To dissect the role of TLR4 or IFNAR1 expression in maternal versus fetal compartments, we compared the infection outcomes of heterogenic pregnancies (where mothers were deficient for the gene of interest [Tlr4 or Ifnar1] but their fetuses were all heterozygous) against those of wild-type or gene-deficient isogenic pregnancies using the mating strategy described in Materials and Methods. This evidence concerns the gene IFNAR1 and infection.