Relationship between induced sputum cell counts and fluid-phase eosinophilcationic protein and clinical or physiologic profiles in mild asthma

Background: Sputum analysis is the only non-invasive method to examine airw ay inflammatory processes in subjects with asthma. The aim of this study was to investigate the relationship between cell coun ts and fluid phase levels in induced sputum in subjects with mild asthma, a nd the severity of asthma as assessed by clinical, physiologic and blood me asurements. Methods: Forty patients with mild asthma, aged 17 to 49 years were studied (goad sputum sample only from 31). On the first day, spirometry and methach oline challenges were performed. After 2 to 4 days, venous blood for absolu te eosinophil count and eosinophil cationic protein (ECP) measurement was o btained and sputum was induced by inhalation of hypertonic saline. For the next 15 days subjects recorded their peak expiratory flow (PEF), symptom sc ores, and beta(2)-agonist require ments twice daily. Differential counts of leukocytes were done on cytospin prepa rations of homogenized sputum and t he supernatant was examined for eosinophil cationic protein (ECP). Results: Sputum eosinophil counts and not neutrophil, epithelial cells, mac rophages, or lymphocytes, were inversely correlated to FEV1/FVC % (r = -.57 , P =.0008) and to PC20-methacholine (r = -.40, P =.024). No statistical re lationship was obtained between eosinophil counts and either symptom scores , bronchodilator requirements, or daily PEF variability. Sputum ECP values were correlated to FEV1/FVC% (r=-.41, P=.026) but not to PC20 (r=-.32, P=.0 8) or clinical scores or PEF variation. A trend to significance was appreci ated between peripheral blood and sputum eosinophil counts (r=.34, P=.067) and no relationship was found between sputum and serum ECP values (r=.10, P =.38). Conclusions: Although sputum markers give some information about disordered lung function and physiologic changes in the airways, they are not the onl y factors concerned in the clinical expression of mild asthma.