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Original Research |

The Neutrophilic Inflammatory Phenotype Is Associated With Systemic Inflammation in AsthmaSystemic Inflammation in Neutrophilic Asthma FREE TO VIEW

Lisa G. Wood, PhD; Katherine J. Baines, PhD; Juanjuan Fu, MD; Hayley A. Scott, BND; Peter G. Gibson, MBBS
Author and Funding Information

From the Centre for Asthma and Respiratory Diseases, University of Newcastle, and Department of Respiratory and Sleep Medicine, Hunter Medical Research Institute, John Hunter Hospital, Newcastle, NSW, Australia.

Correspondence to: Lisa G. Wood, PhD, Department Respiratory and Sleep Medicine, Level 3, Hunter Medical Research Institute, John Hunter Hospital, Locked Bag 1, Hunter Region Mail Centre, NSW, 2310, Australia; e-mail: lisa.wood@newcastle.edu.au

Financial/nonfinancial disclosures: The authors have reported to CHEST the following conflicts of interest: Dr Gibson is the recipient of a National Health and Medical Research Council of Australia Practitioner Fellowship. The remaining authors report no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Funding/Support: The authors have reported to CHEST that no funding was received for this study.


Funding/Support: The authors have reported to CHEST that no funding was received for this study.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2012;142(1):86-93. doi:10.1378/chest.11-1838
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Background:  The role of systemic inflammation in asthma is unclear. The aim of this study was to compare systemic inflammation in subjects with stable asthma, categorized by airway inflammatory phenotype, with healthy control subjects.

Methods:  Adults with stable asthma (n = 152) and healthy control subjects (n = 83) underwent hypertonic saline challenge and sputum induction. Differential leukocyte counts were performed on selected sputum. Plasma high-sensitivity C-reactive protein (CRP), IL-6, and tumor necrosis factor-α levels and sputum IL-8 and neutrophil elastase levels were determined by enzyme-linked immunosorbent assay. Sputum IL-8 receptor α (IL-8RA) and IL-8 receptor β (IL-8RB) messenger RNA expression were determined by real-time polymerase chain reaction.

Results:  Subjects with asthma were classified as having nonneutrophilic asthma or neutrophilic asthma. The asthma (neutrophilic) group had increased systemic inflammation compared with the asthma (nonneutrophilic) and healthy control groups, with median (interquartile range) CRP levels of 5.0 (1.6-9.2), 1.8 (0.9-5.3), and 1.8 (0.8-4.1) mg/L (P = .011), respectively, and IL-6 levels of 2.1 (1.5-3.1), 1.4 (1.0-2.1), and 1.1 (0.8-1.5) pg/mL (P < .001), respectively. The proportion of subjects with elevated CRP and IL-6 levels was also higher in the asthma (neutrophilic) group. Sputum IL-8 and neutrophil elastase protein and IL-8RA and IL-8RB gene expression were significantly increased in the asthma (neutrophilic) group. In multiple regression analysis of subjects with asthma, sex, BMI, statin use, and percent sputum neutrophils were significant predictors of log10CRP. Sex, BMI, and %FEV1 were significant predictors of log10IL-6.

Conclusions:  Systemic inflammation is increased in patients with asthma with neutrophilic airway inflammation and associated with worse clinical outcomes. Systemic inflammation may contribute to the pathophysiology of neutrophilic asthma.

Figures in this Article

The role of systemic inflammation in airways disease has gained attention in recent years. In COPD, systemic inflammation is related to disease progression, with increases in C-reactive protein (CRP) and IL-6 levels associated with lung function decline.1 In asthma, systemic inflammation is less well understood. Airway inflammation in asthma is heterogeneous in nature and may involve an allergen-specific acquired immune response with IL-5-mediated eosinophilic inflammation or a dysregulation of innate immune responses involving IL-8-induced neutrophilic airway inflammation.2,3 In adults with stable asthma treated with inhaled corticosteroids, ~40% have eosinophilic asthma, whereas 25% have neutrophilic asthma.4 In the most severe forms of asthma, sputum neutrophil levels are elevated5 and negatively correlate with lung function and airflow obstruction.4

