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

Abstract

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.

Molecular and biological interaction between major histocompatibility complex class I antigens and luteinizing hormone receptors or beta-adrenergic receptors triggers cellular response in mice.

“…Both receptors are activated by the specific hormone, but both receptors can also be activated by an antireceptor antibody (4,20). Results suggest that bound hormone, LH/hCG, triggers the association of the MHC class I antigen and the receptor, thus activating the respective target cell.…”

“…Receptor aggregation at the molecular level appears to play a critical role in this process (1). Studies with epidermal growth factor (EGF) (2), insulin (3), and luteinizing hormone (LH) (4)(5)(6) suggest that hormone binding alone is a biologically unproductive process without a subsequent step of microredistribution, aggregation, or cross-linking that seems to be a limiting determinant process, although the mechanism by which the bound hormone triggers microaggregation, aggregation, and patch formation is unknown.…”

The Fab fragment of a directly activating monoclonal antibody that precipitates a disulfide-linked heterodimer from a helper T cell clone blocks activation by either allogeneic Ia or antigen and self-Ia.

“…The ability of antireceptor antibodies to mimic the action of ligand has been described in a number of hormonal systems (23,24) and has been studied extensively with B cells using anti-Ig antisera (reviewed in reference 25). This activation is often found to require cross-linking of the receptors on the target cell surface.…”

Stabilized complexes of epidermal growth factor and its receptor on the cell surface stimulate RNA synthesis but not mitogenesis.

“…It has been proposed that microaggregation of the receptor on the cell surface is sufficient for production of the mitogenic signal (21-23), a situation analogous to several other hormone-receptor systems (24)(25)(26)(27). However, there is also evidence that intracellular processing of the EGF-receptor complex is required for stimulation of DNA synthesis (28)(29)(30)(31), and the increased sensitivity of EGF after heterologous down-regulation of its receptor by platelet-derived growth factor (32) 125I-EGF Binding.…”