New insights into the role of the mast cell in asthma.
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Animals↗
Biomedical subjects
P Bradding
Publications and source records attributed to P Bradding.
Comparison of airway immunopathology of eosinophilic bronchitis and asthma.
BACKGROUND: Eosinophilic bronchitis is a condition characterised by a corticosteroid responsive cough, sputum eosinophilia, and normal tests of variable airflow obstruction and airway responsiveness. We performed a detailed comparative immunopathological study to test the hypothesis that the different airway function in patients with eosinophilic bronchitis and asthma reflects differences in the nature of the lower airway inflammatory response. METHODS: Exhaled nitric oxide was measured and induced sputum, bronchoscopy, bronchial wash (BW), bronchoalveolar lavage (BAL), and bronchial biopsy were performed in 16 subjects with eosinophilic bronchitis, 15 with asthma, and 14 normal controls. RESULTS: Both eosinophilic bronchitis and asthma were characterised by an induced sputum, BW and BAL eosinophilia, an increased number of epithelial and subepithelial eosinophils, and increased reticular basement membrane thickness. The median concentration of exhaled nitric oxide was higher in those with eosinophilic bronchitis (12 ppb) or asthma (8.5 ppb) than normal controls (2 ppb) (95% CI of the difference 5 to 16, p<0.0001 and 2 to 11.3, p=0.004, respectively). There were no group differences in epithelial integrity or the number of subepithelial T lymphocytes, mast cells or macrophages. CONCLUSION: With the exception of our previously reported association of smooth muscle mast cell infiltration with asthma, the immunopathology of eosinophilic bronchitis and asthma are similar which suggests that eosinophilic airway inflammation, increased exhaled nitric oxide, and increased basement membrane thickening are regulated independently of airway hyperresponsiveness.
Asthma↗
New insights into the relationship between airway inflammation and asthma.
Asthma is a condition characterized by variable airflow obstruction, airway hyper-responsiveness (AHR) and airway inflammation which is usually, but not invariably, eosinophilic. Current thoughts on the pathogenesis of asthma are focused on the idea that it is caused by an inappropriate response of the specific immune system to harmless antigens, particularly allergens such as cat dander and house dust mite, that result in Th2-mediated chronic inflammation. However, the relationship between inflammation and asthma is complex, with no good correlation between the severity of inflammation, at least as measured by the number of eosinophils, and the severity of asthma. In addition, there are a number of conditions, such as eosinophilic bronchitis and allergic rhinitis, in which there is a Th2-mediated inflammatory response, but no asthma, as measured by variable airflow obstruction or AHR. Bronchoconstriction can also occur without obvious airway inflammation, and neutrophilic inflammation can in some cases be associated with asthma. When we compared the immunopathology of eosinophilic bronchitis and asthma, the only difference we observed was that, in asthma, the airway smooth muscle (ASM) was infiltrated by mast cells, suggesting that airway obstruction and AHR are due to an ASM mast cell myositis. This observation emphasizes that the features that characterize asthma, as opposed to bronchitis, are due to abnormalities in smooth muscle responsiveness, which could be intrinsic or acquired, and that inflammation is only relevant in that it leads to these abnormalities. It also emphasizes the importance of micro-localization as an organizing principle in physiological responses to airway inflammation. Thus, if inflammation is localized to the epithelium and lamina propria, then the symptoms of bronchitis (cough and mucus hypersecretion) result, and it is only if the ASM is involved -- for reasons that remain to be established -- that asthma occurs.
Asthma↗
Resting and activation-dependent ion channels in human mast cells.
The mechanism of mediator secretion from mast cells in disease is likely to include modulation of ion channel activity. Several distinct Ca(2+), K(+), and Cl(-) conductances have been identified in rodent mast cells, but there are no data on human mast cells. We have used the whole-cell variant of the patch clamp technique to characterize for the first time macroscopic ion currents in purified human lung mast cells and human peripheral blood-derived mast cells at rest and following IgE-dependent activation. The majority of both mast cell types were electrically silent at rest with a resting membrane potential of around 0 mV. Following IgE-dependent activation, >90% of human peripheral blood-derived mast cells responded within 2 min with the development of a Ca(2+)-activated K(+) current exhibiting weak inward rectification, which polarized the cells to around -40 mV and a smaller outwardly rectifying Ca(2+)-independent Cl(-) conductance. Human lung mast cells showed more heterogeneity in their response to anti-IgE, with Ca(2+)-activated K(+) currents and Ca(2+)-independent Cl(-) currents developing in approximately 50% of cells. In both cell types, the K(+) current was blocked reversibly by charybdotoxin, which along with its electrophysiological properties suggests it is carried by a channel similar to the intermediate conductance Ca(2+)-activated K(+) channel. Charybdotoxin did not consistently attenuate histamine or leukotriene C(4) release, indicating that the Ca(2+)-activated K(+) current may enhance, but is not essential for, the release of these mediators.
