Immunological evidence for the expression of the Fas antigen in the infant and adult human ovary during follicular regression and atresia.

Immunohistochemical localization of the Fas antigen in the infant and adult human ovary during follicular growth, regression, and atresia was examined by the avidin/biotin immunoperoxidase method with a monoclonal antibody to the Fas antigen. Western blotting was used to confirm the presence of the Fas antigen protein. In primordial and primary follicles within the normal adult ovary, only the oocyte showed moderate immunostaining for the Fas antigen. In secondary and antral follicles, only the oocyte showed weak staining for the Fas antigen, while in preovulatory follicles, neither the oocyte nor the granulosa and theca cells were immunostained for the Fas antigen. In corpora lutea, the Fas antigen staining became apparent in the granulosa lutein cells during the early luteal phase and intensified during the mid luteal phase, while the theca lutein cells became positive for the Fas antigen staining during the mid luteal phase. During the late luteal phase, the staining intensity of the Fas antigen in the regressing corpora lutea further increased. As the regressing corpora lutea were converted into corpora albicans, the staining intensity decreased, and the corpora albicans and stromal cells were negative for the Fas antigen. In atretic primordial and primary follicles, only the degenerating oocyte showed the Fas antigen staining. By contrast, in atretic antral follicles, the Fas antigen staining was profound in the degenerating granulosa cells at the early stage of atresia, and at the mid stage of atresia it was intensified in the cell surface of the scattered granulosa cells and became apparent in the theca cells. At the late stage of atresia the Fas antigen remained only in the hypertrophied theca cells. In the infant ovary, only the oocyte in primordial and primary follicles exhibited intense staining for the Fas antigen. In the postmenopausal ovary, the Fas antigen staining was entirely negative. Western blot analysis revealed the presence of the Fas antigen protein with a molecular mass of 45 kDa in luteal tissues. On the basis of the recent evidence, that the Fas antigen mediates an apoptotic signal in a variety of cells, the abundant expression of the Fas antigen in the regressing corpora lutea and atretic follicles suggests that the Fas antigen participates in luteal regression and follicular atresia through the apoptotic process. Furthermore, notable expression of the Fas antigen in the oocyte of primordial and primary follicles within the infant and adult human ovary followed by the decrease in the Fas antigen expression in the oocyte with the advance of follicular maturation suggests that the Fas antigen expression in the oocyte may play a role in follicular selection.