The human corpus luteum: reduction in macrophages during simulated maternal recognition of pregnancy

It has been shown that immune cells, particularly macrophages, accumulate i n the corpus luteum during luteolysis. This study aimed to investigate the effect of maternal recognition of pregnancy on the localization and numbers of macrophages in the human corpus luteum. Corpora lutea (n = 12) were obt ained from normally cycling women at the time of hysterectomy and were date d on the basis of serial urinary luteinizing hormone (LH) estimation. In ad dition, corpora lutea (n = 4) were collected from women who had received da ily doubling doses of human chorionic gonadotrophin (HCG) to mimic the horm onal changes of early pregnancy. Macrophages were localized by immunohistoc hemistry using an anti-CD68 antibody. Steroidogenic cells, steroidogenic ce lls of thecal origin and endothelial cells were identified on serial sectio ns by immunohistochemistry for 3 beta-hydroxysteroid dehydrogenase, 17 alph a-hydroxylase and von Willebrand factor, respectively. The luteal cells cap able of responding directly to HCG were identified by isotopic in-situ hybr idization for messenger RNA encoding LH/HCG receptors, Macrophages were loc alized primarily to the vascular connective tissue and theca-lutein areas o f the corpus luteum, although some were found in the granulosa-lutein cell layer. Macrophage numbers increased throughout the luteal phase to a maximu m in the late-luteal phase (P < 0.05), Luteal 'rescue' with HCG was associa ted with a marked reduction in the numbers of tissue macrophages when compa red with those of the late-luteal phase (P < 0.001), One of the effects of HCG during maternal recognition of pregnancy is to prevent the normal influ x of macrophages into the corpus luteum, As LH/HCG receptors localized to t he steroidogenic cells, this implies a fundamental role for steroidogenic c ell products in the control of macrophage influx into the human corpus lute um.