Airway and systemic eosinophilia in asthma: does site matter?

Abstract

Asthma is a complex chronic inflammatory disorder of the airways. It involves several cell types and cellular elements, is associated with airway hyperresponsiveness, and is characterised by recurrent episodes of wheezing, breathlessness and cough. These symptoms restrict the patients’ daily activities, impact on their quality of life and, if severe and untreated, may lead to hospitalisation and death [1]. Asthma needs to be monitored and controlled, and treatment schemes follow a step-wise approach, based initially on the level of severity and then on the level of control. The assessment of asthma control includes several clinical parameters such as frequency and severity of symptoms, impact on daily activity, and use of medication. All these parameters involve the patients’ perception and are often subjective [1]. However, monitoring of airway inflammation for the evaluation of asthma control may provide objective markers of assessment but requires time and financial and technological resources. Therefore, the use of inflammatory markers in the monitoring of asthma remains highly controversial. While the evaluation and monitoring of airway inflammation status does not seem warranted in everyday clinical management of controlled mild-to-moderate asthma, the assessment of the inflammatory phenotype is required in severe asthma that is resistant to conventional treatment, while monitoring of inflammation may help control and reduce exacerbation rates [2]. Several attempts have been made to classify patients with treatment-resistant asthma into distinct phenotypes, often involving indices of airways inflammation [3–5]. Early reports suggested that patients with more severe asthma had increased eosinophil [6] and/or neutrophil [7] counts in induced sputum and in bronchial biopsies. Although some severe asthma phenotypes and particularly inhaled corticosteroid (ICS)-resistant asthma have been associated with the presence of neutrophil predominance in sputum [6, 8], many patients …