Enzyme immunoassay of human chorionic gonadotropin employing beta-galactosidase as label

The assessment of fetal blood samples

Fetal blood sampling under ultrasound control is rapidly expanding the study of human fetal biology. Pure fetal blood is required for prenatal diagnosis, establishment of reference ranges for biologic measurements, and assessment of fetal welfare. We present here the methods that we have developed to detect contamination in more than 1500 samples. These include hematologic indexes, blood smear, erythrocyte antigens, beta-human chorionic gonadotropin, and coagulation factor assays. The tests are relatively simple, inexpensive, and widely available. No single test is reliable in all situations, and it is necessary to perform all the tests on each sample of fetal blood. In the clinical setting where irrevocable action may be taken as a consequence of our results, we require absolute assurance of the purity of the sample.

Enzymes as versatile labels and signal amplifiers for monitoring immunochemical reactions

Enzymes have proven to be sensitive and versatile labels for immunochemical assays. The sensitivity of an enzyme label stems from its extraordinary catalytic power which in turn provides a great amplification of signals. Its versatility, however, stems from the fact that enzyme activity can be modulated by a number of substances. Enzyme labeled immunoassays can be divided into two categories: (a) heterogeneous and (b) homogeneous (non-separation). In the heterogeneous systems, the quantitation of the antibody bound and unbound fractions requires a physical separation of these two fractions, whereas the homogeneous or non-separation systems do not require such a separation. In the homogeneous systems, the unbound and antibody bound fractions can be distinguished functionally. A total of 11 unique principles used in the development of enzyme labeled immunoassays are described. The advantages, disadvantages and limitations of them are considered, as well as the future paths for research and developments.

Sandwich-type enzyme immunoassay for human chorionic gonadotropin

We have developed a sandwich-type enzyme immunoassay for human chorionic gonadotropin (hCG), in which antibody Fab'-beta-D-galactosidase complex and an antibody-immobilized silicone rubber solid phase were used. Despite the fact this assay system crossreacted about 40% with human luteinizing hormone (LH) that contains an immunologically very similar subunit to that of hCG, it proved to be highly sensitive with hCG measurable at levels as low as 0.3 mIU per assay tube. Using 25 microliter of urine sample, hCG levels in serum (10-1000 mlU/ml) or in urine (3-300 mlU/ml) could be determine with the same degree of precision as in radioimmunoassay without sample interference with the assay. The coefficients of variation in within-run, and between-run were 9.2-13.3%, and 4.2-18.8%, respectively. Values obtained with enzyme immunoassay correlate well with those of radioimmunoassay (r = 0.961, slope = 1.129, y-intercept = 3.7 mlU/ml for 35 serum samples) and hemagglutination assay (r = 0.954, slope = 0.951, y-intercept = 1.8 mlU/ml for 88 urine samples).

Coupling of delta 5,3-ketosteroid isomerase to human placental lactogen with intermolecular disulfide bond formation. Use of this conjugate for a sensitive enzyme immunoassay

An immunoassay for human placental lactogen (HPL) has been developed with the use of hormone labelled with delta 5,3-ketosteroid isomerase. The enzyme is coupled to the antigen via an intermolecular disulfide interchange reaction. HPL-enzyme conjugates are prepared in high yield and purified by affinity chromatography. An enzyme immunoassay using these hormone-enzyme derivatives is compared with radioimmunoassay for determination of HPL in serum.