Type 2 innate lymphocytes in allergic airway inflammation

LKB1 prevents ILC2 exhaustion to enhance antitumor immunity

Group 2 innate lymphoid cells (ILC2s) play crucial roles in mediating allergic inflammation. Recent studies also indicate their involvement in regulating tumor immunity. The tumor suppressor liver kinase B1 (LKB1) inactivating mutations are associated with a variety of human cancers; however, the role of LKB1 in ILC2 function and ILC2-mediated tumor immunity remains unknown. Here, we show that ablation of LKB1 in ILC2s results in an exhausted-like phenotype, which promotes the development of lung melanoma metastasis. Mechanistically, LKB1 deficiency leads to a marked increase in the expression of programmed cell death protein-1 (PD-1) in ILC2s through the activation of the nuclear factor of activated T cell pathway. Blockade of PD-1 can restore the effector functions of LKB1-deficient ILC2s, leading to enhanced antitumor immune responses in vivo. Together, our results reveal that LKB1 acts to restrain the exhausted state of ILC2 to maintain immune homeostasis and antitumor immunity.

Metabolic outcomes and changes in innate immunity induced by diesel exhaust particles airway exposure and high-fat high-sucrose diet

AIMS

Epidemiological studies have shown that exposure to diesel exhaust particles (DEP) is associated with metabolic diseases. We used mice with nonalcoholic fatty liver disease (NAFLD) caused by a high-fat, high-sucrose diet (HFHSD), which mimics a Western diet, to investigate the mechanism of NAFLD exacerbation via changes in innate immunity in the lungs by airway exposure to DEP.

MAIN METHODS

Six-week-old C57BL6/J male mice were fed HFHSD, and DEP was administered endotracheally once a week for eight weeks. The histology, gene expression, innate immunity cells in the lung and liver, and the serum inflammatory cytokine levels, were investigated.

KEY FINDINGS

Under the HFHSD, DEP increased blood glucose levels, serum lipid levels, and NAFLD activity scores, and also the expression of genes associated with inflammation in the lungs and liver. DEP caused an increase in ILC1s, ILC2s, ILC3s, and M1 macrophages in the lungs and a marked increase in ILC1s, ILC3s, M1 macrophages, and natural killer cells in the liver, while ILC2 levels were not changed. Furthermore, DEP caused high levels of inflammatory cytokines in the serum.

SIGNIFICANCE

Chronic exposure to DEP in HFHSD-fed mice increased inflammatory cells involved in innate immunity in the lungs and raised local inflammatory cytokine levels. This inflammation spread throughout the body, suggesting the association with the progression of NAFLD via increased inflammatory cells involved in innate immunity and inflammatory cytokine levels in the liver. These findings contribute to a better understanding of the role of innate immunity in air pollution-related systemic diseases, especially metabolic diseases.

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.

Role of Interleukin-1 Receptor-Like 1 (ST2) in Cerebrovascular Disease

Following both ischemic and hemorrhagic stroke, innate immune cells initiate a proinflammatory response that further exacerbate tissue injury in the acute phase, but these cells also play an important reparative role thereafter. Numerous cytokines and signaling pathways have been implicated in driving the deleterious proinflammatory response, but less is known about the mediators that connect the initial vascular injury to the systemic immune response and the relationship between proinflammatory and reparative immune responses. The Interleukin-33 (IL-33) and serum stimulation-2 (ST2) axis is an interleukin signaling pathway that is a prime candidate to fulfill this role. In this review, we describe the biology of the IL-33/ST2 system, present evidence that its soluble decoy receptor, soluble ST2 (sST2), plays a key role in secondary neurologic injury after stroke, and discuss this in the context of the known role of IL-33/ST2 in other disease.

Occupational Asthma Caused by Quaternary Ammonium Compounds: A Multicenter Cohort Study

BACKGROUND

Quaternary ammonium compounds (QACs) are used extensively for cleaning and disinfection and have been documented in scattered reports as a cause of occupational asthma (OA) through bronchoprovocation tests (BPTs).

OBJECTIVE

To examine the clinical, functional, and inflammatory profile of QAC-induced OA compared with OA caused by other low-molecular weight (LMW) agents.

