The immunogenetics of asthma and eczema: a new focus on the epithelium

Analysis of the mechanism for the development of allergic skin inflammation and the application for its treatment: overview of the pathophysiology of atopic dermatitis

It has been recognized that atopic dermatitis (AD) involves allergen-driven Th2 cell polarization. In patients with AD, cytokines induce allergic inflammatory responses and subsequently enhance IgE production. Recent reports revealed that a reduced barrier function as well as altered immunity are fundamental to the development of AD because barrier disruption due to aberrant filaggrin expression is a pathological factor. However, although recent studies have improved our understanding of the pathogenesis of AD, the overall pathophysiology remains elusive. I herein discuss it based on the natural history of AD.

Acquired somatic mutations in the microsatellite DNA, in children with bronchial asthma

OBJECTIVES

High incidence of genetic alterations at the microsatellite (MS) DNA level has been reported in asthmatic adults.

WORKING HYPOTHESIS

The aim of this study was to investigate whether microsatellite instability (MSI) and loss of heterozygosity (LOH) were detectable phenomena in children with asthma.

METHODOLOGY

DNA was extracted from sputum and blood cells of 27 children (10.8 +/- 2.5 years) with mild to moderate asthma, and from 8 healthy, never-smoked young adults. Fourteen polymorphic MS markers, namely D5S207, D5S820, D5S637, D6S344, D6S2223, D6S263, SGC35231, D11S1253, D11S1337, D11S97, USAT24G1, D13S273, D14S258, and D14S292, located on chromosomes (chr) 5q, 6p, 11q, 13q, and 14q were used to assess MSI and LOH.

RESULTS

None of the healthy subjects exhibited any genetic alteration. Five out of 27 children (18.5%) exhibited MSI or LOH in sputum cells versus blood samples from which 3 in the marker USAT24G1 (chr 13q14.1), 1 in the marker D14S258 (chr 14q23-q24.3), and 1 in the marker D5S637 (chr 5q12-q13). Compared to a previous study, with asthmatic adults, whereas MSI and/or LOH was exhibited in approximately 60% of the cases, the current study reported <20% of genetic alterations, at the MS DNA, in asthmatic children.

CONCLUSIONS

Our results showed that genetic instability in the MS DNA, is present in asthmatic children, but to less extent than in adult asthmatics from previous studies. These findings may support the hypothesis that somatic mutations may be early acquired in the natural course of asthma and could represent another contributor to the molecular pathogenesis of the disease. However, further studies are needed to clarify this hypothesis.

Biology of lung dendritic cells at the origin of asthma

Dendritic cells (DCs) initiate and maintain adaptive T helper 2 (Th2) cell responses to inhaled allergens in asthma. Various functions like antigen uptake, migration to the draining LNs, and induction of tolerance and adaptive immunity are not equally shared by all subsets of DCs, adding considerable complexity to understanding the immunology of allergic sensitization. Whereas the epithelium was initially considered solely as a physical barrier, it is now seen as a central player in controlling the function of lung DCs through release of Th2 cell-promoting cytokines. Although DCs are sufficient and necessary for induction of Th2 cell responses to many antigens, some allergens might require antigen presentation by basophils. Clinically relevant allergens, as well as environmental and genetic risk factors for allergy and asthma, often interfere directly or indirectly with the innate immune functions of airway epithelial cells, basophils, and DCs. This review summarizes the recent progress on our understanding how DCs control Th2 cell immunity in the lung.

Genetic and environmental risk factors for childhood eczema development and allergic sensitization in the CCAAPS cohort

Eczema is very common and increasing in prevalence. Prospective studies investigating environmental and genetic risk factors for eczema in a birth cohort are lacking. We evaluated risk factors that may promote development of childhood eczema in the Cincinnati Childhood Allergy and Air Pollution Study (CCAAPS) birth cohort (n=762) of infants with at least one atopic parent. Objective environmental exposure data were available for each participant. At annual physical examinations, children underwent skin prick tests (SPTs), eczema was diagnosed by a clinician, and DNA was collected. Among Caucasian children, 39% developed eczema by age 3. Children with a pet dog were significantly less likely to have eczema at age one (odds ratio (OR)=0.62, 95% confidence interval (CI): 0.40-0.97) or at both ages 2 and 3 (OR=0.54, 95% CI: 0.30-0.97). This finding was most significant among children carrying the CD14-159C/T CC genotype. Carriers of the CD14-159C/T and IL4Ralpha I75V single-nucleotide polymorphisms (SNPs) had an increased risk of eczema at both ages 2 and 3 (OR=3.44, 95% CI: 1.56-7.57), especially among children who were SPT+. These results provide new insights into the pathogenesis of eczema in high-risk children and support a protective role for early exposure to dog, especially among those carrying the CD14-159C/T SNP. The results also demonstrate a susceptibility effect of the combination of CD14 and IL4Ralpha SNPs with eczema.

Genome-wide association studies in the genetics of asthma

The field of asthma genetics has progressed rapidly over the past decade, implicating many genes and variants in the etiology of this complex disease. However, many of these factors have failed to replicate consistently, indicating a high false-positive rate and/or insufficient power for the detection of small effects. Technological limitations also have restricted the potential to detect novel mechanisms, fostering a dependence on existing knowledge. Since its inception almost 4 years ago, genome-wide association (GWA) has transformed genetic studies of multifactorial traits and yielded unprecedented insights into mechanisms of causation. Asthma is at the forefront of this revolution, as it uses GWA to map not only genetic determinants of clinical status but also transcript and protein abundance and structural (copy number) variants that may underlie disease susceptibility. In this review, we consider the applications of GWA data to asthma and describe the factors likely to influence the procedure's success.

