ELISA for quantitative measurement of low-molecular-weight bronchial protease inhibitor in human sputum

A double-antibody sandwich enzyme-linked immunosorbent assay is described to quantify the low-molecular-weight bronchial protease inhibitor in sputum and other body fluids. Relatively large amounts of this inhibitor were found in sputum, saliva, nasal secretions, seminal plasma, cervical mucus, and tear fluid. The inhibitor concentration in sputum varied from 4 to 405 micrograms/ml (mean, 66 micrograms/ml). With this assay, it was shown that in sputum the inhibitor is concentrated in the mucin-containing gel phase.