A Solid-Phase, Enzyme-Linked Immunosorbent Assay for a Human Lung Tumor-Associated Antigen

Abstract

A solid-phase, enzyme-linked immunosorbent assay (ELISA) for a human lung tumor-associated antigen (LTA) was based on immobilized LTA that was detected with the use of an antiserum raised in a goat against a highly purified antigen preparation. Bound goat antibodies were detected in a series of steps that included incubation with a) biotinylated rabbit antibodies to goat immunoglobulins, b) glucose oxidase conjugated to avidin, and c) peroxidase and the substrates glucose and 2,2'-azino-di-(3-ethylbenzthiazoline sulfonic acid). The absorbance of the final product was measured at 405 nm, and its formation was dependent on substrate incubation time and antibody concentration. The antigen was immobilized and highly purified, and the goat antiserum was bound to and eluted from an immobilized crude antigen column before use. The ELISA could detect less than 1 ng antigen and was able to discriminate extracts of normal lung tissue from those of lung tumor. As was found earlier with a radioimmunoassay for the same antigen, normal human serum could inhibit in the ELISA but only when used at high concentration, indicating levels of antigen or antigen-like activity in the 100-200 ng/ml range. With the use of this assay, 3 lung cancer patients were monitored 6-12 months prior to death. In all 3 patients, LTA levels rose dramatically 2-4 months before the patients died; in 2 patients the levels exceeded 3,000 ng/ml just before death. In contrast, in 2 of these patients, carcinoembryonic antigen levels remained essentially unchanged, with no more than a twofold increase prior to death.