Group 2 innate lymphoid cells in disease

Overview of the development, characterization, and function of human types 1, 2, and 3 innate lymphoid cells

Hematopoiesis is characterized by the differentiation and maturation of multipotent stem cells into hematopoietic cells. Common lymphoid progenitor cells differentiate into B and T lymphocytes; natural killer cells can also originate from common lymphoid progenitors. In recent years, a cellular subtype of lymphocytes, called innate lymphocytes, has been described. Innate lymphoid cells (ILCs) play an important effector and regulatory role in innate immunity, and similar to natural killer cells, depend on the γc and Id2 chains for their development. These cells are divided into three main subtypes according to their characteristics, namely type 1 innate lymphocytes (ILC1), type 2 (ILC2), and type 3 (ILC3); the production of cytokines and transcription factors is essential for this classification. Furthermore, these cells have high plasticity, which allows them to change their phenotype in response to the environment. ILCs have recently been characterized further and emerged as a family of effectors and regulators of innate immune responses. Uncontrolled activation of these cells can contribute to inflammatory, autoimmune diseases and cancer. The current review aimed to describe their main characteristics, immunophenotypes, and plasticity, and based on the existing literature, suggested a phenotypic analysis to differentiate innate lymphocytes from natural killer cells, and across the subsets.

Blocking group 2 innate lymphoid cell activation and macrophage M2 polarization: potential therapeutic mechanisms in ovalbumin-induced allergic asthma by calycosin

BACKGROUND

Calycosin, a flavonoid compound extracted from Astragalus membranaceus, has shown anti-asthma benefits in house dust mite-induced asthma. Recent studies have suggested that innate-type cells, including group 2 innate lymphoid cells (ILC2s) and macrophages, serve as incentives for type 2 immunity and targets for drug development in asthma. This work focuses on the effects of calycosin on the dysregulated ILC2s and macrophages in allergic asthma.

METHODS

In vivo, the asthmatic mouse model was established with ovalbumin (OVA) sensitization and challenge, and calycosin was intraperitoneally administered at doses of 20 and 40 mg/kg. In vivo, mouse primary ILC2s were stimulated with interleukin (IL)-33 and mouse RAW264.7 macrophages were stimulated with IL-4 and IL-13 to establish the cell models. Cells were treated with calycosin at doses of 5 and 10 µM.

RESULTS

In vivo, we observed significantly reduced numbers of eosinophils, neutrophils, monocyte macrophages and lymphocytes in the bronchoalveolar lavage fluid (BALF) of OVA-exposed mice with 40 mg/kg calycosin. Histopathological assessment showed that calycosin inhibited the airway inflammation and remodeling caused by OVA. Calycosin markedly decreased the up-regulated IL-4, IL-5, IL-13, IL-33, and suppression tumorigenicity 2 (ST2) induced by OVA in BALF and/or lung tissues of asthmatic mice. Calycosin repressed the augment of arginase 1 (ARG1), IL-10, chitinase-like 3 (YM1) and mannose receptor C-type 1 (MRC1) levels in the lung tissues of asthmatic mice. In vivo, calycosin inhibited the IL-33-induced activation as well as the increase of IL-4, IL-5, IL-13 and ST2 in ILC2s. Calycosin also repressed the increase of ARG1, IL-10, YM1 and MRC1 induced by IL-4 and IL-13 in RAW264.7 macrophages. In addition, we found that these changes were more significant in 40 mg/kg calycosin treatment than 20 mg/kg calycosin.

CONCLUSIONS

Collectively, this study showed that calycosin might attenuate OVA-induced airway inflammation and remodeling in asthmatic mice via preventing ILC2 activation and macrophage M2 polarization. Our study might contribute to further study of asthmatic therapy.

JAK3 inhibitor suppresses multipotent ILC2s and attenuates steroid-resistant asthma

Steroids are the standard treatment for allergic airway inflammation in asthma, but steroid-refractory asthma poses a challenge. Group 2 innate lymphoid cells (ILC2s), such as T helper 2 (TH2) cells, produce key asthma-related type 2 cytokines. Recent insights from mouse and human studies indicate a potential connection between ILC2s and steroid-resistant asthma. Here, we highlight that lung ILC2s, rather than TH2 cells, can develop steroid resistance, allowing them to persist and maintain their disease-driving activity even during steroid treatment. The emergence of multipotent IL-5+IL-13+IL-17A+ ILC2s is associated with steroid-resistant ILC2s. The Janus kinase 3 (JAK3)/signal transducer and activator of transcription (STAT) 3, 5, and 6 pathways contribute to the acquisition of steroid-resistant ILC2s. The JAK3 inhibitor reduces ILC2 survival, proliferation, and cytokine production in vitro and ameliorates ILC2-driven Alternaria-induced asthma. Furthermore, combining a JAK3 inhibitor with steroids results in the inhibition of steroid-resistant asthma. These findings suggest a potential therapeutic approach for addressing this challenging condition in chronic asthma.

Nr4a1 marks a distinctive ILC2 activation subset in the mouse inflammatory lung

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) are critical sources of type 2 cytokines and represent one of the major tissue-resident lymphoid cells in the mouse lung. However, the molecular mechanisms underlying ILC2 activation under challenges are not fully understood.

RESULTS

Here, using single-cell transcriptomics, genetic reporters, and gene knockouts, we identify four ILC2 subsets, including two non-activation subsets and two activation subsets, in the mouse acute inflammatory lung. Of note, a distinct activation subset, marked by the transcription factor Nr4a1, paradoxically expresses both tissue-resident memory T cell (Trm), and effector/central memory T cell (Tem/Tcm) signature genes, as well as higher scores of proliferation, activation, and wound healing, all driven by its particular regulons. Furthermore, we demonstrate that the Nr4a1+ILC2s are restrained from activating by the programmed cell death protein-1 (PD-1), which negatively modulates their activation-related regulons. PD-1 deficiency places the non-activation ILC2s in a state that is prone to activation, resulting in Nr4a1+ILC2 differentiation through different activation trajectories. Loss of PD-1 also leads to the expansion of Nr4a1+ILC2s by the increase of their proliferation ability.

CONCLUSIONS

The findings show that activated ILC2s are a heterogenous population encompassing distinct subsets that have different propensities, and therefore provide an opportunity to explore PD-1's role in modulating the activity of ILC2s for disease prevention and therapy.

CD1-mediated immune responses in mucosal tissues: molecular mechanisms underlying lipid antigen presentation system

The cluster of differentiation 1 (CD1) molecule differs from major histocompatibility complex class I and II because it presents glycolipid/lipid antigens. Moreover, the CD1-restricted T cells that recognize these self and foreign antigens participate in both innate and adaptive immune responses. CD1s are constitutively expressed by professional and nonprofessional antigen-presenting cells in mucosal tissues, namely, the skin, lung, and intestine. This suggests that CD1-reactive T cells are involved in the immune responses of these tissues. Indeed, evidence suggests that these cells play important roles in diverse diseases, such as inflammation, autoimmune disease, and infection. Recent studies elucidating the molecular mechanisms by which CD1 presents lipid antigens suggest that defects in these mechanisms could contribute to the activities of CD1-reactive T cells. Thus, improving our understanding of these mechanisms could lead to new and effective therapeutic approaches to CD1-associated diseases. In this review, we discuss the CD1-mediated antigen presentation system and its roles in mucosal tissue immunity.

