Uncontrolled asthmatics have increased FceRI+ and TGF-ß-positive MCTC mast cells and collagen VI in the alveolar parenchyma.

BACKGROUND: Asthma has been associated with increased collagen deposition in both conducting airways and alveolar parenchyma. Mast cells (MCs) are key effector cells in asthma and have the ability to affect collagen synthesis. However, the link between clinical control and changes in bronchial and alveolar MC phenotypes and specific collagens in controlled and uncontrolled asthma remains unknown. OBJECTIVE: To investigate MC phenotypes in correlation with deposition of specific collagen subtypes in patients with controlled and uncontrolled asthma as well as to healthy controls. METHODS: The tissue expression of IgE+ , FcεRI+ and TGF-ß+ MCs, as well as immunoreactivity of collagen I, III and VI, was assessed using immunohistochemistry on bronchial and transbronchial biopsies from controlled asthmatics (n = 9), uncontrolled asthmatics (n = 16) and healthy controls (n = 8). RESULTS: In the alveolar parenchyma, the total number of MCs, as well as the number of FcεRI+ MCs and pro-fibrotic TGF-ß+ MCTC, was significantly increased in uncontrolled asthma compared to both controlled asthma and healthy controls. The proportion of TGF-ß+ MCTC correlated positively to an increased immunoreactivity of alveolar collagen VI but not collagen I and III. Collagen VI was increased in the alveolar parenchyma of uncontrolled asthmatics compared to controlled asthmatics. Controlled asthmatics had an increased deposition of alveolar collagen I. In bronchi, the immunoreactivity of collagen I was increased in both controlled and uncontrolled asthmatics while collagen III was increased only in controlled asthmatics. CONCLUSIONS: Patients with uncontrolled atopic asthma have an altered pro-fibrotic MCTC phenotype in the alveolar parenchyma that is associated with alveolar collagen VI. The present data thus support distal lung mast cell and matrix changes as histopathological features of asthma that may be of particular clinical relevance in patients who have remaining symptoms despite conventional inhaler therapy.

Airway responsiveness to mannitol in asthma is associated with chymase-positive mast cells and eosinophilic airway inflammation.

BACKGROUND: Airway hyperresponsiveness (AHR) to inhaled mannitol is associated with indirect markers of mast cell activation and eosinophilic airway inflammation. It is unknown how AHR to mannitol relates to mast cell phenotype, mast cell function and measures of eosinophilic inflammation in airway tissue. We compared the number and phenotype of mast cells, mRNA expression of mast cell-associated genes and number of eosinophils in airway tissue of subjects with asthma and healthy controls in relation to AHR to mannitol. METHODS: Airway hyperresponsiveness to inhaled mannitol was measured in 23 non-smoking, corticosteroid-free asthmatic individuals and 10 healthy controls. Mast cells and eosinophils were identified in mucosal biopsies from all participants. Mast cells were divided into phenotypes based on the presence of chymase. mRNA expression of mast cell-associated genes was measured by real-time PCR. RESULTS: The proportion of submucosal MCTC was higher in asthmatic individuals with AHR to mannitol compared with asthmatic individuals without AHR (median: 40.3% vs. 18.7%, P = 0.03). Increased submucosal MCTC numbers were associated with increased levels of mRNA for thymic stromal lymphopoietin (TSLP) and CPA3 in asthmatics. Reactivity to mannitol correlated significantly with eosinophils in submucosa (r(s): 0.56, P = 0.01). CONCLUSION: Airway hyperresponsiveness to inhaled mannitol is associated with an altered submucosal mast cell profile in asthmatic individuals. This mast cell profile is associated with increased levels of TSLP and CPA3. The degree of AHR to mannitol is correlated with the degree of eosinophilic inflammation in the airway submucosa.

Mapping of TLR5 and TLR7 in central and distal human airways and identification of reduced TLR expression in severe asthma.

BACKGROUND: The toll-like receptors, TLR5 and TLR7, have recently been proposed in asthma immunopathogenesis. While supporting data come from animal or in vitro studies, little is known about TLR5 and TLR7 expression in human asthmatic airways. METHODS: Advanced immunohistochemical mapping of TLR5 and TLR7 was performed on bronchial and transbronchial biopsies from healthy individuals and patients with moderate and severe asthma. RESULTS: TLR5 was identified in multiple structural cells; bronchial epithelium, alveolar type II pneumocytes, plasma cells, macrophages and neutrophils. Contrary to bronchial TLR5, which had a basolateral expression, alveolar TLR5 had polarized apical localization. Patients with severe asthma had decreased total and epithelial TLR5 expression compared to controls and moderate asthmatics (P < 0.001). TLR7 expression was found in several structural cells and asthma-related immune cells. Whereas TLR7 expression was decreased in severe asthmatics (P < 0.001), nerve-associated TLR7 increased (P = 0.035). Within the asthma groups, both TLR5 and TLR7 expression correlated with multiple lung function parameters. CONCLUSIONS: Our results reveal broad expression patterns of TLR5 and TLR7 in the lung and that the expression is decreased in severe asthma. Hence, severe asthmatics may suffer from insufficient TLR signalling during viral or bacterial infections leading to poor and impaired defence mechanisms.