Filaggrin-deficient mice exhibit TH17-dominated skin inflammation and permissiveness to epicutaneous sensitization with protein antigen

BACKGROUND

Filaggrin is important for skin barrier function and is mutated in 15% to 20% of patients with atopic dermatitis.

OBJECTIVE

To examine whether filaggrin deficiency predisposes to skin inflammation and epicutaneous sensitization with protein antigen.

METHODS

Skin histology in filaggrin-deficient flaky tail (ft)/ft mice and wild-type controls was assessed by Hematoxylin and Eosin (H&E) staining and immunohistochemistry. Cytokine mRNA expression was examined by quantitative RT-PCR. Serum antibody levels and splenocyte secretion of cytokines were measured by ELISA.

RESULTS

The ft/ft mice developed eczematous skin lesions after age 28 weeks and a progressive increase in serum IgE and IgG(1) levels. Normal-appearing skin from 8-week-old ft/ft mice had epidermal thickening and increased dermal infiltration with CD4(+) cells and expression of mRNA for IL-17, IL-6, and IL-23, but not IL-4, IL-13, or IFN-gamma. Lesional skin of 32-week-old ft/ft mice exhibited qualitatively similar, but more pronounced, changes, and elevated IL-4 mRNA levels. Epicutaneous application of ovalbumin to shaved skin of 8-week-old ft/ft mice, but not WT mice, resulted in increased epidermal thickening, dermal infiltration by CD4(+) cells but not eosinophils, and expression of IL-17, IL-6, IL-23, IL-4, and IFN-gamma, but not IL-5 or IL-13, mRNA. Splenocytes from epicutaneously sensitized ft/ft mice, but not controls, secreted cytokines in response to ovalbumin stimulation, and their sera, but not those of controls, contained ovalbumin-specific IgE and IgG(1) antibodies.

CONCLUSION

Filaggrin-deficient mice exhibit T(H)17-dominated skin inflammation and eczematous changes with age, and are permissive to epicutaneous sensitization with protein antigen.

Breakdown in epithelial barrier function in patients with asthma: identification of novel therapeutic approaches

The bronchial epithelium is pivotally involved in the provision of chemical, physical, and immunologic barriers to the inhaled environment. These barriers serve to maintain normal homeostasis, but when compromised, the immunologic barrier becomes activated to protect the internal milieu of the lung. We discuss what is currently understood about abnormalities in these barrier functions in patients with asthma and consider novel therapeutic opportunities that target this key structure.

Epithelium, inflammation, and immunity in the upper airways of humans: studies in chronic rhinosinusitis

The purpose of this review is to discuss recent findings made during studies of the upper airways and sinuses of people with chronic rhinosinusitis (CRS) in the context of the literature. CRS is a chronic inflammatory disorder affecting nearly 30 million Americans and is generally resistant to therapy with antibiotics and glucocorticoids (Meltzer EO and coworkers, J Allergy Clin Immunol 2004;114:155-212). We have formed a collaboration that consists of otolaryngologists, allergists, and basic scientists to address the underlying immunologic and inflammatory processes that are occurring in, and possibly responsible for, this disease. The main emphasis of our work has been to focus on the roles that epithelium, in the sinuses and upper airways, plays as both a mediator and regulator of immune and inflammatory responses. It is not our intention here to provide a comprehensive review of the literature in this area, but we will try to put our work in the context of the findings of others (Kato A and Schleimer RP, Curr Opin Immunol 2007;19:711-720; Schleimer RP and coworkers, J Allergy Clin Immunol 2007;120:1279-1284). In particular, we discuss the evidence that epithelial cell responses are altered in CRS, including those relevant to regulation of dendritic cells, T cells, B cells, and barrier function.

Alterations in epithelial barrier function and host defense responses in chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is characterized by a chronic symptomatic inflammation of the nasal and paranasal sinus mucosae and is one of the most frequently reported chronic diseases in the United States, with an estimated prevalence of greater than 10% of the general population. Although the pathogenesis of CRS remains poorly understood, there is evidence for a role of bacteria and fungi, as well as the presence of a robust adaptive immune response in the upper airways and sinuses. Recent studies of CRS, as well as several other diseases in the skin and respiratory epithelium, have uncovered evidence that deficiencies in epithelial immune barrier function might compromise the interaction between the host and external immune stimuli. Recent studies suggest the hypothesis that reduced expression of antimicrobial S100 proteins, particularly psoriasin and calprotectin, might lead to increased susceptibility to bacterial and fungal colonization in patients with CRS. The main emphasis of this review will be to highlight the current literature that suggests that a defect in the expression of a broad set of epithelially derived genes might lead to barrier compromise and subsequently a dysfunctional host immune response to environmental agents in patients with CRS.