Calcitonin Gene-Related peptide receptor antagonist suppresses allergic asthma responses via downregulation of group 2 innate lymphoid cells in mice

Allergic asthma is caused by chronic inflammation and hyper-responsiveness of the airway and is thought to be mediated by adaptive T helper type 2 (Th2)-driven immunity. However, recent studies have demonstrated that neuropeptide calcitonin gene-related peptide (CGRP)-mediated activation of group 2 innate lymphoid cells (ILC2s) may contribute to the development of asthma pathogenesis. Here, we investigated the therapeutic effects of the systemic administration of rimegepant, a CGRP receptor antagonist, on allergic asthma. Hyperplasia of CGRP-immunoreactive pulmonary neuroendocrine cells (PNECs) was observed in ovalbumin (OVA)-induced asthmatic mice. Concomitant with this, we observed an increase in the content of total lung CGRP. Upon antigen challenge, the concentration of plasma CGRP was transiently upregulated, whereas CGRP immunoreactivity within PNECs was intensively downregulated, suggesting that PNECs were the most likely source of CGRP. When rimegepant was administered according to CGRP kinetics, it suppressed asthma phenotypes, including airway hyper-responsiveness, infiltration of inflammatory cells in bronchoalveolar lavage fluid (BALF), hyperplasia of mucus-producing cells, and production of the Th2 cytokine IL-5. Moreover, we observed a decrease in the number of ILC2s and their capacity for IL-5 release in the presence of IL-33 in rimegepant-treated mice. In the allergic asthma model, rimegepant suppressed the activation of ILC2s mediated by PNEC-derived CGRP and subsequently impaired adaptive Th2-driven immunity, which ameliorated asthmatic phenotypes. Thus, an anti-CGRP signal strategy to target ILC2 will be a novel and attractive approach for treating allergic asthma that is refractory to other treatments.

Mucosal-associated invariant T cells repress group 2 innate lymphoid cells in Alternaria alternata-induced model of allergic airway inflammation

Mucosal-associated invariant T (MAIT) cells, a blossoming member of the innate-like T cells, play a pivotal role in host defense through engaging the mucosal immunity. Although it has been suggested that MAIT cells are somehow implicated in the allergic airway inflammation mediated by group 2 innate lymphoid cells (ILC2s) such as asthma, the precise role(s) of MAIT cells in such inflammation has remained elusive. To explore the possible roles of MAIT cells in the inflammation, we examined whether MAIT cells suppressed the production of T helper (Th) 2 and inflammatory cytokines from ILC2s, and constrained the proliferation of ILC2s, both of which are prerequisite for airway inflammation. Given that laboratory mice are poor at MAIT cells, a novel mouse line rich in MAIT cells was used. We found that mice rich in MAIT cells showed alleviated airway inflammation as evidenced by reduced infiltration of the immune cells and hyperplasia in goblet cells in the lung concomitant with compromised production of Th2 and inflammatory cytokines, while wild type mice exhibited severe inflammation upon challenge with the fungal extracts. In vitro coculture experiments using purified ILC2s and MAIT cells unrevealed that cytokine-stimulated MAIT cells suppressed ILC2s to produce the cytokines as well as to proliferate most likely via production of IFN-γ. Furthermore, reconstitution of the allergic airway inflammation in the highly immunocompromised mice showed that ILC2-mediated inflammation was alleviated in mice that received MAIT cells along with ILC2s. We concluded that MAIT cells played a crucial role in suppressing the cytokine-producing capacity of ILC2s and ILC2 proliferation, that ultimately led to decrease in the allergic airway inflammation. The results open up a novel therapeutic horizon in ILC2-mediated inflammatory diseases by modulating MAIT cell activity.

Emerging Effects of IL-33 on COVID-19

Since the start of COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more than 6 million people have lost their lives worldwide directly or indirectly. Despite intensified efforts to clarify the immunopathology of COVID-19, the key factors and processes that trigger an inflammatory storm and lead to severe clinical outcomes in patients remain unclear. As an inflammatory storm factor, IL-33 is an alarmin cytokine, which plays an important role in cell damage or infection. Recent studies have shown that serum IL-33 is upregulated in COVID-19 patients and is strongly associated with poor outcomes. Increased IL-33 levels in severe infections may result from an inflammatory storm caused by strong interactions between activated immune cells. However, the effects of IL-33 in COVID-19 and the underlying mechanisms remain to be fully elucidated. In this review, we systematically discuss the biological properties of IL-33 under pathophysiological conditions and its regulation of immune cells, including neutrophils, innate lymphocytes (ILCs), dendritic cells, macrophages, CD4⁺ T cells, Th17/Treg cells, and CD8⁺ T cells, in COVID-19 phagocytosis. The aim of this review is to explore the potential value of the IL-33/immune cell pathway as a new target for early diagnosis, monitoring of severe cases, and clinical treatment of COVID-19.

A pathogenic integrated view explaining the different endotypes of asthma and allergic disorders

The inflammation of allergic diseases is characterized by a complex interaction between type 2 and type 3 immune responses, explaining clinical symptoms and histopathological patterns. Airborne stimuli activate the mucosal epithelium to release a number of molecules impacting the activity of resident immune and environmental cells. Signals from the mucosal barrier, regulatory cells, and the inflamed tissue are crucial conditions able to modify innate and adaptive effector cells providing the selective homing of eosinophils or neutrophils. The high plasticity of resident T- and innate lymphoid cells responding to external signals is the prerequisite to explain the multiplicity of endotypes of allergic diseases. This notion paved the way for the huge use of specific biologic drugs interfering with pathogenic mechanisms of inflammation. Based on the response of the epithelial barrier, the activity of resident regulatory cells, and functions of structural non-lymphoid environmental cells, this review proposes some immunopathogenic scenarios characterizing the principal endotypes which can be associated with a precise phenotype of asthma. Recent literature indicates that similar concepts can also be applied to the inflammation of other non-respiratory allergic disorders. The next challenges will consist in defining specific biomarker(s) of each endotype allowing for a quick diagnosis and the most effective personalized therapy.

Th2A cells: The pathogenic players in allergic diseases

Proallergic type 2 helper T (Th2A) cells are a subset of memory Th2 cells confined to atopic individuals, and they include all the allergen-specific Th2 cells. Recently, many studies have shown that Th2A cells characterized by CD3+ CD4+ HPGDS+ CRTH2+ CD161high ST2high CD49dhigh CD27low play a crucial role in allergic diseases, such as atopic dermatitis (AD), food allergy (FA), allergic rhinitis (AR), asthma, and eosinophilic esophagitis (EoE). In this review, we summarize the discovery, biomarkers, and biological properties of Th2A cells to gain new insights into the pathogenesis of allergic diseases.

Tissue Resident and Migratory Group 2 Innate Lymphoid Cells

Group 2 innate lymphoid cells (ILC2s) are present in both mouse and human mucosal and non-mucosal tissues and implicated in initiating type 2 inflammation. ILC2s are considered to be tissue resident cells that develop in the perinatal period and persist throughout life with minimal turning over in adulthood. However, recent studies in animal models have shown their ability to circulate between different organs during inflammation and their potential functions in the destined organs, suggesting their roles in mediating multiple type 2 diseases. Here, we review recent findings on ILC2 migration, including migration within, into and out of tissues during inflammation.

