C5aR interaction and neutrophils are required for the increase in TF expression in aPL-induced fetal damage. (A) Pregnant C3aR^−/− and C3aR^+/+ mice were treated with aPL-IgG or NH-IgG on days 8 and 12 of pregnancy. Fetal resorption frequency was calculated as described ¹⁹in “Materials and methods, Murine aPL-induced fetal loss model.” Treatment with aPL-IgG caused an increase in fetal resorptions in wild-type mice (*P < .001 versus NH-IgG). C3aR^−/− mice were not protected from fetal loss induced by aPL-IgG. Error bars here and in panel E are SD. (B-D,F-H) Immunohistochemical analysis of decidual tissue of day 8 of pregnancy. Decidual tissue was processed for TF as described in legend for Figure 1. (B) Deciduas from C3aR^−/− mice treated with aPL-IgG showed extensive TF staining and embryo debris (ED) comparable with wild-type mice treated with aPL-IgG (not shown). (C) Deciduas from C5^−/− mice showed less TF staining limited to the ectoplacental cone (ec) and intact embryos (E), while in deciduas from C5^+/+ mice (D) there was extensive TF deposition and embryonic debris (ED). (E) Pregnant C6^+/+ and C6^−/− mice were treated with aPL-IgG or NH-IgG on days 8 and 12 of pregnancy. Fetal resorption frequency was calculated as described ¹⁹in “Materials and methods, Murine aPL-induced fetal loss model.” Treatment of C6^+/+ with aPL-IgG caused an increase in fetal resorptions (*P < .005 versus NH-IgG). C6^−/− mice were not protected from fetal loss and showed an increase in TF expression induced by aPL-IgG (F). (G) Deciduas from C5aR^−/− mice treated with aPL-IgG showed limited TF staining and intact embryos (E). (H) TF staining was reduced in deciduas from wild-type mice that had received anti-Gr before aPL-IgG treatment.