Monoclonal antibodies against human chorionic gonadotropin (hCG): II. Affinity and ability to neutralize the biological activity of hCG.

Monoclonal antibodies (MCA) against hCG have been characterized with regard to their affinity and their ability to neutralize the biological activity of hCG in vivo. The production and specificities of these reagents were described in the preceding paper of this series. Equilibrium association constants (Ka) of the MCA, determined by radioimmunological saturation assays, ranged from less than 1 X 10(8)M-1 up to 3.7 X 10(9)M-1 whereas values for conventional polyclonal antisera against hCG ranged from 8.9 X 10(9)M-1 to 1.8 X 10(10)M-1. The ability of MCA to neutralize the biological activity of hCG was tested in a rat bioassay in vivo; 9 of 13 different MCA preparations tested could neutralize hCG. Surprisingly, this property did not correlate with affinity or specificity, and was not restricted to those MCA recognizing the hormone specific beta-subunit. It could be demonstrated that determinants on each individual subunit as well as epitopes formed by both subunits are involved in the expression of the biological activity of hCG.