Systemic inflammation also occurs in asthma, with an increase in circulating proinflammatory cytokines, such as IL-6 and tumor necrosis factor-α (TNF-α), that stimulate hepatic production of acute-phase proteins, such as CRP, and an increase in immune cells, such as neutrophils and natural killer cells.6,7 Circulating TNF-α8 and IL-69 levels are elevated during asthma exacerbation, and blood cells from patients with asthma release more IL-6 after a nonallergic trigger (lipopolysaccharide) than control subjects.10 Plasma CRP has been shown to be elevated in nonallergic11 and steroid-naive patients with asthma12 and correlated with lung function and airway inflammatory cell counts.12

The cause of systemic inflammation in asthma is unknown. Systemic dissemination of local lung inflammation may occur, leading to an overspill effect.13 Systemic inflammation may also result from subclinical respiratory tract infection14; tissue hypoxia15; environmental exposures, such as dietary intake16,17 and smoking; and host factors, including aging and obesity.18 Systemic inflammation involves innate immune activation,7 which is also a feature of neutrophilic asthma.3 Hence, we hypothesized that individuals with neutrophilic asthma have increased levels of systemic inflammation, which contributes to the clinical expression of this phenotype. This study aimed to examine systemic inflammation in subjects with asthma compared with healthy control subjects in relation to airway inflammatory phenotype and clinical asthma outcomes.

Study Participants

Adults aged > 18 years with stable asthma (n = 152) were recruited. Asthma was defined as current respiratory symptoms, physician diagnosis of asthma, and airway hyperresponsiveness to hypertonic saline. Asthma stability was defined as no exacerbation in the past 4 weeks. Healthy control subjects (n = 83) who had normal lung function and no airway hyperresponsiveness were recruited. Individuals were excluded if they were current smokers or had any respiratory illness other than asthma. Informed written consent was obtained, and the study was approved by Hunter New England Human Research Ethics Committee (05/03/09/3.09). Subsets of these data have been previously reported.19,20

Study Procedures

Prior to each visit, subjects fasted for 12 h and withheld β-agonist medications. Spirometry (Minato Autospiro AS-600; Minato Medical Science Co, Ltd) and combined bronchial provocation and sputum induction with hypertonic saline (4.5%) were performed as described.21 If FEV1 dropped below 15% of baseline, salbutamol was administered. Sputum induction ceased once maximum nebulization time of 15 min reached. Asthma control was assessed using the Asthma Control Questionnaire.22 Exhaled nitric oxide (NIOX; Aerocrine AB) was measured, a skin prick test was performed, and blood was collected.

Sputum Processing and Analysis

Sputum was selected from saliva21,23 and placed in buffer RLT, and RNA was extracted using the RNeasy Mini Kit (Qiagen Biosciences GmbH) for gene expression testing. The remaining sputum was dispersed with dithiothreitol, and a total cell count of leukocytes and viability was performed. Cytospins were prepared and stained (May-Grünwald-Giemsa), and nonsquamous cells were used for differential cell count. IL-8 concentration was measured in sputum supernatant by enzyme-linked immunosorbent assay (R&D Systems, Inc), and neutrophil elastase activity was measured using the Human NE Immunocapture Activity Kit (Calbiochem).24 Sputum RNA (200 ng) was reverse-transcribed to complementary DNA using the high-capacity complementary DNA reverse transcription kit (Applied Biosystems, LLC). Taqman primers and probes for IL-8 receptor α (IL-8RA) and IL-8 receptor β (IL-8RB) (Hs_00174146_m1 and Hs_00174304_m1; Applied Biosystems) were combined with Taqman gene expression master mix in duplicate single-plex real-time polymerase chain reactions (7500 Real Time PCR System; Applied Biosystems). Results were calculated using the 2−ΔΔCt method relative to both the housekeeping gene (18S rRNA) and the sample mean.