Alarmin Cytokines as Central Regulators of Cutaneous Immunity

Skin acts as the primary interface between the body and the environment. The skin immune system is composed of a complex network of immune cells and factors that provide the first line of defense against microbial pathogens and environmental insults. Alarmin cytokines mediate an intricate intercellular communication between keratinocytes and immune cells to regulate cutaneous immune responses. Proper functions of the type 2 alarmin cytokines, thymic stromal lymphopoietin (TSLP), interleukin (IL)-25, and IL-33, are paramount to the maintenance of skin homeostasis, and their dysregulation is commonly associated with allergic inflammation. In this review, we discuss recent findings on the complex regulatory network of type 2 alarmin cytokines that control skin immunity and highlight the mechanisms by which these cytokines regulate skin immune responses in host defense, chronic inflammation, and cancer.

Effect of Carbon Black Nanoparticle on Neonatal Lymphoid Tissues Depending on the Gestational Period of Exposure in Mice

Introduction: Particulate air pollution, containing nanoparticles, enhances the risk of pediatric allergic diseases that is potentially associated with disruption of neonatal immune system. Previous studies have revealed that maternal exposure to carbon black nanoparticles (CB-NP) disturbs the development of the lymphoid tissues in newborns. Interestingly, the CB-NP-induced immune profiles were observed to be different depending on the gestational period of exposure. It is important to identify the critical exposure period to prevent toxic effects of nanoparticles on the development of the immune system. Therefore, the present study was aimed to investigate the effect of CB-NP on the development of neonatal lymphoid tissues in mice, depending on the gestational period of exposure.

Methods: Pregnant ICR mice were treated with a suspension of CB-NP (95 μg/kg body weight) by intranasal instillation; the suspension was administered twice during each gestational period as follows: the pre-implantation period (gestational days 4 and 5), organogenesis period (gestational days 8 and 9), and fetal developmental period (gestational days 15 and 16). The spleen and thymus were collected from offspring mice at 1, 3, and 5-days post-partum. Splenocyte and thymocyte phenotypes were examined by flow cytometry. Gene expression in the spleen was examined by quantitative reverse transcription-polymerase chain reaction.

Results: The numbers of total splenocytes and splenic CD3⁻B220⁻ phenotype (non-T/non-B lymphocytes) in offspring on postnatal day 5 were significantly increased after exposure to CB-NP during the organogenesis period compared with other gestational periods of exposure and control (no exposure). In contrast, expression levels of mRNA associated with chemotaxis and differentiation of immune cells in the spleen were not affected by CB-NP exposure during any gestational period.

Conclusion: The organogenesis period was the most susceptible period to CB-NP exposure with respect to lymphoid tissue development. Moreover, the findings of the present and previous studies suggested that long-term exposure to CB-NP across multiple gestational periods including the organogenesis period, rather than acute exposure only organogenesis period, may more severely affect the development of the immune system.

Modified BuShenYiQi formula alleviates experimental allergic asthma in mice by negative regulation of type 2 innate lymphoid cells and CD4+ type 9 helper T cells and the VIP-VPAC2 signalling pathway

CONTEXT

Modified BuShenYiQi formula (M-BYF) is derived from BuShenYiQi formula, used for the treatment of allergic asthma. The exact effect and mechanism of M-BYF on the improvement of asthma remain unclear.

OBJECTIVE

We investigated the mechanism underlying the therapeutic effect of M-BYF on allergic asthma.

MATERIALS AND METHODS

The asthma model was established in female BALB/c mice that were sensitized and challenged with ovalbumin (OVA). Mice in the treated groups were orally treated once a day with M-BYF (7, 14 and 28 g/kg/d) or dexamethasone before OVA challenge. Control and Model group received saline. Pathophysiological abnormalities and percentages of lung type 2 innate lymphoid cells (ILC2s) and Th9 cells were measured. Expression levels of type 2 cytokines and transcription factors required for these cells function and differentiation were analysed. Expression of vasoactive intestinal polypeptide (VIP)-VPAC2 signalling pathway-related proteins, and percentages of VIP expressing (VIP⁺) cells and VPAC2, CD90 co-expressing (VPAC2⁺CD90⁺) cells were detected.

RESULTS

M-BYF alleviated airway hyperresponsiveness, inflammation, mucus hypersecretion and collagen deposition in asthmatic mice. M-BYF down-regulated percentages of ILC2s and Th9 cells with lower expression of GATA3, PU.1 and IRF4, reduced IL-5, IL-13, IL-9 and VIP production. The decrease in the expression of VIP-VPAC2 signalling pathway and percentages of VIP⁺ cells, VPAC2⁺CD90⁺ cells were observed after M-BYF treatment. The LD₅₀ value of M-BYF was higher than 90 g/kg.

DISCUSSION AND CONCLUSIONS

M-BYF alleviated experimental asthma by negatively regulating ILC2s and Th9 cells and the VIP-VPAC2 signalling pathway. These findings provide the theoretical basis for future research of M-BYF in asthma patient population.

Group-2 Innate Lymphoid Cells Promote HCC Progression Through CXCL2-Neutrophil-Induced Immunosuppression

BACKGROUND AND AIMS

Due to their inherent characteristics, the function of group-2 innate lymphoid cells (ILC2s) varies in a context-dependent manner. ILC2s are involved in certain liver diseases; however, their involvement in HCC is unknown. In the present study, we assessed the role of an HCC-derived ILC2 population in tumor progression.

APPROACH AND RESULTS

Through FACS and single-cell RNA sequencing, we discovered that ILC2s were highly enriched in human HCC and correlated significantly with tumor recurrence and worse progression-free survival as well as overall survival in patients. Mass cytometry identified a subset of HCC-derived ILC2s that had lost the expression of killer cell lectin-like receptor subfamily G, member 1 (KLRG1). Distinct from their circulating counterparts, these hepatic ILC2s highly expressed CD69 and an array of tissue resident-related genes. Furthermore, reduction of E-cadherin in tumor cells caused the loss of KLRG1 expression in ILC2s, leading to their increased proliferation and subsequent accumulation in HCC sites. The KLRG1^- ILC2 subset showed elevated production of chemotaxis factors, including C-X-C motif chemokine (C-X-C motif) ligand (CXCL)-2 and CXCL8, which in turn recruited neutrophils to form an immunosuppressive microenvironment, leading to tumor progression. Accordingly, restoring KLRG1 in ILC2s, inhibiting CXCL2 in ILC2s, or depleting neutrophils inhibited tumor progression in a murine HCC model.

CONCLUSIONS

We identified HCC-associated ILC2s as an immune regulatory cell type that promotes tumor development, suggesting that targeting these ILC2s might lead to new treatments for HCC.

Migration of Lung Resident Group 2 Innate Lymphoid Cells Link Allergic Lung Inflammation and Liver Immunity

Group 2 innate lymphoid cells (ILC2s) are tissue resident in the lung and activated by inhaled allergens via epithelial-derived alarmins including IL-33. Activated ILC2s proliferate, produce IL-5 and IL-13, and induce eosinophilic inflammation. Here, we report that intranasal IL-33 or the protease allergen papain administration resulted in increased numbers of ILC2s not only in the lung but also in peripheral blood and liver. Analyses of IL-33 treated parabiosis mice showed that the increase in lung ILC2s was due to proliferation of lung resident ILC2s, whereas the increase in liver ILC2s was due to the migration of activated lung ILC2s. Lung-derived ILC2s induced eosinophilic hepatitis and expression of fibrosis-related genes. Intranasal IL-33 pre-treatment also attenuated concanavalin A-induced acute hepatitis and cirrhosis. These results suggest that activated lung resident ILC2s emigrate from the lung, circulate, settle in the liver and promote type 2 inflammation and attenuate type 1 inflammation.