METHODS

The study was conducted in a retrospective multicenter cohort of 871 subjects with OA ascertained by a positive BPT. Subjects with QAC-induced OA (n = 22) were identified based on a positive BPT to QACs after exclusion of those challenged with cleaning products or disinfectants that contained other potential respiratory sensitizers. They were compared with 289 subjects with OA caused by other LMW agents.

RESULTS

Most subjects with QAC-induced OA were working in the health care sector (n = 14). A twofold or greater increase in the postchallenge level of nonspecific bronchial hyperresponsiveness was recorded in eight of 11 subjects with QAC-induced OA (72.7%) and in 49.7% of those with OA caused by other LMW agents. Although sputum assessment was available in only eight subjects with QAC-induced OA, they showed a significantly greater median (interquartile) increase in sputum eosinophils (18.1% [range, 12.1% to 21.1%]) compared with those with OA caused by other LMW agents (2.0% [range, 0% to 5.2%]; P < .001).

CONCLUSIONS

This study indicates that QAC-induced OA is associated with a highly eosinophilic pattern of airway response and provides further evidence supporting the sensitizing potential of QACs. The findings highlight the heterogeneous nature of the pathobiologic pathways involved in OA caused by LMW agents.

Innate lymphoid cells in asthma: pathophysiological insights from murine models to human asthma phenotypes

PURPOSE OF REVIEW

The current review describes the role of different types of innate lymphoid cells (ILCs) in the pathogenesis of asthma inflammatory phenotypes by linking findings from murine asthma models with human studies. Novel treatment options are needed for patients with steroid-insensitive asthma. Strategies targeting ILCs, or their upstream or downstream molecules are emerging and discussed in this review.

RECENT FINDINGS

In eosinophilic asthma, ILCs, and especially type 2 ILCs (ILC2s), are activated by alarmins such as IL-33 upon allergen triggering of the airway epithelium. This initiates IL-5 and IL-13 production by ILC2, resulting in eosinophilic inflammation and airway hyperreactivity. Type 3 ILCs (ILC3s) have been shown to be implicated in obesity-induced asthma, via IL-1β production by macrophages, leading ILC3 and release of IL-17. ILC1s might play a role in severe asthma, but its role is currently less investigated.

SUMMARY

Several studies have revealed that ILC2s play a role in the induction of eosinophilic inflammation in allergic and nonallergic asthmatic patients mainly via IL-5, IL-13, IL-33 and thymic stromal lymphopoietin. Knowledge on the role of ILC3s and ILC1s in asthmatic patients is lagging behind. Further studies are needed to support the hypothesis that these other types of ILCs contribute to asthma pathogenesis, presumably in nonallergic asthma phenotypes.

Contribution of IDO to human respiratory syncytial virus infection

IDO is an enzyme that participates in the degradation of tryptophan (Trp), which is an essential amino acid necessary for vital cellular processes. The degradation of Trp and the metabolites generated by the enzymatic activity of IDO can have immunomodulating effects, notably over T cells, which are particularly sensitive to the absence of Trp and leads to the inhibition of T cell activation, cell death, and the suppression of T cell effector functions. Noteworthy, T cells participate in the cellular immune response against the human respiratory syncytial virus (hRSV) and are essential for viral clearance, as well as the total recovery of the host. Furthermore, inadequate or non‐optimal polarization of T cells is often seen during the acute phase of the disease caused by this pathogen. Here, we discuss the capacity of hRSV to exploit the immunosuppressive features of IDO to reduce T cell function, thus acquiring relevant aspects during the biology of the virus. Additionally, we review studies on the influence of IDO over T cell activation and its relationship with hRSV infection.

Ulinastatin protects rats from sepsis-induced acute lung injury by suppressing the JAK-STAT3 pathway

Sepsis is usually accompanied by pulmonary inflammations, leading to acute lung injury. During this process, endogenous factors that play a regulatory role could be exploited to therapeutically alleviate such lethal tissue injury. Here, we showed that ulinastatin (UTI) administration could reduce lung tissue necrosis and swelling during sepsis in rats. UTI treatment also decreased the levels of inflammatory mediators both in the lung and in the serum. Mechanistically, we showed that the phosphorylation levels of JAK2 and STAT3 in the lung of UTI-treated rats were lower than control rats and were correlated with the decreased levels of inflammatory mediators. Taken together, these results demonstrate the protective role of UTI in sepsis-induced acute lung injury.

