Tohoku J. Exp. Med., 2020 January, 250(1)

Review

Endometrial Immunity for Embryo Implantation and Pregnancy Establishment

JUN KITAZAWA,1 FUMINORI KIMURA,1 AKIKO NAKAMURA,1 AINA MORIMUNE,1 AKIMASA TAKAHASHI,1 AKIKO TAKASHIMA,1 TSUKURU AMANO,1 SHUNICHIRO TSUJI,1 SHOJI KAKU,1 KYOKO KASAHARA1 and TAKASHI MURAKAMI1

1Department of Obstetrics and Gynecology, Shiga University of Medical Science, Otsu, Shiga, Japan

The uterus is an organ for raising the fetus, and its lumen is lined by the endometrium. The endometrium is an important site for the implantation and maturation of fertilized eggs. The endometrium undergoes repetitive proliferation, maturation (decidualization), and exfoliation changes every menstrual cycle. At the same time, the number and type of endometrial immunocompetent cells vary during the menstrual cycle. At the implantation stage, the immunocompetent cells occupy approximately half of the endometrial cells. Immunocompetent cells normally eliminate pathogenic microorganisms to protect the body; however, they also promote immune tolerance to accept the fetus during pregnancy. The immunocompetent cells in the uterus can perform both these functions. With the establishment of pregnancy, stimuli from the trophoblast (placenta) and fetus can also change the immune environment of the uterus, and pregnancy can be maintained only when the immune system is well adapted to the stimuli of some hormones and the fetus. Immunity for the establishment of pregnancy is not simple because multiple immunocompetent cells are involved in establishing and maintaining pregnancy. To understand the immune mechanisms associated with the establishment of pregnancy, we have to learn about each immune cell. This review, therefore, discusses the roles and distribution of the immunocompetent cells inside the uterus during menstruation and early pregnancy.

Key words —— decidua; implantation; lymphocytes; regulatory T cells; Th17 cells

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Tohoku J. Exp. Med., 2020, 250, 49-60

Correspondence: Jun Kitazawa, M.D., Department of Obstetrics and Gynecology, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192, Japan.

e-mail: jk110530@belle.shiga-med.ac.jp