A simplified solid-phase radioimmunoassay for carcinoembryonic antigen

Specific interference with the determination of the tumour-associated glycoprotein 72 by human anti-idiotypic antibodies formed after treatment with the anti-tumour-associated glycoprotein 72 antibody B72.3

Recorded concentrations of the tumour-associated glycoprotein 72 (TAG-72) in ovarian cancer patients after repeated infusion of the antibody B72.3 were found to be falsely elevated when measured with an homologous immunometric assay involving the anti-TAG-72 antibody B72.3 (Test 1), or with an heterologous assay involving CC49 capture and B72.3 detector antibodies (Test 2). Test 1 yielded falsely elevated values up to 10(4) kU/l. Test 2 gave slightly false positive elevations up to 10(2) kU/l for only some of the samples with very high false-positive values in Test 1. The interfering serum components bound to Protein G-Sepharose and could be precipitated with perchloric acid or by heating serum samples to 100 degrees C. Addition of non-specific murine immunoglobulins only partly suppressed false-positive values in both tests. Our results suggest that this interference is caused by human anti-B72.3 IgG induced by B72.3 application, which to some extent specifically binds to determinants of the B72.3 antibody. Heat extraction of serum samples effectively eliminated interferences probably caused by anti-idiotypic antibodies, but did not affect real TAG-72.

Capture and detection of carcinoembryonic antigen on antibody coated beads used in enzyme immunoassay

We have evaluated antibody coated beads for capture and detection of carcinoembryonic antigen (CEA). Assay parameters of time, temperature, buffer molarity, specificity of antibody on the bead and reagent addition sequence have been studied. Optimal assay kinetics occurred at a temperature of 45 degrees C and a buffer molarity of 0.1M or above. The type and quantity of antibody on the bead surface were also critical to optimal CEA detection. Beads coated with baboon or goat anti-CEA antibody were able to capture a higher percentage of CEA than monoclonal mouse anti-CEA antibody or guinea pig anti-CEA antibody. The sequence of addition of CEA, anti-CEA antibody coated bead, and anti-CEA-horse radish peroxidase conjugate was important for optimal CEA detection. Formation of an immune complex of CEA with the anti-CEA horse radish peroxidase conjugate prior to capture of the CEA on an antibody bead resulted in the optimal detection of CEA.

Antigenic reactivities of purified preparations of carcinoembryonic antigen (CEA) and related normal antigens using four different radioimmunoassay systems for CEA

Antigenic reactivities of 4 purified carcinoembryonic antigen (CEA) preparations including the WHO standard CEA and 4 CEA-related antigens--nonspecific cross-reacting antigen (NCA) from normal lungs, nonspecific cross-reacting antigen-2 (NCA-2) from meconium, normal fecal antigen-1 (NFA-1) and normal fecal antigen-2 (NFA-2) from normal adult feces--were investigated using 4 different radioimmunoassay (RIA) systems (Hoffman-La Roche, CEA-IRE-SORIN, Dainabot and our system). In general, all CEA preparations including the respective standard CEAs gave similar reactions with these assay systems. Differences in reaction intensity were, however, observed among the CEA preparations, and the order of reaction intensity among the preparations varied due to assay systems, e.g., a given CEA preparation which reacted most strongly with an assay system reacted very weakly with another assay system, and vice versa. Both NCA-2 and NFA-2, which possessed physiochemical properties very similar to those of CEA, revealed reactivities indistinguishable from those of the CEA preparations in all systems. NCA, which showed a partial cross-reactivity with CEA in the double immunodiffusion test, revealed a remarkably weak reactivity in all systems. NFA-1, however, which was also partially cross-reactive with CEA but antigenically unrelated to NCA, showed a fairly strong reactivity in all systems, but its dose-dependent slope was apparently different from that of the other antigen preparations.

Interference of heparin in carcinoembryonic antigen radioimmunoassays

A false Roche carcinoembryonic antigen (CEA) activity could be detected in all commercial and noncommercial heparin preparations we examined. The possibility of 'due to contamination' has been ruled out. Using the Roche procedure, heparin solutions, in the absence of CEA, gave positive CEA activity; on the other hand, no CEA activity was detected in solutions containing only heparin when the Abbott Kit was used. When heparin was present in specimens containing CEA, the Abbott Kit underestimated the CEA activity, whereas the Roche Kit gave false elevated values. However, the negative effect of heparin could be reduced by heat treatment in the presence of plasma proteins.

A new direct solid-phase radioimmunoassay for carcinoembryonic antigen without pretreatment of serum samples

We examined some fundamental conditions for establishing a new simplified radioimmunoassay system for CEA. The system consists of antibody-coated plastic beads and radiolabeled tracer antibody. The reactivity of this system with several purified CEA preparations can vary due to differences in the nature of antibody preparations used either for coating beads or for tracer antibody. Among purified CEA preparations, we also found some differences in reactivity with a given immobilized antibody preparation. The assay system that resulted, referred to as bead-direct-RIA, needs neither pretreatment of serum samples nor centrifugation in any of its steps, and has a wide assay range, measuring CEA concentrations of 1-300 ng/ml using only 50 microliters of a serum sample. Its accuracy, reproducibility, dilution effect, and analytical recovery proved the reliability of this method. The mean value +/- S.D. for 48 normal adults was 2.5 +/- 1.0 ng/ml. It was found by comparative studies that the Z-gel method of Hoffmann-La Roche generally gave the highest values, the antibody-disc method of Dainabot gave the lowest, and the values by bead-direct-RIA fell between those of the 2 other methods and correlated well with either value. Follow-up studies on patients with malignancy indicated that the values by bead-direct-RIA fluctuated in parallel with those by Roche and Dainabot kits.

A stable, sensitive assay for human fibronectin

A solid-phase radioimmunoassay system to quantitate human fibronectin has been developed. This assay utilizes 125I-labeled affinity purified IgG directed against human plasma fibronectin. The sensitivity of this system is comparable to conventional (labeled antigen) radioimmunoassays having a detection limit of approximately 0.5 ng. This assay is relatively rapid (less than 24 h), the reagents are stable at 4 degrees C (less than 2 months), and the reproducibility is excellent. Both human plasma and cellular fibronectin react equivalently in this assay.

Improved performance of a double antibody radioimmunoassay for carcinoembryonic antigen

A new double antibody solid-phase radioimmunoassay (RIA) for carcinoembryonic antigen (CEA) is critically analyzed. The aim of the study was 4-fold: (a) to define the level of sensitivity (a comparison of 3 different assay procedures revealed that our sequential assay was more sensitive than most previously reported RIAs, while competitive and non-equilibrium assay had wider measuring ranges); (b) to analyze recoveries of CEA in either serum, plasma or urine (the recovery, even in urine, was very close to expected values, indicating that no CEA is lost or degraded during brief storage or in the extraction procedure); (c) to evaluate inter- and intra-assay variations, since most clinical management is dependent on serial assays rather than single determinations. The coefficients of variation were low both within and between assays. A change of 3 ng CEA is required for significant change (greater than 2 S.D.) at the normal serum level which is 16 ng CEA/ml in our assay. At levels above normal, a change of 4 ng is required; (d) the assay was also developed for determination of CEA levels in a large series of perchlorid acid treated serum, plasma or urine samples. This forms the basis for an assay suitable for serial assays with high sensitivity and accuracy in various neoplastic diseases.