Lysosome biogenesis regulated by the amino-acid transporter SLC15A4 is critical for functional integrity of mast cells

Mast cells possess specialized lysosomes, so-called secretory granules, which play a key role not only in allergic responses but also in various immune disorders. The molecular mechanisms that control secretory-granule formation are not fully understood. Solute carrier family member 15A4 (SLC15A4) is a lysosome-resident amino-acid/oligopeptide transporter that is preferentially expressed in hematopoietic lineage cells. Here, we demonstrated that SLC15A4 is required for mast-cell secretory-granule homeostasis, and limits mast-cell functions and inflammatory responses by controlling the mTORC1-TFEB signaling axis. In mouse Slc15a4-/- mast cells, diminished mTORC1 activity increased the expression and nuclear translocation of TFEB, a transcription factor, which caused secretory granules to degranulate more potently. This alteration of TFEB function in mast cells strongly affected the FcεRI-mediated responses and IL-33-triggered inflammatory responses both in vitro and in vivo. Our results reveal a close relationship between SLC15A4 and secretory-granule biogenesis that is critical for the functional integrity of mast cells.

Role of the TSLP-DC-OX40L pathway in asthma pathogenesis and airway inflammation in mice

This study aimed to explore the effect of the TSLP-DC-OX40L pathway in asthma pathogenesis and airway inflammation in mice. For this, 65 male BALF/c mice were distributed among the control, asthma, immunoglobulin G (IgG) + asthma (IgG, 500 μg/500 μL, intratracheal injection of 50 μL each time), LY294002 (OX40L inhibitor) + asthma (intratracheal injection of 2 mg/kg LY294002), and anti-TSLP + asthma (intratracheal injection of 500 μg/500 μL TSLP antibody, 50 μL each time) groups. ELISA was applied to measure the serum levels of immunoglobulin E (IgE), ovalbumin (OVA)-sIgE, interleukin-4 (IL-4), IL-5, IL-13, and interferon-γ (IFN-γ); flow cytometry was employed to detect Treg cells and dendritic cell (DC) and lymphopoiesis. RT-qPCR and Western blot assays were used to measure the levels of TSLP, OX40L, T-bet, GATA-3, NF-κB, p38, and ERK. Treatment with LY294002 and anti-TSLP resulted in increases in the numbers of total cells, eosinophils, neutrophils, and lymphocytes in the bronchoalveolar lavage fluid; total serum levels of IgE, OVA-sIgE, IL-4, IL-5, and IL-13; levels of DC cells; lymphopoiesis; and levels of TSLP, OX40L, GATA-3, NF-κB, p38, and ERK, whereas there were decreases in the levels of IFN-γ and CD4⁺CD25⁺Treg cells; CD4⁺Foxp3⁺Treg cells; and T-bet. The TSLP-DC-OX40L pathway may contribute to asthma pathogenesis and airway inflammation by modulating the levels of CD4⁺CD25⁺Treg cells and inflammatory cytokines.

New Insights Contributing to the Development of Effective Vaccines and Therapies to Reduce the Pathology Caused by hRSV

Human Respiratory Syncytial Virus (hRSV) is one of the major causes of acute lower respiratory tract infections (ALRTI) worldwide, leading to significant levels of immunocompromisation as well as morbidity and mortality in infants. Its main target of infection is the ciliated epithelium of the lungs and the host immune responses elicited is ineffective at achieving viral clearance. It is thought that the lack of effective immunity against hRSV is due in part to the activity of several viral proteins that modulate the host immune response, enhancing a Th2-like pro-inflammatory state, with the secretion of cytokines that promote the infiltration of immune cells to the lungs, with consequent damage. Furthermore, the adaptive immunity triggered by hRSV infection is characterized by weak cytotoxic T cell responses and secretion of low affinity antibodies by B cells. These features of hRSV infection have meant that, to date, no effective and safe vaccines have been licensed. In this article, we will review in detail the information regarding hRSV characteristics, pathology, and host immune response, along with several prophylactic treatments and vaccine prototypes. We will also expose significant data regarding the newly developed BCG-based vaccine that promotes protective cellular and humoral response against hRSV infection, which is currently undergoing clinical evaluation.

