Temporal and Spatial Expression of Tumor-Associated Antigen RCAS1 in Pregnant Mouse Uterus Ekaterine Tskitishvili 1 , Hitomi Nakamura 1 , Yukiko Kinugasa-Taniguchi 1 , Takeshi Kanagawa 1 , Tadashi Kimura 1 , Takuji Tomimatsu 1 , Koichiro Shimoya 2 1 Department of Obstetrics and Gynecology, Osaka University Graduate School of Medicine, Suita City, Osaka, Japan; 2 Department of Obstetrics and Gynecology, Kawasaki Medical School, Kurashiki city, Okayama, Japan Introduction Normal pregnancy corresponds to a controlled sys- temic state of inflammation, as well as a maternal systemic inflammatory response with the activation of monocytes, granulocytes, and endothelium, which is a feature of normal human pregnancy in the third trimester. Apoptotic or necrotic debris shed from the syncytial surface of the placenta constitutes an inflammatory stimulus in all pregnancies, 1–3 whereas decidualization of the endometrium is associated with a massive recruitment of natural killer (NK) cells following embryo implantation. Moreover, it has been reported that human T and NK cells express the receptor for RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) at a high level after being activated, and that RCAS1 inhibits the proliferation and induces apoptotic cell death of receptor-positive immune cells. 4 RCAS1 protein is identical to EBAG9 (estrogen receptor-binding frag- ment-associated gene9) protein, and according to a recent study, incubation of NIH3T3 mouse fibroblas- tic cells with recombinant murine EBAG9 protein resulted in the suppression of cell growth. 5 These Keywords Normal pregnancy, placenta, pregnant mice, RCAS1, uterus Correspondence Ekaterine Tskitishvili, Department of Obstetrics and Gynecology, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita City, Osaka 565-0871, Japan. E-mail: ekaterinet@hotmail.com Submitted August 28, 2009; accepted October 1, 2009. Citation Tskitishvili E, Nakamura H, Kinugasa-Taniguchi Y, Kanagawa T, Kimura T, Tomimatsu T, Shimoya K. Temporal and spatial expression of tumor-associated antigen RCAS1 in pregnant mouse uterus. Am J Reprod Immunol 2010; 63: 137–143 doi:10.1111/j.1600-0897.2009.00772.x Problem The tumor-associated antigen RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is considered to play a role in the inhibition of maternal immune response during pregnancy, and participates in the initiation of labor and placental detachment. The aim of our study was to investigate the expression of RCAS1 protein in the uteri of normal pregnant mice. Method of study Uteri with fetuses were collected from pregnant ICR mice on days 1.5, 3.5, 5.5, 7.5, and 9.5 p.c., and uterine and placental tissues were obtained separately on days 11.5, 13.5, 15.5, and 17.5 p.c. Samples were examined using real-time (RT)-PCR, Western blotting, and immunohis- tochemical analyses. Results In normal pregnant mice, RCAS1 protein mRNA was significantly increased on day 7.5 p.c. Antigen localization was detected in the pla- centa, decidua, and fetus. Conclusion The results of this study suggest the importance of day 7.5 p.c. for RCAS1 protein expression in connection with placentation as a possible target for future in vivo studies. ORIGINAL ARTICLE American Journal of Reproductive Immunology 63 (2010) 137–143 ª 2009 John Wiley & Sons A/S 137