Plasma Inflammatory Mediator Analysis

Ethylenediaminetetraacetic acid (EDTA) blood was centrifuged (4°C; 3,000 g; 10 min) and plasma stored at −80°C. Plasma IL-6 and TNF-α (R&D Systems, Inc) and high-sensitivity CRP (MP Biomedicals, LLC) were assessed by enzyme-linked immunosorbent assay.

Statistical Analysis

Results were analyzed using Minitab, version 13.32 (Minitab Inc). Asthma inflammatory phenotypes were classified using sputum cell counts as follows: asthma (neutrophilic), neutrophils ≥ 64%; asthma (nonneutrophilic), neutrophils < 64%25; eosinophilic asthma, eosinophils > 1.01% and neutrophils < 64%; and paucigranulocytic asthma, eosinophils < 1.01% and neutrophils < 64%. High CRP and IL-6 levels were defined as plasma concentrations above the lower limit of the upper quartile for healthy control subjects. These cutoffs were CRP ≥ 4.12 mg/mL, and IL-6 ≥ 1.55 pg/mL. Statistical comparisons were performed using the Student t test for normally distributed data, with results reported as mean ± SEM, or Mann-Whitney U test for nonparametric data, with results reported as median (interquartile range [IQR]). Group comparisons were conducted using analysis of variance with Bonferroni post hoc test for normally distributed data, Kruskal-Wallis test with Dunn post hoc test for nonparametric data, and Fisher exact test for categorical data. Associations were examined using Pearson correlation coefficients for normally distributed data and Spearman rank correlation coefficients for nonparametric data. P < .05 was considered significant.

Clinical characteristics of subjects are described in Table 1. An adequate sputum sample was obtained from 132 of 152 subjects (87%) with asthma (Tables 1, 2). The asthma groups had lower lung function than the healthy control group. The proportion of subjects with atopy was higher in the asthma (nonneutrophilic) group than in both the asthma (neutrophilic) and the healthy control groups. The asthma (neutrophilic) group had a higher BMI and worse smoking history than the asthma (nonneutrophilic) and healthy control groups. There were no differences in the number of comorbidities between the healthy control and the asthma groups. However, in the asthma (neutrophilic) group, there were significantly more subjects with cardiovascular complications than in the asthma (nonneutrophilic) group (Fig 1).

Table Graphic Jump Location
Table 1 —Asthma (Neutrophilic and Nonneutrophilic) vs Healthy Control Subjects: Clinical Characteristics

Data are presented as median (interquartile range) or mean ± SEM, unless otherwise indicated. Asthma (neutrophilic) is defined as sputum neutrophils ≥ 64%, and asthma (nonneutrophilic) is defined as sputum neutrophils < 64%. ACQ = Asthma Control Questionnaire; ICS = inhaled corticosteroid; NA = not applicable; PD15 = provocation dose resulting in 15% fall in baseline FEV1.

a 

P < .05 vs healthy control group.

b 

P < .05 vs asthma (nonneutrophilic) group.

c 

Expressed as geometric mean ± logSD.

Table Graphic Jump Location
Table 2 —Asthma (Neutrophilic and Nonneutrophilic) vs Healthy Control Subjects: Airway and Systemic Inflammation

Data are presented as median (interquartile range). Asthma (neutrophilic) is defined as sputum neutrophils ≥ 64%, and asthma (nonneutrophilic) is defined as sputum neutrophils < 64%. CRP = C-reactive protein; IL-8RA = IL-8 receptor α; IL-8RB = IL-8 receptor β; mRNA = messenger RNA; NE = neutrophil elastase; NO = nitric oxide; ppb = parts per billion; TNF-α = tumor necrosis factor-α.

a 

P < .05 vs healthy control group.

b 

P < .05 vs asthma (nonneutrophilic) group.

c 

n = 57.

d 

n = 78.

e 

n = 23.

