Variability in the secretory IgA system in sputum sol phase in stable chronic obstructive bronchitis.

Within and between patient variability in the sputum sol phase secretory IgA system was studied in 31 patients with clinically stable chronic obstructive bronchitis. Within patient coefficients of variation (CV) were similar for secretory component (SC), free secretory component (FSC), total immunoglobulin A (IgA) and the immunological amount of IgA present in its dimeric (11S) form (average CV 32%). The immunological proportion of IgA present in the dimeric form was about 70% of the total and relatively constant (average CV 7%). Between patients, variability was greater but also similar for SC, FSC, total IgA and the amount of dimeric IgA (average CV 50%). The proportion of IgA present in dimeric form was again less variable (CV 21.1%). 'Standardisation' of samples, using protein ratios to either albumin or the 'local' components of the secretory IgA system, did not produce variability. Furthermore, the effect of such standardisation was to increase the between patient variability for total IgA and FSC (2p less than 0.01). However, despite this variability, 4 patients studied previously remained clearly distinct, suggesting defects of the secretory IgA system. The methods described provide a means of identifying such patients.