Two-site immunoassays for osteoclastic tartrate-resistant acid phosphatasebased on characterization of six monoclonal antibodies

Tartrate-resistant acid phosphatase (TRAP), an enzyme expressed in bone-res orbing osteoclasts, is secreted into the circulation during bone resorption , We used six monoclonal antibodies (MAbs) to optimize direct two-site fluo roimmunoassays for determining serum TRAP concentrations. Four of the MABs, 1F1, 2H1, 4E6, and 5C1, were raised against recombinant human TRAP, and th e other two, O1A and J1B, against human bone TRAP. 2H1, J1B, and O1A appear ed to be highly specific for TRAP. 1F1 and 4E6 were poor in recognizing bon e TRAP and were not useful in the assay, 5C1, while having a good affinity for the bone enzyme, was not specific. Serum TRAP is relatively stable, bec ause 7 days of storage of serum samples at 4 degrees C and -20 degrees C or five thawing-freezing cycles, did not change the TRAP concentration detect ed using the two-site assays, All studied assays detected an increase in se rum TRAP concentrations of postmenopausal women compared with premenopausal women, the difference being highest,vith MAB pairs 2H1-5C1 and O1A-J1B. Th ese results suggest that serum TRAP may be a useful bone resorption marker, and the MAB pairs 2H1-5C1 and O1A-J1B may be useful in determining the bon e resorption rate.