Mapping Rora expression in resting and activated CD4+ T cells

The transcription factor Rora has been shown to be important for the development of ILC2 and the regulation of ILC3, macrophages and Treg cells. Here we investigate the role of Rora across CD4+ T cells in general, but with an emphasis on Th2 cells, both in vitro as well as in the context of several in vivo type 2 infection models. We dissect the function of Rora using overexpression and a CD4-conditional Rora-knockout mouse, as well as a RORA-reporter mouse. We establish the importance of Rora in CD4+ T cells for controlling lung inflammation induced by Nippostrongylus brasiliensis infection, and have measured the effect on downstream genes using RNA-seq. Using a systematic stimulation screen of CD4+ T cells, coupled with RNA-seq, we identify upstream regulators of Rora, most importantly IL-33 and CCL7. Our data suggest that Rora is a negative regulator of the immune system, possibly through several downstream pathways, and is under control of the local microenvironment.

Innate Lymphoid Cells in Airway Inflammation

Airways are constantly exposed to antigens and various pathogens. Immune cells in the airways act as first line defense system against these pathogens, involving both innate and acquired immunity. There is accumulating evidence that innate lymphoid cells, newly identified lymphoid lineage cells, play a critical role in regulating tissue homeostasis and in the pathogenesis of inflammation. Cytokines produced by other cells activate innate lymphoid cells, which in turn produce large amount of cytokines that result in inflammation. Type 2 innate lymphoid cells (ILC2s) are recognized as key component of T helper type 2 (Th2) inflammation, and are known to be elevated in type 2 (T2) human airway diseases (asthma). Th2 cytokines produced by ILC2s amplify inflammation via activation of eosinophils, B cells, mast cell, and macrophages. "T2 high asthma" has an increased Th2 response triggered by elevation of IL-4, IL-5 and IL-13 and other inflammatory mediators, leading to increased eosinophilic inflammation. The growing evidence of ILC2 contribution in the induction and maintenance of allergic inflammation suggests that targeting upstream mediators may affect both the innate and adaptive immune responses and all disease phenotypes. Blocking ILC2 activators, activation of inhibitory pathways of ILC2, or suppression of ILC2-mediated pathways may be therapeutic strategies for the type 2 airway diseases.

Eosinophils in the Tumor Microenvironment

Eosinophils are rare blood-circulating and tissue-infiltrating immune cells studied for decades in the context of allergic diseases and parasitic infections. Eosinophils can secrete a wide array of soluble mediators and effector molecules, with potential immunoregulatory activities in the tumor microenvironment (TME). These findings imply that these cells may play a role in cancer immunity. Despite these cells were known to infiltrate tumors since many years ago, their role in TME is gaining attention only recently. In this chapter, we will review the main biological functions of eosinophils that can be relevant within the TME. We will discuss how these cells may undergo phenotypic changes acquiring pro- or antitumoricidal properties according to the surrounding stimuli. Moreover, we will analyze canonical (i.e., degranulation) and unconventional mechanisms (i.e., DNA traps, exosome secretion) employed by eosinophils in inflammatory contexts, which can be relevant for tumor immune responses. Finally, we will review the available preclinical models that could be employed for the study of the role in vivo of eosinophils in cancer.

Current Preventions and Treatments of aGVHD: From Pharmacological Prophylaxis to Innovative Therapies

Graft versus host disease (GVHD) is one of the main causes of mortality and the reason for up to 50% of morbidity after hematopoietic stem cell transplantations (HSCT) which is the treatment of choice for many blood malignancies. Thanks to years of research and exploration, we have acquired a profound understanding of the pathophysiology and immunopathology of these disorders. This led to the proposition and development of many therapeutic approaches during the last decades, some of them with very promising results. In this review, we have focused on the recent GVHD treatments from classical chemical and pharmacological prophylaxis to more innovative treatments including gene therapy and cell therapy, most commonly based on the application of a variety of immunomodulatory cells. Furthermore, we have discussed the advantages and potentials of cell-free therapy as a newly emerging approach to treat GVHD. Among them, we have particularly focused on the implication of the TNFα-TNFR2 axis as a new immune checkpoint signaling pathway controlling different aspects of many immunoregulatory cells.

Group 2 Innate Lymphoid Cells: A Double-Edged Sword in Cancer?

Group 2 Innate Lymphoid Cells (ILC2s) belong to the family of helper ILCs which provide host defense against infectious agents, participate in inflammatory responses and mediate lymphoid organogenesis and tissue repair, mainly at the skin and mucosal level. Based on their transcriptional, phenotypic and functional profile, ILC2s mirror the features of the adaptive CD4+ Th2 cell subset, both contributing to the so-called type 2 immune response. Similar to other ILCs, ILC2s are rapidly activated by signals deriving from tissue and/or other tissue-resident immune cells. The biologic activity of ILCs needs to be tightly regulated in order to prevent them from contributing to severe inflammation and damage in several organs. Indeed, ILC2s display both enhancing and regulatory roles in several pathophysiological conditions, including tumors. In this review, we summarize the actual knowledge about ILC2s ability to induce or impair a protective immune response, their pro- or antitumor activity in murine models, human (children and adults) pathologies and the potential strategies to improve cancer immunotherapy by exploiting the features of ILC2s.

Analysis of the percentages of monocyte subsets and ILC2s, their relationships with metabolic variables and response to hypocaloric restriction in obesity

PURPOSE

Obesity results from excess energy intake over expenditure and is characterized by chronic low-grade inflammation involving circulating monocytes (Mo) and group 2 innate lymphoid cells (ILC2s) imbalance. We analyzed circulating Mo subsets and ILC2s percentages and β2-adrenergic receptor (β2AR) expression in lean and obese subjects, and the possible effect of hypocaloric restriction on these innate immune cells.

METHODS

In 139 individuals aged 45 to 57 years, classified in 74 lean individuals (>18.9kg/m2 BMI <24.9kg/m2) and 65 with obesity (n = 65), we collected fasting blood samples to detect Mo subsets, ILC2s number, and β2AR expression by flow cytometry. Lipids, insulin, leptin, and acylated-ghrelin concentrations were quantified. Resting energy expenditure (REE) was estimated by indirect calorimetry. These measurements were repeated in obese subjects after 7-weeks of hypocaloric restriction.

RESULTS

Non-classical monocytes (NCM) and β2AR expression on intermediate Mo (IM) were increased in obese individuals (p<0.001, in both cases), whereas the percent of ILC2s was decreased (p<0.0001). Stepwise regression analysis showed significantly negative associations of ILC2s with caloric intake, β2AR expression on IM with REE, but a positive relationship between NCM and HOMA-IR. Caloric restriction allowed a significant diminution of NCM and the β2AR expression on IM, as well as, an increase in the percent of classical Mo (CM), and ILC2s. ΔREE was related to ΔCD16+/CD16- ratio.

CONCLUSIONS

These findings show that in obesity occur changes in NCM, ILC2s and β2AR expression, which contribute to the low-grade inflammation linked to obesity and might revert with caloric restriction.