Adult↗
The relative contribution of mast cell subsets to conjunctival TH2-like cytokines.
PURPOSE: To investigate the distribution of the T-helper (TH)2-like cytokines, interleukin (IL)-4, IL-5, IL-6, and IL-13 between mast cell subsets in conjunctival biopsy specimens from normal subjects and those with seasonal allergic conjunctivitis (SAC) during and outside of the grass pollen season. METHODS: Sequential and double in situ hybridization (ISH) and immunohistochemistry (IHC) were performed on thin sections of human conjunctiva to determine the colocalization of the immunoreactivity of IL-4, IL-5, IL-6, and IL-13 to mast cell subsets in normal subjects and subjects with atopy and to detect IL-4 mRNA in conjunctival mast cells. RESULTS: More than 90% of IL-4+-immunoreactive cells were observed to be mast cells in conjunctival biopsy specimens from all patient groups. The majority of IL-5+, IL-6+, and IL-13+ cells were also noted to be mast cells for each group. IL-4 preferentially colocalized to the tryptase+-chymase+ mast cell phenotype (MC(TC)) with MC(TC) cells comprising 93.3% of cytokine+ mast cells in symptomatic SAC (P = 0.0017), 89.2% in asymptomatic SAC (P = 0.0008), and 77.8% in normal subjects (P = 0.0472). IL-13 appeared to colocalize preferentially to the MC(TC) phenotype and IL-5 and IL-6 to the MC(T) phenotype. ISH showed that 75.8% of mast cells in normal subjects, 78.7% in subjects with symptomatic SAC, and 18.7% in subjects with asymptomatic SAC expressed mRNA for IL-4. CONCLUSIONS: Conjunctival mast cells are an important source of IL-4, IL-5, IL-6, and IL-13 immunoreactivity, with preferential colocalization of IL-4 and IL-13 on the MC(TC) subset and IL-5 and IL-6 to the MC(T) subset. This evidence suggests that differences in protease phenotype may also reflect functional differences evidenced by the different patterns of cytokine distribution.
Adult↗
Voltage-dependent and calcium-activated ion channels in the human mast cell line HMC-1.
The mechanisms underlying the recruitment, differentiation, and sustained activation of mast cells in disease are likely to include modulation of ion channels. Specific Ca(2+), K(+), and Cl(-) conductances have been identified in rodent mast cells, but there are no equivalent data on human mast cells. We have used the whole-cell patch-clamp technique to characterize macroscopic ion currents in both the human mast cell line HMC-1 and human skin mast cells (HSMCs) at rest and in HMC-1 after activation with calcium ionophore. HSMCs were electrically silent at rest. In contrast, HMC-1 expressed a strong outwardly rectifying voltage-dependent Cl(-) conductance characteristic of ClC-4 or ClC-5 and a small inwardly rectifying K(+) current not carried by the classical Kir family of K(+) channels. Calcium ionophore induced the appearance of outwardly rectifying Ca(2+)-activated Cl(-) and K(+) currents, while hypotonicity induced another outwardly rectifying conductance typical of ClC-3. Reverse transcription-PCRs confirmed that mRNAs for the voltage-dependent Cl(-) channels ClC-3 and -5 were expressed. This is the first definitive description of a ClC-4/5-like current in a native leukocyte. We suggest that this current may contribute to the malignant phenotype while the Ca(2+)-activated K(+) and Cl(-) currents may be involved in cell activation.
Calcium↗
Interleukin-5 enhances eosinophil adhesion to bronchial epithelial cells.