Prolonged activation of IL-5-producing ILC2 causes pulmonary arterial hypertrophy

IL-33 is one of the critical cytokines that activates group 2 innate lymphoid cells (ILC2s) and mediates allergic reactions. Accumulating evidence suggests that IL-33 is also involved in the pathogenesis of several chronic inflammatory diseases. Previously, we generated an IL-5 reporter mouse and revealed that lung IL-5-producing ILC2s played essential roles in regulating eosinophil biology. In this study, we evaluated the consequences of IL-33 administration over a long period, and we observed significant expansion of ILC2s and eosinophils surrounding pulmonary arteries. Unexpectedly, pulmonary arteries showed severe occlusive hypertrophy that was ameliorated in IL-5- or eosinophil-deficient mice, but not in Rag2-deficient mice. This indicates that IL-5-producing ILC2s and eosinophils play pivotal roles in pulmonary arterial hypertrophy. Administration of a clinically used vasodilator was effective in reducing IL-33-induced hypertrophy and repressed the expansion of ILC2s and eosinophils. Taken together, these observations demonstrate a previously unrecognized mechanism in the development of pulmonary arterial hypertrophy and the causative roles of ILC2 in the process.

Role of Eosinophil Granulocytes in Allergic Airway Inflammation Endotypes

Eosinophil granulocytes are intriguing members of the innate immunity system that have been considered important defenders during parasitic diseases as well as culprits during allergy-associated inflammatory diseases. Novel studies have, however, found new homoeostasis-maintaining roles for the cell. Recent clinical trials blocking different Th2 cytokines have uncovered that asthma is heterogeneous entity and forms different characteristic endotypes. Although eosinophils are present in allergic asthma with early onset, the cells may not be essential for the pathology. The cells are, however, likely disease causing in asthma with a late onset, which is often associated with chronic rhinosinusitis. Assessment of eosinophilia, fraction exhaled nitric oxide (FeNO) and periostin are markers that have emerged useful in assessing and monitoring asthma severity and endotype. Current scientific knowledge suggests that eosinophils are recruited by the inflammatory environment, activated by the innate interleukin (IL)-33 and prevented from apoptosis by both lymphocytes and innate immune cells such as type two innate immune cells. Eosinophils contain four specific granule proteins that exhibit an array of toxic and immune-modulatory activates. The granule proteins can be released by different mechanisms. Additionally, eosinophils contain a number of inflammatory cytokines and lipid mediators as well as radical oxygen species that might contribute to the disease both by the recruitment of other cells and the direct damage to supporting cells, leading to exacerbations and tissue fibrosis. This review aimed to outline current knowledge how eosinophils are recruited, activated and mediate damage to tissues and therapies used to control the cells.

PGI2 Controls Pulmonary NK Cells That Prevent Airway Sensitization to House Dust Mite Allergen

In allergic asthma, inhalation of airborne allergens such as the house dust mite (HDM) effectively activates both innate and adaptive immunity in the lung mucosa. To determine the role of the eicosanoid PGI₂ and its receptor IP during allergic airway sensitization, HDM responses in mice lacking a functional IP receptor (i.e., PGI₂ IP receptor-deficient [IP^-/-]) were compared with wild type (WT) mice. Surprisingly, IP^-/- mice had increased numbers of pulmonary CD3^-NK1.1⁺Ly49b⁺ NK cells producing IFN-γ that was inversely associated with the number of type 2 innate lymphoid cells (ILC2s) expressing IL-33Rα and IL-13 compared with WT animals. This phenomenon was associated with elevated CX₃CL1 levels in the airways of IP^-/- mice and treatment with a neutralizing Ab to CX₃CL1 reduced IFN-γ production by the lung NK cells. Remarkably, IP^-/- mice were less responsive to HDM challenge than WT counterparts because intranasal instillation of the allergen induced markedly reduced levels of airway eosinophils, CD4⁺ lymphocyte infiltration, and mucus production, as well as depressed levels of CCL2 chemokine and Th2 cytokines. NK cells were responsible for such attenuated responses because depletion of NK1.1⁺ cells in IP^-/- mice restored both the HDM-induced lung inflammation and ILC2 numbers, whereas transfer of CD3^-NK1.1⁺ NK cells into the airways of WT hosts suppressed the inflammatory response. Collectively, these data demonstrate a hitherto unknown role for PGI₂ in regulating the number and properties of NK cells resident in lung tissue and reveal a role for NK cells in limiting lung tissue ILC2s and preventing allergic inflammatory responses to inhaled HDM allergen.

