Reversible immunoneutralization of human follitropin receptor

Investigations of the human Follitropin receptor (hFSHR) have failed to ide ntify the tertiary structure that forms the active hormone-receptor interac tion site which is essential to develop an immunocontraceptive based upon t he receptor. To identify such a domain of hFSHR, an immunoneutralizing mono clonal antibody (mAb) 106-105 (IgG2b) was generated. Flow cytometry tested whether mAb 106-105 recognized native hFSHR. The epitope of mAb 106-105 was mapped by western blot and by peptide ELISA. Inhibition of hFSH binding an d bioactivity was determined by radioreceptor assay and by cAMP production. respectively. MAb 106-105 bound native hFSHR through an epitope including residues 300-315. MAb 106-105 completely blocked hormone binding to recepto r and cAMP production by Y1-R cells expressing hFSHR. These effects were co mpletely reversible by increasing the concentration of hFSH. Coincubation o f this antibody with peptide D300-F315 blocked antibody activity. These dat a demonstrate that a discrete linear hFSHR epitope is a target for interfer ence with hormone activity. These results further demonstrate that antibody binding to the extracellular domain (ECD) of hFSHR and subsequent bioactiv ation can be modulated through a domain specific hindrance, offering a reve rsible immunoneutralizing tal gel. (C) 2001 Elsevier Science Ireland Ltd. A ll rights reserved.