Genetics of asthma: a molecular biologist perspective

Asthma belongs to the category of classical allergic diseases which generally arise due to IgE mediated hypersensitivity to environmental triggers. Since its prevalence is very high in developed or urbanized societies it is also referred to as "disease of civilizations". Due to its increased prevalence among related individuals, it was understood quite long back that it is a genetic disorder. Well designed epidemiological studies reinforced these views. The advent of modern biological technology saw further refinements in our understanding of genetics of asthma and led to the realization that asthma is not a disorder with simple Mendelian mode of inheritance but a multifactorial disorder of the airways brought about by complex interaction between genetic and environmental factors. Current asthma research has witnessed evidences that are compelling researchers to redefine asthma altogether. Although no consensus exists among workers regarding its definition, it seems obvious that several pathologies, all affecting the airways, have been clubbed into one common category called asthma. Needless to say, genetic studies have led from the front in bringing about these transformations. Genomics, molecular biology, immunology and other interrelated disciplines have unearthed data that has changed the way we think about asthma now. In this review, we center our discussions on genetic basis of asthma; the molecular mechanisms involved in its pathogenesis. Taking cue from the existing data we would briefly ponder over the future directions that should improve our understanding of asthma pathogenesis.

Fluocinolone acetonide 0.01% in peanut oil: safety and efficacy data in the treatment of childhood atopic dermatitis in infants as young as 3 months of age

Fluocinolone acetonide 0.01% in a blend of refined peanut and mineral oils has been established as effective and safe treatment for atopic dermatitis in patients 2 years and older, including those with peanut sensitivity, for several years. We sought to study the safety of fluocinolone acetonide 0.01% oil and its potential for adrenal axis suppression in infants as young as 3 months of age. A controlled, open-label study was performed in children aged 3 months to 2 years with moderate to severe atopic dermatitis at two academic pediatric dermatology centers. Patients received topical fluocinolone acetonide 0.01% oil twice daily to affected areas involving a minimum of 20% body surface ratio for 4 weeks. Cortisol stimulation testing was performed at baseline and at the end of the treatment phase. Patients were monitored for medication use and adverse events. Efficacy was assessed using the Investigator Global Severity and Response scales. Thirty-two patients with moderate to severe atopic dermatitis were recruited into the study and 30 were evaluated with the Physician's Global Improvement Assessment tool. The mean body surface ratio treated for all age groups was 48%. Eighty-three percent of patients had marked or better improvement scores by week 2 and 96% by week 4, with 40% completely cleared. No adrenal suppression occurred in the 24 patients that met inclusion criteria for hypothalamus-pituitary axis (HPA) axis analysis. No relevant adverse events occurred. Results of this study support the safety and efficacy of fluocinolone acetonide 0.01% in refined peanut oil vehicle, for infants as young as 3 months of age with atopic dermatitis. No evidence of adrenal suppression or adverse local effects was demonstrated after 4 weeks of twice daily treatment.

Beta-defensin-2 protein is a serum biomarker for disease activity in psoriasis and reaches biologically relevant concentrations in lesional skin

BACKGROUND

Previous studies have extensively documented antimicrobial and chemotactic activities of beta-defensins. Human beta-defensin-2 (hBD-2) is strongly expressed in lesional psoriatic epidermis, and recently we have shown that high beta-defensin genomic copy number is associated with psoriasis susceptibility. It is not known, however, if biologically and pathophysiologically relevant concentrations of hBD-2 protein are present in vivo, which could support an antimicrobial and proinflammatory role of beta-defensins in lesional psoriatic epidermis.

METHODOLOGY/PRINCIPAL FINDINGS

We found that systemic levels of hBD-2 showed a weak but significant correlation with beta defensin copy number in healthy controls but not in psoriasis patients with active disease. In psoriasis patients but not in atopic dermatitis patients, we found high systemic hBD-2 levels that strongly correlated with disease activity as assessed by the PASI score. Our findings suggest that systemic levels in psoriasis are largely determined by secretion from involved skin and not by genomic copy number. Modelling of the in vivo epidermal hBD-2 concentration based on the secretion rate in a reconstructed skin model for psoriatic epidermis provides evidence that epidermal hBD-2 levels in vivo are probably well above the concentrations required for in vitro antimicrobial and chemokine-like effects.

CONCLUSIONS/SIGNIFICANCE

Serum hBD-2 appears to be a useful surrogate marker for disease activity in psoriasis. The discrepancy between hBD-2 levels in psoriasis and atopic dermatitis could explain the well known differences in infection rate between these two diseases.

Thymic stromal lymphopoietin overproduced by keratinocytes in mouse skin aggravates experimental asthma

Atopic dermatitis (AD) is often the initial step in the "atopic march," given that more than half of AD patients with moderate to severe AD develop asthma later in life. Both AD and asthma share a similar "atopy" phenotype that includes T helper type 2 inflammation with eosinophilia and hyper-IgE immunoglobulinemia, but the molecular mechanisms underlying the "atopic march" remain elusive. In the present study, we show that induced expression of thymic stromal lymphopoietin (TSLP) in mouse epidermal keratinocytes upon topical application of MC903 (a low calcemic analogue of vitamin D3) not only triggers AD as we previously reported but also aggravates experimental allergic asthma induced by ovalbumin sensitization and challenge. Our study, which provides a mouse model to study human "atopic march," indicates that keratinocyte-produced TSLP may represent an important factor in the link of atopic dermatitis to asthma.

