Receptor aggregation induced by antilutropin receptor antibody and biological response in rat testis Leydig cells.

Antibodies against the lutropin receptor have been obtained by the monoclonal antibody technique. Mice were immunized with luteal membrane from ovaries from pseudopregnant rats, containing high lutropin receptor concentration. Hybridoma cells were obtained by fusing mouse myeloma cells with spleen cells from the immunized animal. Five clones were produced that secreted monoclonal antibodies that specifically inhibited lutropin binding to its receptor in a competitive fashion. Antibodies from three clones were capable of blocking biological response to lutropin (e.g., testosterone production by isolated rat Leydig cells). Antibodies secreted by two other clones, however, were capable of acting as Leydig cell stimulators. Immunofluorescence studies demonstrated the presence of receptor capping which may be associated with receptor-mediated testosterone production. Antagonist antibodies could be transformed into agonist by the addition of a second crosslinking anti-mouse IgG. The discovery of agonist antibodies against the receptor molecule proves that the biological information of the lutropin-receptor complex resides in the receptor and not in the hormone.