TF expression by myeloid cells but not fetal-derived cells contributes to aPL-induced fetal loss. (A) Low TF female mice (mTF^−/−,hTF⁺) mated with wild-type males (mTF^+/+) and wild-type female mice mated with wild-type males (mTF^+/+ × mTF^+/+) were treated on days 8 and 12 with aPL-IgG or NH-IgG. On day 15, fetal resorption rates were calculated as described ¹⁹in “Materials and methods, Murine aPL-induced fetal loss model.” Approximately 40% of the embryos in wild-type matings treated with aPL-IgG were resorbed. Low TF female mice mated with wild-type males showed a reduction in aPL-induced fetal resorption frequency compared with wild-type mice (P < .005). Error bars here and in panel B are SD. (B) Pregnant TF^{floxed/floxed} and TF^{floxed/floxed}/LysM-Cre mice were treated with aPL-IgG or NH-IgG on days 8 and 12 of pregnancy. Fetal resorption frequency was calculated as described¹⁹  in “Materials and methods, Murine aPL-induced fetal loss model.” Treatment with aPL-IgG caused an increase in fetal resorptions in TF^{floxed/floxed} mice (*P < .001 versus NH-IgG). TF^{floxed/floxed}/LysM-Cre mice were protected from fetal loss induced by aPL-IgG. Fetal resorption frequency in these mice was comparable with TF^{floxed/floxed} mice treated with NH-IgG. (C) Immunohistochemical analysis for neutrophils in sections of deciduas from aPL-IgG–treated mice. Intense staining for neutrophils (brown color) was observed in deciduas from TF^{floxed/floxed} mice treated with aPL-IgG (Ci). In contrast, less neutrophil infiltration was observed in deciduas from TF^{floxed/floxed}/LysMCre mice that had received aPL-IgG (Cii). Counterstain: hematoxylin. Original magnification × 500. (D) Superoxide (O₂⁻) generation in decidual tissue was determined using dihydroethidium fluorescence. aPL-induced O₂⁻ formation (Di) is attenuated in TF^{floxed/floxed}/LysM-Cre mice (Dii) and low TF mice (Diii) to a similar extent to NH-IgG–treated mice (Div). Original magnification × 800.