Neutrophilic inflammation in severe persistent asthma

Inflammatory cell distribution in guinea pig airways and its relationship to airway reactivity

Although airway inflammation and airway hyperreactivity are observed after allergen inhalation both in allergic humans and animals, little is known about the mechanisms by which inflammatory cells can contribute to allergen-induced airway hyperreactivity. To understand how inflammatory cell infiltration can contribute to airway hyperreactivity, the location of these cells within the airways may be crucial Using a guinea pig model of acute allergic asthma, we investigated the inflammatory cell infiltration in different airway compartments at 6 and 24 h (i.e. after the early and the late asthmatic reaction, respectively) after allergen or saline challenge in relation to changes in airway reactivity (AR) to histamine. At 6 h after allergen challenge, a threefold (p < 0.01) increase in the AR to histamine was observed. At 24 h after challenge, the AR to histamine was lower, but still significantly enhanced (1.6-fold, p < 0.05). Adventitial eosinophil and neutrophil numbers in both bronchi and bronchioli were significantly increased at 6 h post-allergen provocation as compared with saline (p < 0.01 for all), while there was a strong tendency to enhanced eosinophils in the bronchial submucosa at this time point (p = 0.08). At 24h after allergen challenge, the eosinophilic and neutrophilic cell infiltration was reduced. CD3+ T lymphocytes were increased in the adventitial compartment of the large airways (p < 0.05) and in the parenchyma (p < 0.05) at 24h post-allergen, while numbers of CD8+ cells did not differ from saline treatment at any time point post-provocation. The results indicate that, after allergen provocation, inflammatory cell numbers in the airways are mainly elevated in the adventitial compartment. The adventitial inflammation could be important for the development of allergen-induced airway hyperreactivity.

Evidence for different subgroups of difficult asthma in children

BACKGROUND

Children with difficult asthma experience frequent symptoms despite treatment with high dose inhaled steroids. Persistent symptoms may result from persistent airway inflammation which can be monitored by measuring exhaled nitric oxide (NO). This study aimed to assess the role of airway inflammation, using NO as a surrogate, in children with difficult asthma and to investigate the response to oral prednisolone.

METHODS

NO was measured in 23 children (mean age 11.7 years) with difficult asthma, before and after 2 weeks of treatment with oral prednisolone. The clinical response was assessed by spirometric tests, peak flow, bronchodilator use, and symptoms. Adherence to treatment was assessed by measuring serum prednisolone and cortisol concentrations. NO was measured in 55 healthy children to establish a normal range.

RESULTS

NO concentrations were higher in asthmatic patients than in controls (geometric mean 11.2 v 5.3 ppb, p<0.01). Using grouped data, the concentration of NO fell following prednisolone (11.2 v 7.5 ppb, p<0.01) accompanied by an improvement in morning peak flow (p<0.05). The baseline NO concentration was raised (>12.5 ppb) in nine asthmatic patients and remained high after prednisolone in five. Thirteen had normal levels of NO (<12.5 ppb) before and after prednisolone. Thirteen asthmatic patients remained symptomatic following prednisolone; NO levels were raised on both occasions in five of these and were normal in seven.

CONCLUSIONS

As a group, the asthmatic subjects demonstrated evidence of airway inflammation which responded to prednisolone. At least two subgroups of patients were identified: one with persistently raised NO levels despite treatment with oral prednisolone indicating ongoing steroid insensitive inflammation, and another with normal levels of NO. Both subgroups included patients with persistent symptoms, which suggests that different patterns of difficult asthma in children exist.

Bronchoalveolar lavage in asthmatic children: evidence of neutrophil activation in mild-to-moderate persistent asthma

Little information is available on cell profiles and mediator production in the lower airways of children with asthma by comparison with the adult population. To study the bronchoalveolar lavage (BAL) cell profiles and production of eosinophil cationic protein (ECP) and myeloperoxidase (MPO) in childhood bronchial asthma, a retrospective study was performed in 29 children (13 allergic asthmatic children and 16 controls). Six of the asthmatics had mild-to-moderate persistent disease and seven had intermittent asthma. The BAL cell count and ECP and MPO values of asthmatic children were compared with those from 16 controls. The asthmatic patients had higher values than controls for the total cell count (p = 0.08), for neutrophils (p = 0.02), and for ECP and MPO (p < 0.001). MPO levels (p = 0.04), neutrophil count (p = 0.06), and ECP values (p = 0.06) were higher in patients with mild-to-moderate persistent asthma than in those with intermittent asthma. Our results demonstrate that neutrophil-mediated inflammation is greater in patients with more severe asthma.