Repeated Mouse Lung Exposures to Stachybotrys chartarum Shift Immune Response from Type 1 to Type 2

After a single or multiple intratracheal instillations of Stachybotrys chartarum (S. chartarum or black mold) spores in BALB/c mice, we characterized cytokine production, metabolites, and inflammatory patterns by analyzing mouse bronchoalveolar lavage (BAL), lung tissue, and plasma. We found marked differences in BAL cell counts, especially large increases in lymphocytes and eosinophils in multiple-dosed mice. Formation of eosinophil-rich granulomas and airway goblet cell metaplasia were prevalent in the lungs of multiple-dosed mice but not in single- or saline-dosed groups. We detected changes in the cytokine expression profiles in both the BAL and plasma. Multiple pulmonary exposures to S. chartarum induced significant metabolic changes in the lungs but not in the plasma. These changes suggest a shift from type 1 inflammation after an acute exposure to type 2 inflammation after multiple exposures to S. chartarum. Eotaxin, vascular endothelial growth factor (VEGF), MIP-1α, MIP-1β, TNF-α, and the IL-8 analogs macrophage inflammatory protein-2 (MIP-2) and keratinocyte chemoattractant (KC), had more dramatic changes in multiple- than in single-dosed mice, and parallel the cytokines that characterize humans with histories of mold exposures versus unexposed control subjects. This repeated exposure model allows us to more realistically characterize responses to mold, such as cytokine, metabolic, and cellular changes.

Relationships among aeroallergen sensitization, peripheral blood eosinophils, and periostin in pediatric asthma development

BACKGROUND

Biomarkers, preferably noninvasive, that predict asthma inception in children are lacking.

OBJECTIVE

Little is known about biomarkers of type 2 inflammation in early life in relation to asthma inception. We evaluated aeroallergen sensitization, peripheral blood eosinophils, and serum periostin as potential biomarkers of asthma in children.

METHODS

Children enrolled in the Childhood Origins of ASThma study were followed prospectively from birth. Blood samples were collected at ages 2, 4, 6, and 11 years, and serum-specific IgE levels, blood eosionophil counts, and periostin levels were measured in 244 children. Relationships among these biomarkers, age, and asthma were assessed.

RESULTS

Serum periostin levels were approximately 2- to 3-fold higher in children than previously observed adult levels. Levels were highest at 2 years (145 ng/mL), and did not change significantly between 4 and 11 years (128 and 130 ng/mL). Age 2 year periostin level of 150 ng/mL or more predicted asthma at age 6 years (odds ratio [OR], 2.3; 95% CI, 1.3-4.4). Eosinophil count of 300 cells/μL or more and aeroallergen sensitization at age 2 years were each associated with increased risk of asthma at age 6 years (OR, 3.1; 95% CI, 1.7-6.0 and OR, 3.3; 95% CI, 1.7-6.3). Children with any 2 of the biomarkers had a significantly increased risk of developing asthma by school age (≥2 biomarkers vs none: OR, 6.6; 95% CI, 2.7-16.0).

CONCLUSIONS

Serum periostin levels are significantly higher in children than in adults, likely due to bone turnover, which impairs clinical utility in children. Early life aeroallergen sensitization and elevated blood eosinophils are robust predictors of asthma development. Children with evidence of activation of multiple pathways of type 2 inflammation in early life are at greatest risk for asthma development.

Dysregulation of type 2 innate lymphoid cells and TH2 cells impairs pollutant-induced allergic airway responses

BACKGROUND

Although the prominent role of T_H2 cells in type 2 immune responses is well established, the newly identified type 2 innate lymphoid cells (ILC2s) can also contribute to orchestration of allergic responses. Several experimental and epidemiologic studies have provided evidence that allergen-induced airway responses can be further enhanced on exposure to environmental pollutants, such as diesel exhaust particles (DEPs). However, the components and pathways responsible remain incompletely known.

