The immunological measurements of 'free' secretory piece and its relationship to local IgA production.

Free secretory piece (FSP) was studied in the sputum of patients with chronic bronchitis. The concentrations were higher both in the presence of infection and when greater quantities of total secretory piece were present compared to the amount of 11S IgA. A significant inverse correlation was found between the amount of FSP and 11S IgA in the individual samples when standardized for their total secretory piece content (2P less than 0 . 01). This suggests that the amount of FSP in any sample is partly dependent upon the amount of 11S IgA. The techniques employed offer a method for the study of the secretory IgA system in biological fluids. The preliminary results suggest that the secretory IgA system is independent of the systemic IgA system.