High constitutive glucocorticoid receptor beta in human neutrophils enables them to reduce their spontaneous rate of cell death in response to corticosteroids

Neutrophils are markedly less sensitive to glucocorticoids than T cells, making it difficult to control inflammation in neutrophil-mediated diseases. Development of new antiinflammatory strategies for such diseases would be aided by an understanding of mechanisms underlying differential steroid responsiveness. Two protein isoforms of the human glucocorticoid receptor (GR) exist, GRalpha and GRbeta, which arise from alternative splicing of the GR pre-mRNA primary transcripts. GRbeta does not bind glucocorticoids and is an inhibitor of GRalpha activity. Relative amounts of these two GRs can therefore determine the level of glucocorticoid sensitivity. In this study, human neutrophils and peripheral blood mononuclear cells (PBMCs) were studied to determine the relative amounts of each GR isoform. The mean fluorescence intensity (MFI) using immunofluorescence analysis for GRalpha was 475 +/- 62 and 985 +/- 107 for PBMCs and neutrophils, respectively. For GRbeta, the MFI was 350 +/- 60 and 1,389 +/- 143 for PBMCs and neutrophils, respectively (P < 0.05). After interleukin (IL)-8 stimulation of neutrophils, there was a statistically significant increase in intensity of GRbeta staining to 2,497 +/- 140 (P < 0.05). No change in GRalpha expression was observed. This inversion of the GRalpha/GRbeta ratio in human neutrophils compared with PBMCs was confirmed by quantitative Western analysis. Increased GRbeta mRNA expression in neutrophils at baseline, and after IL-8 exposure, was observed using RNA dot blot analysis. Increased levels of GRalpha/GRbeta heterodimers were found in neutrophils as compared with PBMCs using coimmunoprecipitation/Western analysis. Transfection of mouse neutrophils, which do not contain GRbeta, resulted in a significant reduction in the rate of cell death when treated with dexamethasone.We conclude that high constitutive expression of GRbeta by human neutrophils may provide a mechanism by which these cells escape glucocorticoid-induced cell death. Moreover, upregulation of this GR by proinflammatory cytokines such as IL-8 further enhances their survival in the presence of glucocorticoids during inflammation.

Anti-inflammatory and lung function effects of montelukast in asthmatic volunteers exposed to sulfur dioxide

BACKGROUND

Sulfur dioxide (SO(2)) gas may induce acute asthmatic responses when inhaled by individuals in the setting of community or occupational air pollution during exercise. Some asthma medications mitigate the SO(2) response, which is not fully understood but appears to involve multiple mechanisms.

OBJECTIVE

We tested the hypothesis that pretreatment with the cysteinyl-leukotriene inhibitor montelukast sodium protects against the inflammatory and bronchoconstrictive effects of SO(2) in the airways of asthmatic subjects.

METHODS

Asthmatic volunteers (enrolled, 12 subjects; completed study, 11 subjects) were exposed to 0.75 ppm SO(2) for 10-min periods during exercise (mean ventilation, 35 L/min) and were exposed similarly to filtered air (control condition) after double-blinded pretreatments with montelukast (10 mg/d for 3 days) and placebo.

RESULTS

After montelukast pretreatment, specific airways resistance, FEV(1), symptoms, and eosinophil counts in induced sputum showed statistically and clinically significant improvements in preexposure measurements and/or decreased responses to SO(2) exposure or exercise. The mean FEV(1) immediately after exposure was 95% of baseline FEV(1) with montelukast pretreatment vs 82% with placebo.

CONCLUSION

Montelukast significantly protects against airways eosinophilic inflammation and bronchoconstriction from SO(2) exposure during exercise. This implies a role for leukotrienes in SO(2)-induced lung effects.

