Eosinophil Activation Markers in Induced Sputum in Asthmatics

OBJECTIVES Eosinophils play an important role in asthmatic airway inflammation collaborately with other inflammatory cells. The present study was aimed to determine whether the eosinophil activation markers in induced sputum reflect the clinical status in asthmatics. METHODS The clinical severity and FEV1 were measured. Hypertonic saline induced sputum was obtained from 25 asthmatics and ten control subjects. We processed freshly expectorated sputum separated from saliva by treatment with an equal volume of dithiothreitol 0.1%, cytospins for cell count and special stain, and a collection of the supernatant for biochemical assay. We used a fluoroimmunoassay to detect eosinophil cationic protein (ECP), and a sandwich ELISA to detect interleukin (IL)-5. RESULTS Asthmatics, compared with control subjects, had a significantly higher proportion of eosinophils (25.6 +/- 4.6% vs 1.7 +/- 0.2%, p < 0.01) and higher levels of ECP (1117.8 +/- 213.9 micrograms/L vs 154.6 +/- 47.4 micrograms/L, p < 0.01) in their sputum. IL-5 was detected more frequently in asthmatics than in control subjects [11/25 (44%) vs 1/10 (10%), p < 0.05]. Moderate to severe asthmatics had a significantly higher proportion of eosinophils, higher levels of ECP and IL-5 compared to mild asthmatics. FEV1, FEV1/FVC were significantly correlated with the proportion of eosinophils and the levels of ECP and IL-5. Significant positive correlations were noted between the proportion of eosinophils and the level of ECP and IL-5. Sputum ECP level showed a significant positive correlation with IL-5 level. CONCLUSION These findings demonstrate that eosinophils and the eosinophil activation markers, such as ECP and IL-5 in induced sputum, are closely related to the clinical status in asthmatics. Induced sputum study may thus be useful in clinically measuring indices of airway inflammation in asthma.