An enzyme-amplified monoclonal immunoenzymometric assay for prostatic acid phosphatase

Monoclonal antibodies to enzymes

The production, identification, and utilisation of monoclonal antibodies to enzymes are reviewed. Such antibodies may be produced in vitro by the mouse-hybridoma technique, may occur naturally in vivo as enzyme-binding immunoglobulins and may be produced in the laboratory from the lymphocytes of patients whose sera contains such immunoglobulins. The diagnostic application of monoclonal antibodies to enzymes is considered, with special reference to their use in the measurement of the MB-isoenzyme of creatine kinase, pancreatic isoamylase, prostatic acid phosphatase, and the isoenzymes of alkaline phosphatase.

Amperometric enzyme-amplified immunoassays

Enzyme-amplified immunoassays have been adapted for electrochemical measurement, using an NAD+/NADH redox cycle coupled to an electrode via the active site of diaphorase. Two amperometric methods are described, the first employs an organic conducting salt electrode, NMP+/TCNQ-; the second a platinum wire with ferricyanide as electron transfer mediator. In an immunoenzymometric assay for human prostatic acid phosphatase the sensitivities of the electrochemical methods were comparable to that achieved with the existing optical technique, but the dynamic range of the electrochemical assays was increased by at least two orders of magnitude. It is proposed that electrochemical enzyme-amplified immunoassays may eventually replace their optical counterparts.

The selection and performance of monoclonal and polyclonal anti-respiratory syncytial virus (RS) antibodies in capture ELISAs for antigen detection

Six monoclonal antibodies directed against fusion protein (F) or nucleoprotein (NP) of respiratory syncytial virus (RS) have been investigated in an antigen capture ELISA for virus detection. The potency, spectrum and pattern of reactivity were investigated with the intention of selecting antibodies reacting with RS-common antigen determinants and with complementary rather than competitive activity. Two anti-F protein antibodies satisfied these criteria and were used with enzyme amplified detection in a two site monoclonal assay (MCA/MCA) or as detectors with a polyclonal antibody as capture (PCA/MCA). Comparative studies were performed with immunofluorescence (FA) as the reference test and nasopharyngeal aspirates processed in different ways. The PCA/MCA assay was superior to that using monoclonal antibodies alone and gave results comparable to the reference method. However, the apparent sensitivity related to FA varied with the type of sample processing used. These results emphasise the need for a critical analysis of the factors which can influence the sensitivity of a particular assay system before judgements on relative sensitivity are made.

Enzyme-amplified immunoassays

The sensitivity of enzyme immunoassays may be enhanced by the use of enzyme-amplification. This technique uses the enzyme label in the immunoassay to provide a trigger substance for a secondary system that can generate a large quantity of coloured product. Two examples of enzyme amplifiers are described, using either a substrate cycle with phosphorylated hexose sugars, or a redox cycle involving the coenzyme NAD(+). The redox enzyme-amplifier has a detection limit of less than one attomole for the enzyme label, alkaline phosphatase. The limited dynamic range of enzyme-amplified immunoassays may be overcome by kinetic analysis of the colour development in the enzyme-amplifier, to add at least a further order of magnitude to the range of directly measured analyte concentrations in the immunoassay. This is illustrated in an enzyme-amplified immunoassay for human thyroid stimulating hormone. Amperometric measurement of the enzyme-amplifier provides a method to extend the dynamic range still further and compares favourably with the performance of a gamma counter, a luminometer or a fluorimeter.

Comparison of radioimmunoassay and immunoradiometric assay for serum prostatic acid phosphatase

We have compared the laboratory performance of immunoradiometric (IRMA) and radioimmunoassay (RIA) methods developed in this laboratory for measurement of serum prostatic acid phosphatase (PAP). The IRMA utilizes a radiolabelled mouse monoclonal anti-PAP and a solid phased rabbit polyclonal anti-PAP. The same rabbit antibody is used in the RIA. The IRMA shows excellent precision over a much wider working range (0.25-1000 micrograms/l) than the RIA (0.73-14.0 micrograms/l), and can be completed in 5 h, while the RIA requires 3 days. Levels in healthy males and in patients with benign prostatic hypertrophy are similar in both assays, upper limits of normal being 1.8 micrograms/l (IRMA) and 4.7 micrograms/l (RIA). The two assay methods correlate very well (r = 0.97) when PAP is measured in serum from prostatic cancer patients, although IRMA results are generally lower than those obtained by RIA. About 20% of patients with non-metastatic prostatic carcinoma had elevated serum PAP, whereas about 80% of those with metastatic disease had raised levels. The diagnostic efficiencies of the RIA and IRMA appeared similar. The value of the IRMA in follow-up and staging remains to be determined.

Herpes simplex virus detection by ELISA: effect of enzyme amplification, nature of lesion sampled and specimen treatment

The relative sensitivity of two enzyme detection procedures was investigated in a simultaneous "monoclonal" ELISA for herpes simplex virus (HSV). A cyclical enzyme amplified detection system with alkaline phosphatase, rather than horse-radish peroxidase and a conventional chromogenic substrate, gave an increase in absolute sensitivity and a 20 to 30% increase in the detection of HSV in routine isolation-positive genital specimens collected in transport medium. The HSV detection rate, with both procedures, was shown to vary with the site and clinical stage of lesion sampled; it was highest with penile vesicular lesions. Direct extraction of the swab specimen in a small volume of diluent further increased the sensitivity of antigen detection giving positive and negative predictive values of 100 and 96% respectively. The overall sensitivity of HSV detection was equivalent to that obtained by isolation in cell culture. The amplified ELISA offers an alternative, rapid, simple, non-culture technique for routine HSV diagnosis that does not rely upon retention of virus viability.