IFNγ inhibits the replication of <i>S. flexneri</i> in the host cytoplasm.

<p>(A) Growth of <i>S. flexneri</i> in MEFs that were unstimulated or stimulated with IFNγ for 24 hours prior to infection. (B) Quantification of <i>S. flexneri</i> invasion at 1 hpi. (C) Quantification of <i>S. flexneri</i> vacuole escape. Unstimulated or IFNγ-stimulated cells were infected and subsequently treated with gentamicin alone or gentamicin and choloroquine (50 µg/ml), as indicated. Bacterial CFU were determined at 2 hpi. (D) Fluorescence micrographs showing actin tail formation by <i>S. flexneri</i>. Unstimulated or IFNγ-stimulated MEFs were infected with GFP-expressing <i>S. flexneri</i> (green) and stained for host cell actin (red) at 2 hpi. White arrows indicate actin tails. Data for quantification of actin tail formation was gathered from at least 50 infected cells per condition, for 2 independent experiments. (E) Growth of WT or non-motile <i>icsA</i> in unstimulated or IFNγ-stimulated MEFs. MEFs were infected with WT or <i>icsA S. flexneri</i>, and CFU were determined at 15 hpi. (F) Normalization of CFU in IFNγ-stimulated cells for infections with different strains. CFU recovered from IFNγ-stimulated cells for each strain were normalized against CFU recovered from unstimulated cells. All data shown (A–C, E–F) are means and standard deviations. Experiments are representative experiments from 3 (A, B) or 2 (C–F) independent experiments. Where appropriate, significant statistical differences are indicated as follows: ns, not significant; *, p<0.05; **, p<0.005 (Student's t test). Unless indicated otherwise, noted statistical differences are between unstimulated and IFNγ-stimulated cells for each condition.