Evidence of apoptosis in human primordial and primary follicles

BACKGROUND: Apoptosis may operate the 'selection' between follicles destined for atresia and follicles that will remain available for ovulation. The aim of this study is to assess the expression of apoptosis in quiescent follicles. METHODS: Ovarian cortex samples from women of reproductive age, fixed in formalin, were used for immunohistochemical and terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end labelling (TUNEL) methods. In histological sections the follicles were classified as primordial, primary, secondary and antral. Follicle density was defined as the total number of follicles/0.5 cm(2) of ovarian cortical tissue. Mab DO-7 (anti-p53) and Mab 124 (anti-bcl-2) were used in the immunohistochemical study. RESULTS: TUNEL was positive in 23.4% of the primordial follicles, and in 23.2% of the primary follicles, both in oocytes and granulosa cells, whereas all secondary follicles were negative. Bcl-2 activity was expressed in 75% of secondary follicles. p53 was negative in all samples. CONCLUSIONS: Apoptosis could be the process responsible for atresia of quiescent follicles and hence depletion of the ovarian germ stockpile. Follicular cells expressing Bcl-2 may therefore be the viable cells that escape the apoptotic process. Negative p53 patterns may be a favourable prognostic finding showing genome integrity in the replicating follicular cells of women of reproductive age.