Eosinophils in chronic obstructive pulmonary disease

Chronic Obstructive Pulmonary Disease (COPD) is a heterogeneous lung condition characterised by chronic respiratory symptoms, fixed airway obstruction and persistent inflammation that leads to a progressive airflow limitation. Although COPD has traditionally been linked to neutrophilic inflammation, recent studies have identified a subset of patients - approximately 20%-40% - with elevated eosinophil levels in blood and sputum. Emerging evidence suggests that eosinophilic inflammation has a pivotal role in a subset of COPD patients and may influence disease progression, exacerbation frequency and therapeutic responses. This narrative review provides a comprehensive analysis of the role of eosinophils in COPD with particular attention to their role as biomarkers in blood and sputum. We evaluate the prevalence of eosinophilic inflammation in COPD exanimating different thresholds used in blood and in sputum to define it. In addition, we focus on eosinophilic COPD phenotype as a treatable trait, emphasising recent evidence that supports the effectiveness of biological target therapy.