Figure 6.

Plasminogen activator protease (Pla) proteolytic activity is essential for early bacterial growth in the lungs and resistance to neutrophil-mediated bacterial killing. A, Bacterial burden in the lungs of C57BL/6 mice infected intranasally with 10⁴ colony-forming units (CFUs) of wild-type Yersinia pestis CO92, CO92 Δpla, CO92 Δpla + pla wild type (WT), CO92 Δpla + plaS99A, or CO92 Δpla + plaD206A at 12, 24, 36, and 48 hours after infection. B, Bacterial burden in the lungs of C57BL/6 mice treated (Ly-6G) or not treated (No Ly-6G) with anti–Ly-6G to deplete neutrophils. Mice were infected intranasally with 10⁴ CFUs of CO92 Δpla, CO92 Δpla + plaS99A, or CO92 Δpla + plaD206A after 24 hours of antibody treatment and bacterial burdens were assessed 24 hours after infection. C, Neutrophil killing assay with primary human neutrophils. CO92, CO92 Δpla, CO92 Δpla + pla WT, CO92 Δpla + plaS99A, or CO92 Δpla + plaD206A was incubated with neutrophils to obtain a multiplicity of infection of 5 for 2 and 4 hours. Bacterial survival was measured by analyzing CFUs at each time point. Experiments were performed in triplicate; error bars represent standard deviations (n = 5 or 7 animals; n = 3 cells). *P < .05; †P < .01; ‡P < .001 (2-way analysis of variance).