The Immune Function of Tuft Cells at Gut Mucosal Surfaces and Beyond

Tuft cells were first discovered in epithelial barriers decades ago, but their function remained unclear until recently. In the last 2 years, a series of studies has provided important advances that link tuft cells to infectious diseases and the host immune responses. Broadly, a model has emerged in which tuft cells use chemosensing to monitor their surroundings and translate environmental signals into effector functions that regulate immune responses in the underlying tissue. In this article, we review the current understanding of tuft cell immune function in the intestines, airways, and thymus. In particular, we discuss the role of tuft cells in type 2 immunity, norovirus infection, and thymocyte development. Despite recent advances, many fundamental questions about the function of tuft cells in immunity remain to be answered.

The group 2 innate lymphoid cell (ILC2) regulatory network and its underlying mechanisms

Group 2 innate lymphoid cells (ILC2s) play critical roles in the induction of type 2 inflammation, response to parasite infection, metabolic homeostasis, and tissue repair. These multifunctional roles of ILC2s are tightly controlled by complex regulatory systems in the local microenvironment, the disruption of which may cause various health problems. This review summarizes up-to-date knowledge regarding positive and negative regulators for ILC2s based on their function and signaling pathways, including activating cytokines (IL-33, IL-25; MAPK, NF-κB pathways), co-stimulatory cytokines (IL-2, IL-7, IL-9, TSLP; STAT5, IL-4; STAT6, TNF superfamily; MAPK, NF-κB pathways), suppressive cytokines (type1 IFNs, IFN-γ, IL-27; STAT1, IL-10, TGF-β), transdifferentiation cytokines (IL-12; STAT4, IL-1β, IL-18), lipid mediators (LTC4, LTD4, LTE4, PGD2; Ca²⁺ -NFAT pathways, PGE2, PGI2; AC/cAMP/PKA pathways, LXA4, LTB4), neuropeptides (NMU; Ca²⁺ -NFAT, MAPK pathways, VIP, CGRP, catecholamine, acetylcholine), sex hormones (androgen, estrogen), nutrients (butyrate; HDAC inhibitors, vitamins), and cell-to-cell interactions (ICOSL-ICOS; STAT5, B7-H6-NKp30, E-cadherin-KLRG1). This comprehensive review affords a better understanding of the regulatory network system for ILC2s, providing impetus to develop new treatment strategies for ILC2-related health problems.

Single cell RNA sequencing reveals regional heterogeneity of hepatobiliary innate lymphoid cells in a tissue-enriched fashion

IL-33 promotes type 2 immunity, epithelial repair, and tissue fibrosis by activating group 2 innate lymphoid cells (ILC2). ILC2 lack all known surface markers of mature T, B, NK, and myeloid cell lineages (Linneg), express the IL-33 receptor ST2, and release type 2 cytokines which contribute to cholangiocyte proliferation and activation of hepatic stellate cells. This pathway results in massive proliferation of the extrahepatic bile duct (EHBD) but also exacerbates liver fibrosis, suggesting that there may be tissue-specific subpopulations of IL-33-induced ILC. To determine the tissue-specific subsets of ILC in the hepatobiliary system, we analyzed CD45+Linneg mononuclear cells from IL-33 treated adult Balb/c mouse liver or EHBD by single cell RNA sequencing. Principal component analysis identified 6 major CD45+Linneg cell classes, two of which were restricted to the EHBD. One of these classes, biliary immature myeloid (BIM) cells, was predicted to interact with ILC2 by a network of shared receptor-ligand pairs. BIM highly expressed Gp49 and ST2 receptors on the cell surface while lacking surface expression of markers for mature myeloid cells. In conclusion, single cell RNA sequencing identified IL-33 responsive cell groups regionally confined to the liver or extrahepatic bile duct, including a novel population of CD45+Linneg Gp49-expressing mononuclear cells.

Transcription Factors in the Development and Function of Group 2 Innate Lymphoid Cells

Group 2 innate lymphoid cells (ILC2s) are tissue-resident cells and are a major source of innate T_H2 cytokine secretion upon allergen exposure or parasitic-worm infection. Accumulating studies have revealed that transcription factors, including GATA-3, Bcl11b, Gfi1, RORα, and Ets-1, play a role in ILC2 differentiation. Recent reports have further revealed that the characteristics and functions of ILC2 are influenced by the physiological state of the tissues. Specifically, the type of inflammation strongly affects the ILC2 phenotype in tissues. Inhibitory ILC2s, memory-like ILC2s, and ex-ILC2s with ILC1 features acquire their characteristic properties following exposure to their specific inflammatory environment. We have recently reported a new ILC2 population, designated as exhausted-like ILC2s, which emerges after a severe allergic inflammation. Exhausted-like ILC2s are featured with low reactivity and high expression of inhibitory receptors. Therefore, for a more comprehensive understanding of ILC2 function and differentiation, we review the recent knowledge of transcriptional regulation of ILC2 differentiation and discuss the roles of the Runx transcription factor in controlling the emergence of exhausted-like ILC2s. The concept of exhausted-like ILC2s sheds a light on a new aspect of ILC2 biology in allergic diseases.

The Endothelin-A Receptor Antagonist Zibotentan Induces Damage to the Nasal Olfactory Epithelium Possibly Mediated in Part through Type 2 Innate Lymphoid Cells

Zibotentan, an endothelin-A receptor antagonist, has been used in the treatment of various cardiovascular disorders and neoplasia. Castrated athymic nude mice receiving zibotentan for a preclinical xenograft efficacy study experienced weight loss, gastrointestinal bloat, and the presence of an audible respiratory click. Human side effects have been reported in the nasal cavity, so we hypothesized that the nasal cavity is a target for toxicity in mice receiving zibotentan. Lesions in the nasal cavity predominantly targeted olfactory epithelium in treated mice and were more pronounced in castrated animals. Minimal lesions were present in vehicle control animals, which suggested possible gavage-related reflux injury. The incidence, distribution, and morphology of lesions suggested direct exposure to the nasal mucosa and a possible systemic effect targeting the olfactory epithelium, driven by a type 2 immune response, with group 2 innate lymphoid cell involvement. Severe nasal lesions may have resulted in recurrent upper airway obstruction, leading to aerophagia and associated clinical morbidity. These data show the nasal cavity is a target of zibotentan when given by gavage in athymic nude mice, and such unanticipated and off-target effects could impact interpretation of research results and animal health in preclinical studies.

Runx/Cbfβ complexes protect group 2 innate lymphoid cells from exhausted-like hyporesponsiveness during allergic airway inflammation

Group 2 innate lymphoid cells (ILC2s) have tissue-resident competence and contribute to the pathogenesis of allergic diseases. However, the mechanisms regulating prolonged ILC2-mediated TH2 cytokine production under chronic inflammatory conditions are unclear. Here we show that, at homeostasis, Runx deficiency induces excessive ILC2 activation due to overly active GATA-3 functions. By contrast, during allergic inflammation, the absence of Runx impairs the ability of ILC2s to proliferate and produce effector TH2 cytokines and chemokines. Instead, functional deletion of Runx induces the expression of exhaustion markers, such as IL-10 and TIGIT, on ILC2s. Finally, these 'exhausted-like' ILC2s are unable to induce type 2 immune responses to repeated allergen exposures. Thus, Runx confers competence for sustained ILC2 activity at the mucosa, and contributes to allergic pathogenesis.

