Development and characterization of monoclonal antibodies to pregnancy-specific beta 1-glycoprotein.

Six monoclonal antibodies were developed to pregnancy-specific beta 1-glycoprotein (PS beta 1G). Studies of ascitic fluid antibodies by a double-antibody radioimmunoassay (RIA) included an evaluation of titers, dose-response parameters, and mass action properties. Four of the antibodies demonstrated moderate to high titers ranging from 1/40 000 to greater than 1/120 000, as determined by the specific binding of 125I-labeled PS beta 1G. In inhibition studies utilizing a standard containing known quantities of placental PS beta 1G, two of the antibodies (AR#11 and B#2) were highly sensitive and only slightly lower in this regard than a high affinity polyclonal antiserum. The binding affinities of AR#11 and B#2 monoclonals were greater than 10(9) mol-1 which underline their importance as potential clinical reagents for the RIA of PS beta 1G. The Scatchard plots, for several of the antibodies, were linear and in full agreement with a single order of binding sites predicted for specific monoclonal reagents. Immunodiffusion results provide preliminary evidence that at least three distinct determinants on PS beta 1G are recognized by a number of the monoclonal antibodies. Further studies on the fine specificities of the antibodies by solid-phase RIA, as well as a detailed evaluation of their clinical applications, are in progress.