Trophoblast protection of the inner cell mass from macrophage destruction

R. V. Sionov*, R. Gallily

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

Abstract

The semiallogeneic blastocyst may be considered a foreign graft due to its expression of paternal antigens. Nevertheless, the blastocyst, with as few as 64-128 cells, is not rejected by the maternal immune system during implantation, the first direct contact between the developing embryo and the maternal tissue. Both in the virgin and pregnant uterus there is an abundance of macrophages. During the periimplantation period their density doubles, and more than half of the uterine mouse macrophages undergo activation. These macrophages are potentially cytotoxic to the blastocyst's inner cell mass (ICM), which is protected from macrophage destruction by the surrounding trophectodermal layer. At the time of implantation the trophectoderm attaches to the endometrium and develops into giant trophoblasts which penetrate and invade it. During this process, the embryo proper is well sequestered within the trophoblasts. In an in vitro implantation model, we have shown that these giant trophoblasts are not only non-adhesive for the macrophages but also repel them, thereby preventing their approach to the developing embryo. Moreover, the trophoblasts are resistant to the cytotoxic effects of activated macrophages. These findings clearly demonstrate the important role of trophoblasts in protecting the ICM, eventually the embryo proper, from macrophage destruction. We suggest that defects in trophoblast function could result in implantation failure and exposure of the ICM to macrophages. Macrophage destruction of the ICM would then be of benefit, preventing uncontrolled growth of these cells which could occur in the absence of trophoblasts.

Original languageEnglish
Pages (from-to)51-73
Number of pages23
JournalAdvances in Contraceptive Delivery Systems
Volume10
Issue number1-2
StatePublished - 1994

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