(A) C3 Western blot analysis. Serum of PBS- or CVF-treated pregnant mice at E8.5 was separated by SDS-PAGE and immunostained with anti-C3 antibody. C3 protein was only detectable in PBS-treated mice, but was depleted in CVF-treated pregnant mice. Anti-albumin staining was used as loading control. (B) C3 immunohistochemical staining of sagittal paraffin sections of E8.5 embryos within the uterus of PBS- or CVF-treated mice. In PBS-treated mothers, C3 reactivity was restricted to the EPC in control implants, but was expanded to the entire fetal-maternal interface in Cmas^–/– embryos, with strong staining at the surface of TGCs. In implants of CVF-treated mothers, the C3 reactivity was abolished irrespective of the genotype. Insets show fetal TGCs. (C) Ly6G immunohistochemical staining for neutrophils on sagittal paraffin sections of E8.5 uteri from PBS- or CVF-treated mice. Ly6G-positive cells are sparsely distributed in proximity of control embryos of PBS-treated mothers. In contrast, the entire fetal-maternal boundary of Cmas^–/– implants is infiltrated with Ly6G-positive cells in PBS-treated mice. CVF treatment does not change the phenotype of controls but reverts Ly6G staining of Cmas^–/– implants to that of controls. (D) Quantification of Ly6G-positive cells (neutrophils) on sagittal paraffin sections of E8.5 uteri of PBS- or CVF-treated pregnant mice. Error bars indicate SD. Statistical analyses were performed by ANOVA with Newman-Keuls post test (***P < 0.001). Images are representative of experiments of 3 PBS-treated pregnant mice with n = 5 control and n = 3 Cmas^–/– embryos, and of 3 CVF-treated pregnant mice with n = 5 control and n = 4 Cmas^–/– embryos (B–D).