Elimination of atretic follicles from the mouse ovary: a TEM and immunohistochemical study in mice.

We examined numerous ovarian follicles from 32-35 d virgin mice by transmission electron microscopy and light microscopic immunohistochemistry. No macrophages were seen, but various stages of apoptotic granulosa cells were encountered. Presumably a granulosa cell or its debris in an advanced stage of apoptosis was destined to be phagocytosed by adjacent normal-looking granulosa cells. Other granulosa cells of normal appearance were seen in the region of the zona pellucida in contact with and apparently phagocytosing atrophic oocytes. Such granulosa cells were characterised by the presence of gap junctions with other cells and frequently contained annular gap junctions in the cytoplasm. To confirm the lack of involvement of macrophages in the process of follicular atresia and elimination, specially prepared ovarian sections were incubated with antimouse macrophage monoclonal antibodies (F4/80, Mac-1, Mac-2). None of the follicles examined showed positive immunoreactivity with these antibodies. Atretic follicles may shrink and eventually disappear from the ovary as a result of repeated apoptosis and phagocytosis by granulosa cells. There is no evidence for the presence or involvement of macrophages in the atretic follicles, at least in prereproductive mice as examined.