Vitamin D and asthma.

Vitamin D deficiency and asthma are common conditions that share risk factors such as African American ethnicity, inner-city residence, and obesity. This review provides a critical examination of current experimental and epidemiologic evidence of a causal association between vitamin D status and asthma or asthma morbidity, including potential protective mechanisms such as antiviral effects and enhanced steroid responsiveness. Because most published epidemiologic studies of vitamin D and asthma or asthma morbidity are observational, a recommendation for or against vitamin D supplementation as preventive or secondary treatment for asthma is not advisable and must await results of ongoing clinical trials. Should these trials confirm a beneficial effect of vitamin D, others will be needed to assess the role of vitamin D supplementation to prevent or treat asthma in different groups such as infants, children of school age, and ethnic minorities.

T(H)17 cells in asthma and inflammation.

BACKGROUND: The chronic airway disease asthma causes significant burden to patients as well as the healthcare system with limited options for prevention or cure. Inadequate treatment strategies are most likely due to the complex heterogeneous nature of asthma. Furthermore, the severe asthma phenotype is characterized by the lack of a response to standard medication, namely, corticosteroids. SCOPE OF REVIEW: In the last several years it has been shown that the eosinophilic/atopic phenotype of asthma driven by T(H)2 mechanisms is not the only immunologic pathway contributing to disease. In fact, there has been evidence revealing that severe asthmatics in particular have neutrophilic inflammation, and this is associated with corticosteroid resistance. T(H)17 cells, a recently discovered lineage of T helper cells, play an important role in lung host defense against multiple pathogens via production of the cytokine IL-17. IL-17 promotes neutrophil production and chemotaxis via multiple factors. MAJOR CONCLUSIONS: Mouse and human studies provide robust evidence that T(H)17 cells and IL-17 play a role in severe asthma and may contribute to corticosteroid resistance. GENERAL SIGNIFICANCE: As we learn more about T(H)17 cells in severe asthma, the goal is to potentially target this pathway for treatment in the hope of significantly improving the quality of life for those children and adults affected with this disease. This article is part of a Special Issue entitled: Biochemistry of Asthma.

Requirement of IL-17RA in Con A induced hepatitis and negative regulation of IL-17 production in mouse T cells.

Th17 cells, a subset of T cells involved in autoimmunity and host defense against extracellular Gram-negative infection, express both IL-17A and IL-17F. Both IL-17A and IL-17F can signal via the IL-17RA; however, IL-17F does so at a 1- to 2-log higher concentration than IL-17A. In this study, we show that the IL-17F homodimer via IL-17RA is a negative regulator of IL-17 production in T cells and suggest a mechanism whereby IL-17RA on T cells serves as an autocrine/paracrine regulator of IL-17 synthesis in T cells.

Baseline Features of the Severe Asthma Research Program (SARP III) Cohort: Differences with Age.

BACKGROUND: The effect of age on asthma severity is poorly understood. OBJECTIVES: The objective of this study was to compare the baseline features of severe and nonsevere asthma in the Severe Asthma Research Program (SARP) III cohort, and examine in cross section the effects of age on those features. METHODS: SARP III is a National Institutes of Health/National Heart Lung Blood Institute multisite 3-year cohort study conducted to investigate mechanisms of severe asthma. The sample included 188 children (111 severe, 77 nonsevere) and 526 adults (313 severe, 213 nonsevere) characterized for demographic features, symptoms, health care utilization, lung function, and inflammatory markers compared by age and severity. RESULTS: Compared with children with nonsevere asthma, children with severe asthma had more symptoms and more historical exacerbations, but no difference in body weight, post-bronchodilator lung function, or inflammatory markers. After childhood, and increasing with age, the cohort had a higher proportion of women, less allergen sensitization, and overall fewer blood eosinophils. Enrollment of participants with severe asthma was highest in middle-aged adults, who were older, more obese, with greater airflow limitation and higher blood eosinophils, but less allergen sensitization than adults with nonsevere asthma. CONCLUSIONS: The phenotypic features of asthma differ by severity and with advancing age. With advancing age, patients with severe asthma are more obese, have greater airflow limitation, less allergen sensitization, and variable type 2 inflammation. Novel mechanisms besides type 2 inflammatory pathways may inform the severe asthma phenotype with advancing age.

Airway molecular phenotypes in pediatric asthma.

PURPOSE OF REVIEW: The review discusses what is known regarding airway molecular phenotypes in pediatric asthma, specifically biomarkers that have been studied and their relation to the various clinical phenotypes of asthma. RECENT FINDINGS: Pediatric asthma is a complex and heterogeneous disease that consists of several clinical phenotypes. There have been numerous studies investigating inflammatory markers that would increase our understanding of the underlying pathogenesis of asthma as well as facilitate the discovery of therapies for these patients. Some of these biomarkers, such as exhaled nitric oxide, exhaled breath condensate, urine leukotriene E4 and induced sputum are less invasive measures of inflammation than obtaining bronchoalveolar lavage fluid in children. Although recent data reveal that some of these measures may be helpful in classifying and managing pediatric asthma, further studies are critically needed before any of these biomarkers are able to be routinely used in clinical asthma care. SUMMARY: The search for noninvasive biomarkers to help elucidate specific underlying molecular phenotypes in pediatric asthma should be a continued priority as we work towards improved care and management of these children.

Vitamin D3 attenuates Th2 responses to Aspergillus fumigatus mounted by CD4+ T cells from cystic fibrosis patients with allergic bronchopulmonary aspergillosis.