New insights into the mechanism and management of allergic diseases: atopic dermatitis

Rapidly increasing knowledge on the complex background of atopic dermatitis (AD) on the genetic, immunological and environmental level in combination with the continuous improvement in our diagnostic options has initiated an ongoing discussion on factors, which primarily promote the disease on one hand and mechanisms which emerge rather secondarily as a consequence of disease-specific modifications, on the other hand. Beside a sustained search for reliable and meaningful diagnostic tools for elicitors of the disease, novel therapeutic approaches are required, as most of the treatments of AD are limited to symptomatic therapies. In contrast, therapeutic approaches selectively regulating aberrant pathophysiological mechanisms in AD itself would be much more effective and promising.

New insights into the pathogenesis and genetics of psoriatic arthritis

Psoriasis vulgaris and psoriatic arthritis (PsA) are inter-related heritable diseases. Psoriatic skin is characterized by hyperproliferative, poorly differentiated keratinocytes and severe inflammation. Psoriatic joints are characterized by highly inflamed synovia and entheses with focal erosions of cartilage and bone. Genetic analyses have uncovered risk factors shared by both psoriasis and PsA. Predisposition to psoriasis and PsA arising from common variation is most strongly conferred by the HLA class I region. Other genetic risk factors implicate the interleukin (IL)-23 pathway and the induction and regulation of type 17 T-helper cells in the pathogenesis of both diseases. Secretion of cytokines, such as IL-22 and IL-17, could result in the hyperproliferative phenotype of keratinocytes and potentially synoviocytes, leading to a vicious cycle of cellular proliferation and inflammation in both the skin and joints. In synovial tissue, disease-related cytokines could also promote osteoclast formation, resulting in bone erosion. The next step will be to identify genetic risk factors specifically associated with PsA. Although therapies that target tumor necrosis factor are often highly successful in the treatment of both diseases, genetic findings are likely to lead to the development of treatments tailored to an individual's genetic profile.

Determinants of allergenicity

The question "What makes an allergen an allergen?" has puzzled generations of researchers, and we still do not have a conclusive answer. Despite increasing knowledge about the molecular and functional characteristics of allergens that have been identified, we still do not fully understand why some proteins are clinically relevant allergens and most are not. Different approaches have been taken to identify the structural and functional features of allergens, aiming at developing methods to predict allergenicity and thus to identify allergens. However, none of these methods has allowed a reliable discrimination between allergenic and nonallergenic compounds on its own. This review sums up diverse determinants that contribute to the phenomenon of allergenicity and outlines that in addition to the structure and function of the allergen, factors derived from allergen carriers, the environment, and the susceptible individual are of importance.

Cellular and molecular mechanisms in atopic dermatitis

Atopic dermatitis (AD) is a pruritic inflammatory skin disease associated with a personal or family history of allergy. The prevalence of AD is on the rise and estimated at approximately 17% in the USA. The fundamental lesion in AD is a defective skin barrier that results in dry itchy skin, and is aggravated by mechanical injury inflicted by scratching. This allows entry of antigens via the skin and creates a milieu that shapes the immune response to these antigens. This review discusses recent advances in our understanding of the abnormal skin barrier in AD, namely abnormalities in epidermal structural proteins, such as filaggrin, mutated in approximately 15% of patients with AD, epidermal lipids, and epidermal proteases and protease inhibitors. The review also dissects, based on information from mouse models of AD, the contributions of the innate and adaptive immune system to the pathogenesis of AD, including the effect of mechanical skin injury on the polarization of skin dendritic cells, mediated by keratinocyte-derived cytokines such as thymic stromal lymphopoietin (TSLP), IL-6, and IL-1, that results in a Th2-dominated immune response with a Th17 component in acute AD skin lesions and the progressive conversion to a Th1-dominated response in chronic AD skin lesions. Finally, we discuss the mechanisms of susceptibility of AD skin lesions to microbial infections and the role of microbial products in exacerbating skin inflammation in AD. Based on this information, we discuss current and future therapy of this common disease.

Atopic eczema and the filaggrin story

The discovery that null mutations in the filaggrin gene (FLG) are associated with atopic eczema represents the single most significant breakthrough in understanding the genetic basis of this complex disorder. The association has been replicated in multiple independent studies during the past 2 years with the use of various methodologies, from populations in Europe, the United States, and Japan. Filaggrin plays a key role in epidermal barrier function, and its association with atopic eczema emphasizes the importance of barrier dysfunction in eczema pathogenesis. This review aims to summarize the current state of knowledge regarding the role of FLG mutations in ichthyosis vulgaris, atopic eczema, and other skin disorders, with an emphasis on potential clinical applications. Further research is needed to clarify the precise role of filaggrin in skin and systemic atopic disease, to pave the way for novel therapeutic interventions.

Topical therapy in pediatric atopic dermatitis

With a prevalence of 10% to 20% in the first decade of life, atopic dermatitis (AD) is one of the most common skin disorders in young children. It is a chronic illness with limited therapeutic options. Topical anti-inflammatory agents remain at the core of medical management; however, their efficacy must be balanced with safety concerns, especially as they relate to the pediatric population. This article discusses the principles of topical AD therapy with a detailed review of the differences between topical corticosteroids and topical calcineurin inhibitors. It also includes specialized topical treatment strategies for AD, such as wet wraps and diluted bleach baths, and highlights the most common challenges to patient compliance in atopic dermatitis.

