IMMUNOLOCALIZATION OF BCL-2 PROTEIN IN HUMAN ENDOMETRIUM IN THE MENSTRUAL-CYCLE AND SIMULATED EARLY-PREGNANCY

Cell death by apoptosis is now regarded as an important feature of nor mal endometrial physiology Recent reports have suggested that bcl-2, a proto-oncogene responsible for the suppression of apoptosis, is expre ssed in endometrium and may be involved in the regulation of menstruat ion. Using standard immunohistochemical procedures, the immunoreactivi ty of bcl-2 and progesterone receptors has been investigated in normal human endometrium throughout the menstrual cycle (n = 25) as well as endometrium exposed to continued oestradiol and progesterone stimulati on by 'rescue' of corpus luteum (n = 4) with exogenous human chorionic gonadotrophin (HCG) administration (pseudopregnancy). Marked immunore activity, consistent with previous reports, was noted in the glandular epithelium during the proliferative phase of the cycle. Immunostainin g persisted in the glandular epithelium during the secretory phase, al though the percentage and intensity of staining was markedly reduced. Staining in the stromal compartment was only noted during the late sec retory phase of the cycle. Co-localization with an antibody against CD 56 demonstrated that this immunoactivity largely reflected the presenc e of lymphocytes in the stroma. Endometrium from subjects who underwen t 'luteal rescue' displayed limited immunostaining in either glands or stroma. The absence of significant bcl-2 expression in endocrinologic ally maintained endometrium makes it highly unlikely that bcl-2 is imp ortant in prolonging endometrial cell survival in the luteal phase of the menstrual cycle.