Small-molecule-mediated OGG1 inhibition attenuates pulmonary inflammation and lung fibrosis in a murine lung fibrosis model.

Interstitial lung diseases such as idiopathic pulmonary fibrosis (IPF) are caused by persistent micro-injuries to alveolar epithelial tissues accompanied by aberrant repair processes. IPF is currently treated with pirfenidone and nintedanib, compounds which slow the rate of disease progression but fail to target underlying pathophysiological mechanisms. The DNA repair protein 8-oxoguanine DNA glycosylase-1 (OGG1) has significant roles in the modulation of inflammation and metabolic syndromes. Currently, no pharmaceutical solutions targeting OGG1 have been utilized in the treatment of IPF. In this study we show Ogg1-targeting siRNA mitigates bleomycin-induced pulmonary fibrosis in male mice, highlighting OGG1 as a tractable target in lung fibrosis. The small molecule OGG1 inhibitor, TH5487, decreases myofibroblast transition and associated pro-fibrotic gene expressions in fibroblast cells. In addition, TH5487 decreases levels of pro-inflammatory mediators, inflammatory cell infiltration, and lung remodeling in a murine model of bleomycin-induced pulmonary fibrosis conducted in male C57BL6/J mice. OGG1 and SMAD7 interact to induce fibroblast proliferation and differentiation and display roles in fibrotic murine and IPF patient lung tissue. Taken together, these data suggest that TH5487 is a potentially clinically relevant treatment for IPF but further study in human trials is required.

Alveolar mast cells shift to an FcεRI-expressing phenotype in mild atopic asthma: a novel feature in allergic asthma pathology.

BACKGROUND: A unique feature of alveolar mast cells is their low high-affinity IgE receptor (FcεRI) expression. Recent discoveries in uncontrolled asthma suggest that the appearance of FcεRI-expressing alveolar mast cells may be a novel disease-specific feature of allergic asthma. This study investigates whether increased FcεRI-expressing alveolar mast cells are present in patients with mild allergic asthma or even in non-asthmatic allergic rhinitis patients (AR) who have developed bronchial hyperactivity (BHR). METHODS: Bronchial and alveolar tissues were obtained from healthy controls, AR patients with or without BHR, and AR patients with concurrent asthma. Samples were processed for immunohistochemical identification of MC(T) and MC(TC) and expression of FcεRI and surface-bound IgE. RESULTS: Bronchial mast cell expression of FcεRI was high in all groups. In contrast, in the alveolar tissue, the expression of FcεRI on mast cells was low in healthy controls and in the AR patient groups, whereas a high expression was present in AR patients with concurrent asthma (P = 0.006 compared to controls). The asthmatics had a 29-fold increase in numbers (P = 0.006) and a 19-fold increase in proportion (P = 0.007) of alveolar mast cells that expressed surface-bound IgE. CONCLUSIONS: The present data show that alveolar mast cells in patients with mild atopic asthma, but not atopic patients with AR, have turned into a highly FcεRI- and IgE-expressing phenotype. These data support the hypothesis that increased FcεRI expression on alveolar mast cells is a novel disease-specific feature of allergic asthma that is important for understanding asthma phenotypes and designing new therapeutic strategies.

Novel site-specific mast cell subpopulations in the human lung.

BACKGROUND: Lung mast cells are stereotypically divided into connective tissue (MC(TC)) and mucosal (MC(T)) mast cells. This study tests the hypothesis that each of these subtypes can be divided further into site-specific populations created by the microenvironment within each anatomical lung compartment. METHODS: Surgical resections and bronchial and transbronchial biopsies from non-smoking individuals were obtained to study mast cells under non-inflamed conditions. Morphometric and molecular characteristics of mast cell populations were investigated in multiple lung structures by immunohistochemistry and electron microscopy. RESULTS: MC(T) and MC(TC) coexisted in all compartments, with MC(T) being the prevailing type in bronchi, bronchioles and the alveolar parenchyma and MC(TC) being more abundant in pulmonary vessels and the pleura. Each of the MC(TC) and MC(T) phenotypes could be further differentiated into site-specific populations. MC(TC) were significantly larger in pulmonary vessels than in small airway walls, while the reverse was observed for MC(T). Within each MC(TC) and MC(T) population there were also distinct site-specific expression patterns of the IgE receptor, interleukin-9 receptor, renin, histidine decarboxylase, vascular endothelial growth factor, fibroblast growth factor, 5-lipoxygenase and leukotriene C4 synthase (eg, bronchial MC(T) consistently expressed more histidine decarboxylase than alveolar MC(T)). Renin content was high in vascular MC(TC) but markedly lower in MC(TC) in other compartments. For both MC(TC) and MC(T), the IgE receptor was highly expressed in conducting airways but virtually absent in alveolar parenchyma. CONCLUSIONS: These findings demonstrate novel site-specific subpopulations of lung MC(TC) and MC(T) at baseline conditions. This observation may have important implications in the future exploration of mast cells in a number of pulmonary diseases.