Fig. 3. Type I IFN suppresses ActA degradation in phagosomes and promotes Lm actin recruitment.

a Schematic of GFP reporter Lm strains developed to measure actA transcription activation. Representative images (b) and quantification (c) of actA:GFP reporter expression and ActA degradation of BMDMs infected for 4 h with indicated Lm strains measured by GFP fluorescence and antibody staining, with or without treatment of IFNβ, bafilomycin A or protease inhibitors. Representative images at 1.25 hr p.i. (d) and quantification (e) of WT Lm actin recruitment, measured by phalloidin staining, after phagosome escape over 4 h time course. f Measurement of WT Lm actin-based motility with phalloidin-positive comet tails 4 h p.i. Data shown are means ± s.d. for n = 3 independent experiments. P value was calculated using (c, e) two-way ANOVA and (f) two-tailed unpaired t-test. *P = 0.0285, **P = 0.001, ****P < 0.0001. Scale bars, 11 µm.