Figure Jump LinkFigure 1. Prevalence of comorbidities in subjects with neutrophilic asthma and nonneutrophilic asthma. Cardiovascular includes hypertension, atrial fibrillation, and angina. Bowel disease includes inflammatory bowel and celiac disease. GORD = gastro-esophageal reflux disorder; OSAS = obstructive sleep apnea syndrome. *P < .05 vs asthma (nonneutrophilic) group.Grahic Jump Location

Systemic and airway inflammation is described in Table 2. Plasma CRP concentration and the proportion of subjects with high CRP (Fig 2A) were higher in the asthma (neutrophilic) group than in the asthma (nonneutrophilic) and healthy control groups. Within the asthma (nonneutrophilic) group, there was no difference in plasma CRP concentrations in subjects with eosinophilic asthma (median, 1.8 mg/L; IQR, 0.9-5.4 mg/L) vs paucigranulocytic asthma (median, 2.0 mg/L; IQR, 1.0-7.4 mg/L; P = .251). Plasma IL-6 concentrations and the proportion of subjects with high IL-6 levels (Fig 2B) were higher in both asthma groups compared with the healthy control group and were further elevated in the asthma (neutrophilic) group compared with the asthma (nonneutrophilic) group. Within the asthma (nonneutrophilic) group, there was no difference in plasma IL-6 concentrations in subjects with eosinophilic asthma (median, 1.4 pg/mL; IQR, 0.9-1.9 pg/mL) vs paucigranulocytic asthma (median, 1.3 pg/mL; IQR, 0.9-2.0 pg/mL; P = .258). Protein release of neutrophil elastase and IL-8 and gene expression of IL-8RA and IL-8RB were increased in the asthma (neutrophilic) group compared with the asthma (nonneutrophilic) and healthy control groups. Subanalysis of the asthma (neutrophilic) group according to smoking history revealed no differences in plasma CRP (never smoker median, 7.3 mg/L; IQR, 1.8-13.4 mg/L; ex-smoker median, 4.1 mg/L; IQR, 1.3-8.2 mg/L; P = .234) or IL-6 (never smoker median, 1.8 pg/mL; IQR, 1.2-2.9 pg/mL; ex-smoker median, 2.4 pg/mL; IQR, 1.6-3.1 pg/mL; P = .246) levels.

Figure Jump LinkFigure 2. A, Proportions of subjects with high plasma concentrations CRP. B, Proportions of subjects with high plasma concentrations of IL-6. High CRP is defined as plasma concentration > 4.12 mg/mL, and high IL-6 is defined as plasma concentration > 1.55 pg/mL (lower limit of upper quartile for healthy control subjects).*P < .05 vs asthma (neutrophilic) group. †P < .05 vs asthma (nonneutrophilic) group. CRP = C-reactive protein.Grahic Jump Location

Clinical characteristics of subjects with asthma with normal vs high CRP levels are shown in Figure 3A. Subjects with a high CRP concentration were not different in terms of lung function or asthma control score. In contrast, subjects with a high IL-6 concentration had worse lung function and worse asthma control (Fig 3B).

Figure Jump LinkFigure 3. A, Comparison of lung function and asthma control in subjects with normal vs high CRP levels. B, Comparison of lung function and asthma control in subjects with normal vs high IL-6 levels. High CRP is defined as plasma concentration > 4.12 mg/mL, and high IL-6 is defined as plasma concentration > 1.55 pg/mL (lower limit of upper quartile for healthy control subjects). Data are presented as median (interquartile range). ACQ = Asthma Control Questionnaire. See Figure 2 legend for expansion of other abbreviation.Grahic Jump Location

Weak associations were observed between plasma CRP concentrations and percent sputum neutrophils, sputum IL-8 concentrations, and BMI (Table 3). Multiple regression analysis revealed that significant predictors of log10CRP in asthma were sex, BMI, statin use, and percent sputum neutrophils (Table 4). Weak associations were observed between plasma IL-6 level and percent sputum neutrophils, and sputum neutrophil elastase activity (Table 3). Moderate associations were observed between plasma IL-6 concentration and age, smoking, and BMI. Plasma IL-6 concentration was negatively correlated with %FEV1, %FVC, and FEV1/FVC (Table 3). Multiple regression analysis indicated that log10IL-6 was predicted by sex, BMI, and %FEV1 (Table 4).