OBJECTIVE

We sought to investigate the relative contribution of ILC2 and adaptive T_H2 cell responses in a murine model of DEP-enhanced allergic airway inflammation.

METHODS

Wild-type, Gata-3^+/nlslacZ (Gata-3-haploinsufficient), RAR-related orphan receptor α (RORα)^fl/flIL7R^Cre (ILC2-deficient), and recombination-activating gene (Rag) 2^-/- mice were challenged with saline, DEPs, or house dust mite (HDM) or DEP+HDM. Airway hyperresponsiveness, as well as inflammation, and intracellular cytokine expression in ILC2s and T_H2 cells in the bronchoalveolar lavage fluid and lung tissue were assessed.

RESULTS

Concomitant DEP+HDM exposure significantly enhanced allergic airway inflammation, as characterized by increased airway eosinophilia, goblet cell metaplasia, accumulation of ILC2s and T_H2 cells, type 2 cytokine production, and airway hyperresponsiveness compared with sole DEPs or HDM. Reduced Gata-3 expression decreased the number of functional ILC2s and T_H2 cells in DEP+HDM-exposed mice, resulting in an impaired DEP-enhanced allergic airway inflammation. Interestingly, although the DEP-enhanced allergic inflammation was marginally reduced in ILC2-deficient mice that received combined DEP+HDM, it was abolished in DEP+HDM-exposed Rag2^-/- mice.

CONCLUSION

These data indicate that dysregulation of ILC2s and T_H2 cells attenuates DEP-enhanced allergic airway inflammation. In addition, a crucial role for the adaptive immune system was shown on concomitant DEP+HDM exposure.

Insights into Group 2 Innate Lymphoid Cells in Human Airway Disease

Recent discoveries have led to the identification of a novel group of immune cells, the innate lymphoid cells (ILCs). The members of this group are divided into three subpopulations: ILC1s, ILC2s, and ILC3s. ILC2s produce Th2 cytokines, IL-4, IL-5, and IL-13, upon activation by epithelial cell-derived cytokines, lipid mediators (cysteinyl leukotrienes and prostaglandin D2), and TNF family member TL1A and promote structural and immune cell responses in the airways after antigen exposure. In addition, ILC2 function is also influenced by inducible T cell costimulator (ICOS)/ICOS-ligand (ICOS-L) interactions via direct contact between immune cells. The most common airway antigens are allergens and viruses which are highly linked to the induction of airway diseases with underlying type 2 inflammation including asthma and allergic rhinitis. Based on recent findings linking ILC2s and airway Th2 responses, there is intensive investigation into the role of ILC2s in human disease with the hope of a better understanding of the pathophysiology and the discovery of novel potential therapeutic targets. This review summarizes the recent advances made in elucidating ILC2 involvement in human Th2 airway disease.

Interleukin 13-positive mast cells are increased in immunoglobulin G4-related sialadenitis

Interleukin (IL)-13 is a T helper 2 (Th2) cytokine that plays important roles in the pathogenesis of asthma. IL-13 induces hypersensitivity of the airways, increased mucous production, elevated serum immunoglobulin (Ig) E levels, and increased numbers of eosinophils. Many patients with IgG4-related disease have allergic backgrounds and show elevated serum IgE levels and an increase in the number of eosinophils. Upregulation of Th2/regulatory T (Treg) cytokines, including IL-13, has been detected in affected tissues of patients with IgG4-related disease. We previously reported that mast cells might be responsible for the production of the Th2/Treg cytokines IL-4, IL-10, and transforming growth factor (TGF)-β1 in IgG4-related disease. In this study, immunohistochemical analysis showed increased numbers of IL-13-positive mast cells in IgG4-related disease, which suggests that mast cells also produce IL-13 and contribute to elevation of serum IgE levels and eosinophil infiltration in IgG4-related disease.

Innate lymphoid cells and cytokines of the novel subtypes of helper T cells in asthma

BACKGROUND

In this study, the expression of interleukin-9 (IL-9), IL-17, IL-22, and IL-25 genes that might be the potential predisposing factors for asthma as well as count of innate lymphoid cells (ILCs) as another source of inflammatory cytokines have been evaluated.

