Update on innate lymphoid cells in atopic and non-atopic inflammation in the airways and skin

Innate lymphoid cells: a new key player in atopic dermatitis

Atopic dermatitis (AD) is a common allergic inflammatory skin condition mainly caused by gene variants, immune disorders, and environmental risk factors. The T helper (Th) 2 immune response mediated by interleukin (IL)-4/13 is generally believed to be central in the pathogenesis of AD. It has been shown that innate lymphoid cells (ILCs) play a major effector cell role in the immune response in tissue homeostasis and inflammation and fascinating details about the interaction between innate and adaptive immunity. Changes in ILCs may contribute to the onset and progression of AD, and ILC2s especially have gained much attention. However, the role of ILCs in AD still needs to be further elucidated. This review summarizes the role of ILCs in skin homeostasis and highlights the signaling pathways in which ILCs may be involved in AD, thus providing valuable insights into the behavior of ILCs in skin homeostasis and inflammation, as well as new approaches to treating AD.

Relationship between Immune Cells, Depression, Stress, and Psoriasis: Could the Use of Natural Products Be Helpful?

Psoriasis is one of the most widespread chronic inflammatory skin diseases, affecting about 2%-3% of the worldwide adult population. The pathogenesis of this disease is quite complex, but an interaction between genetic and environmental factors has been recognized with an essential modulation of inflammatory and immune responses in affected patients. Psoriatic plaques generally represent the clinical psoriatic feature resulting from an abnormal proliferation and differentiation of keratinocytes, which cause dermal hyperplasia, skin infiltration of immune cells, and increased capillarity. Some scientific pieces of evidence have reported that psychological stress may play a key role in psoriasis, and the disease itself may cause stress conditions in patients, thus reproducing a vicious cycle. The present review aims at examining immune cell involvement in psoriasis and the relationship of depression and stress in its pathogenesis and development. In addition, this review contains a focus on the possible use of natural products, thus pointing out their mechanism of action in order to counteract clinical and psychological symptoms.

Innate Lymphoid Cells in Tissue Homeostasis and Disease Pathogenesis

Innate lymphoid cells (ILCs) are the most recently discovered family of innate immune cells. ILCs can be categorized into three groups on the basis of the transcription factors that direct their functions and the cytokines they produce. Notably, these functions parallel the effector functions of T lymphocytes. ILCs play a frontline role in host defense and tissue homeostasis by responding rapidly to environmental factors, conducting effector responses in a tissue-specific manner, and interacting with hematopoietic and non-hematopoietic cells throughout the body. Moreover, recent studies reveal that ILCs are involved in development of various inflammatory diseases, such as respiratory diseases, autoimmune diseases, or cancer. In this review, we discuss the recent findings regarding the biology of ILCs in health and inflammatory diseases.

Innate Lymphocytes in Inflammatory Arthritis

Inflammatory arthritis (IA) refers to a group of chronic diseases, including rheumatoid arthritis (RA), psoriatic arthritis (PsA), ankylosing spondylitis (AS), and other spondyloarthritis (SpA). IA is characterized by autoimmune-mediated joint inflammation and is associated with inflammatory cytokine networks. Innate lymphocytes, including innate-like lymphocytes (ILLs) expressing T or B cell receptors and innate lymphoid cells (ILCs), play important roles in the initiation of host immune responses against self-antigens and rapidly produce large amounts of cytokines upon stimulation. TNF (Tumor Necrosis Factor)-α, IFN (Interferon)-γ, Th2-related cytokines (IL-4, IL-9, IL-10, and IL-13), IL-17A, IL-22, and GM-CSF are involved in IA and are secreted by ILLs and ILCs. In this review, we focus on the current knowledge of ILL and ILC phenotypes, cytokine production and functions in IA. A better understanding of the roles of ILLs and ILCs in IA initiation and development will ultimately provide insights into developing effective strategies for the clinical treatment of IA patients.

