Recognition of serum alkaline phosphatase by murine monoclonal antibodies against human osteosarcoma cells.

Using OST6 and OST7 monoclonal antibodies against human osteosarcoma cells, a solid-phase radioimmunosandwich assay was developed to quantitate a human osterosarcoma-associated antigen in a total of 242 sera from healthy adults and patients with various diseases. The levels of the antigen in sera were high in patients with osteosarcoma and in children without tumorous diseases compared with healthy adults; however, the highest level of the antigen was found in patients with obstructive jaundice. The quantity of the antigen correlated with serum alkaline phosphatase (EC 3.1.3.1.) activity, and showed a strong correlation (correlation coefficient, 0.94) in 50 sera. Immunolocalization of enzyme activity assay using monoclonal antibodies was performed to ascertain whether the antigen had alkaline phosphatase activity. This assay proved that OST6, OST7, and OST15 monoclonal antibodies recognized serum alkaline phosphatase; furthermore, these monoclonal antibodies seemed to react with not only the bone isoenzyme but also the liver isoenzyme.