Table Graphic Jump Location
Table 3 —Associations Between Systemic and Airway Inflammatory Markers and Clinical Characteristics of Subjects With Asthma (Spearman Rank Correlation)

NS = not significant. See Table 1 and 2 legends for expansion of other abbreviations.

Table Graphic Jump Location
Table 4 —Multivariate Predictors of Systemic Inflammation in Asthma

See Table 2 legend for expansion of abbreviation.

This study demonstrates for the first time to our knowledge that systemic inflammation is associated with neutrophilic airway inflammation in asthma. Subjects with neutrophilic asthma had increased systemic inflammation, with increased plasma IL-6 and CRP levels. Furthermore, the proportion of subjects with elevated IL-6 and CRP levels was higher in the asthma (neutrophilic) group than both the asthma (nonneutrophilic) and the healthy control groups. Plasma IL-6 concentrations were associated with worse clinical asthma outcomes, including lung function and asthma control. Within the subjects with asthma, there were weak associations between airway and systemic inflammatory mediators.

Systemic inflammation was increased in the asthma (neutrophilic) group, with > 50% of subjects having elevated plasma CRP and > 70% having elevated plasma IL-6 levels. Chronic, low-grade systemic inflammation increases the risk of various diseases. For example, elevated CRP levels increase cardiovascular disease risk,26 and circulating IL-6 levels predict risk of mortality from myocardial infarction27 and hemodialysis.28 Although the long-term consequences of systemic inflammation in neutrophilic asthma are not known, the risk of comorbidities involving a systemic inflammatory component may be increased. Indeed, asthma has been reported to increase the risk of atherogenesis,29 myocardial infarction, and stroke in some populations.3032 In the present study, the number of cardiovascular complications in the asthma (neutrophilic) group was increased. This cross-sectional study cannot elucidate whether this is a cause or consequence of increased systemic inflammation. Nonetheless, several studies have demonstrated a link between impaired lung function and cardiovascular disease.33,34 Longitudinal studies are needed to investigate whether this association is driven by systemic inflammation.

The finding that increased systemic inflammation was associated with neutrophilic asthma explains the inconsistency of previous studies in asthma. We found that in nonneutrophilic asthma, plasma CRP levels were similar to that of healthy control subjects and that plasma IL-6 levels were only marginally higher than those of the control subjects. When the asthma (nonneutrophilic) group was further subdivided, we found no difference in plasma IL-6 or CRP levels in subjects with eosinophilic vs paucigranulocytic asthma, suggesting that systemic inflammation only occurs in patients with airway neutrophilia. Evidence to date has not explicitly linked increased systemic inflammation to airway neutrophilia in asthma. However, studies reporting increased systemic inflammation in asthma are generally from subgroups known to involve noneosinophilic inflammation, such as during asthma exacerbations,8,9 in asthmatic blood cells stimulated with a nonallergic trigger (lipopolysaccharide),10 and in nonallergic asthma.11 The present data also showed that subjects with systemic inflammation had lower rates of allergic sensitization (atopy).

Subjects with high CRP levels were not different in terms of lung function or asthma control. Plasma CRP levels were predicted by BMI, sex, and percent sputum neutrophils. BMI predicts CRP level because adipose tissue is a source of CRP. The relationship between percent sputum neutrophils and plasma CRP indicates that there is some interaction between systemic and airway inflammatory pathways. Subjects with high IL-6 levels had worse lung function and asthma control. Plasma IL-6 level was inversely correlated with lung function and asthma control score and positively correlated with smoking history and BMI. Multiple regression analysis demonstrated that %FEV1 was a predictor of plasma IL-6 concentration, suggesting that IL-6 levels may be more closely associated with clinical asthma outcomes than CRP levels. CRP is released from the liver in response to a variety of stimuli, including circulating IL-6. The present observations suggest that IL-6 may be more closely linked to airway pathology, with CRP being a more general marker of inflammation. This is consistent with our previous study, which demonstrated that plasma IL-6, and not CRP, level was associated with reduced lung function in a cohort of older individuals.35 A similar observation has been made in patients with stable chronic heart failure.36

