BISPECIFIC-AB-BASED IMMUNOASSAY OF THYROID-STIMULATING HORMONE

A bispecific F(ab')(2) fragment recognizing both human thyroid-stimula ting hormone (TSH) and alkaline phosphatase (AP) was prepared by disul fide bond exchange between F(ab')(2) fragments of IgG1 mAb against TSH and AP. AP was polymerized by glutaraldehyde, and a sandwich enzyme-l inked immunosorbent assay for TSH was developed by using the AP polyme rs and the bispecific F(ab')(2) fragment. In this assay, the preparati on of covalently linked AP-mAb conjugates was not needed, and the inte raction of mAb with non-specific proteins was greatly reduced. The sen sitivity for TSH increased in proportion to the degree of AP polymeriz ation, and the lower detection limit obtained with the AP trimer was 0 .5 mu U/ml. The use of the bispecific F(ab')(2) fragment allows us to use monomers and polymers of AP and thereby regulates the sensitivity of the assay.