Eosinophilic inflammation in COPD: prevalence and clinical characteristics.

Eosinophilic inflammation is thought to be a characteristic feature of asthma rather than COPD. However, studies have shown that a subset of COPD patients with eosinophilic airway inflammation exists, even after the careful exclusion of patients with any features of asthma, such as b-agonist reversibility, bronchial hyperresponsiveness, atopy or a childhood history of asthma [1–4]. Interestingly, these patients exhibit the greatest response to corticosteroid treatment [1–4]. Likewise, sputum eosinophil numbers are increased in a subset of COPD exacerbations [5, 6], and titrating corticosteroid therapy according to sputum eosinophil counts reduces exacerbation rates [7]. Furthermore, there are similar increases in sputum and blood eosinophil numbers during COPD exacerbations [5]; using blood eosinophils as a surrogate maker for airway eosinophils to direct oral corticosteroid therapy for the treatment of COPD exacerbations enhances clinical recovery [8]. Taken together, these observations suggest that eosinophilic airway inflammation in COPD is a predictive biomarker of corticosteroid responsiveness during clinical stability and exacerbations.