A small molecule CRTH2 antagonist inhibits FITC-induced allergic cutaneous inflammation

A FITC-induced allergic contact hypersensitivity model was used to investigate the role that the prostaglandin D(2) receptor-chemoattractant receptor-homologous molecule expressed on T(h)2 cells (CRTH2) plays in modulating cutaneous inflammation. Our results show that inhibition of CRTH2, achieved via administration of a potent, small molecule antagonist, Compound A (Cmpd A), effectively blocked edema formation and greatly reduced the inflammatory infiltrate and skin pathology observed in drug vehicle-treated animals. Gene expression analysis revealed that Cmpd A administration down-regulated the transcription of a wide range of pro-inflammatory mediators. This correlated with decreases in cytokine and chemokine protein levels, notably IL-4, IL-1beta, tumor necrosis factor-alpha, transforming growth factor-beta, GRO-alpha, MIP-2 and thymic stromal lymphopoietin (TSLP) in FITC-challenged ears. The administration of an anti-TSLP-neutralizing antibody was only partially effective in lowering the FITC-induced inflammatory infiltrate and cytokine production compared with the CRTH2 antagonist. Taken together, these data suggest that blockade of CRTH2 inhibits multiple pathways leading to cutaneous inflammation in this model. This suggests that CRTH2 antagonism may be a viable route for therapeutic intervention in allergic skin diseases, such as atopic dermatitis.

Antagonism of CRTH2 ameliorates chronic epicutaneous sensitization-induced inflammation by multiple mechanisms

Prostaglandin D(2) (PGD(2)) and its receptor chemoattractant receptor homologous molecule expressed on T(h)2 cells (CRTH2) have been implicated in the pathogenesis of numerous allergic diseases. We investigated the role of PGD(2) and CRTH2 in allergic cutaneous inflammation by using a highly potent and specific antagonist of CRTH2. Administration of this antagonist ameliorated cutaneous inflammation caused by either repeated epicutaneous ovalbumin or FITC sensitization. Gene expression and ELISA analysis revealed that there was reduced pro-inflammatory cytokine mRNA or protein produced. Importantly, the CRTH2 antagonist reduced total IgE, as well as antigen-specific IgE, IgG1 and IgG2a antibody levels. This reduction in antibody production correlated to reduced cytokines produced by splenocytes following in vitro antigen challenge. An examination of skin CD11c(+) dendritic cells (DC) showed that in mice treated with the CRTH2 antagonist, there was a decrease in the number of these cells that migrated to the draining lymph nodes in response to FITC application to the skin. Additionally, naive CD4(+) T lymphocytes co-cultured with skin-derived DC from CRTH2 antagonist-treated mice showed a reduced ability to produce a number of cytokines compared with DC from vehicle-treated mice. Collectively, these findings suggest that CRTH2 has a pivotal role in mediating the inflammation and the underlying immune response following epicutaneous sensitization.

Genes in asthma: new genes and new ways

PURPOSE OF REVIEW

Asthma is a disease of unknown aetiology characterized by intermittent inflammation of the small airways of the lung. Asthma is familial due to an interaction between strong genetic and environmental factors. This article aims to review the current understanding of the genetic factors underlying asthma, looking historically as well as highlighting the latest developments in the field.

RECENT FINDINGS

Findings from recent candidate gene studies and microsatellite genome screens have continued to highlight the importance of the epithelial barrier and its defence mechanisms in asthma. Completion of the human genome sequence and the advent of genome-wide association studies have resulted in the identification of two novel asthma susceptibility genes, ORMDL3 and CHI3L1, in the past year.

SUMMARY

With the advances in genetics and genomics substantial steps have been taken in the last decade in understanding the genetic factors underlying asthma. Studies have highlighted the importance of the role of the epithelium with many of the genes so far identified being expressed in this key barrier. With the application of genome-wide expression, microRNA studies, metagenomics, proteomics and metabolomics the next decade will undoubtedly result in a further substantial increment in our understanding of the mechanisms underlying asthma.

The role of filaggrin loss-of-function mutations in atopic dermatitis

PURPOSE OF REVIEW

To provide a comprehensive summary of recent genetic advances as they relate to the pathogenesis of atopic dermatitis.

RECENT FINDINGS

Atopic dermatitis is a common inflammatory skin disease with a complex cause, resulting from an elaborate interplay between environmental, immunological and genetic factors. The disease is often the prelude to an atopic diathesis that includes asthma and other allergic diseases. The identification of mutations in the barrier protein filaggrin as conferring major susceptibility to atopic dermatitis and atopic dermatitis related asthma has reconfigured our understanding of disease mechanisms and highlights the importance of epidermal barrier disruption as a primary event in the disease.

SUMMARY

In this review we highlight recent advances in our understanding of how filaggrin might influence the environmental-immune interface, impacting disease penetrance, severity and trajectory, and the implications for both research and therapeutics in this field. Focusing on the downstream biological consequences of altered filaggrin expression and the sequence of immunological and environmental triggers that ensue will provide the rationale for targeted therapeutics capable of restoring or preventing disruption of barrier function.

