INDUCED SPUTUM EOSINOPHIL CATIONIC PROTEIN (ECP) MEASUREMENT IN ASTHMA AND CHRONIC OBSTRUCTIVE AIRWAY DISEASE (COAD)

Background induced sputum is a useful way to monitor airway inflammati on in asthma, but cell counts are time-consuming and labour intensive. Objective The aim of this study was to evaluate a novel processing me thod using eosinophil cationic protein (ECP) as a biochemical marker o f sputum eosinophil number and activation in subjects with asthma and other airway diseases. Methods Sputum was dispersed with dithiothreito l and centrifuged to yield cell free supernatant and a cell pellet. Th e pellet was treated with a cellular lysis buffer to release cell-asso ciated ECP. ECP was measured in sputum supernatant and in the lysed ce ll pellet and was compared with sputum eosinophil counts in 31 adults with asthma, chronic obstructive airway disease (COAD), bronchiectasis and healthy controls. The ratio of supernatant to pellet ECP was eval uated as an index of eosinophil degranulation. The effect of sputum pr ocessing reagents and storage time on ECP measurement was also evaluat ed. Results ECP measured in the cell pellet lysate correlated closely with sputum absolute eosinophil counts across a range of subject group s (r = 0.72, P = 0.004). Sputum eosinophil counts were less well corre lated with supernatant ECP levels (r = 0.54, P < 0.05). Incubation wit h dithiothreitol or lysis buffer did not influence ECP measurement and sputum ECP levels were stable over a 6-9 month period. Sputum superna tant and pellet lysate ECP concentrations were increased in stable ast hma, asthma exacerbations and COAD/bronchiectasis (P < 0.05). The rati o of supernatant to pellet ECP was used as an index of eosinophil degr anulation and found to be elevated in asthma exacerbations, GOAD and b ronchiectasis, but not in stable asthma. Conclusion The measurement of ECP in the sputum cell pellet provides a reliable and efficient estim ate of sputum eosinophil counts which can potentially be used in clini cal trials and epidemiological surveys. The ECP ratio may be a useful marker of eosinophil activation, and was increased in asthma exacerbat ion and GOAD. The increased ECP in GOAD reflects a non-selective accum ulation of eosinophils in this condition.