Elevation of specific immunoglobulin A antibodies to both allergen and bacterial antigen in induced sputum from asthmatics.

The antigenic specificity and pathogenetic significance of immunoglobulins in airway secretion from asthmatic patients have not been established. Elevated levels of B-cells and immunoglobulin (Ig)A antibodies have been reported in sputum of asthmatics and these levels correlated with the eosinophil counts and levels of degranulated cytotoxic proteins from eosinophils. This study aimed to investigate the antigen specificity and possible pathogenetic significance of antibodies in airway secretion from asthmatic patients. Specific IgA and IgG antibodies to both allergen (Dermatophagoides farinae) and bacterial antigen (capsular polysaccharide antigen from Streptococcus pneumoniae) were measured in sputum from 16 atopic asthmatic patients sensitized to D. farinae and 12 nonatopic, nonasthmatic controls by enzyme-linked immunosorbent assay. Sputum was induced by inhalation of hypertonic saline. Eosinophil cationic protein (ECP) levels in sputum from asthmatic patients were measured by the Pharmacia CAP system. Levels of IgA to both D. farinae and S. pneumoniae and IgG to D. farinae in the sputum from asthmatic patients were significantly higher than those from controls (p<0.005). No significant difference was found in the levels of IgG to S. pneumoniae between the two groups. In asthmatic patients, there were significant correlations between IgA to D. farinae and S. pneumoniae (r=0.76, p=0.003). Sputum ECP levels correlated significantly with IgA to D. farinae (r=0.55, p=0.03) and S. pneumoniae (r=0.56, p=0.03) and IgG to D. farinae (r=0.52, p=0.04), but not with IgG to S. pneumoniae in asthmatic patients. In conclusion, specific immunoglobulin A antibodies to both allergen and bacterial antigen were elevated in induced sputum from atopic asthmatics and their possible involvement in eosinophil degranulation was suggested.