The negative association between IL-6 and %FEV1 may be driven by the proinflammatory and proangiogenic responses that IL-6 stimulates in airway smooth muscle by interacting with the soluble form of its receptor (sIL-6Rα) and recruiting glycoprotein 130.37 This initiates cellular events that lead to secretion of eotaxin and vascular endothelial growth factor37 and airway wall thickening.38

The accumulation and activation of airway neutrophils is important in both COPD and asthma.39,40 IL-8 mediates its chemoattractant effects through interacting with its receptors α (IL-8RA, CXCR1) and β (IL-8RB, CXCR2), leading to activation and migration of neutrophils.41 IL-8RA and IL-8RB are coordinately expressed in neutrophils.42 Blocking IL-8 significantly attenuates sputum neutrophil chemotactic activity in patients with COPD.43 In the present study, both receptors were upregulated in neutrophilic asthma, further supporting a role of this pathway in neutrophil accumulation and its functional relevance.44

Subanalysis of the asthma (neutrophilic) group revealed no differences in plasma CRP or IL-6 concentrations between never smokers and ex-smokers. Furthermore, in multiple regression models, smoking history was not a significant predictor of plasma CRP and IL-6 levels. Hence, systemic inflammation in neutrophilic asthma is not due to the systemic effects of smoking.

The correlations that we observed between systemic and airway inflammatory mediators in asthma were significant, yet weak. Thus, although spillover from the lungs contributes to systemic inflammation, other factors are involved. It appears likely that dysregulated innate immune responses are not confined to the airways, but also occur systemically. Indeed, recent analysis from our laboratory has reported that individuals with neutrophilic asthma have systemic upregulation of α-defensins and neutrophil proteases, including neutrophil elastase,45 and that isolated blood neutrophils release increased IL-8 in vitro,2 suggesting systemic neutrophil activation. Understanding the mechanisms of systemic inflammation in asthma is an important area for future research.

Through this cross-sectional study, we were unable to determine the direction of the association between systemic and airway inflammation. The data support the hypothesis that airway inflammation leads to systemic inflammation, however, systemic inflammation may also modulate airway inflammation. Indeed, in this study, airway neutrophils and expression of IL-8RA and IL-8RB were increased in subjects with elevated IL-6 and CRP levels (data not shown), suggesting that systemic inflammation may mediate airway inflammation through the regulation of these receptors. Intervention studies are needed to determine the direction of the association. We were also unable to elucidate whether levels of systemic inflammation change over time. However, a previous study reported that serum IL-6 and CRP levels are repeatable over 12 months in COPD.46 Furthermore, because the subjects in the present study were clinically stable, increased systemic inflammation is likely a usual feature of neutrophilic asthma.

In conclusion, we have observed that systemic inflammation is increased in neutrophilic asthma. In addition, plasma IL-6 may be more clinically relevant than plasma CRP and may provide a useful therapeutic target in neutrophilic asthma. Weak associations between airway and systemic inflammatory markers suggest that some spillover of airway inflammation occurs, but other factors must also contribute to increased systemic inflammation in neutrophilic asthma. Although the causes and consequences remain to be elucidated, it is likely that increased systemic inflammation is contributing to the pathophysiology of neutrophilic asthma.

Author contributions: Drs Wood and Gibson had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Dr Wood: contributed to the study design, supervision of the laboratory analysis, data analysis, and writing of the manuscript.

Dr Baines: contributed to the laboratory analysis, interpretation of the data, and review of the manuscript.

Dr Fu: contributed to the interpretation of the data, and writing and review of the manuscript.

Dr Scott: contributed to the study design, data collection, and review of the manuscript.

Dr Gibson: contributed to the study design, supervision of laboratory analysis and collection of samples, interpretation of the data, and review of the manuscript.

Financial/nonfinancial disclosures: The authors have reported to CHEST the following conflicts of interest: Dr Gibson is the recipient of a National Health and Medical Research Council of Australia Practitioner Fellowship. The remaining authors report no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Other contributions: We acknowledge the staff of Respiratory and Sleep Medicine, Hunter Medical Research Institute, particularly Joanne Smart; Amber Wood, BND; Anne-Marie Gibson; Michelle Gleeson; and Lakshitha Gunawardhana, BBiotech, who collected and processed the samples and performed the laboratory analysis.

