Correlation between IgA antibody and eosinophil cationic protein levels in induced sputum from asthmatic patients

BACKGROUND: Eosinophils are known to be main effector cells in allergic inflammation and IgA antibody has been shown to be a potent stimulus for eosinophil degranulation in in vitro conditions. OBJECTIVE: To evaluate the possible role of IgA antibodies on eosinophil degranulation in lower respiratory mucosa of asthmatics, we tried to find a correlation between total IgA and eosinophil cationic protein (ECP) levels in induced sputum from asthmatics. METHODS: We measured total IgA and albumin levels by nephelometry, and eosinophil cationic protein levels by Pharmacia CAP system in induced sputum from 23 atopic asthmatics and 12 healthy controls. RESULTS: IgA and albumin levels in induced sputum from asthmatics with sputum eosinophilia (sputum eosinophil count > or = 5% of 200 counted non-squamous cells) were significantly higher (P < 0.05) than those from controls. However, IgA and albumin levels in induced sputum from asthmatics without sputum eosinophilia were not significantly different with those from controls (P > 0.05). In induced sputum from asthmatics, ECP levels were significantly correlated with albumin (r = 0.44, P = 0.04) and IgA levels (r = 0.67, P = 0.002). ECP/albumin ratio was also significantly correlated with IgA/ albumin ratio (r = 0.61, P = 0.004). CONCLUSION: Our results support the hypothesis that IgA antibodies in tracheobronchial secretion may be involved in eosinophil degranulation in asthma, and further study is needed to prove this hypothesis.