OBJECTIVE

The aim of this study was to evaluate the expression of newly identified helper T cells signature cytokines and amount of ILCs.

METHODS

Blood and sputum samples from 23 patients with moderate to severe asthma and 23 healthy volunteers were collected. The types of allergens to which our patients were sensitive were defined using immunoblotting method. Gene expression of studied cytokines was evaluated using quantitative transcription-polymerase chain reaction and ILCs were counted by the flow cytometry method.

RESULTS

In this research, the gene expressions of IL-9, IL-17, IL-22, and IL-25 were significantly higher in asthmatics, especially in the severe form of the disease. This increase was even higher in serum samples compared with sputum samples. Counting ILCs revealed their increase in comparison with normal people.

CONCLUSION

We showed the importance of IL-25, IL-22, IL-17, and IL-9 cytokines in patients with asthma as their expression levels are increased and these increase are correlated with the severity of the disease. We also showed that the increased amount of ILCs in asthmatics could confirm their potential role in the immunopathogenesis of asthma as another source of inflammatory cytokines.

Type 2 Innate Lymphoid Cells in Allergic Disease

Type II innate lymphoid cells (ILC2) are a novel population of lineage-negative cells that produce high levels of Th2 cytokines IL-5 and IL-13. ILC2 are found in human respiratory and gastrointestinal tissue as well as in skin. Studies from mouse models of asthma and atopic dermatitis suggest a role for ILC2 in promoting allergic inflammation. The epithelial cytokines IL-25, IL-33, and TSLP, as well as the lipid mediator leukotriene D4, have been shown to potently activate ILC2 under specific conditions and supporting the notion that many separate pathways in allergic disease may result in stimulation of ILC2. Ongoing investigations are required to better characterize the relative contribution of ILC2 in allergic inflammation as well as mechanisms by which other cell types including conventional T cells regulate ILC2 survival, proliferation, and cytokine production. Importantly, therapeutic strategies to target ILC2 may reduce allergic inflammation in afflicted individuals. This review summarizes the development, surface marker profile, cytokine production, and upstream regulation of ILC2, and focuses on the role of ILC2 in common allergic diseases.

Group 2 innate lymphoid cells in lung inflammation

Although allergic asthma is a heterogeneous disease, allergen-specific T helper 2 (Th2) cells producing the key cytokines involved in type 2 inflammation, interleukin-4 (IL-4), IL-5 and IL-13, are thought to play a major role in asthma pathogenesis. This model is challenged by the recent discovery of group 2 innate lymphoid cells (ILC2) that represent a critical innate source of type 2 cytokines. These ILC2 are activated by epithelial cell-derived cytokines, including IL-25 and IL-33, which have been implicated in the initiation of asthma. In this review, we will discuss recent studies supporting a significant role for ILC2 in lung inflammation, with special attention to allergen-induced asthma.

Modulation of Signal Strength Switches Notch from an Inducer of T Cells to an Inducer of ILC2

Innate lymphoid cells (ILCs) are emerging key players of the immune system with close lineage relationship to T cells. ILC2 play an important role in protective immunity against multicellular parasites, but are also involved in the pathogenesis of type 2 immune diseases. Here, we have studied the developmental requirements for human ILC2. We report that ILC2 are present in the thymus of young human donors, possibly reflecting local differentiation. Furthermore, we show that uncommitted lineage⁻CD34⁺CD1a⁻human thymic progenitors have the capacity to develop into ILC2 in vitro under the influence of Notch signaling, either by stimulation with the Notch ligand Delta like 1 (Dll1) or by expression of the active intracellular domain of NOTCH1 (NICD1). The capacity of NICD1 to mobilize the ILC2 differentiation program was sufficiently potent to override commitment to the T cell lineage in CD34⁺CD1a⁺ progenitors and force them into the ILC2 lineage. As Notch is an important factor also for T cell development, these results raise the question how one and the same signaling pathway can elicit such distinct developmental outcomes from the same precursors. We provide evidence that Notch signal strength is a critical determinant in this decision: by tuning signal amplitude, Notch can be converted from a T cell inducer (low signal strength) to an ILC2 inducer (high signal strength). Thus, this study enhances our understanding of human ILC2 development and identifies a mechanism determining specificity of Notch signal output during T cell and ILC2 differentiation.