The Antigenic Surface of Human Chorionic Gonadotropin as Mapped by Murine Monclonal Antibodies*

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Abstract
We present a map describing the antigenic determinants (epitopes) of the human CG (hCG) molecule. A panel of monoclonal antibodies to hCG, previously characterized by us was incorporated into two-site binding assays to probe hCG by a 21 × 11 matrix of 231 pairs of MCA. Nine different reaction patterns of reciprocal homology were distinguished and interpreted as representing nine separate and distinct epitopes. Three of them localize on the α-subunit, 4 on the β-subunit and 2 were expressed by the intact hCG (holo-hCG) molecule only, hence designated conformational (c) epitopes. Epitope-contingency analysis revealed that each of the 2 subunits of hCG possesses 1 epitope that is neither adjacent to nor overlapping with any of the other 8 epitopes. The latter were arranged in a complex cluster from which the c-epitopes protrude. Whereas the α- and c-epitopes are specific for glycoprotein hormones of human origin and for hCG, respectively, the β-epitopes appeared to be evolutionarily highly conserved structures: with 1 exception, they were also present on the β-chain of LH from many different mammalian species. (Endocrinology118: 189-197,1986)