Primary Sjogren Syndrome: Focus on Innate Immune Cells and Inflammation

Primary Sjogren Syndrome (pSS) is a complex, multifactorial rheumatic disease that mainly targets salivary and lacrimal glands, inducing epithelitis. The cause behind the autoimmunity outbreak in pSS is still elusive; however, it seems related to an aberrant reaction to exogenous triggers such as viruses, combined with individual genetic pre-disposition. For a long time, autoantibodies were considered as the hallmarks of this disease; however, more recently the complex interplay between innate and adaptive immunity as well as the consequent inflammatory process have emerged as the main mechanisms of pSS pathogenesis. The present review will focus on innate cells and on the principal mechanisms of inflammation connected. In the first part, an overview of innate cells involved in pSS pathogenesis is provided, stressing in particular the role of Innate Lymphoid Cells (ILCs). Subsequently we have highlighted the main inflammatory pathways, including intra- and extra-cellular players. A better knowledge of such processes could determine the detection of new therapeutic targets that are a major need for pSS.

ILC2 Lung-Homing in Cystic Fibrosis Patients: Functional Involvement of CCR6 and Impact on Respiratory Failure

Cystic fibrosis patients suffer from a progressive, often fatal lung disease, which is based on a complex interplay between chronic infections, locally accumulating immune cells and pulmonary tissue remodeling. Although group-2 innate lymphoid cells (ILC2s) act as crucial initiators of lung inflammation, our understanding of their involvement in the pathogenesis of cystic fibrosis remains incomplete. Here we report a marked decrease of circulating CCR6⁺ ILC2s in the blood of cystic fibrosis patients, which significantly correlated with high disease severity and advanced pulmonary failure, strongly implicating increased ILC2 homing from the peripheral blood to the chronically inflamed lung tissue in cystic fibrosis patients. On a functional level, the CCR6 ligand CCL20 was identified as potent promoter of lung-directed ILC2 migration upon inflammatory conditions in vitro and in vivo using a new humanized mouse model with light-sheet fluorescence microscopic visualization of lung-accumulated human ILC2s. In the lung, blood-derived human ILC2s were able to augment local eosinophil and neutrophil accumulation and induced a marked upregulation of pulmonary type-VI collagen expression. Studies in primary human lung fibroblasts additionally revealed ILC2-derived IL-4 and IL-13 as important mediators of this type-VI collagen-inducing effect. Taken together, the here acquired results suggest that pathologically increased CCL20 levels in cystic fibrosis airways induce CCR6-mediated lung homing of circulating human ILC2s. Subsequent ILC2 activation then triggers local production of type-VI collagen and might thereby drive extracellular matrix remodeling potentially influencing pulmonary tissue destruction in cystic fibrosis patients. Thus, modulating the lung homing capacity of circulating ILC2s and their local effector functions opens new therapeutic avenues for cystic fibrosis treatment.

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.

New insights into the function, development, and plasticity of type 2 innate lymphoid cells

Group 2 innate lymphoid cells (ILC2s) are the most well defined group of ILCs. ILC2 development is controlled by the GATA-3 transcription factor and these cells produce archetypal type 2 cytokines, such as IL-5 and IL-13. These cytokines mediate parasite expulsion and tissue repair, but also contribute to type 2 inflammatory diseases, including allergy, asthma and chronic rhinosinusitis with nasal polyps. In response to tightly regulated local environmental cues ILCs can generate characteristics of other subtypes, a process known as plasticity. Recent advances in the ILC2 field has led to the discovery that ILC2s can promptly shift to functional IFN-γ-producing ILC1s or IL-17-producing ILC3s, depending on the cytokines and chemokines produced by antigen presenting cells or epithelial cells. Due to yet unknown triggers, this complex network of signals may become dysregulated. In this review, we will discuss general ILC characteristic, ILC2 development, plasticity, memory function, and implications in disease.

