Copyright ©ERS Journals Ltd 2007 Eotaxin-2 in sputum cell culture to evaluate asthma inflammationDepts of 1 Medicine and 3 Pharmacology, University of S. Paulo Medical School at Ribeirão Preto, Sãu Paulo, Depts of 2 Biochemistry and Immunology, Institute of Biological Sciences, and 4 Internal Medicine, Medical School, Federal University of Minas Gerais, Minas Gerais, Brazil. CORRESPONDENCE: E. O. Vianna, Pulmonary Division, Dept of Medicine, University of S. Paulo Medical School at Ribeirão Preto, Av. Bandeirantes 3900, Ribeirão Preto, Sãu Paulo, 14048-900, Brazil. Fax: 55 1636336695. E-mail: evianna{at}uol.com.br Keywords: Asthma, cell culture, inflammatory mediators, sputum, steroid
Received: August 5, 2006
The aim of the present study was to elucidate whether the culture of cells recovered from induced sputum may represent a suitable model to evaluate cytokine and chemokine production by airway inflammatory cells.
Sputum induction was performed in 21 normal subjects and 30 asthmatic patients. A total of 21 out of the 30 asthmatic patients were taking inhaled corticosteroids, while the remaining nine were steroid-naive asthmatics. The steroid-naive group was evaluated before and after a 14-day treatment with oral prednisone (40 mg·day1). The supernatant of lysed and centrifuged sputum and the supernatant of sputum cell culture were analysed. Tumour necrosis factor- Eotaxin-2 production by cell culture was higher in the asthma group (131±108 pg·mL1) than in the control group (36±41 pg·mL1) and treatment with oral corticosteroids eliminated this difference. In addition, reduction of eotaxin-2 levels by corticosteroid treatment was greater in cell culture (81.3% reduction) than in sputum (26.4%). There was correlation between the decrease in eotaxin-2 production and the decrease in blood eosinophil number and between eotaxin-2 and eosinophils in sputum. Eotaxin-2 may play an important role in asthma and the response to corticosteroid treatment suggests that analysis of sputum cell culture is relevant as an inflammatory parameter. Asthma is defined as a chronic lung disease with the following attributes: airflow obstruction that is reversible either spontaneously or with treatment, and airway inflammation and increased airway responsiveness to a variety of stimuli, including cold air, methacholine, hypertonic solution inhalation and exercise 1. The aetiology of asthma is complex and involves the interaction between genetic factors and environment. The vast majority of the data regarding the pathogenesis of asthma concentrates on atopic asthma and the imbalance between the T-helper cell (Th) type 1 and Th2 phenotypes 2. Further evidence of an inflammatory response in asthma is the presence of cells and mediators in bronchoalveolar lavage (BAL), sputum and respiratory tissues. Eosinophil recruitment from peripheral blood into the airways is controlled by adhesion molecules and chemokines. The chemokines are a group of chemotactic cytokines that have been subdivided into four families: CXCL, CCL, CL and CX3CL 3, 4. Members of the CCL branch include regulated on activation, normal T-cell expressed and secreted (RANTES; CCL5), monocyte chemotactic protein (MCP)-2 (CCL8), MCP-3 (CCL7), MCP-4 (CCL13) and eotaxin-1 (CCL11), -2 (CCL24) and -3 (CCL26). RANTES and MCP-3 and -4 are chemotactic for eosinophils, monocytes and lymphocytes, while eotaxins chemoattract eosinophils, basophils and Th2 lymphocytes 4. Due to their eosinophil chemotactic properties, these chemokines have attracted major attention in allergic inflammation 5. Studies conducted in adult asthmatics have shown that RANTES, MCP-3 and -4 and eotaxin-1 and -2 are implicated in asthmatic reactions 610. In clinical practice, the assessment of airway inflammation and the effect of medication on inflammation is difficult. Subjective assessment of symptoms has often been found to be unsatisfactory for monitoring asthma severity 11. Measurements of levels of exhaled gases, such as nitric oxide (NO), may be useful but more data are needed to fully evaluate the