IgA subclasses in sputum from patients with bronchiectasis.

The concentrations of IgA1 and IgA2 were measured in the serum and sputum from 27 clinically stable patients with bronchiectasis. Of the 27 patients, nine were regularly producing mucoid secretions, nine mucopurulent and nine purulent secretions. No significant differences were observed in serum IgA2 concentrations between the patient groups, although IgA1 concentrations were higher in the serum from the patients producing mucopurulent sputum than those producing mucoid or purulent sputum. The sputum concentrations of both IgA1 and IgA2 increased significantly with purulence. Furthermore, there was a significant increase in the proportion of IgA2 as the secretions became more purulent. The sputum concentrations of both IgA subclasses indicated significant local synthesis, with increased production (especially of IgA2) in the presence of inflammation due to infection.