Comparison of monoclonal luteinizing hormone (LH) receptor antibody and LH binding sites in vibratome sections of rat ovary by immunohistochemistry.

To identify luteinizing hormone (LH) receptors, a monoclonal antibody (MAb) was produced by immunization of Balb/c mice with rat luteal cell membranes. Hybridomas, produced by a method for proteins of low antigenicity, were selected by competition with [125I]-hCG (LH) for luteal membrane binding. Conditions for analysis of LH receptor antibody (IgG2b isotype) binding by immunohistochemistry with an avidin-biotin-peroxidase complex were examined and results compared to localization of bound hCG, to detect receptors. By light microscopy, both bound hCG and the LH receptor antibody were located on luteal cell surfaces. In addition, the LH receptor antibody was associated with luteal cell cytoplasm. Cell surface membrane binding, but not cytoplasmic staining, was reduced in ovaries from rats injected with hCG. By electron microscopy, LH receptor antibody was observed in patches on luteal cell surface membranes and was associated with polysomes, small vesicles, and occasionally with discrete areas of endoplasmic reticulum. Therefore, detection of LH receptors with bound hCG may be limited to receptors found on cell surfaces, while additional LH receptors are revealed by use of a receptor antibody. The cytoplasmic LH receptor may represent stages in the processing of receptor protein. Furthermore, the methodology used in this study should be generally useful for immunohistochemistry with other MAb to receptors.