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Many investigators have suggested that prostaglandins (PGs) may have immunoregulatory function at the implantation site. In this study, in order to identify prostaglandin producing cells in human endometrium in non-pregnant state and the decidua basalis, an immuno-peroxidase staining was applied in their tissue sections using rabbit anti-PGE_2 and -PGF_<2α> antisera and mouse monoclonal antibodies. The following results were obtained. 1) The localization of PGE_2-positive cells in the endometrium was almost the same as that of PGF_<2α>-positive cells. As most of them were positive for HLA-DR and Leu-M_3, they were considered to be monocytes/macrophages. 2) In non-pregnant endometrium, PGE_2-positive cells were more numerous in the secretory phase than in the proliferative phase, showing an increasing tendency after the implantation. 3) The number of PGE_2 positive cells in the decidua was slightly smaller than that in secretory phase, showing a gradual decrease with gestational age. 4) None of PGE_2 or PGF_<2α>-positive cells reacted with anti-Leu-1 antibody. 5) Most of PGE_2-positive cells were stained with anti-HLA-DR in non-pregnant state, while some of PGE_2-positive cells were not stained with anti-HLA-DR in the decidua of the first trimester.

Several investigations have suggested that prostaglandins may play an important role in successful implantation of a conceptus at the endometrium. The present studies were designed to identify prostaglandin-producing cells and to reveal their localization at the implantation site. Eighteen early human pregnant uteri (7-12 weeks of gestation) were analyzed by means of a double immunoperoxidase technique using antibodies to PGE_2, PGF_2α, HLA-DR and Leu-M_3. The results were as follows. 1. A large number of PGE_2 and PGF_2α positive cells were observed in stromal tissues of the decidua and the myometrium. 2. These cells were identified as monocyte/macrophage because of their macrophage-like appearance and positive reaction to anti-Leu-M_3 and anti-HLA-DR antibodies. 3. PGE_2 and PGF_2α positive cells were also observed in stromal tissues of chorionic villi and they were identified as Hofbauer' cells from the same findings mentioned above. Trophoblast cells themselves were negative for PGE_2 or PGF_2α. It was thus suggested that monocyte/macrophage in the decidua may take part in creation of a local environment prohibiting maternal immune response by producing prostaglandins.