Eosinophil cationic protein and interleukin-8 levels in bronchial lavage fluid from children with asthma and infantile wheeze

It has been shown previously that airway eosinophils characterize childhood asthma and neutrophils contribute to the pathophysiology of both infantile wheezing and asthma. Therefore, eosinophil cationic protein (ECP) and interleukin-8 (IL-8) levels in bronchoalveolar lavage fluid (BALF) from asthmatics (n = 16) and infantile wheezers (n = 30) were analyzed as markers of eosinophil- and neutrophil-mediated inflammation. To aid the interpretation, a control group of children (n = 10) with no lower airway pathology were included. Disease severity was assessed by using a symptom score. Surprisingly, no significant difference was found in IL-8 or ECP levels among asthma, infantile wheeze, and control groups. Asthma was characterized by: a correlation between ECP levels and eosinophil counts (r = 0.618, p = 0.014); a correlation between neutrophil number and IL-8 levels (r = 0.747, p = 0.002); and increasing IL-8 levels with symptom score (p = 0.03). In infantile wheezers, IL-8 levels were poorly related to neutrophil number but were significantly increased when neutrophils were > 10%. Although detectable levels were found in all but one symptomatic infant, IL-8 concentrations did not reflect the symptom score in infantile wheeze. ECP was unexpectedly correlated to neutrophil percentages (Rho = 0.832, p = 0.001), and a threshold of ECP>20 ng/ml was associated with persistent symptoms in these infantile wheezers. Hence, in accordance with BALF cellularity, activation of eosinophils was suggested by raised levels of ECP in childhood asthma, but not in infantile wheeze. Neutrophil-mediated inflammation appeared to better reflect the severity of asthma than that of infantile wheeze. Although its meaning remains to be elucidated, ECP was suggested to be a helpful indicator of persistent infantile wheeze. However, its utility as a marker predicting ongoing asthma remains to be established.

The relationship of sputum eosinophilia and sputum cell generation of IL-5

BACKGROUND

Eosinophil recruitment to the airway after antigen challenge is regulated by many factors, including airway cell generation of cytokines.

OBJECTIVES

The purpose of this study was to determine the relationship between sputum cell generation of IL-5 and the appearance of eosinophils in the sputum after antigen challenge.

METHODS

Sputum samples from 11 allergic subjects were collected before and again 4 and 24 hours after antigen challenge. In 6 of these subjects, induced sputum samples were also obtained 48 hours and 7 days after challenge. Sputum leukocyte differential and cell counts and eosinophil-derived neurotoxin levels were determined. Sputum cells were then cultured with PHA (10 microg/mL) to stimulate IL-5 and IFN-gamma, which were measured in culture supernatants.

RESULTS

An increase in sputum eosinophils and eosinophil-derived neurotoxin levels was detected at 4 hours after antigen challenge, with peak values at 24 hours. In contrast, significant increases in ex vivo generation of IL-5 by sputum cells was not seen until 24 hours after challenge. At 24 hours, PHA-induced IL-5 correlated with airspace eosinophil values (r (s) = 0.78, P <.01). In addition, the ratio of IFN-gamma/IL-5 decreased at 24 hours (P <.05) and had an inverse correlation with sputum eosinophils (r (s)= -0.68, P <.05).

CONCLUSION

Although eosinophils are increased in the airway lumen as early as 4 hours, the ex vivo generation of IL-5 by sputum cells is first noted in samples obtained 24 hours after antigen challenge. This suggests that the early (4 hours) recruitment of eosinophils to the airway lumen may be regulated by factors other than IL-5 or that mucosal cells (rather than airspace cells) contribute to the IL-5 generation at this time point. Furthermore, IL-5 generation by airspace cells may be more responsible for either eosinophil recruitment or retention at later time points.

Endotoxins, asthma, and allergic immune responses

Asthma severity depends to a great extent on the levels of endotoxin present in the microenvironment. Although favouring a Th1 cytokine response that could be beneficial to the asthmatic, lipopolysaccharide (LPS) aggravates bronchopulmonary inflammation by several mechanisms. These include neutrophil and eosinophil recruitment, and release by activated macrophages of pro-inflammatory cytokines and nitric oxide. LPS exerts its biological actions through its interaction with CD14. The genetic locus of CD14 is close to the genomic region controlling levels of IgE. A polymorphism in the CD14 promoter region seems to favour high serum IgE levels. Genetic influences may thus control circulating levels of sCD14 and by this mechanism modulate Th1/Th2 balance and IgE synthesis. LPS exposure, although hazardous to the asthmatic, seems to exert a role in the maturation of the immune system in children towards a Th1-skewed pattern.

