILC2s) are abundant in non-lymphoid tissues and increase following infectious and inflammatory insults. In solid tumors, however, ILC2s constitute a relatively small proportion of immune cells. Here, we show, using melanoma as a model, that while the IL-33/IL C2/eosinophil axis suppresses tumor growth, tumor-derived lactate attenuates the function and survival of ILC2s. Melanomas with reduced lactate production (LDHAlow) are growth delayed and typified by an increased number of ILC2s compared with control tumors. Upon IL-33 stimulation, ILC2s accompanied by eosinophils more effectively restrain the growth of LDHAlow tumors than control melanomas. Furthermore, database analysis reveals a negative correlation between the expression of LDHA and markers associated with ILC2s and the association of high expression of IL33 and an eosinophil marker SIGLEC8 with better overall survival in human cutaneous melanoma patients. This work demonstrates that the balance between the IL-33/ILC2/eosinophil axis and lactate production by tumor cells regulates melanoma growth.

A Series of Compounds Bearing a Dipyrido-Pyrimidine Scaffold Acting as Novel Human and Insect Pest Chitinase Inhibitors.

Chitinases not only play vital roles in the human innate immune system but are also essential for the development of pathogenic fungi and pests. Chitinase inhibitors are efficient tools to investigate the elusive role of human chitinases and to control pathogens and pests. Via hierarchical virtual screening, we have discovered a series of chitinase inhibitors with a novel scaffold that have high inhibitory activities and selectivities against human and insect chitinases. The most potent human chitotriosidase inhibitor, compound 40, exhibited a Ki of 49 nM, and the most potent inhibitor of the insect pest chitinase OfChi-h, compound 53, exhibited a Ki of 9 nM. The binding of these two most potent inhibitors was confirmed by X-ray crystallography. In a murine model of bleomycin-induced pulmonary fibrosis, compound 40 was found to suppress the chitotriosidase activity by 60%, leading to a significant increase in inflammatory cells and suggesting that chitotriosidase played a protective role.

Cell type-specific actions of Bcl11b in early T-lineage and group 2 innate lymphoid cells.

The zinc finger transcription factor, Bcl11b, is expressed in T cells and group 2 innate lymphoid cells (ILC2s) among hematopoietic cells. In early T-lineage cells, Bcl11b directly binds and represses the gene encoding the E protein antagonist, Id2, preventing pro-T cells from adopting innate-like fates. In contrast, ILC2s co-express both Bcl11b and Id2. To address this contradiction, we have directly compared Bcl11b action mechanisms in pro-T cells and ILC2s. We found that Bcl11b binding to regions across the genome shows distinct cell type-specific motif preferences. Bcl11b occupies functionally different sites in lineage-specific patterns and controls totally different sets of target genes in these cell types. In addition, Bcl11b bears cell type-specific post-translational modifications and organizes different cell type-specific protein complexes. However, both cell types use the same distal enhancer region to control timing of Bcl11b activation. Therefore, although pro-T cells and ILC2s both need Bcl11b for optimal development and function, Bcl11b works substantially differently in these two cell types.

The Neuropeptide CGRP Induces Bipolar Syndrome in Group 2 Innate Lymphoid Cells.

In this issue of Immunity, Nagashima et al., Wallrapp et al., and Xu et al. demonstrate that the neuropeptide calcitonin gene-related peptide (CGRP) fine tunes type 2 innate immune response via suppressing group 2 innate lymphoid cells (ILC2s).

Three-step transcriptional priming that drives the commitment of multipotent progenitors toward B cells.

Stem cell fate is orchestrated by core transcription factors (TFs) and epigenetic modifications. Although regulatory genes that control cell type specification are identified, the transcriptional circuit and the cross-talk among regulatory factors during cell fate decisions remain poorly understood. To identify the "time-lapse" TF networks during B-lineage commitment, we used multipotent progenitors harboring a tamoxifen-inducible form of Id3, an in vitro system in which virtually all cells became B cells within 6 d by simply withdrawing 4-hydroxytamoxifen (4-OHT). Transcriptome and epigenome analysis at multiple time points revealed that ∼10%-30% of differentially expressed genes were virtually controlled by the core TFs, including E2A, EBF1, and PAX5. Strikingly, we found unexpected transcriptional priming before the onset of the key TF program. Inhibition of the immediate early genes such as Nr4a2, Klf4, and Egr1 severely impaired the generation of B cells. Integration of multiple data sets, including transcriptome, protein interactome, and epigenome profiles, identified three representative transcriptional circuits. Single-cell RNA sequencing (RNA-seq) analysis of lymphoid progenitors in bone marrow strongly supported the three-step TF network model during specification of multipotent progenitors toward B-cell lineage in vivo. Thus, our findings will provide a blueprint for studying the normal and neoplastic development of B lymphocytes.