BACKGROUND: Eosinophil-bronchial epithelial cell interactions are thought to be central to the pathogenesis of asthma, both in terms of the epithelium as a source of pro-inflammatory mediators and as a target for eosinophil-mediated damage. We have therefore investigated adhesion interactions between these two cell types. OBJECTIVES: To determine the role of eosinophil and epithelial activation on eosinophil adhesion to bronchial epithelium and to characterize the adhesion receptors mediating eosinophil adhesion. METHODS: Eosinophils were purified from human peripheral blood by immunomagnetic selection and adhesion to confluent cultures of the airway epithelial cell lines A549 and BEAS-2B was studied. RESULTS: Stimulation of A549 cells with TNFalpha, IFNgamma or a combination of 50 ng/mL of TNFalpha, IFNgamma and IL-1 (cytomix) did not effect eosinophil binding despite an increase in ICAM-1 expression. Similarly stimulation of eosinophils with PAF or IL-5 had no effect on eosinophil binding to medium- or cytokine-treated A549 cells. In contrast stimulation of BEAS-2B cells with cytomix caused a significant increase in eosinophil adhesion. This was associated with an increase in expression of ICAM-1 and induced expression of VCAM-1. Treatment of eosinophils with Mn2+ and IL-5 but not eotaxin, RANTES or PAF also significantly enhanced eosinophil adhesion to medium-treated BEAS-2B cells. Using blocking mAbs we were able to demonstrate that the increased adhesion resulting from stimulation of eosinophils or BEAS-2B cells was in both cases mediated by a combination of CD18 and alpha4 integrins. CONCLUSIONS: This study demonstrates a selective role for IL-5 in mediating integrin-dependent eosinophil adhesion to airway epithelium and once again emphasizes the importance of this cytokine in controlling eosinophil activation in diseases such as asthma.
Antigens, CD↗
Localization of interleukin (IL) -4 but not IL-5 to human mast cell secretory granules by immunoelectron microscopy.
BACKGROUND: Human mast cells synthesize and secrete many cytokines of relevance to the pathogenesis of allergic diseases such as asthma and rhinitis. In particular, interleukin (IL) -4 and IL-5 are likely to play key roles in the development of the inflammatory response that characterizes these diseases. Immunohistochemical studies on human nasal and bronchial mucosal biopsies suggest that IL-4 and IL-5 may be stored preformed in mast cells. OBJECTIVE: To identify whether IL-4 and IL-5 are stored within mast cell secretory granules. METHODS: We used immunogold electron microscopic analysis on bronchial mucosa and lung parenchyma from resected lung specimens, and a nasal mucosal biopsy from a patient with active allergic rhinitis. Samples were fixed in 4% paraformaldehyde plus 0.5% glutaraldehyde and processed into Lowicryl K4M resin by the 'Progressive Lowering of Temperature' technique. Ultrathin sections were stained immunohistochemically by an indirect immunogold method. RESULTS: Immunoreactivity for IL-4, but not IL-5, was localized to the granules of mast cells in all tissue samples. IL-5 was localized to the matrix of eosinophil granules in these samples, but neither cytokine was detected in T cells. IL-4 immunoreactivity increased in the granules of mast cells 24 h after immunoglobulin (Ig) E-dependent activation (mean 17.5 +/- 1.4 gold particles per granule) compared with nonactivated mast cells (mean 6.8 +/- 0.8 gold particles per granule, P < 0.001), suggesting replenishment of stores by newly generated protein. Immunoreactive IL-5 remained undetectable in mast cells 24 h after activation, a time point at which they are known to secrete large quantities of this cytokine. CONCLUSION: Human mast cells store IL-4 within the matrix of their granules. Very few, if any, lung or nasal mast cells store IL-5. A store of preformed IL-4 within mast cell granules is likely to have an important influence during the initiation and maintenance of the allergic immunological response.
Cytoplasmic Granules↗
Induced sputum inflammatory mediator concentrations in eosinophilic bronchitis and asthma.