CRP

C-reactive protein

IL-8RA

IL-8 receptor α

IL-8RB

IL-8 receptor β

IQR

interquartile range

TNF-α

tumor necrosis factor-α

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Lazaar AL, Panettieri RAJ Jr.. Airway smooth muscle: a modulator of airway remodeling in asthma. J Allergy Clin Immunol. 2005;116(3):488-495.
 
Norzila MZ, Fakes K, Henry RL, Simpson J, Gibson PG. Interleukin-8 secretion and neutrophil recruitment accompanies induced sputum eosinophil activation in children with acute asthma. Am J Respir Crit Care Med. 2000;161(3 pt 1):769-774.
 
Mukaida N. Pathophysiological roles of interleukin-8/CXCL8 in pulmonary diseases. Am J Physiol Lung Cell Mol Physiol. 2003;284(4):L566-L577.
 
Stemmler S, Arinir U, Klein W, et al. Association of interleukin-8 receptor alpha polymorphisms with chronic obstructive pulmonary disease and asthma. Genes Immun. 2005;6(3):225-230.
 
Morohashi H, Miyawaki T, Nomura H, et al. Expression of both types of human interleukin-8 receptors on mature neutrophils, monocytes, and natural killer cells. J Leukoc Biol. 1995;57(1):180-187.
 
Beeh KM, Kornmann O, Buhl R, Culpitt SV, Giembycz MA, Barnes PJ. Neutrophil chemotactic activity of sputum from patients with COPD: role of interleukin 8 and leukotriene B4. Chest. 2003;123(4):1240-1247.
 
Balish E, Wagner RD, Vazquez-Torres A, Jones-Carson J, Pierson C, Warner T. Mucosal and systemic candidiasis in IL-8Rh-/- BALB/c mice. J Leukoc Biol. 1999;66(1):144-150.
 
Baines KJ, Simpson JL, Wood LG, Scott RJ, Gibson PG. Systemic upregulation of neutrophil α-defensins and serine proteases in neutrophilic asthma. Thorax. 2011;66(11):942-947.
 
Kolsum U, Roy K, Starkey C, et al. The repeatability of interleukin-6, tumor necrosis factor-alpha, and C-reactive protein in COPD patients over one year. Int J Chron Obstruct Pulmon Dis. 2009;4:149-156.
 

Figures

Figure Jump LinkFigure 1. Prevalence of comorbidities in subjects with neutrophilic asthma and nonneutrophilic asthma. Cardiovascular includes hypertension, atrial fibrillation, and angina. Bowel disease includes inflammatory bowel and celiac disease. GORD = gastro-esophageal reflux disorder; OSAS = obstructive sleep apnea syndrome. *P < .05 vs asthma (nonneutrophilic) group.Grahic Jump Location
Figure Jump LinkFigure 2. A, Proportions of subjects with high plasma concentrations CRP. B, Proportions of subjects with high plasma concentrations of IL-6. High CRP is defined as plasma concentration > 4.12 mg/mL, and high IL-6 is defined as plasma concentration > 1.55 pg/mL (lower limit of upper quartile for healthy control subjects).*P < .05 vs asthma (neutrophilic) group. †P < .05 vs asthma (nonneutrophilic) group. CRP = C-reactive protein.Grahic Jump Location
Figure Jump LinkFigure 3. A, Comparison of lung function and asthma control in subjects with normal vs high CRP levels. B, Comparison of lung function and asthma control in subjects with normal vs high IL-6 levels. High CRP is defined as plasma concentration > 4.12 mg/mL, and high IL-6 is defined as plasma concentration > 1.55 pg/mL (lower limit of upper quartile for healthy control subjects). Data are presented as median (interquartile range). ACQ = Asthma Control Questionnaire. See Figure 2 legend for expansion of other abbreviation.Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1 —Asthma (Neutrophilic and Nonneutrophilic) vs Healthy Control Subjects: Clinical Characteristics