Perspectives on the etiology of chronic rhinosinusitis: an immune barrier hypothesis

BACKGROUND

Chronic rhinosinusitis (CRS) has been defined as persistent symptomatic inflammation of the nasal and sinus mucosa resulting from the interaction of multiple host and environmental factors. Recent studies have implicated Alternaria fungi or toxigenic Staphylococcus aureus as critical agents in CRS pathogenesis. The emphasis on environmental agents in CRS etiology has focused interest toward elimination of those agents as the prime mechanism of therapy. This viewpoint is in marked contrast to the current perspective on some other chronic inflammatory epithelial disorders that afflict the skin, lungs, and gut, wherein host factors are believed to predispose to disease expression in the presence of ubiquitous environmental agents.

METHODS

The current review evaluates CRS etiology from this perspective and considers that CRS develops, in part, as an outcome of a dysfunctional host response. Specifically, evidence from our laboratory and others will be reviewed indicating that CRS is associated with a failure of the mechanical and immunologic barriers across the nasal mucosa. The hypothesis would further propose that genetic and epigenetic variation predisposes susceptible individuals to barrier failure in the presence of environmental stress leading to CRS.

RESULTS

From this unifying perspective, bacteria and fungi are seen as disease modifiers rather than primary etiologic agents.

CONCLUSION

The goal is to place concepts of CRS pathophysiology in a framework consistent with a current understanding of chronic inflammation in general and epithelial disease in particular.

Management of atopic dermatitis in the pediatric population

Atopic dermatitis, one of the most common skin disorders in young children, has a prevalence of 10% to 20% in the first decade of life. It is a chronic illness that requires a multifaceted treatment strategy in the setting of limited therapeutic options. Balancing safety concerns with efficacious treatment is of particular importance in the pediatric population. Parents of patients with atopic dermatitis turn to their primary caregivers for guidance regarding this physically demanding and psychologically stressful condition. In addition to serving as a review of atopic dermatitis, this article delves into the state-of-the-art therapeutic options and includes a detailed review of the differences between topical corticosteroids and topical calcineurin inhibitors. We also discuss new treatment strategies that are being used by atopic dermatitis specialists, such as comprehensive "education-as-intervention" models, wet wraps, bleach baths, and systemic immunomodulatory therapies.

The development of allergic inflammation

Allergic disorders, such as anaphylaxis, hay fever, eczema and asthma, now afflict roughly 25% of people in the developed world. In allergic subjects, persistent or repetitive exposure to allergens, which typically are intrinsically innocuous substances common in the environment, results in chronic allergic inflammation. This in turn produces long-term changes in the structure of the affected organs and substantial abnormalities in their function. It is therefore important to understand the characteristics and consequences of acute and chronic allergic inflammation, and in particular to explore how mast cells can contribute to several features of this maladaptive pattern of immunological reactivity.

Filaggrin in atopic dermatitis

The recent identification of loss-of-function mutations in the structural protein filaggrin as a widely replicated major risk factor for eczema sheds new light on disease mechanisms in eczema, a disease that had heretofore largely been considered to have a primarily immunologic etiopathogenesis. The filaggrin gene (FLG) mutation findings are consistent with a recently proposed unifying hypothesis that offers a mechanistic understanding of eczema pathogenesis synthesizing a heritable epithelial barrier defect and resultant diminished epidermal defense mechanisms to allergens and microbes, followed by polarized T(H)2 lymphocyte responses with resultant chronic inflammation, including autoimmune mechanisms. Although compelling evidence from genetic studies on FLG implicates perturbed barrier function as a key player in the pathogenesis of eczema in many patients, much is still unknown about the sequence of biologic, physicochemical, and aberrant regulatory events that constitute the transition from an inherited barrier defect to clinical manifestations of inflammatory eczematous lesions and susceptibility to related atopic disorders. The exact contribution of FLG to the wider atopic story, factors modifying FLG expression, and the role of other barrier proteins remain to be delineated. In this review we highlight recent advances in our understanding of the FLG genetics in the cause of eczema and related complex diseases.

CRTH2 antagonism significantly ameliorates airway hyperreactivity and downregulates inflammation-induced genes in a mouse model of airway inflammation

Prostaglandin D(2), the ligand for the G protein-coupled receptors DP1 and CRTH2, has been implicated in the pathogenesis of the allergic response in diseases such as asthma, rhinitis, and atopic dermatitis. This prostanoid also fulfills a number of physiological, anti-inflammatory roles through its receptor DP1. We investigated the role of PGD(2) and CRTH2 in allergic pulmonary inflammation by using a highly potent and specific antagonist of CRTH2. Administration of this antagonist ameliorated inflammation caused by either acute or subchronic sensitization using the cockroach egg antigen. Gene expression and ELISA analysis revealed that there was reduced proinflammatory cytokine mRNA or protein produced, as well as a wide array of genes associated with the Th2-type proinflammatory response. Importantly, the CRTH2 antagonist reduced antigen-specific IgE, IgG1, and IgG2a antibody levels as well as decreased mucus deposition and leukocyte infiltration in the large airways. Collectively, these findings suggest that the PGD(2)-CRTH2 activation axis has a pivotal role in mediating the inflammation and the underlying immune response in a T cell-driven model of allergic airway inflammation.

Epithelial genes in chronic rhinosinusitis with and without nasal polyps

BACKGROUND

Genetic studies on chronic inflammatory diseases have resulted in an emphasis on the epithelial interface with the environment and the genes that influence this interaction. This study examines the expression of key epithelial genes implicated in the pathogenesis of other inflammatory disorders for their role in chronic rhinosinusitis (CRS).

