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

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Abstract
Quantification of [human] .alpha.1-antitrypsin (.alpha.1AT) by standard immunological techniques is altered by interaction of the protein with leukocyte elastase. Results obtained for .alpha.1-antitrypsin-leukocyte elastase mixtures in the presence of a functional excess of the inhibitor were relatively accurate for the first 6 h. Continued incubation for more than 24 h led to a major overestimation of the .alpha.1AT as the result of breakdown of the enzyme-inhibitor complex releasing a partially proteolyzed form of the inhibitor. In the presence of excess enzyme, up to a 2-fold overestimation of .alpha.1AT occurred within 1 h and the degree of overestimation increased with time (up to 3-fold at 24 h). This was eventually associated with the presence of only a partially proteolyzed form of .alpha.1AT (MW .simeq. 50,000). Different results for each sample were obtained when different polyclonal antisera were used to quantify the .alpha.1AT. Complete inactivation of .alpha.1AT by oxidation resulted in little change in the immunological quantification of the protein. Further addition of H2O2 led to a progressive underestimation of the .alpha.1AT. Effect of physicochemical alteration on the immunological quantification of .alpha.1AT by different antisera should be considered for all studies assessing this protein in lung secretions.

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