A Derivative of Butyric Acid, the Fermentation Metabolite of Staphylococcus epidermidis, Inhibits the Growth of a Staphylococcus aureus Strain Isolated from Atopic Dermatitis Patients

The microbiome is a rich source of metabolites for the development of novel drugs. Butyric acid, for example, is a short-chain fatty acid fermentation metabolite of the skin probiotic bacterium Staphylococcus epidermidis (S. epidermidis). Glycerol fermentation of S. epidermidis resulted in the production of butyric acid and effectively hindered the growth of a Staphylococcus aureus (S. aureus) strain isolated from skin lesions of patients with atopic dermatitis (AD) in vitro and in vivo. This approach, however, is unlikely to be therapeutically useful since butyric acid is malodorous and requires a high concentration in the mM range for growth suppression of AD S. aureus. A derivative of butyric acid, BA–NH–NH–BA, was synthesized by conjugation of two butyric acids to both ends of an –NH–O–NH– linker. BA–NH–NH–BA significantly lowered the concentration of butyric acid required to inhibit the growth of AD S. aureus. Like butyric acid, BA–NH–NH–BA functioned as a histone deacetylase (HDAC) inhibitor by inducing the acetylation of Histone H3 lysine 9 (AcH3K9) in human keratinocytes. Furthermore, BA–NH–NH–BA ameliorated AD S. aureus-induced production of pro-inflammatory interleukin (IL)-6 and remarkably reduced the colonization of AD S. aureus in mouse skin. These results describe a novel derivative of a skin microbiome fermentation metabolite that exhibits anti-inflammatory and S. aureus bactericidal activity.

Dynamics of helper CD4 T cells during acute and stable allergic asthma

Asthma comprises heterogeneous clinical subtypes driven by diverse pathophysiological mechanisms. We characterized the modulation of the inflammatory environment with the phenotype, gene expression, and function of helper CD4 T cells among acutely exacerbated and stable asthma patients. Systemic Th2 immune deviation (IgE and Th2 cytokines) and inflammation (IL-6, CRP) were associated with increased Th17 cells during acute asthma. Th2/Th17 cell differentiation during acute asthma was regulated by the enhanced expression of transcription factors (c-MAF, IRF-4). The development of pathogenic Th2 cells during acute asthma was characterized by the secretion of inflammatory cytokines coupled with Th2 molecules and PPARγ expression. The acquisition of CD15S, CD39, CD101, and CCR4 contributed to the increased heterogeneity of Regulatory T cells during asthma. Two clusters were derived from above cytokines, CD4 T cell phenotypes, and clinical data. Cluster 1, characterized by high eosinophils, Th2 and ILC2 frequencies, and higher exacerbation rates, may represent Th2-high subtype. Cluster 2 represents a more complex subtype; it is constituted by higher neutrophils or Th17 frequencies, higher inhaled corticosteroids dose and poor asthma control. In conclusion, we characterized systematically and longitudinally Th2-high and non-Th2 asthma subtypes and the heterogeneity of CD4 T cells in stable and acute asthma.

Human innate lymphoid cells (ILCs) in filarial infections

Filarial infections are characteristically chronic and can cause debilitating diseases governed by parasite-induced innate and adaptive immune responses. Filarial parasites traverse or establish niches in the skin (migrating infective larvae), in nonmucosal tissues (adult parasite niche) and in the blood or skin (circulating microfilariae) where they intersect with the host immune response. While several studies have demonstrated that filarial parasites and their antigens can modulate myeloid cells (monocyte, macrophage and dendritic cell subsets), T- and B-lymphocytes and skin resident cell populations, the role of innate lymphoid cells during filarial infections has only recently emerged. Despite the identification and characterization of innate lymphoid cells (ILCs) in murine helminth infections, little is actually known about the role of human ILCs during parasitic infections. The focus of this review will be to highlight the composition of ILCs in the skin, lymphatics and blood; where the host-parasite interaction is well-defined and to examine the role of ILCs during filarial infections.

Prostaglandin E2 suppresses human group 2 innate lymphoid cell function

Background

Group 2 innate lymphoid cells (ILC2s) are involved in the initial phase of type 2 inflammation and can amplify allergic immune responses by orchestrating other type 2 immune cells. Prostaglandin (PG) E₂ is a bioactive lipid that plays protective roles in the lung, particularly during allergic inflammation.