Data are presented as median (interquartile range) or mean ± SEM, unless otherwise indicated. Asthma (neutrophilic) is defined as sputum neutrophils ≥ 64%, and asthma (nonneutrophilic) is defined as sputum neutrophils < 64%. ACQ = Asthma Control Questionnaire; ICS = inhaled corticosteroid; NA = not applicable; PD15 = provocation dose resulting in 15% fall in baseline FEV1.

a 

P < .05 vs healthy control group.

b 

P < .05 vs asthma (nonneutrophilic) group.

c 

Expressed as geometric mean ± logSD.

Table Graphic Jump Location
Table 2 —Asthma (Neutrophilic and Nonneutrophilic) vs Healthy Control Subjects: Airway and Systemic Inflammation

Data are presented as median (interquartile range). Asthma (neutrophilic) is defined as sputum neutrophils ≥ 64%, and asthma (nonneutrophilic) is defined as sputum neutrophils < 64%. CRP = C-reactive protein; IL-8RA = IL-8 receptor α; IL-8RB = IL-8 receptor β; mRNA = messenger RNA; NE = neutrophil elastase; NO = nitric oxide; ppb = parts per billion; TNF-α = tumor necrosis factor-α.

a 

P < .05 vs healthy control group.

b 

P < .05 vs asthma (nonneutrophilic) group.

c 

n = 57.

d 

n = 78.

e 

n = 23.

Table Graphic Jump Location
Table 3 —Associations Between Systemic and Airway Inflammatory Markers and Clinical Characteristics of Subjects With Asthma (Spearman Rank Correlation)

NS = not significant. See Table 1 and 2 legends for expansion of other abbreviations.

Table Graphic Jump Location
Table 4 —Multivariate Predictors of Systemic Inflammation in Asthma

See Table 2 legend for expansion of abbreviation.

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Lazaar AL, Panettieri RAJ Jr.. Airway smooth muscle: a modulator of airway remodeling in asthma. J Allergy Clin Immunol. 2005;116(3):488-495.
 
Norzila MZ, Fakes K, Henry RL, Simpson J, Gibson PG. Interleukin-8 secretion and neutrophil recruitment accompanies induced sputum eosinophil activation in children with acute asthma. Am J Respir Crit Care Med. 2000;161(3 pt 1):769-774.
 
Mukaida N. Pathophysiological roles of interleukin-8/CXCL8 in pulmonary diseases. Am J Physiol Lung Cell Mol Physiol. 2003;284(4):L566-L577.
 
Stemmler S, Arinir U, Klein W, et al. Association of interleukin-8 receptor alpha polymorphisms with chronic obstructive pulmonary disease and asthma. Genes Immun. 2005;6(3):225-230.
 
Morohashi H, Miyawaki T, Nomura H, et al. Expression of both types of human interleukin-8 receptors on mature neutrophils, monocytes, and natural killer cells. J Leukoc Biol. 1995;57(1):180-187.
 
Beeh KM, Kornmann O, Buhl R, Culpitt SV, Giembycz MA, Barnes PJ. Neutrophil chemotactic activity of sputum from patients with COPD: role of interleukin 8 and leukotriene B4. Chest. 2003;123(4):1240-1247.
 
Balish E, Wagner RD, Vazquez-Torres A, Jones-Carson J, Pierson C, Warner T. Mucosal and systemic candidiasis in IL-8Rh-/- BALB/c mice. J Leukoc Biol. 1999;66(1):144-150.
 
Baines KJ, Simpson JL, Wood LG, Scott RJ, Gibson PG. Systemic upregulation of neutrophil α-defensins and serine proteases in neutrophilic asthma. Thorax. 2011;66(11):942-947.
 
Kolsum U, Roy K, Starkey C, et al. The repeatability of interleukin-6, tumor necrosis factor-alpha, and C-reactive protein in COPD patients over one year. Int J Chron Obstruct Pulmon Dis. 2009;4:149-156.
 
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