Localisation of a 40kDa protein in rat steroid producing cells identified by a monoclonal antibody.

OBJECTIVE To localize (by the light and electron microscopy) and partially characterize the antigen recognized by the Mab4E6 in rat ovaries. METHODS Monoclonal antibody (4E6) against a rat ovarian granulosa cell antigen was prepared and identified the 40kDa protein specific for rat steroid producing cells. The localization of this antigen was studied by light and electron microscopic immunocytochemistry. RESULTS The immunocytochemical observation suggested that the recognized antigen was localized in granulosa and thecal cells in all stages of follicular development. The intensity of immunostaining was found to depend on the developmental stage. In granulosa and thecal stage (health follicle) Mab 4E6 binding molecule was localized on the membranes of rough endoplasmic reticulum (RER) and on the surface of lipid droplets in close association with the RER. In atretic follicles we established that the final destination of the visualized antigen is in structures which we refer as the autophagic vacuoles in close contact with the steroidogenic organelles. In addition, we observed Mab 4E6 binding molecule in the cytoplasm of luteal cells. Leydig cells and adrenocortical cells. CONCLUSIONS The results indicate that the 40kDa antigen may be common to all of rat steroidogenic organs. Our results suggest that the 40kDa protein may be associated with the processes governing steroidogenesis and/or follicular development.