Fig. 6: Virus-induced IFN-I aggravates secondary LM infection by inhibiting neutrophil swarming.

a–c Mice were infected with 1 × 10⁶ PFU b VSV (P = 0.0286) or c MCMV (P = 0.0002) 24 h prior to LM infection, and bacterial load in the liver was assessed at 48 h post-infection with 1 × 10⁶ CFU LM-GFP. Data are from 3 to 4 mice in each group. d–g Mice were infected with 1 × 10⁶ PFU d VSV or f MCMV 24 h prior to LM-GFP infection, and representative intravital images showing neutrophil clusters in the liver 24 h post-infection with 1 × 10⁶ CFU LM-GFP. Scale bar, 200 μm. e, g Quantification of the size of neutrophil clusters, with each dot representing an infection focus. Data were from 3 to 5 mice in each group. (P < 0.0001; P < 0.0001). h Mice were infected with vehicle control, 1 × 10⁶ PFU VSV or MCMV 24 h prior to with LM-GFP infection, and dynamic intravital images showing the neutrophil swarming in the liver 16 h post-infection with 1 × 10⁶ CFU LM-GFP. Scale bar, 50 μm. i Quantification of neutrophil cluster sizes at 5-min intervals. Data of the LM group were from three mice. Data of the VSV + LM group were from five mice. Data from the MCMV + LM group were from three mice. j WT and Ifnar^−/− mice were infected with 1 × 10⁶ PFU MCMV 24 h prior to LM infection, and representative intravital images showed neutrophil clusters in the liver 24 h post-infection with 1 × 10⁶ CFU LM-GFP. Scale bar, 200 μm. k Quantification of the size of neutrophil clusters, with each dot representing an infected focus. Data were from three mice in each group. (P < 0.0001). l Mice were infected with 1 × 10⁶ PFU VSV or MCMV 24 h before LM infection. 1 × 10⁶ WT and 1 × 10⁶ Ifnar^−/− neutrophils were co-transferred 12 h after LM infection. Quantification of the number of donor neutrophils within foci, with each dot representing an infection focus. Scale bar, 50 μm. Data were from three mice in each group. (P < 0.0001; P < 0.0001). Data are represented as mean ± SEM. *P < 0.05; ***P < 0.001.