Pg. Gibson et al., INDUCED SPUTUM EOSINOPHIL CATIONIC PROTEIN (ECP) MEASUREMENT IN ASTHMA AND CHRONIC OBSTRUCTIVE AIRWAY DISEASE (COAD), Clinical and experimental allergy, 28(9), 1998, pp. 1081-1088
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.