CCR5 Is Involved in Interruption of Pregnancy in Mice Infected with Toxoplasma gondii during Early Pregnancy.

Toxoplasmosis can cause abortion in pregnant humans and other animals; however, the mechanism of abortion remains unknown. C-C chemokine receptor type 5 (CCR5) is essential for host defense against Toxoplasma gondii infection. To investigate the relationship between CCR5 and abortion in toxoplasmosis, we inoculated wild-type and CCR5-deficient (CCR5-/-) mice with T. gondii tachyzoites intraperitoneally on day 3 of pregnancy (embryonic day 3 [E3]). The pregnancy rate decreased as pregnancy progressed in infected wild-type mice. Histopathologically, no inflammatory lesions were observed in the fetoplacental tissues. Although wild-type mice showed a higher parasite burden at the implantation sites than did CCR5-/- mice at E6 (3 days postinfection [dpi]), T. gondii antigen was detected only in the uterine tissue and not in the fetoplacental tissues. At E8 (5 dpi), the embryos in infected wild-type mice showed poor development compared with those of infected CCR5-/- mice, and apoptosis was observed in poorly developed embryos. Compared to uninfected mice, infected wild-type mice showed increased CCR5 expression at the implantation site at E6 and E8. Furthermore, analyses of mRNA expression in the uterus of nonpregnant and pregnant mice suggested that a lack of the CCR5 gene and the downregulation of tumor necrosis factor alpha (TNF-α) and CCL3 expression at E6 (3 dpi) are important factors for the maintenance of pregnancy following T. gondii infection. These results suggested that CCR5 signaling is involved in embryo loss in T. gondii infection during early pregnancy and that apoptosis is associated with embryo loss rather than direct damage to the fetoplacental tissues.