Macrophages are present not only in atretic mature follicles but also in the growing follicles of the guinea pig ovary.

In atretic ovarian follicles, massive groups of apoptotically dead granulosa cells are eliminated by two kinds of phagocytic cells: intact granulosa cells and macrophages. Using mature guinea pig ovaries, this study further examined whether or not phagocytic cells are present in the growing follicles by means of light and electron microscopy. Within healthily growing follicles, small numbers of large round cells were found among the granulosa cells. By electron microscopy, the nucleus of the large cells appeared to be pushed aside by prominently expanded large cytoplasmic vacuoles together with abundant large and small lysosomes. These cells were identified as macrophages. This is the first report to demonstrate macrophages within the growing follicles of the guinea pig. The importance of the intrafollicular macrophages is suggested in connection with the dynamics of the follicle, such as its development and atresia.