Sex-associated TSLP-induced immune alterations following early-life RSV infection leads to enhanced allergic disease

Many studies have linked severe RSV infection during early-life with an enhanced likelihood of developing childhood asthma, showing a greater susceptibility in boys. Our studies show that early-life RSV infection leads to differential long-term effects based upon the sex of the neonate; leaving male mice prone to exacerbation upon secondary allergen exposure while overall protecting female mice. During initial viral infection, we observed better viral control in the female mice with correlative expression of interferon-β that was not observed in male mice. Additionally, we observed persistent immune alterations in male mice at 4 weeks post infection. These alterations include Th2 and Th17-skewing, innate cytokine expression (Tslp and Il33), and infiltration of innate immune cells (DC and ILC2). Upon exposure to allergen, beginning at 4 weeks following early-life RSV-infection, male mice show severe allergic exacerbation while female mice appear to be protected. Due to persistent expression of TSLP following early-life RSV infection in male mice, genetically modified TSLPR-/- mice were evaluated and demonstrated an abrogation of allergen exacerbation in male mice. These data indicate that TSLP is involved in the altered immune environment following neonatal RSV-infection that leads to more severe responses in males during allergy exposure, later in life. Thus, TSLP may be a clinically relevant therapeutic target early in life.

Interplay of innate lymphoid cells and the microbiota

Innate lymphoid cells (ILC) are a recently identified group of innate lymphocytes that are preferentially located at barrier surfaces. Barrier surfaces are in direct contact with complex microbial ecosystems, collectively referred to as the microbiota. It is now believed that the interplay of the microbiota with host components (i.e. epithelial cells and immune cells) promotes host fitness by regulating organ homeostasis, metabolism, and host defense against pathogens. In this review, we will give an overview of this multifaceted interplay between ILC and components of the microbiota.

Endotypes of severe allergic asthma patients who clinically benefit from anti-IgE therapy

BACKGROUND

Omalizumab, a recombinant monoclonal anti-IgE antibody, was developed for the treatment of severe allergic asthma. Not all these patients respond to omalizumab.

OBJECTIVE

This study aimed to evaluate whether the proinflammatory cytokine profiles in the severe allergic asthma patients were different between who responded and nonresponded to omalizumab therapy.

METHODS

A prospective study was conducted to examine type 2 cytokines and epithelium-derived cytokines in the bronchial tissues by immunohistochemistry, Western blot and PCR analysis among patients with severe allergic asthma before and after omalizumab therapy.

RESULTS

Fourteen of 23 patients with unstable severe allergic asthma improved their asthma control after 4 months of omalizumab treatment (Responders), while nine failed to improve (Non-Responders). Most of Responders were type 2-high endotype (12/14) with upregulated expression of IL-33, IL-25 and TSLP in their bronchial tissues, while most of Non-Responders were type 2-low endotype (8/9). Repeated bronchoscopic biopsy was done in nine responders after omalizumab treatment and showed a decline in IL-13, IL-33, IL-25 and TSLP expression in the bronchial tissues. Among 14 Responders who continued omalizuamb treatments to a total 12 months, six patients achieved a well control of asthma (ACT ≥ 23), while eight patients required additional treatment for asthma symptoms and had more rhinosinusitis comorbidities and a mixed eosinophilic and neutrophilic inflammation in their bronchial tissues.

CONCLUSION

Most of the severe allergic asthma patients who benefited from omalizumab treatment were IL-33, IL-25 and TSLP aggravated type 2-high endotype. Rhinosinusitis or with a mixed eosinophilic and neutrophilic airway inflammation should be evaluated in patients who partially responded to omalizumab treatment.

Type 2 immunity: Expanding our view

The classical vision of type 2 immune reactions is that they are characterized by a distinct cellular and cytokine repertoire that is critical for host resistance against helminthic worm infections but, when dysregulated, may cause atopic reactions that result in conditions such as asthma, rhinitis, dermatitis, and anaphylaxis. In this traditional view, the type 2 response is categorized as an adaptive immune response with differentiated T helper cells taking center stage, driving eosinophil recruitment and immunoglobulin production via the secretion of a distinct repertoire of cytokines that include interleukin-4 (IL-4), IL-5, and IL-13. The recent discovery of a group of innate cells that has the capacity to secrete copious amounts of type 2 cytokines, potentially in the absence of adaptive immunity, has reignited interest in type 2 biology. The discovery that these innate lymphoid cells and type 2 cytokines are involved in diverse biological processes-including wound healing, control of metabolic homeostasis, and temperature-has considerably changed our view of type 2 responses and the cytokines, chemokines, and receptors that regulate these responses.

Group 2 innate lymphocytes at the interface between innate and adaptive immunity

Group 2 innate lymphoid cells (ILC2) are innate immune cells that respond rapidly to their environment through soluble inflammatory mediators and cell-to-cell interactions. As tissue-resident sentinels, ILC2 help orchestrate localized type 2 immune responses. These ILC2-driven type 2 responses are now recognized in diverse immune processes, different anatomical locations, and homeostatic or pathological settings. ILC2-derived cytokines and cell surface signaling molecules function as key regulators of innate and adaptive immunity. Conversely, ILC2 are governed by their environment. As such, ILC2 form an important nexus of the immune system and may present an attractive target for immune modulation in disease.

Interleukin-10 Modulation of Virus Clearance and Disease in Mice with Alphaviral Encephalomyelitis

Alphaviruses are an important cause of mosquito-borne outbreaks of arthritis, rash, and encephalomyelitis. Previous studies in mice with a virulent strain (neuroadapted SINV [NSV]) of the alphavirus Sindbis virus (SINV) identified a role for Th17 cells and regulation by interleukin-10 (IL-10) in the pathogenesis of fatal encephalomyelitis (K. A. Kulcsar, V. K. Baxter, I. P. Greene, and D. E. Griffin, Proc Natl Acad Sci U S A 111:16053-16058, 2014, https://doi.org/10.1073/pnas.1418966111). To determine the role of virus virulence in generation of immune responses, we analyzed the modulatory effects of IL-10 on disease severity, virus clearance, and the CD4+ T cell response to infection with a recombinant strain of SINV of intermediate virulence (TE12). The absence of IL-10 during TE12 infection led to longer morbidity, more weight loss, higher mortality, and slower viral clearance than in wild-type mice. More severe disease and impaired virus clearance in IL-10-/- mice were associated with more Th1 cells, fewer Th2 cells, innate lymphoid type 2 cells, regulatory cells, and B cells, and delayed production of antiviral antibody in the central nervous system (CNS) without an effect on Th17 cells. Therefore, IL-10 deficiency led to more severe disease in TE12-infected mice by increasing Th1 cells and by hampering development of the local B cell responses necessary for rapid production of antiviral antibody and virus clearance from the CNS. In addition, the shift from Th17 to Th1 responses with decreased virus virulence indicates that the effects of IL-10 deficiency on immunopathologic responses in the CNS during alphavirus infection are influenced by virus strain.IMPORTANCE Alphaviruses cause mosquito-borne outbreaks of encephalomyelitis, but determinants of outcome are incompletely understood. We analyzed the effects of the anti-inflammatory cytokine IL-10 on disease severity and virus clearance after infection with an alphavirus strain of intermediate virulence. The absence of IL-10 led to longer illness, more weight loss, more death, and slower viral clearance than in mice that produced IL-10. IL-10 influenced development of disease-causing T cells and entry into the brain of B cells producing antiviral antibody. The Th1 pathogenic cell subtype that developed in IL-10-deficient mice infected with a less virulent virus was distinct from the Th17 subtype that developed in response to a more virulent virus, indicating a role for virus strain in determining the immune response. Slow production of antibody in the nervous system led to delayed virus clearance. Therefore, both the virus strain and the host response to infection are important determinants of outcome.

