Quantitative immunoenzymatic assay of human lutropin, with use of a bi-specific monoclonal antibody

In this immunoenzymatic assay for human lutropin (hLH) we used bi-specific antibodies (BiAbs) obtained from the fusion of two hybridomas producing antibodies to beta-D-galactosidase and hLh. The BiAb complexed with the enzyme beta-D-galactosidase was used as tracer in a double-determinant assay. We compared the assay involving the BiAb (Bi-EIA) with an immunoenzymatic assay (EIA) in which the same capture antibody was used but the tracer was an enzyme-conjugated hLH-specific monoclonal antibody produced by the same parental cell line used to produce the BiAb. The coefficient of correlation (r) between the two assays was 0.979 but the Bi-EIA was more sensitive (detection limits: 0.8 int. units/L for the Bi-EIA, 2.0 int. units/L for the EIA) and more specific (less than 0.04% vs less than 1.2% cross-reactions with human choriogonadotropin). Mean intra- and interassay CVs for the Bi-EIA were 2.9% and 5.9%, respectively. Correlation (r) with an immunoradiometric assay (IRMA, Serono kit) was 0.960, with radioimmunoassay (RIA, Biodata kit) 0.909, and with an enzyme-linked immunosorbent assay (ELISA kit, Specialty Medical Industries Inc.) 0.888, (n = 25). Evidently, bi-specific antibodies can be used successfully in immunoenzymatic assays, and with potentially greater sensitivity and specificity than assay with a traditional antibody-enzyme conjugate.