METHODS

Epithelial cells were collected from the inferior turbinate, middle turbinate, and/or uncinate from 62 subjects undergoing sinonasal surgery. Patient groups included 21 CRS patients with nasal polyposis, 23 CRS patients without nasal polyposis, and 18 controls. Samples were analyzed for S100A7, S100A8, S100A9, SLC9A3R1, G-protein-coupled receptor for asthma, and serine protease inhibitor kazal type 5 (SPINK5) by quantitative real-time polymerase chain reaction. Immunohistochemistry (IHC) was performed to analyze expression of SPINK5 lympho epithelial kazal-type inhibitor (LEKTI) in sinonasal samples.

RESULTS

Expression of S100A7 and S100A8 was significantly decreased in CRS with and without nasal polyps when compared with controls. S100A9 expression was significantly decreased in CRS without nasal polyps, and SPINK5 expression was significantly decreased in CRS with nasal polyps. SPINK5 (LEKTI) protein was detected in sinonasal tissue and was significantly decreased in polyp samples using IHC.

CONCLUSION

This study shows marked reductions in the level of expression of several genes involved in epithelial barrier maintenance and repair in the inflammatory state of CRS.

Advances in asthma and allergy genetics in 2007

This review discusses the main advances in the genetics of asthma and allergy published in the Journal in 2007. The association studies discussed herein addressed 3 main topics: the effect of the environment and gene-environment interactions on asthma/allergy susceptibility, the contribution of T(H)2 immunity gene variants to allergic inflammation, and the role of filaggrin mutations in atopic dermatitis and associated phenotypes. Other articles revealed novel, potentially important candidate genes or confirmed known ones. Collectively, the works published in 2007 reiterate that allergy and asthma are typical complex diseases; that is, they are disorders in which intricate interactions among environmental and genetic factors modify disease susceptibility by altering the fundamental structural and functional properties of target organs at critical developmental windows.

Genetically programmed differences in epidermal host defense between psoriasis and atopic dermatitis patients

In the past decades, chronic inflammatory diseases such as psoriasis, atopic dermatitis, asthma, Crohn’s disease and celiac disease were generally regarded as immune-mediated conditions involving activated T-cells and proinflammatory cytokines produced by these cells. This paradigm has recently been challenged by the finding that mutations and polymorphisms in epithelium-expressed genes involved in physical barrier function or innate immunity, are risk factors of these conditions. We used a functional genomics approach to analyze cultured keratinocytes from patients with psoriasis or atopic dermatitis and healthy controls. First passage primary cells derived from non-lesional skin were stimulated with pro-inflammatory cytokines, and expression of a panel of 55 genes associated with epidermal differentiation and cutaneous inflammation was measured by quantitative PCR. A subset of these genes was analyzed at the protein level. Using cluster analysis and multivariate analysis of variance we identified groups of genes that were differentially expressed, and could, depending on the stimulus, provide a disease-specific gene expression signature. We found particularly large differences in expression levels of innate immunity genes between keratinocytes from psoriasis patients and atopic dermatitis patients. Our findings indicate that cell-autonomous differences exist between cultured keratinocytes of psoriasis and atopic dermatitis patients, which we interpret to be genetically determined. We hypothesize that polymorphisms of innate immunity genes both with signaling and effector functions are coadapted, each with balancing advantages and disadvantages. In the case of psoriasis, high expression levels of antimicrobial proteins genes putatively confer increased protection against microbial infection, but the biological cost could be a beneficial system gone awry, leading to overt inflammatory disease.

Thymic stromal lymphopoietin: a new cytokine in asthma

Airway epithelial cells provide mechanical and immune protection against pathogens and allergens. Following activation, these cells produce a wide range of cytokines including thymic stromal lymphopoietin (TSLP). Recently it was established that a high level of TSLP is associated with asthma in mice and in humans. These findings suggest that interfering with the ability of cells to respond to TSLP might prevent the development of airway inflammation. Our review presents current knowledge on mediators that induce TSLP production and on the actions of TSLP on different populations of cells that are related to airway inflammation. TSLP affects dendritic cells, T cells, NKT cells, and mast cells, indicative of the broad role of TSLP in the regulation of inflammatory/allergic processes.

Discovering susceptibility genes for asthma and allergy

Asthma and asthma-related traits are complex diseases with strong genetic and environmental components. Rapid progress in asthma genetics has led to the identification of several candidate genes that are associated with asthma-related traits. Typically the phenotypic impact of each of these genes, including the ones most often replicated in association studies, is mild, but larger effects may occur when multiple variants synergize within a permissive environmental context. Despite the achievements made in asthma genetics formidable challenges remain. The development of novel, powerful tools for gene discovery, and a closer integration of genetics and biology, should help to overcome these challenges.

Dendritic cells and epithelial cells: linking innate and adaptive immunity in asthma

Dendritic cells (DCs) are generally held responsible for initiating and maintaining allergic T helper 2 (T(H)2)-cell responses to inhaled allergens in asthma. Although the epithelium was initially considered to function solely as a physical barrier, it is now seen as a central player in the T(H)2-cell sensitization process by influencing the function of DCs. Clinically relevant allergens, as well as known environmental and genetic risk factors for allergy and asthma, often interfere directly or indirectly with the innate immune functions of airway epithelial cells and DCs. A better understanding of these interactions, ascertained from human and animal studies, might lead to better prevention and treatment of asthma.