Chemokine regulation of innate lymphoid cell tissue distribution and function

Three groups of innate lymphoid cells (ILCs) can be defined based on transcription factor requirements, cytokine production profiles, and roles in immunity. Given their strategic anatomical location into barrier tissues and the ability to rapidly produce cytokines and to cross-talk with other immune and non-immune cells, ILCs play fundamental functions in tissue homeostasis and regulation of immune responses. Several members of the chemokine family influence ILC tissue localization in the correct microenvironment by regulating their release from the bone marrow as well as their homing and retention in the tissues. In this review, we discuss the recent advances on how chemokine regulation of ILC tissue-positioning and functional interaction with other cells play essential roles in tissue-specific regulation of innate and adaptive immune responses.

Group 2 ILCs: A way of enhancing immune protection against human helminths?

Group 2 innate lymphoid cells (ILC2s) play crucial roles in type 2 immune responses associated with allergic and autoimmune diseases, viral and helminth infections and tissue homoeostasis. Experimental models show that in helminth infections ILC2s provide an early source of type 2 cytokines and therefore are essential for the induction of potentially protective type 2 responses. Much of our knowledge of ILC2s in helminth infections has come from experimental mouse models with very few studies analysing ILC2s in natural human infections. In attempts to harness knowledge from paradigms of the development of protective immunity in human helminth infections for vaccine development, the role of ILC2 cells could be pivotal. So far, potential vaccines against human helminth infections have failed to provide effective protection when evaluated in human studies. In addition to appropriate antigen selection, it is apparent that more detailed knowledge on mechanisms of induction and maintenance of protective immune responses is required. Therefore, there is need to understand how ILC2 cells induce type 2 responses and subsequently support the development of a protective immune response in the context of immunizations. Within this review, we summarize the current knowledge of the biology of ILC2s, discuss the importance of ILC2s in human helminth infections and explore how ILC2 responses could be boosted to efficiently induce protective immunity.

Sentinels of the Type 2 Immune Response

Type 2 immune responses have evolved to sense and respond to large, non-replicating infections or non-microbial noxious compounds in tissues. The development of these responses therefore depends upon highly coordinated and tightly regulated tissue-residing cellular sensors and responders. Multiple exposure to type 2 helper T cell (Th2)-inducing stimuli further enhances both the diversity and potency of the response. This review discusses advances in our understanding of the interacting cellular subsets that comprise both primary and secondary type 2 responses. Current knowledge regarding type 2 immune responses in the lung are initially presented and are then contrasted with what is known about the small intestine. The studies described portray an immune response that depends upon well-organized tissue structures, and suggest their modulation as a therapeutic strategy.

Male-specific IL-33 expression regulates sex-dimorphic EAE susceptibility

The cellular and molecular basis of sex-dimorphic autoimmune diseases, such as the CNS demyelinating disease multiple sclerosis (MS), remains unclear. Our studies in the SJL mouse model of MS, experimental autoimmune encephalomyelitis (EAE), reveal that sex-determined differences in Il33 expression by innate immune cells in response to myelin peptide immunization regulate EAE susceptibility. IL-33 is selectively induced in PLP_139-151-immunized males and activates type 2 innate lymphoid cells (ILC2s), cells that promote and sustain a nonpathogenic Th2 myelin-specific response. Without this attenuating IL-33 response, females generate an encephalitogenic Th17-dominant response, which can be reversed by IL-33 treatment. Mast cells are one source of IL-33 and we provide evidence that testosterone directly induces Il33 gene expression and also exerts effects on the potential for Il33 gene expression during mast cell development. Thus, in contrast to their pathogenic role in allergy, we propose a sex-specific role for both mast cells and ILC2s as attenuators of the pathogenic Th response in CNS inflammatory disease.

Group 2 Innate Lymphoid Cells Exhibit a Dynamic Phenotype in Allergic Airway Inflammation

Group 2 innate lymphoid cells (ILC2) are implicated in allergic asthma as an early innate source of the type 2 cytokines IL-5 and IL-13. However, their induction in house dust mite (HDM)-mediated airway inflammation additionally requires T cell activation. It is currently unknown whether phenotypic differences exist between ILC2s that are activated in a T cell-dependent or T cell-independent fashion. Here, we compared ILC2s in IL-33- and HDM-driven airway inflammation. Using flow cytometry, we found that surface expression levels of various markers frequently used to identify ILC2s were dependent on their mode of activation, highly variable over time, and differed between tissue compartments, including bronchoalveolar lavage (BAL) fluid, lung, draining lymph nodes, and spleen. Whereas in vivo IL-33-activated BAL fluid ILC2s exhibited an almost uniform CD25⁺CD127⁺T1/ST2⁺ICOS⁺KLRG1⁺ phenotype, at a comparable time point after HDM exposure BAL fluid ILC2s had a very heterogeneous surface marker phenotype. A major fraction of HDM-activated ILC2s were CD25^lowCD127⁺T1/ST2^low ICOS^lowKLRG1^low, but nevertheless had the capacity to produce large amounts of type 2 cytokines. HDM-activated CD25^low ILC2s in BAL fluid and lung rapidly reverted to CD25^high ILC2s upon in vivo stimulation with IL-33. Genome-wide transcriptional profiling of BAL ILC2s revealed ~1,600 differentially expressed genes: HDM-stimulated ILC2s specifically expressed genes involved in the regulation of adaptive immunity through B and T cell interactions, whereas IL-33-stimulated ILC2s expressed high levels of proliferation-related and cytokine genes. In both airway inflammation models ILC2s were present in the lung submucosa close to epithelial cells, as identified by confocal microscopy. In chronic HDM-driven airway inflammation ILC2s were also found inside organized cellular infiltrates near T cells. Collectively, our findings show that ILC2s are phenotypically more heterogeneous than previously thought, whereby their surface marker and gene expression profile are highly dynamic.

Arachidonic acid: Physiological roles and potential health benefits - A review

It is time to shift the arachidonic acid (ARA) paradigm from a harm-generating molecule to its status of polyunsaturated fatty acid essential for normal health. ARA is an integral constituent of biological cell membrane, conferring it with fluidity and flexibility, so necessary for the function of all cells, especially in nervous system, skeletal muscle, and immune system. Arachidonic acid is obtained from food or by desaturation and chain elongation of the plant-rich essential fatty acid, linoleic acid. Free ARA modulates the function of ion channels, several receptors and enzymes, via activation as well as inhibition. That explains its fundamental role in the proper function of the brain and muscles and its protective potential against Schistosoma mansoni and S. haematobium infection and tumor initiation, development, and metastasis. Arachidonic acid in cell membranes undergoes reacylation/deacylation cycles, which keep the concentration of free ARA in cells at a very low level and limit ARA availability to oxidation. Metabolites derived from ARA oxidation do not initiate but contribute to inflammation and most importantly lead to the generation of mediators responsible for resolving inflammation and wound healing. Endocannabinoids are oxidation-independent ARA derivatives, critically important for brain reward signaling, motivational processes, emotion, stress responses, pain, and energy balance. Free ARA and metabolites promote and modulate type 2 immune responses, which are critically important in resistance to parasites and allergens insult, directly via action on eosinophils, basophils, and mast cells and indirectly by binding to specific receptors on innate lymphoid cells. In conclusion, the present review advocates the innumerable ARA roles and considerable importance for normal health.