Allergic bronchopulmonary aspergillosis (ABPA) is caused by a dominant Th2 immune response to antigens derived from the opportunistic mold Aspergillus, most commonly Aspergillus fumigatus. It occurs in 4%-15% of patients with cystic fibrosis (CF); however, not all patients with CF infected with A. fumigatus develop ABPA. Therefore, we compared cohorts of A. fumigatus-colonized CF patients with and without ABPA to identify factors mediating tolerance versus sensitization. We found that the costimulatory molecule OX40 ligand (OX40L) was critical in driving Th2 responses to A. fumigatus in peripheral CD4+ T cells isolated from patients with ABPA. In contrast, CD4+ T cells from the non-ABPA cohort did not mount enhanced Th2 responses in vitro and contained a higher frequency of TGF-beta-expressing regulatory T cells. Heightened Th2 reactivity in the ABPA cohort correlated with lower mean serum vitamin D levels. Further, in vitro addition of 1,25 OH-vitamin D3 substantially reduced DC expression of OX40L and increased DC expression of TGF-beta. This in vitro treatment also resulted in increased Treg TGF-beta expression and reduced Th2 responses by CD4+ T cells from patients with ABPA. These data provide rationale for a therapeutic trial of vitamin D to prevent or treat ABPA in patients with CF.

IL-22 mediates mucosal host defense against Gram-negative bacterial pneumonia.

Emerging evidence supports the concept that T helper type 17 (T(H)17) cells, in addition to mediating autoimmunity, have key roles in mucosal immunity against extracellular pathogens. Interleukin-22 (IL-22) and IL-17A are both effector cytokines produced by the T(H)17 lineage, and both were crucial for maintaining local control of the Gram-negative pulmonary pathogen, Klebsiella pneumoniae. Although both cytokines regulated CXC chemokines and granulocyte colony-stimulating factor production in the lung, only IL-22 increased lung epithelial cell proliferation and increased transepithelial resistance to injury. These data support the concept that the T(H)17 cell lineage and its effector molecules have evolved to effect host defense against extracellular pathogens at mucosal sites.

Th17 cells and mucosal host defense.

Th17 cells are a new lineage of T-cells that are controlled by the transcription factor RORgammat and develop independent of GATA-3, T-bet, Stat 4 and Stat 6. Novel effector molecules produced by these cells include IL-17A, IL-17F, IL-22, and IL-26. IL-17RA binds IL-17A and IL-17F and is critical for host defense against extracellular planktonic bacteria by regulating chemokine gradients for neutrophil emigration into infected tissue sites as well as host granulopoiesis. Moreover, IL-17 and IL-22 regulate the production of antimicrobial proteins in mucosal epithelium. Although TGF-beta1 and IL-6 have been shown to be critical for development of Th17 cells from naive precursors, IL-23 is also important in regulating IL-17 release in mucosal tissues in response to infectious stimuli. Compared to Th1 cells, IL-23 and IL-17 show limited roles in controlling host defense against primary infections with intracellular bacteria such as Mycobacterium tuberculosis suggesting a predominate role of the Th17 lineage in host defense against extracellular pathogens. However, in the setting of chronic biofilm infections, as that occurs with cystic fibrosis or bronchiectasis, Th17 cells may be key contributors of tissue injury.

Interleukin-17 in pulmonary host defense.

Interleukin (IL)-17A and IL-17F are produced by a novel class of effector alphabeta T cells called Th17 cells as well as gammadelta T cells. alphabeta IL-17-producing T cells are controlled by the transcription factor RORgammat and develop independent of GATA-3, T-bet, Stat 4, and Stat 6. Effector molecules produced by these cells include IL-17A, IL-17F, and IL-22. IL-17A and IL-17F bind to IL-17 receptor (IL-17R) and receptor signaling is critical for host defense against extracellular bacteria by regulating chemokine gradients for neutrophil emigration into infected tissue sites as well as via regulation of host granulopoiesis. Furthermore, it has recently been shown that IL-17 and IL-22 regulate the production of antimicrobial proteins in epithelium. Although Th17 cells are important in mucosal host defense, in the setting of retained antigenic stimulation, such as in the setting of asthma or chronic infection, such as in cystic fibrosis, or in the setting of autoimmunity, these cells can mediate immunopathology.

Identification of the IL-17 receptor related molecule IL-17RC as the receptor for IL-17F.

The proinflammatory cytokines IL-17A and IL-17F have a high degree of sequence similarity and share many biological properties. Both have been implicated as factors contributing to the progression of inflammatory and autoimmune diseases. Moreover, reagents that neutralize IL-17A significantly ameliorate disease severity in several mouse models of human disease. IL-17A mediates its effects through interaction with its cognate receptor, the IL-17 receptor (IL-17RA). We report here that the IL-17RA-related molecule, IL-17RC is the receptor for IL-17F. Notably, both IL-17A and IL-17F bind to IL-17RC with high affinity, leading us to suggest that a soluble form of this molecule may serve as an effective therapeutic antagonist of IL-17A and IL-17F. We generated a soluble form of IL-17RC and demonstrate that it effectively blocks binding of both IL-17A and IL-17F, and that it inhibits signaling in response to these cytokines. Collectively, our work indicates that IL-17RC functions as a receptor for both IL-17A and IL-17F and that a soluble version of this protein should be an effective antagonist of IL-17A and IL-17F mediated inflammatory diseases.