[Serum level of Pseudomonas aeruginosa-specific IgA in patients with chronic lower respiratory tract infection and its clinical significance].

Elevation of the serum IgA level has been observed in many cases of chronic lower respiratory tract infection. To determine the specificity of elevated serum IgA for the pathogen colonizing the respiratory tract of patients, we measured Pseudomonas aeruginosa-specific IgA titers in patients with chronic lower respiratory tract infections by ELISA. Sonicated P. aeruginosa strain BB5746 was used as the coating antigen. Optical density was significantly elevated in sera from patients in whom P. aeruginosa was consistently isolated from sputum cultures, when they were respondent to the antigen, indicating that bacteria-specific IgA is not localized in the respiratory tract surface, but is circulating in the blood stream of these patients. The other two groups, chronic bronchitis patients from whom bacteria other than P. aeruginosa were occasionally isolated from sputum culture, and IgA nephropathy patients, had no detectable specific IgA in their sera as is the case in normal adults. Our results indicate that bacteria-specific serum IgA levels appeared to correlate with duration from the time of bacterial colonization with P. aeruginosa and the degree of bronchial and alveolar destruction seen on chest X-rays. In addition, detection of increased serum P. aeruginosa-specific IgA seems to contribute to the recognition of persistent bacterial colonization of the respiratory tract.