Biological mechanisms underlying the clinical effects of allergen-specific immunotherapy in asthmatic children

INTRODUCTION

Allergen-specific immunotherapy (AIT) is indicated for patients with allergic asthma and/or allergic rhinitis, and can be implemented by either subcutaneous injection (SCIT) or sublingual administration (SLIT). AIT reduces asthma symptoms, lowers the use of pharmacologic controller therapy, and decreases the need for rescue medications. SLIT appears to be safer than SCIT, but SCIT seems to be more efficacious and acts earlier in allergic asthmatic children.

AREAS COVERED

This review looks at the pathobiology of allergic asthma as well as the role of regulatory T and B cells in allergen tolerance. It also reviews the immunological mechanisms underlying the clinical effects induced by AIT in allergic asthmatic children.

EXPERT OPINION

AIT is very effective in allergic asthmatic children, who can significantly benefit from this particular type of immunotherapy in order to achieve a better control of their disease. AIT is also capable of modifying the natural history of allergic asthma. Furthermore, AIT can potentially represent a valuable therapeutic tool within the context of precision medicine, as recombinant allergen technology might allow the creation of targeted extracts able to be effective against specific proteins to which individual asthmatic children are allergic, thus helping to implement a personalized approach to treatment.

Interactions between Innate Lymphoid Cells and Cells of the Innate and Adaptive Immune System

Type 2 innate lymphoid cells (ILC2s) are a major source of cytokines, which are also produced by Th2 cells and several cell types of the innate immune system. Work over the past few years indicates that ILC2s play a central role in regulating type 2 immune responses against allergens and helminths. ILC2s can interact with a variety of cells types of the innate and adaptive immune system by cell–cell contacts or by communication via soluble factors. In this review, we provide an overview about recent advances in our understanding how ILC2s orchestrate type 2 immune responses with focus on direct interactions between ILC2s and other cells of the immune system.

Cyclosporin A indirectly attenuates activation of group 2 innate lymphoid cells in papain-induced lung inflammation

Cyclosporin A (CsA) is a well-known immunosuppressant that is used against steroid-resistant asthma. Group 2 innate lymphoid cells (ILC2s) and type 2 helper T (Th2) cells produce Th2 cytokines including IL-5 and play important roles in asthma pathogenesis. Here, we studied the effects of CsA in allergen-induced lung inflammation in mice and found that CsA decreased the number of lung ILC2s and attenuated papain-induced activation of ILC2s accompanied with IL-5 expression. The ILC2 suppression mediated by CsA was not observed in culture or in lymphocyte-deficient Rag2^-/- mice. Thus, we propose a new suppressive effect of CsA, i.e., administration of CsA indirectly suppresses maintenance and activation of lung ILC2s in addition to direct suppression of T-cell activation and cytokine production.

Pathological and therapeutic roles of innate lymphoid cells in diverse diseases

Innate lymphoid cells (ILCs) are a recently defined type of innate-immunity cells that belong to the lymphoid lineage and have lymphoid morphology but do not express an antigen-specific B cell or T-cell receptor. ILCs regulate immune functions prior to the formation of adaptive immunity and exert effector functions through a cytokine release. ILCs have been classified into three groups according to the transcription factors that regulate their development and function and the effector cytokines they produce. Of note, ILCs resemble T helper (Th) cells, such as Th1, Th2, and Th17 cells, and show a similar dependence on transcription factors and distinct cytokine production. Despite their short history in immunology, ILCs have received much attention, and numerous studies have revealed biological functions of ILCs including host defense against pathogens, inflammation, tissue repair, and metabolic homeostasis. Here, we describe recent findings about the roles of ILCs in the pathogenesis of various diseases and potential therapeutic targets.

Role of Type 2 Innate Lymphoid Cells in Allergic Diseases

PURPOSE OF REVIEW

The adaptive immune response orchestrated by type 2 T helper (Th2) lymphocytes, strictly cooperates with the innate response of group 2 innate lymphoid cells (ILC2), in the protection from helminths infection, as well as in the pathogenesis of allergic disease. The aim of this review is to explore the pathogenic role of ILC2 in different type 2-mediated disorders.

RECENT FINDINGS

Recent studies have shown that epithelial cell-derived cytokines and their responding cells, ILC2, play a pathogenic role in bronchial asthma, chronic rhinosinusitis, and atopic dermatitis. The growing evidences of the contribution of ILC2 in the induction and maintenance of allergic inflammation in such disease suggest the possibility to target them in therapy. Biological therapies blocking ILC2 activation or neutralizing their effector cytokines are currently under evaluation to be used in patients with type 2-dominated diseases.

Innate lymphoid cells as regulators of immunity, inflammation and tissue homeostasis

Research over the last 7 years has led to the formal identification of innate lymphoid cells (ILCs), increased the understanding of their tissue distribution and has established essential functions of ILCs in diverse physiological processes. These include resistance to pathogens, the regulation of autoimmune inflammation, tissue remodeling, cancer and metabolic homeostasis. Notably, many ILC functions appear to be regulated by mechanisms distinct from those of other innate and adaptive immune cells. In this Review, we focus on how group 2 ILC (ILC2) and group 3 ILC (ILC3) responses are regulated and how these cells interact with other immune and non-immune cells to mediate their functions. We highlight experimental evidence from mouse models and patient-based studies that have elucidated the effects of ILCs on the maintenance of tissue homeostasis and the consequences for health and disease.

Globule Leukocytes and Other Mast Cells in the Mouse Intestine

Only 2 major mast cell (MC) subtypes are commonly recognized in the mouse: the large connective tissue mast cells (CTMCs) and the mucosal mast cells (MMCs). Interepithelial mucosal inflammatory cells, most commonly identified as globule leukocytes (GLs), represent a third MC subtype in mice, which we term interepithelial mucosal mast cells (ieMMCs). This term clearly distinguishes ieMMCs from lamina proprial MMCs (lpMMCs) while clearly communicating their common MC lineage. Both lpMMCs and ieMMCs are rare in normal mouse intestinal mucosa, but increased numbers of ieMMCs are seen as part of type 2 immune responses to intestinal helminth infections and in food allergies. Interestingly, we found that increased ieMMCs were consistently associated with decreased mucosal inflammation and damage, suggesting that they might have a role in controlling helminth-induced immunopathology. We also found that ieMMC hyperplasia can develop in the absence of helminth infections, for example, in Treg-deficient mice, Arf null mice, some nude mice, and certain graft-vs-host responses. Since tuft cell hyperplasia plays a critical role in type 2 immune responses to intestinal helminths, we looked for (but did not find) any direct relationship between ieMMC and tuft cell numbers in the intestinal mucosa. Much remains to be learned about the differing functions of ieMMCs and lpMMCs in the intestinal mucosa, but an essential step in deciphering their roles in mucosal immune responses will be to apply immunohistochemistry methods to consistently and accurately identify them in tissue sections.