Eosinophilic bronchitis is a common cause of chronic cough, which like asthma is characterized by sputum eosinophilia, but in contrast to asthma there is no variable airflow obstruction or airway hyperresponsiveness. Our hypothesis was that the differences in airway pathophysiology maybe due to less active airway inflammation in eosinophilic bronchitis, with reduced release of important effector mediators. We measured the concentration of various proinflammatory mediators in induced sputum cell-free supernatant in eight patients with eosinophilic bronchitis, 17 patients with asthma matched for sputum eosinophil count, and 10 normal subjects. Cysteinyl-leukotrienes (cys-LT) were measured by enzyme immunoassay, eosinophilic cationic protein (ECP) by fluoroimmunoassay, prostanoids (PGE(2), PGD(2), TXB(2), and PGF(2alpha)) by gas chromatography-negative ion chemical ionization-mass spectroscopy, and histamine by radioenzymic assay. The geometric mean sputum eosinophil count was similar in asthma (13.4%) and eosinophilic bronchitis (12.5%). Sputum cys-LT and ECP were a mean (95% CI) 1.6-fold (1.1, 2.5) and 6.4-fold (1.4, 28) higher in eosinophilic bronchitis and 1.9-fold (1.3, 2.9) and 7.7-fold (1.2, 46) higher in asthma compared with that in control subjects (geometric mean, 5.9 and 95 ng/ml, respectively). In eosinophilic bronchitis the mean concentration of sputum PGD(2) (0.79 ng/ml) and histamine (168 ng/ml) were significantly higher than in asthma (mean absolute difference in PGD(2) concentration, 0.47 ng/ml [95% CI, 0.19 to 0. 74] and mean-fold difference in histamine concentration, 6.7 [95% CI 1.7 to 26]) and normal subjects (0.64 ng/ml [0.36 to 0.90] and 11-fold [3.3 to 36]), respectively. In conclusion, eosinophilic bronchitis is associated with active airway inflammation with increased release of vasoactive and bronchoconstrictor mediators.
Adult↗
Adhesion of human lung mast cells to bronchial epithelium: evidence for a novel carbohydrate-mediated mechanism.
Mast cells contribute to the pathophysiology of asthma through their immunomediator-secretory activity in response to both immunological and nonimmunological stimuli, and infiltrate the bronchial epithelium in this disease. We hypothesized that human lung mast cells (HLMC) localize to the bronchial epithelium via a specific cell-cell adhesion mechanism. We investigated the adhesion of HLMC to primary bronchial epithelial cells and the bronchial epithelial cell line BEAS-2B. HLMC adhered avidly to both primary cultures of bronchial epithelial cells and BEAS-2B cells (mean adhesion 68.4 and 60.1%, respectively) compared with eosinophil adhesion to BEAS-2B (mean adhesion 10.3%). HLMC adhesion did not alter after epithelial activation with cytokines, did not require Ca2+, and was not integrin-mediated. IgE-dependent activation of HLMC produced an approximately 40% inhibition of adhesion. There was significant attenuation of adhesion after incubation of HLMC with pronase, beta-galactosidase, and endo-alpha-N-acetylgalactosaminidase, indicating that HLMC adhere to bronchial epithelial cells via galactose-bearing carbohydrates expressed on a cell-surface peptide(s).
Antibodies, Monoclonal↗
Immunopathology and human mast cell cytokines.
The mast cell is a virtual pharmacopoeia of biological substances. It used to be believed that mast cell activation was all-or-nothing, with IgE cross-linking inducing symptoms of allergy and anaphylaxis. However, the activity of mast cells in health and disease is clearly much more complicated than this. The discovery that human mast cells secrete many pleiotropic cytokines suggested there may be many novel mast cell functions, and many of these are now being realised. The ubiquitous distribution of mast cells throughout connective tissues, along epithelial surfaces, and in close proximity to blood vessels, makes their products available to a large variety of cell types including fibroblasts, glandular epithelial cells, nerves, vascular endothelial cells, smooth muscle cells, and other cells of the immune system. This tissue distribution, and the vast array of lipid mediators, proteases, proteoglycans and cytokines identified as potential products of human mast cells, explains how this interesting cell has the potential to contribute to so many diverse biological events.
Animals↗
As-required versus regular nebulized salbutamol for the treatment of acute severe asthma.