Objective

We set out to investigate how PGE₂ regulates human ILC2 function.

Methods

The effects of PGE₂ on human ILC2 proliferation and intracellular cytokine and transcription factor expression were assessed by means of flow cytometry. Cytokine production was measured by using ELISA, and real-time quantitative PCR was performed to detect PGE₂ receptor expression.

Results

PGE₂ inhibited GATA-3 expression, as well as production of the type 2 cytokines IL-5 and IL-13, from human tonsillar and blood ILC2s in response to stimulation with a combination of IL-25, IL-33, thymic stromal lymphopoietin, and IL-2. Furthermore, PGE₂ downregulated the expression of IL-2 receptor α (CD25). In line with this observation, PGE₂ decreased ILC2 proliferation. These effects were mediated by the combined action of E-type prostanoid receptor (EP) 2 and EP4 receptors, which were specifically expressed on ILC2s.

Conclusion

Our findings reveal that PGE₂ limits ILC2 activation and propose that selective EP2 and EP4 receptor agonists might serve as a promising therapeutic approach in treating allergic diseases by suppressing ILC2 function.

Dysregulation of Innate Lymphoid Cells in Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is the most prevalent symptomatic primary immune deficiency. With widespread use of immunoglobulin replacement therapy, non-infectious complications, such as autoimmunity, chronic intestinal inflammation, and lung disease, have replaced infections as the major cause of morbidity and mortality in this immune deficiency. The pathogenic mechanisms that underlie the development of these complications in CVID are not known; however, there have been numerous associated laboratory findings. Among the most intriguing of these associations is elevation of interferon signature genes in CVID patients with inflammatory/autoimmune complications, as a similar gene expression profile is found in systemic lupus erythematosus and other chronic inflammatory diseases. Linked with this heightened interferon signature in CVID is an expansion of circulating IFN-γ-producing innate lymphoid cells. Innate lymphoid cells are key regulators of both protective and pathogenic immune responses that have been extensively studied in recent years. Further exploration of innate lymphoid cell biology in CVID may uncover key mechanisms underlying the development of inflammatory complications in these patients and may inspire much needed novel therapeutic approaches.

IL33-mediated ILC2 activation and neutrophil IL5 production in the lung response after severe trauma: A reverse translation study from a human cohort to a mouse trauma model

BACKGROUND

The immunosuppression and immune dysregulation that follows severe injury includes type 2 immune responses manifested by elevations in interleukin (IL) 4, IL5, and IL13 early after injury. We hypothesized that IL33, an alarmin released early after tissue injury and a known regulator of type 2 immunity, contributes to the early type 2 immune responses after systemic injury.

METHODS AND FINDINGS

Blunt trauma patients admitted to the trauma intensive care unit of a level I trauma center were enrolled in an observational study that included frequent blood sampling. Dynamic changes in IL33 and soluble suppression of tumorigenicity 2 (sST2) levels were measured in the plasma and correlated with levels of the type 2 cytokines and nosocomial infection. Based on the observations in humans, mechanistic experiments were designed in a mouse model of resuscitated hemorrhagic shock and tissue trauma (HS/T). These experiments utilized wild-type C57BL/6 mice, IL33-/- mice, B6.C3(Cg)-Rorasg/sg mice deficient in group 2 innate lymphoid cells (ILC2), and C57BL/6 wild-type mice treated with anti-IL5 antibody. Severely injured human blunt trauma patients (n = 472, average injury severity score [ISS] = 20.2) exhibited elevations in plasma IL33 levels upon admission and over time that correlated positively with increases in IL4, IL5, and IL13 (P < 0.0001). sST2 levels also increased after injury but in a delayed manner compared with IL33. The increases in IL33 and sST2 were significantly greater in patients that developed nosocomial infection and organ dysfunction than similarly injured patients that did not (P < 0.05). Mechanistic studies were carried out in a mouse model of HS/T that recapitulated the early increase in IL33 and delayed increase in sST2 in the plasma (P < 0.005). These studies identified a pathway where IL33 induces ILC2 activation in the lung within hours of HS/T. ILC2 IL5 up-regulation induces further IL5 expression by CXCR2+ lung neutrophils, culminating in early lung injury. The major limitations of this study are the descriptive nature of the human study component and the impact of the potential differences between human and mouse immune responses to polytrauma. Also, the studies performed did not permit us to make conclusions about the impact of IL33 on pulmonary function.