importance of these markers in assessing airway inflammation in asthma, especially because NO can be produced in large amounts in paranasal sinuses and the stomach 11. Repeated bronchoscopic sampling is not feasible on a large scale. The ability to study inflammation has changed considerably with the development of the induced sputum technique as a research and, increasingly, as a clinical tool 12, 13. Induced sputum was used for the first time in asthmatic patients in 1992, when Pin et al. 14 adapted the technique used until then for diagnosis of Pneumocystis carinii in patients with HIV. In recent years, sputum induction with a hypertonic saline solution and subsequent processing have been refined as a noninvasive research tool providing important information about inflammatory events in the lower airways. The technique of cell culture has been especially developed for blood cells in an attempt to reproduce in vitro what happens in vivo. Several studies 1517 have used the culture of blood cells to examine asthma pathophysiology and the responsiveness to treatment. However, very few studies have employed the culture of sputum cells 1822. It is likely that cells from the airways provide better information due to their proximity to the site of asthmatic inflammation. The aim of the present study was to elucidate whether the culture of cells recovered from induced sputum may represent a suitable model to evaluate cytokine and chemokine production by airway inflammatory cells. Thus, the present authors have assessed culture time (viability) and the production of inflammatory mediators from stimulated and nonstimulated, adherent and nonadherent cells in asthmatics and in healthy subjects. The response to corticosteroid treatment was also measured by analysis of sputum cell culture.
Subjects In total, 51 subjects were included in the present study. A group of 30 stable asthmatic patients (13 males and 17 females of mean age 41.0 yrs) were recruited from the asthma clinic of the University Hospital of Ribeirão Preto (University of São Paulo, São Paulo, Brazil). A total of 21 asthmatic patients used regular inhaled corticosteroids (mean daily dose 409.5±40.1 µg budesonide) and were studied in a single visit. This group was denominated the asthma inhaled corticosteroid (IC) group. Nine uncontrolled, untreated asthmatics (on bronchodilator) were studied at two time-points: before (pre-treatment) and after (post-treatment) oral corticosteroid (OC) treatment for 14 days (40 mg·day1 prednisone). This group was denominated the asthma OC group. These patients did not present acute asthma and they were scheduled for prednisone treatment independently of asthma severity. The choice for this treatment was due to research purposes. The variables under study and blood eosinophil counts were determined in these patients before and after treatment. A total of 21 normal volunteers (six males and 15 females of mean age 41.1 yrs) with forced expiratory volume in one second (FEV1) values 90% of predicted formed a control group (table 1
The diagnosis of asthma was confirmed on the basis of a history of dyspnoea and wheezing with a reversible airflow obstruction characterised by a 15% increase in FEV1 after inhalation of 200400 µg albuterol and/or a methacholine provocative concentration causing a 20% fall in FEV1 <8 mg·mL1 23. The study was approved by the ethics committee of the University of S. Paulo Medical School at Ribeirão Preto. All volunteers gave informed consent to participate in the study.
Sputum induction and processing
Characteristics of sputum induction are shown in table 1
Cell culture In order to perform differential cell counts of the adherent cell culture, sputum cells were also plated on sterile chambers mounted on Permanox slides with covers (Chamber Slide System; Nalge Nunc International Corp., Napersville, IL, USA). At the end of culture time, the slides with adherent cells were detached from the media chamber. At the end of culture time, nonadherent cells were aspirated and slides were prepared by cytospin staining.
