Two-site "simultaneous" immunoassay with monoclonal antibodies for the determination of surfactant apoproteins in human amniotic fluid.

Monoclonal antibodies against human surfactant apoproteins were prepared, which recognized 37, 34, and 62 kilodalton proteins in human lung lavage fluid and amniotic fluid. Two-site "simultaneous" immunoassay for the surfactant apoproteins was developed using the monoclonal antibodies. The assay was capable of measuring 10-640 ng of the apoproteins per ml of human amniotic fluid. The immunoassay was used to quantitate the apoproteins in 59 amniotic fluid samples from 23 to 41 wk gestation. The concentration of the surfactant apoproteins at less than 30 wk gestation was very low (mean 0.84 micrograms/ml). It then increased 6.5-fold from 34 to 36 wk gestation and 15.5-fold at more than 37 wk gestation. The simultaneous immunoassay with the monoclonal antibodies presented herein seems to be ideal for clinical use because of its high specificity, sensitivity, rapidity, simplicity, and a continuous unlimited supply of the antibodies. The results in this study show that the clinical use of the two-site simultaneous immunoassay with monoclonal antibodies to pulmonary surfactant apoproteins can predict fetal lung maturity more precisely.