Increased nitrotyrosine in exhaled breath condensate of patients with asthma

The reaction of nitric oxide (NO) and superoxide anions (O(2)(-)) in the airway results in the formation of peroxynitrite, a highly reactive oxidant species. Peroxynitrite reacts with tyrosine residues in proteins to form the stable product nitrotyrosine. We investigated whether nitrotyrosine in exhaled breath condensates may be increased in patients with asthma. Four groups of nonsmoking subjects were studied. We measured exhaled NO, nitrotyrosine, and leukotrienes concentrations in breath condensate in healthy nonatopic subjects (n = 15) and in patients with mild asthma (steroid naive, n = 15), moderate asthma (inhaled steroid treatment, n = 12), and severe asthma (oral steroid treatment, n = 12). Exhaled NO was increased significantly in patients with mild (19.2 +/- 2.7 ppb, p < 0.01) and moderate asthma (14.0 +/- 1.53 ppb, p < 0.05), as compared with normal control (6.58 +/- 0.61 ppb). The levels of LTC(4)/D(4)/E(4) and LTB(4) were increased significantly in patients with moderate and severe asthma treated with steroids. Nitrotyrosine concentrations were detectable (6.3 +/- 0.8 ng/ml) in breath condensate of normal subjects, and were increased significantly in patients with mild asthma (15.3 +/- 2.0 ng/ml, p < 0.01). However, the levels of nitrotyrosine in exhaled condensate were lower in patients with moderate (5.0 +/- 0.6 ng/ml) and severe asthma (3.3 +/- 0.6 ng/ml, p < 0.05). There was a significant correlation between nitrotyrosine in breath condensate and exhaled NO in patients with mild asthma (r = 0.65, p < 0.05). We conclude that nitrotyrosine formation in exhaled breath condensates may be a marker of oxidative stress in airways of asthma.

Increased matrix metalloproteinase-9 in the airway after allergen challenge

Persistent asthma is associated with airway inflammation, tissue damage, and deposition of extracellular matrix (ECM) proteins, which may be mediated, in part, through release of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinase-1 (TIMP-1). To investigate the role of allergen in the induction of MMP-9 and TIMP-1, bronchoscopy and segmental bronchoprovocation (SBP) with saline (SAL) and antigen (AG) were performed in 17 allergic subjects. Bronchoalveolar lavage (BAL) was done 5 min and 48 h after challenge and concentrations of MMP-9 and TIMP-1 in BAL fluid (BALF) were measured by ELISA. Forty-eight hours after AG challenge, concentrations of MMP-9 and TIMP-1 were increased in the airway, but not in serum. Zymography demonstrated that MMP-9 was the predominant metalloproteinase and was present in a latent proform. MMP-9 immunoreactivity was associated primarily with neutrophils, and concentrations of MMP-9 in BALF correlated with airway neutrophils and, to a lesser extent, with alveolar macrophages. These data suggest that AG challenge leads to generation of factors, including MMP-9, that may be associated with the initiation of bronchial injury, which may then lead to remodeling in asthma.

Glucocorticoid receptor alpha and beta in glucocorticoid dependent asthma

Patients with glucocorticoid (GC)-dependent asthma present an ongoing inflammation of the airways despite chronic long-term treatment with oral GC. Interleukin (IL)-8 and granulocyte/macrophage colony-stimulating factor (GM-CSF) have been implicated in airway inflammation in severe asthma and their synthesis is normally repressed by GC. To further characterize the inflammatory process in GC-dependent asthma, we measured the release of IL-8 and GM-CSF by peripheral blood mononuclear cells (PBMC) of eight normal subjects, six untreated controlled asthmatics, six untreated uncontrolled asthmatics, and nine GC-dependent asthmatics. We show that PBMC from GC-dependent asthmatics released high amounts of these cytokines despite chronic in vivo exposure to GC (p < 0.001 versus normal subjects). In contrast, when untreated uncontrolled asthmatics were given a short course of oral GC, IL-8 and GM-CSF production was inhibited (p = 0.0078). Release of IL-8 and GM-CSF by PBMC of GC-dependent asthmatics was reduced after in vitro GC treatment (p < 0.002). We investigated whether the incapacity of GC to inhibit production of these cytokines in vivo was the result of a dysregulation of the glucocorticoid receptor (GR) in GC-dependent asthma. GRalpha and GRbeta are, respectively, the functional receptor and a putative dominant negative form of the receptor. Western blot and polymerase chain reaction (PCR) analyses indicated that GRalpha was expressed at similar level in all groups and was largely predominant over GRbeta. Thus, persistent release of IL-8 and GM-CSF in GC-dependent asthma is not associated with low expression of GRalpha or overexpression of GRbeta.