Antibody binding to alpha 2-macroglobulin facilitates direct quantitation of elastase-alpha 2-macroglobulin complexes by a simple ELISA technique.

In order to investigate the effect which the binding of anti-alpha 2-macroglobulin (anti-A2M) antibody has on subsequent antigen-antibody reaction between the complexed elastase and the solid phase anti-elastase antibody, elastase alpha 2-macroglobulin complex (EMC) was incubated with anti-A2M antibody and then extracted by a solid-phase bound rabbit anti-elastase antibody. A doubling dilution series of EMC generated dose related absorbance values. The critical factor permitting the immunological detection of A2M-bound elastase is the pre-incubation of anti-A2M antibody with EMC in solution. The assay exhibited a lower detection limit of 0.5 ng bound elastase per ml and EMC levels in serum samples from ten volunteers were significantly higher than in plasma (28 vs. 21 ng/ml, p < 0.05, Student's t test for paired samples). The EMC levels measured with this assay were essentially identical to those obtained when phenyl methyl sulfonyl fluoride (PMSF) was added to the assay buffer solution.