CONCLUSIONS

These results suggest that IL33 may initiate early detrimental type 2 immune responses after trauma through ILC2 regulation of neutrophil IL5 production. This IL33-ILC2-IL5-neutrophil axis defines a novel regulatory role for ILC2 in acute lung injury that could be targeted in trauma patients prone to early lung dysfunction.

An Update on the Pathophysiology of Atopic Dermatitis

Atopic dermatitis (AD) is increasingly recognized as a complex, inflammatory skin disease involving interplay of multiple elements. This article notes key advances in understanding of immune dysregulation, skin barrier dysfunction, environmental, genetic, and microbial influences orchestrating disease pathogenesis, and the relevance of therapeutic interventions in each area. Accumulating evidence and the discovery of new T-cell subsets has matured AD as a multiple-cytokine-axes-driven disorder, evolved from the widely held belief of it being a biphasic Th1/Th2 disease. These new insights have led to active trials testing multiple, targeted therapeutics with better efficacy and safety-profiles.

Skin barrier in atopic dermatitis: beyond filaggrin

Atopic dermatitis is a chronic inflammatory skin disease with a complex pathogenesis, where changes in skin barrier and imbalance of the immune system are relevant factors. The skin forms a mechanic and immune barrier, regulating water loss from the internal to the external environment, and protecting the individual from external aggressions, such as microorganisms, ultraviolet radiation and physical trauma. Main components of the skin barrier are located in the outer layers of the epidermis (such as filaggrin), the proteins that form the tight junction (TJ) and components of the innate immune system. Recent data involving skin barrier reveal new information regarding its structure and its role in the mechanic-immunological defense; atopic dermatitis (AD) is an example of a disease related to dysfunctions associated with this complex.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

Prostaglandin I2 Signaling and Inhibition of Group 2 Innate Lymphoid Cell Responses

RATIONALE

Group 2 innate lymphoid cells (ILC2s) robustly produce IL-5 and IL-13, cytokines central to the asthma phenotype; however, the effect of prostaglandin (PG) I2 on ILC2 function is unknown.

OBJECTIVES

To determine the effect of PGI2 on mouse and human ILC2 cytokine expression in vitro and the effect of endogenous PGI2 and the PGI2 analog cicaprost on lung ILC2s in vivo.

METHODS

Flow-sorted bone marrow ILC2s of wild-type (WT) and PGI2 receptor-deficient (IP(-/-)) mice were cultured with IL-33 and treated with the PGI2 analog cicaprost. WT and IP(-/-) mice were challenged intranasally with Alternaria alternata extract for 4 consecutive days to induce ILC2 responses, and these were quantified. Prior to A. alternata extract, challenged WT mice were treated with cicaprost. Human flow-sorted peripheral blood ILC2s were cultured with IL-33 and IL-2 and treated with the PGI2 analog cicaprost.

MEASUREMENT AND MAIN RESULTS

We demonstrate that PGI2 inhibits IL-5 and IL-13 protein expression by IL-33-stimulated ILC2s purified from mouse bone marrow in a manner that was dependent on signaling through the PGI2 receptor IP. In a mouse model of 4 consecutive days of airway challenge with an extract of A. alternata, a fungal aeroallergen associated with severe asthma exacerbations, endogenous PGI2 signaling significantly inhibited lung IL-5 and IL-13 protein expression, and reduced the number of lung IL-5- and IL-13-expressing ILC2s, as well as the mean fluorescence intensity of IL-5 and IL-13 staining. In addition, exogenous administration of a PGI2 analog inhibited Alternaria extract-induced lung IL-5 and IL-13 protein expression, and reduced the number of lung IL-5- and IL-13-expressing ILC2s and the mean fluorescence intensity of IL-5 and IL-13 staining. Finally, a PGI2 analog inhibited IL-5 and IL-13 expression by human ILC2s that were stimulated with IL-2 and IL-33.

