Figure 1.

Time course of neutrophil influx and vascular remodeling after M. pulmonis infection. A–C: Whole mounts of mouse trachea stained for endothelial cells (Pecam1, red) and neutrophils (S100a9, green). In a pathogen-free mouse, capillaries (arrows) span a cartilage ring and join a venule (arrowhead) between cartilages; neutrophils are sparse (A). B: There were a moderate number of neutrophils on day 3 of infection. Capillaries were mostly narrow but had focal enlargements (arrows) and joined a venule (arrowhead). C: Neutrophils were abundant on day 7. Vessels over cartilage were enlarged (arrows). D and E: Values per mouse and group means show the time course after infection of enlargement of capillaries over cartilage rings (D) and influx of S100a9-immunoreactive neutrophils (E). N = 4 to 5 mice per group; ^∗P < 0.05 compared with the pathogen-free group. F: Linear regression of blood vessel size versus the number of neutrophils in the trachea from 0 to 7 days after infection. N = 4 to 5 mice per group, P < 0.001. G: Distribution of the diameter of blood vessels located over tracheal cartilage in pathogen-free and 7-day-infected mice. Capillaries (green) in pathogen-free mice were remodeled into larger venules (red) by day 7 of infection. N = 3 mice per group, P < 0.05; Kolmogorov-Smirnov test. H: Neutrophils (arrowheads) inside a venule located between cartilage rings on day 3 of infection. Scattered extravascular neutrophils also were present. I: Size distribution of blood vessels (median, 22.5 μm) that contain adherent neutrophils on day 3 of infection. N = 3 mice. Scale bars: 50 μm (A–C); 20 μm (H).