The immunological assessment of q-antitrypsin with reference to its function in bronchial secretions

1 . The quantification of alantitrypsin (alAT) by standard immunological techniques is altered by interaction of the protein with leucocyte elastase. 2. The results obtained for al-antitrypsinleucocyte elastase mixtures in the presence of a functional excess of the inhibitor were relatively accurate for the fust 6 h. However, continued incubation for more than 24 h led to a major overestimation of the alAT as the result of breakdown of the enzyme-inhibitor complex releasing a partially proteolysed form of the inhibitor. 3. In the presence of excess enzyme up to a twofold overestimation of alAT occurred within 1 h and the degree of overestimation increased with time (up to threefold at 24h). Th’ IS was eventually associated with the presence of only a partially proteolysed form of alAT (mol wt.==‘ 50 000). 4. Different results for each sample were obtained when different polyclonal antisera were used to quantify the alAT. 5. Complete inactivation of alAT by oxidation resulted in little change in the immunological quantification of the protein. However, further addition of HzOz led to a progressive underestimation of the alAT. 6. The effect of physicochemical alteration on the immunological quantification of alAT by different antisera should be borne in mind for all studies assessing this protein in lung secretions.