CONCLUSIONS

These results suggest that PGI2 may be a potential therapy to reduce the ILC2 response to protease-containing aeroallergens, such as Alternaria.

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.

Immune Mechanisms of Chronic Rhinosinusitis

Chronic rhinosinusitis (CRS) is a common inflammatory disease that results in a significant decrease in patient quality of life and a large economic burden. However, the lack of population-based epidemiologic studies and robust model systems has made it difficult to fully elucidate the key inflammatory pathways that drive the chronic inflammatory responses observed in CRS. This review will highlight the wide variety of factors that likely contribute to CRS disease pathogenesis. Defects in the innate immune function of the airway epithelium, including decreases in barrier function, mucociliary clearance, and production of antimicrobial peptides, all likely play a role in the initial inflammatory response. Subsequent recruitment and activation of eosinophils, mast cells, and innate lymphoid cells (ILCs) further contributes to the chronic inflammatory response and directly activates adaptive immune cells, including T and B cells. However, development of new tools and model systems is still needed to further understand the chronicity of this inflammatory response and which specific factors are necessary or sufficient to drive CRS pathogenesis. Such studies will be critical for the development of improved therapeutic strategies aimed at treating this highly prevalent and costly disease.

Innate lymphoid cells in graft-versus-host disease

Innate lymphoid cells (ILC) are lymphocytes lacking rearranged antigen receptors such as those expressed by T and B cells. ILC are important effector and regulatory cells of the innate immune system, controlling lymphoid organogenesis, tissue inflammation, and homeostasis. The family of ILC consists of cytotoxic NK cells and the more recently described noncytotoxic group 1, 2, and 3 ILC. The classification of noncytotoxic ILC-in many aspects-mirrors that of T helper cells, which is based on the expression of master transcription factors and signature cytokines specific for each subset. The IL-22 producing RORγt(+) ILC3 subset was recently found to be critical in the prevention of intestinal graft-versus-host disease (GVHD) following allogeneic hematopoietic cell transplantation (HCT) via strengthening the intestinal mucosal barrier. In this review, we summarize the current view of the immunological functions of human noncytotoxic ILC subsets and discuss the potentially beneficial features of IL-22 producing ILC3 in improving allo-HCT efficacy by attenuating susceptibility to GVHD. In addition, we explore the possibility of other ILC subsets playing a role in GVHD.

Pathogenesis of nasal polyposis

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a complex inflammatory condition that affects a large proportion of the population world-wide and is associated with high cost of management and significant morbidity. Yet, there is a lack of population-based epidemiologic studies using current definitions of CRSwNP, and the mechanisms that drive pathogenesis in this disease remain unclear. In this review, we summarize the current evidence for the plethora of factors that likely contribute to CRSwNP pathogenesis. Defects in the innate function of the airway epithelial barrier, including diminished expression of antimicrobial products and loss of barrier integrity, combined with colonization by fungi and bacteria likely play a critical role in the development of chronic inflammation in CRSwNP. This chronic inflammation is characterized by elevated expression of many key inflammatory cytokines and chemokines, including IL-5, thymic stromal lymphopoietin and CCL11, that help to initiate and perpetuate this chronic inflammatory response. Together, these factors likely combine to drive the influx of a variety of immune cells, including eosinophils, mast cells, group 2 innate lymphoid cells and lymphocytes, which participate in the chronic inflammatory response within the nasal polyps. Importantly, however, future studies are needed to demonstrate the necessity and sufficiency of these potential drivers of disease in CRSwNP. In addition to the development of new tools and models to aid mechanistic studies, the field of CRSwNP research also needs the type of robust epidemiologic data that has served the asthma community so well. Given the high prevalence, costs and morbidity, there is a great need for continued research into CRS that could facilitate the development of novel therapeutic strategies to improve treatment for patients who suffer from this disease.

