Asthma is a complex respiratory disease characterised by a variable degree of airway obstruction in which the fundamental abnormality is airway inflammation. Eosinophils are one of the major effector cells found in the lungs in patients with asthma. Their well-documented cytotoxic potential results in damage to the airway epithelium and tissue while their release of lipid mediators such as cysteinyl leukotrienes can obstruct airflow.

Eosinophils are not present in healthy lungs while in asthmatics there are well-documented correlations between eosinophil numbers and disease severity. Thus there is much interest in understanding how eosinophils preferentially accumulate in the asthmatic lung.