IglG is required for intracellular replication, phagosomal escape and triggering of cytosolic innate immune responses.

(A) J774 macrophages were infected at an MOI of 1 with the indicated F. novicida strains and the intracellular burden was assessed by determination of viable counts at 2 and 24 h. (B) Phagosomal rupture in BMDMs infected with the indicated strains at an MOI of 100 was determined at 2 h by flow cytometry using the β-lactamase/CCF4 assay. Concatenates from three samples are shown for each strain after exclusion of doublets and dead cells. Quantification is shown in the right panel using the gating strategy presented in the left panel. (C) Type I IFN secretion in the culture supernatant of BMDMs infected with the indicated strains at an MOI of 1 was determined by the ISRE-luciferase bioassay and normalized to the value of the bioassay in uninfected macrophages. (D) Cell death of BMDMs infected with the indicated strains at an MOI of 1 was monitored in real time in the presence of propidium iodide by fluorescence readings every 15 min. (A-D) Mean and (A-C) SD of triplicates from one experiment representative of 3 independent experiments are shown. Unpaired t-tests were performed, two-tailed P-values are shown (ns, not significant; **, P ≤ 0.01; ***, P ≤ 0.001).