Isolation and preliminary characterization of a monoclonal antibody that interacts preferentially with the liver isoenzyme of human alkaline phosphatase.

We have prepared murine monoclonal antibodies against isolated human bone alkaline phosphatase (ALP, EC 3.1.3.1). Hybridoma supernates were separately screened for reactivity against both human liver and bone ALP. Although most antibody-positive hybrids showed similar reactivity against both isoenzymes, one hybridoma produced an antibody that interacted preferentially with liver ALP. This antibody was purified and used to establish an immunoassay to differentiate liver ALP from bone ALP. When equal activities of the two isoenzymes (as determined by a conventional enzymic assay) were measured by the immunoassay, a fivefold greater response was obtained with liver than with bone ALP. The immunoassay can be used to measure the proportions of the bone and liver isoenzymes in mixtures of them. Cross reactivity with human placental and intestinal ALP is less than 3% relative to liver ALP. These findings support the feasibility of developing immunological methods to differentiate these isoenzymes in the clinical laboratory.