Timeresponse analysis
Lipopolysaccharide response
Detection of cytokines and chemokines
Statistical analysis
Characterisation of cell culture The first part of the analysis of cell culture was performed in asthmatic subjects (asthma IC group) only. Viability was high and of similar magnitude for adherent and nonadherent cells up to 72 h of culture. After 72 h, the viability dropped significantly (fig. 1 , IL-8 and IL-1ß production by adherent cells reached the highest values at 48 h of culture: 1,417±1,128 pg·mL1, 785±321 pg·mL1 and 94±153 pg·mL1, respectively. The production of TNF- and eotaxin-2 by nonadherent cells was also highest at 48 h. Therefore, this time-point was used to monitor the production of inflammatory markers. Cytokine levels with and without stimulation at the highest concentration of LPS or PHA were not statistically different (table 2
Effects of oral corticosteroid treatment Squamous cell percentage in induced sputum was 21.6±5.0% in the control group, 19.9±2.4% for the asthma OC group pre-treatment, 28.4±5.1% for the asthma OC group post-treatment and 12.3±6.2% in the asthma IC group (nonsignificant differences). Differential cell counts of sputum, adherent and nonadherent cell cultures for all groups are shown in table 4
The number of nonadherent cells at the end of 48 h of culture was similar among the groups (p = 0.92). The value for the control group was 2.8±3.0x104 cells·mL1, for patients treated with IC it was 2.4±1.2x104 cells·mL1 and for patients treated with OC it was 2.3±1.0x104 cells·mL1.
Eotaxin-2 production in culture of nonadherent cells (fig. 2
Sputum eotaxin-2 levels correlated with cell culture eotaxin-2 production (r = 0.67; p = 0.04). The response to OC treatment was evaluated by calculating the difference between the levels of eotaxin-2 before and after prednisone treatment in induced sputum and in sputum cell culture (fig. 3
The blood eosinophil count in the asthma OC group fell from the pre-treatment, 8.6±4.8%, to the post-treatment period, 1.5±1.6% (p = 0.002). The pre-treatment blood eosinophil number correlated with eotaxin-2 production by cell culture (r = 0.71; p = 0.02). The response in cell culture eotaxin-2 production to steroid treatment correlated with the response in blood eosinophil number and sputum eosinophil number (r = 0.74; p = 0.04). Sputum eosinophil number correlated with eotaxin-2 level in sputum (r = 0.56; p = 0.01) but not with eotaxin-2 production by cell culture.
In the present study, the possibility of evaluating in vitro the inflammatory status of asthmatic patients has been shown. The present authors cultured sputum inflammatory cells of asthmatic and normal subjects. In the few studies that tried to keep sputum cells in culture to evaluate the inflammatory characteristics of asthma, sputum cells were cultured without fractionation 1822. The cells were separated into two fractions, adherent and nonadherent, and cytokines, chemokines and cell composition were evaluated in each fraction. In the culture of adherent cells, TNF- , IL-8 and IL-1ß were detected from both the asthma and control groups. In the culture of nonadherent cells, eotaxin-1 and -2, and TNF- were detected. Of the measured mediators, eotaxin-2 appeared to show the greatest differences between the various groups. Indeed, eotaxin-2 production was higher in the asthma group compared to the control group and treatment with OC abolished this difference. In addition, reduction of eotaxin-2 levels by this treatment was greater in cell culture than in sputum. The present study was the first to evaluate and detect eotaxin-2 in sputum and sputum cell culture of asthmatic patients. The first eotaxin was discovered using a guinea pig model of allergic airway disease characterised by marked lung eosinophilia 26, 27. In humans, Mattoli et al. 28 showed that the numbers of cells expressing mRNA for eotaxin-1 correlated significantly with the number of eosinophils, bronchial hyperreactivity and symptom score in asthmatics. Furthermore, increased eotaxin-1 protein has been detected in the BAL fluid of asthmatic subjects 29. According to Miotto et al. 10, eotaxin-1 is selectively increased in Th2-mediated airway diseases and this chemokine plays a central role in the pathogenesis of asthma. In addition to stimulating eosinophil chemotaxis, eotaxin-1 induces aggregation of eosinophils, an elevation in their intracellular calcium levels 29 and respiratory burst activity. Similarly to eotaxin-1, eotaxin-2 is known to be a potent eosinophil chemoattractant in vitro and in vivo 