An enzyme immunoassay for carcinoembryonic antigen (CEA) with homogeneous reactivity to different CEA preparations and low cross-reactivity with CEA-related normal antigens.

A new sandwich-type solid-phase enzyme immunoassay (EIA) for carcinoembryonic antigen (CEA) was established by using two selected monoclonal antibodies (MAbs). One MAb, F82-61, which is immobilized on polystyrene beads, reacts with an epitope present on the N-terminal domain (N) of the CEA molecule and the other, F11-39, which is conjugated to horseradish peroxidase (HRP), recognizes an epitope present on the C-terminal domain (B3) of the CEA molecule. The assay consists of incubating 0.05 ml of test serum both with F82-61-coated beads and HRP-labeled F11-39 at room temperature for 2 h. The assay system, referred to as New EIA, showed very homogeneous reactivity with purified CEA preparations from different tumors and could discriminate CEA from four CEA-related normal antigens tested; nonspecific cross-reacting antigen (NCA), NCA-2, normal fecal antigen-1 (NFA-1) and NFA-2. The assessment of technical qualities, such as reproducibility, recovery and dilution tests, demonstrated the excellent performance of New EIA. Serum samples (n = 604) from patients with malignant or non-malignant disease, as well as from healthy individuals, were analyzed by New EIA and by two commercial CEA immunoassays which both showed heterogeneous reactivity with different CEA preparations and reacted to a greater or lesser extent with NCA-2 and NFA-2, and it was found that New EIA significantly increased the sensitivity and specificity of tumor diagnosis as compared with the commercial assays.