ASTHMA

Evaluation of airway inflammation by quantitative Th1/Th2 cytokine mRNA measurement in sputum of asthma patients

E Truyen¹, L Coteur¹, E Dilissen¹, L Overbergh², L J Dupont³, J L Ceuppens¹, D M A Bullens^1,4

¹ Clinical Immunology, University Hospital Gasthuisberg, Katholieke Universiteit Leuven, (KULeuven), Leuven, Belgium
² Laboratory for Experimental Medicine and Endocrinology (LEGENDO), KULeuven, Leuven, Belgium
³ Pneumology, University Hospital Gasthuisberg, KULeuven, Leuven, Belgium
⁴ Paediatrics, University Hospital Gasthuisberg, KULeuven, Leuven, Belgium

Correspondence to:
Dr D M A Bullens
Clinical Immunology, University Hospital, Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium; Dominique.Bullens{at}med.kuleuven.be

Background: Asthma is a chronic inflammatory disorder of the airways driven by T cell activation. Th2 cells and their cytokines are thought to play a role in the pathophysiology of allergic as well as non-allergic asthma.

Methods: Airway cells were obtained by sputum induction from 15 healthy and 39 asthmatic individuals and the airway T cell cytokine profiles (interleukin (IL)-4, IL-5, IL-13, IL-10 and interferon (IFN)-) at the mRNA level were studied by real time RT-PCR.

Results: Asthma patients had increased expression of IL-5 (p = 0.001) and IL-13 (p = 0.03) mRNA in sputum compared with non-asthmatic controls. IL-4 mRNA and IFN- mRNA were detectable in the sputum of 44% and 21% of patients, respectively, but not in controls. Sputum IL-10 mRNA levels did not differ significantly between patients and controls. Sputum mRNA expression levels of IL-4, IL-5, and IL-13 were significantly correlated with the percentage of eosinophils and were higher in subjects with allergic asthma than in those with non-allergic asthma (p = 0.03, p = 0.02 and p = 0.0002, respectively); they did not differ between mild asthmatic subjects and those with moderate to severe asthma. In contrast, IFN- mRNA expression was higher in non-allergic than in allergic patients (p = 0.04) and higher in patients with moderate to severe asthma than in those with mild asthma (p<0.01). Sputum IL-5 mRNA levels (but not the other cytokine mRNA levels) were also correlated with exhaled nitric oxide (eNO) and with bronchial hyperreactivity expressed as the histamine concentration resulting in a 20% decrease in forced expiratory volume in 1 second.

Conclusion: Real time RT-PCR analysis of mRNA in induced sputum confirms a predominance of Th2 cytokines in both allergic and non-allergic asthma. IL-5 levels reflect eosinophil infiltration as well as eNO levels and hyperreactivity, and levels of the Th1 cytokine IFN- indicate asthma severity. The technique is a promising tool for use in further studies of asthma severity and disease activity.

Abbreviations: ASS, asthma symptom score; eNO, exhaled nitric oxide; FEV₁, forced expiratory volume in 1 second; ICS, inhaled corticosteroids; IFN-, interferon ; IL, interleukin; mAb, monoclonal antibody; mRNA, messenger RNA; PC₂₀, histamine concentration provoking a 20% decrease in FEV₁; Th, T helper

Keywords: induced sputum; Th1/Th2 cytokines; asthma; severity

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