3032. A study of the late-phase allergic reactions in the skin of human atopic subjects suggested that eotaxin-1 is involved in the early 6-h recruitment of eosinophils, whereas eotaxin-2 is involved in the later 24-h infiltration of these cells 32. The present findings demonstrate a relationship between eotaxin-2 and asthma. Eotaxin-2 production in cell culture correlated with eosinophil number in peripheral blood, and eotaxin-2 concentration in sputum correlated with eosinophil number in sputum. Furthermore, the decrease in eotaxin-2 production induced by systemic steroid treatment was associated with the decrease in eosinophil number in sputum and blood. In culture, eotaxin-2 levels of patients treated with IC were significantly higher than those of controls and patients treated with OC. This may indicate that the inflammatory status of patients treated with regular IC remains high. The detected percentage of eosinophils in sputum corroborates this theory. In a study on mild asthma, Jatakanon et al. 33 evaluated the effect of differing doses of inhaled budesonide on airway inflammation markers. Jatakanon et al. 33 showed a significant trend towards greater reduction in inflammatory markers with higher dose of budesonide (1,600 µg·day1), suggesting a dose-dependent effect of inhaled steroids on airway inflammation. The elevated concentration of eotaxin-2 found in the present study may have been due to the fact that most asthmatic patients were treated with a low-dose IC. In contrast, there was no significant difference in eotaxin-2 levels between patients treated with OC and controls. The effectiveness of OC in the treatment of chronic asthma (OC are the most potent anti-inflammatory drugs used in the treatment of asthma) probably results from a combination of anti-inflammatory actions 34, which inhibit gene transcription of the majority of cytokines involved in asthmatic airway inflammation 3537. With regard to the constitution of sputum cell cultures, asthmatic patients had a higher proportion of eosinophils in all fractions at baseline. In the post-treatment evaluation, those numbers of eosinophils fell to values that were not different from the control group values. The proportion of macrophages increased from the time of sputum collection to the end of cell culture period in both adherent and nonadherent fractions, which may represent cell proliferation in culture. Further studies are necessary to evaluate the mechanisms of cell number changes and to determine whether the decrease in eotaxin production reflects changes in cell number or suppression by steroid effect.
A series of spike and recovery experiments with eotaxin-2 have been performed (data not shown). The results observed clearly demonstrate that the processing of samples with DTT diminishes the recovery of the chemokine in sputum samples by The interference of DTT on eotaxin-2 measurements may explain, at least partially, the advantage of cell culture supernatant over sputum supernatant. Sputum cell culture supernatant has no DTT and eotaxin-2 is produced de novo. Thus, the assay to measure mediators in culture supernatant is free of the DTT interference, which may account for the superior performance of sputum cell culture in detecting a response to patient treatment.
The cytokines and chemokines could be detected in vitro without any additional stimulus in the culture medium. The results demonstrated no significant difference in inflammatory markers with stimulation of the adherent and nonadherent cells with LPS or PHA, respectively. The present results are consistent with the cells being activated during their migration to the airway and agree with those of Bettiol et al. 18. Conversely, Liu et al. 19 had to add PHA in order to obtain detectable levels of interferon- In conclusion, the present study demonstrates the usefulness of in vitro sputum cell generation of cytokines and chemokines as a suitable model to evaluate the airway inflammation observed in asthmatic patients. The present findings show a correlation between eotaxin-2 production in cell culture and eosinophil number in peripheral blood or sputum. In addition, there was a greater fall in eotaxin-2 levels measured in cell culture than in induced sputum following treatment. Overall, the present results suggest that analysis of sputum cell culture is sensitive for the detection of the effects of anti-inflammatory drugs and are consistent with an important role of eotaxin-2 in the pathophysiology of asthma.
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