The Immunological Assessment of α₁-Antitrypsin with Reference to Its Function in Bronchial Secretions

1. The quantification of α₁-antitrypsin (α₁AT) by standard immunological techniques is altered by interaction of the protein with leucocyte elastase.

2. The results obtained for α₁-antitrypsinleucocyte elastase mixtures in the presence of a functional excess of the inhibitor were relatively accurate for the first 6 h. However, continued incubation for more than 24 h led to a major over-estimation of the α₁AT 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 α₁AT occurred within 1 h and the degree of overestimation increased with time (up to threefold at 24 h). This was eventually associated with the presence of only a partially proteolysed form of α₁AT (mol wt. ⋍ 50000).

4. Different results for each sample were obtained when different polyclonal antisera were used to quantify the α₁AT.

5. Complete inactivation of α₁AT by oxidation resulted in little change in the immunological quantification of the protein. However, further addition of H₂O₂ led to a progressive underestimation of the α₁AT.

6. The effect of physicochemical alteration on the immunological quantification of α₁AT by different antisera should be borne in mind for all studies assessing this protein in lung secretions.