Current British guidelines for the administration of beta2-agonists in acute severe asthma recommend regular nebulized therapy in hospitalized patients, followed by as-required (p.r.n.) use via hand-held devices after discharge. Since beta2-agonists do not possess anti-inflammatory activity in vivo, and are thus unlikely to influence the rate of recovery from an asthma exacerbation, it was hypothesized that patients given the short-acting beta2-agonist salbutamol on an as-required basis after admission to hospital would recover as quickly as those on regular treatment, but with potential reductions in the total dose delivered. Forty-six patients with acute severe asthma were randomly assigned to either regular prescriptions of nebulized salbutamol or to usage on a p.r.n. basis, from 24 h after hospital admission. The primary outcome measures were length of hospital stay, time to recovery, and frequency of salbutamol nebulization from 24 h after admission to discharge. Secondary outcome measures were treatment side-effects (tremor, palpitations), and patient satisfaction. Length of hospital stay was reduced in those patients allocated to p.r.n. salbutamol (geometric mean (GM) 3.7 days) versus regular salbutamol (GM 4.7 days). Time taken for peak expiratory flow to reach 75% of recent best was the same in both groups. There was a highly significant reduction in the number of times nebulized therapy was delivered to the p.r.n. group (GM 7.0, range 1-30) compared with the regular treatment group (GM 14.0, range 4-57; p=0.003; 95% confidence interval for ratio of GMs 1.29-3.09). In addition, patients reported less tremor (p=0.062) and fewer palpitations (p=0.049) in the p.r.n. group. Of the patients in the p.r.n. group who had received regular nebulized therapy on previous admissions (n=12), all preferred the p.r.n. regimen. Prescribing beta2-agonists on a p.r.n. basis from 24 h after hospital admission is associated with reduced amount of drug delivered, incidence of side-effects, and possibly length of hospital stay. This has implications for the efficient use of healthcare resources.
Acute Disease↗
The long-acting beta2-agonist salmeterol xinafoate: effects on airway inflammation in asthma.
Salmeterol xinafoate is an inhaled long-acting beta2-adrenoceptor agonist recently introduced for the treatment of asthma. Both in vitro and animal studies suggest that it may have anti-inflammatory activities of benefit in this disease. To assess this directly, the effects of 6 weeks' treatment with salmeterol on indices of clinical activity, airway dysfunction and inflammation in subjects with stable atopic asthma were investigated. In a double blind study, asthmatic patients were randomized to 6 weeks' treatment with either salmeterol 50 microg twice daily (n=14) or placebo (n=12). They underwent bronchoscopy with bronchoalveolar lavage (BAL) and bronchial biopsy immediately before starting treatment and again after 6 weeks. Treatment with salmeterol improved clinical indices of asthma activity, but there were no changes in BAL differential cell counts or mediator levels, and no change in T-cell numbers or activation status. In the biopsy specimens there were no changes in numbers of inflammatory cells, sub-basement membrane collagen deposition or mast cell degranulation. Regular treatment with salmeterol improves clinical indices of asthma but has no effect on the underlying inflammatory process. These findings strengthen guideline recommendations that long-acting beta2-agonists should not be prescribed as sole antiasthma medication.
Adolescent↗
Allergen immunotherapy and mast cells.
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Allergens↗
The dos and don'ts of examining the respiratory system: a survey of British Thoracic Society members.
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Clinical Competence↗
Mucosal inflammation in severe glucocorticoid-dependent asthma.
To improve our understanding of the inflammatory mechanisms underlying severe disease, a biopsy study was performed comparing 15 clinically unstable glucocorticoid-dependent asthmatics, 10 mild asthmatics, and 10 control subjects. Compared with mild asthma, severe asthma was characterized by reduced mucosal eosinophilia. Whilst no significant differences were found in the numbers of mast cells, neutrophils, CD3+ and CD4+ T-cells between the three groups, up to a 4-fold increase In the numbers of activated T-lymphocytes bearing the interleukin (IL)-2 receptor (IL-2R) was found in the mucosa in severe asthma compared to mild asthma (p = 0.03) and control subjects (p = 0.003). Compared to control subjects, the mucosa of severe asthmatics contained significantly (p = 0.02) higher numbers of IL-5+ cells, with no differences between mild and severe disease. In contrast, staining for the anti-IL-4 monoclonal antibody 3H4 revealed that biopsies from mild asthmatics contained more IL4+ cells than biopsies from severe asthmatics and control subjects (p = 0.0008). In the severe asthmatics, a close correlation (r(s) = 0.76, p = 0.005) was found between the numbers of IL-2R-bearing cells and the variability in peak expiratory flow. In conclusion, persistent T-cell activation is a prominent feature of severe asthma. These results also indicate that interleukin-5, and not interleukin-4, is upregulated in severe disease.
Administration, Topical↗