ISG15 and infection: In contrast, expression of other genes in the IFN signaling pathway (G1p2, Ifi35, Ifit1 and Stat2) were shown to be higher in the infected WT as compared to the infected Ifnar1-/- mice after days 2 and 3 of infection (Fig 4D), when the bacterial load was lower in the infected Ifnar1-/- mice (Fig 3A).