In an attempt to examine whether genes stimulated by IFN were induced in response to Listeria infection in the placenta, we quantified the expression of representative IFN-responsive genes, IFIT1 and Mx1/2, in placenta infected or not by L. monocytogenes. As shown in Fig. 4C, 72 h after intravenous inoculation of mice with L. monocytogenes, the expression of IFIT1 and Mx1/2 was induced in placentas, in contrast to that of a control gene, IGF2. These results indicate that L. monocytogenes infection can promote IFN-λ expression and an IFN response in the placenta. Here, IFNA1 is linked to listeriosis.