Role of airway epithelial cells in development of asthma and allergic rhinitis

Asthma and allergic rhinitis frequently coexist in the same patient. There is a similarity and variation as well as potential relationship between asthma and allergic rhinitis. There is an increasing evidence to suggest a major involvement of airway epithelial cells in the pathogenesis of asthma and allergic rhinitis. The present review describes the importance of the airway epithelial cell in the development of allergic airway diseases, its role as the primary airway defense against exposure of the airway and lung to inflammatory stimuli and antigens and as an important player through activation of epithelial Toll-like receptors (TLRs) to provide an important link between innate immunity and allergic disease. Additionally, airway epithelial cells can act as inflammatory promoters capable of directing dendritic cells (DCs) towards a T helper 2 (Th2) response, and as active producers of several inflammatory/anti-inflammatory mediators. It is hypothesized that airway epithelial cells may play as both inflammatory initiator and immuno-pathological feedback regulation between allergic rhinitis and asthma via release of systemic inflammatory mediators. Thus, airway epithelial cells may be valuable therapeutic targets for discovery and development of new drugs and/or new therapeutic strategies to treat asthma and allergic rhinitis.

Do boys do the atopic march while girls dawdle?

BACKGROUND

The atopic march hypothesis suggests that infants with eczema are at increased risk of asthma. Others argue that eczema is not a risk factor for asthma unless there is also sensitization or early wheezing.

OBJECTIVE

To examine the role of infantile eczema as a predictor of risk of childhood asthma, while allowing for the effects of early wheeze, sensitization, and sex, both as independent effects and possible effect modifiers.

METHODS

A total of 620 infants with a family history of allergic disease was recruited. Eczema and wheeze was prospectively documented to 2 years of age. Sensitization was determined by skin prick tests at 6, 12, and 24 months to 6 common food and inhalant allergens. Interviews were conducted at 6 and 7 years to ascertain current asthma.

RESULTS

Sufficiently complete data were available for 403 children. Eczema within the first 2 years of life was clearly associated with an increased risk of childhood asthma in boys (adjusted odds ratio, 2.45; 95% CI, 1.31-4.46) but not in girls (odds ratio, 0.88; 95% CI, 0.43-1.77; P for interaction = .031) even with adjustment for the effects of early allergic sensitization and wheeze. If these relationships are causal, an intervention to prevent eczema in boys might reduce the incidence of childhood asthma by as much as 28%.

CONCLUSION

Eczema in the first 2 years of life is associated with an increased risk of childhood asthma in boys, but there is no evidence of this in girls.

Prevalence and associated factors of allergic rhinitis and atopic dermatitis in children

Allergic disorders are the chronic diseases of greatest pediatric morbidity, affecting over 25 % of the pediatric population. Indeed, this situation has been referred to as an "allergic epidemic". In comparison with asthma, atopic dermatitis and allergic rhinitis have been less extensively investigated, although this does not mean that they should be regarded as minor disorders but rather as alterations that affect the quality of life of the patients and their families, which generate considerable direct and indirect costs. Despite an important research effort, the reason for this allergic epidemic is not well known. These are multifactor disorders without a single causal agent, in which the most important component is the genetic predisposition of the patient (atopy), modulated by environmental factors, exposure to allergens, infections and irritants, among others. A confounding element is the fact that the concept of allergic diseases encompasses phenotypes of rhinitis, atopic dermatitis or asthma in which no IgE-mediated atopic mechanism is demonstrated, and which can manifest in a way similar to true allergic phenotypes. Differentiation between the two is difficult to establish on the basis of self-administered questionnaires alone, in the absence of a precise etiological diagnosis. The present article reviews the numerous factors suggested to be responsible for the increase in allergic diseases recorded in the last few decades, and for the differences in prevalence observed among centres. For most of these factors the results published in the literature are contradictory, in some cases due to a lack of control of the associated interacting or confounding factors. Consensus exists for only some of these causal factors, such as the established parallelism between the increase in allergic diseases and the reduction in infectious processes on one hand, and the increase in particles generated by diesel fuel combustion on the other. In addition, the implicated factors could act differently (and in some cases even antagonically) upon atopy and on the different disease phenotypes, thereby complicating the study of these interactions even further.

Glucocorticoid actions on airway epithelial responses in immunity: functional outcomes and molecular targets

Research on the biology of airway epithelium in the last decades has progressively uncovered the many roles of this cell type during the immune response. Far from the early view of the epithelial layer simply as a passive barrier, the airway epithelium is now considered a central player in mucosal immunity, providing innate mechanisms of first-line host defense as well as facilitating adaptive immune responses. Alterations of the epithelial phenotype are primarily involved in the pathogenesis of allergic airways disease, particularly in severe asthma. Appreciation of the epithelium as target of glucocorticoid therapy has also grown, because of studies defining the pathways and mediators affected by glucocorticoids, and studies illustrating the relevance of the control of the response from epithelium in the overall efficacy of topical and systemic therapy with glucocorticoids. Studies of the mechanism of action of glucocorticoids within the biology of the immune response of the epithelium have uncovered mechanisms of gene regulation involving both transcriptional and posttranscriptional events. The view of epithelium as therapeutic target therefore has plenty of room to evolve, as new knowledge on the role of epithelium in immunity is established and novel pathways mediating glucocorticoid regulation are elucidated.