Innate lymphocyte cells in asthma phenotypes

T helper type 2 (T_H2) cells were previously thought to be the main initiating effector cell type in asthma; however, exaggerated T_H2 cell activities alone were insufficient to explain all aspects of asthma. Asthma is a heterogeneous syndrome comprising different phenotypes that are characterized by their different clinical features, treatment responses, and inflammation patterns. The most-studied subgroups of asthma include T_H2-associated early-onset allergic asthma, late-onset persistent eosinophilic asthma, virus-induced asthma, obesity-related asthma, and neutrophilic asthma. The recent discovery of human innate lymphoid cells capable of rapidly producing large amounts of cytokines upon activation and the mouse data pointing to an essential role for these cells in asthma models have emphasized the important role of the innate immune system in asthma and have provided a new means of better understanding asthma mechanisms and differentiating its phenotypes.

Eosinophilia in Pulmonary Disorders

Lung disease associated with marked peripheral blood eosinophilia is unusual and nearly always clinically significant. Once recognized, it is generally easy to manage, albeit with long-term systemic corticosteroids. A failure to respond to oral steroids in the context of good compliance suggests a malignant cause for the eosinophilia. An important development is the introduction of antieosinophil therapies, particularly those directed against the interleukin 5 pathway, which is hoped to provide benefit in the full spectrum of eosinophilic lung disease as well as asthma, reducing the burden of side effects and resultant comorbidities.

Epithelial cytokines and pulmonary allergic inflammation

The triad of epithelial derived cytokines, IL-25, IL-33 and TSLP are important for the initiation and development of pulmonary immune responses to environmental stimuli. Data from experiments using mouse models provide compelling evidence for their involvement in both innate and adaptive immunity to drive type-2 responses, allergic inflammation and airway remodelling. These cytokines are known to be expressed in human lung tissue and immune cells, however their involvement in mediating allergic pulmonary responses in patients is less clear than in murine models of disease. This article focuses on evidence for the role of IL-25, IL-33 and TSLP in human allergic disease and discusses their potential as therapeutic targets for severe asthma.

Effects of oral administration of Lactobacillus acidophilus L-92 on the symptoms and serum cytokines of atopic dermatitis in Japanese adults: a double-blind, randomized, clinical trial

OBJECTIVES

Several studies on lactobacilli have demonstrated they are effective against atopic dermatitis (AD) in children, but there are very few reports of their effects in adults. We investigated the changes in AD symptoms in adults after the ingestion of the Lactobacillus acidophilus strain L-92 (L-92), which has been shown to have a curative effect on AD in children.

METHODS

A double-blind, parallel-group, placebo-controlled comparison was performed on 49 AD patients aged ≥16 years using heat-killed L-92. Skin lesions were assessed using the SCORing AD (SCORAD) index before the start of L-92 ingestion and 4 and 8 weeks after ingestion. Serum cytokine and blood marker levels were measured 8 weeks after the start of L-92 ingestion.

RESULTS

The group that ingested L-92 had lower SCORAD scores than the controls (p = 0.002). The L-92 group also had decreased ratios of change for eosinophil count (p = 0.03) and increased ratios of change for serum TGF-β (p = 0.03). Ratios of change for serum TGF-β rose significantly (p = 0.04) in patients showing mitigated symptoms with L-92 administration.

CONCLUSIONS

Administration of heat-killed L-92 was effective for AD symptoms in adults. L-92 may contribute to the suppression of Th2-dominant inflammation. Our preliminary trial is the first to report the effects of L-92 on adult AD.

Innate lymphoid cells in the skin

Innate lymphoid cells (ILCs) are part of a heterogeneous family of innate immune cells with newly identified roles in mediating immunity, tissue homeostasis and pathologic inflammation. Here, we review recent studies delineating the roles of ILCs in the pathogenesis of multiple inflammatory skin disorders and their unique effector functions. Finally, we address how these studies have informed our understanding of the regulation of ILCs and the therapeutic potential of targeting these cells in the context of skin inflammation.