utrophil recruitment might be suppressed after infection with B. anthracis Sterne compared to the DLF/EF mutant strain. To examine the effects of anthrax toxins on neutrophil chemotaxis in vivo, we analyzed neutrophil recruitment to the site of infection using two independent assays. First, neutrophil recruitment was assessed upon subcutaneous injection of B. anthracis Sterne or the DLF/EF mutant strain into the right or left flank of mice, respectively, After 4 hours, mice were euthanized and the site of subcutaneous injection was excised, homogenized and analyzed for the neutrophil enzyme myeloperoxidase, which serves as an effective indicator of neutrophil infiltration. MPO levels and therefore accumulating neutrophils were significantly lower upon infection with B. anthracis Sterne compared to the DLF/EF mutant strain. Using a second independent measurement, we quantified the amount of neutrophils entering the peritoneal cavity upon i.p. injection of B. anthracis Sterne or DLF/EF mutant bacteria. PBS and a 3% thioglycolate solution were included as negative and positive controls, respectively. After 4 hours, cells were extracted from the peritoneal cavity and the amount of accumulated neutrophils was quantified by flow cytometry. Although neutrophils were recruited upon infection by B. anthracis Sterne compared to the PBS control, neutrophil accumulation was significantly reduced compared to the toxindeficient isogenic mutant. In general, neutrophil accumulation by the DLF/EF mutant was comparable to the positive 3% thioglycolate control. Overall, these results suggest that B. anthracis anthrax toxins interfere with transcription and secretion of neutrophil chemokines, as well as neutrophil recruitment during active infection. Anthrax meningitis mouse model Our data suggest that B. anthracis is capable of penetrating the BBB. In addition, anthrax toxins suppress 16434391 the brain endothelial 7 Toxins and Anthrax Meningitis host response which could promote unrestricted RU 58841 proliferation and further dissemination of B. anthracis in the CNS. To test the contribution of anthrax toxins to the pathogenesis of CNS infection, we developed a mouse model of anthrax meningitis. Mice were injected intravenously with B. anthracis Sterne or DLF/ EF bacteria. Mice were euthanized when they became moribund with severely labored breathing after which brain and blood were collected. All of the DLF/EF-infected mice and approximately 10% of the Sterne-infected mice survived until the experimental endpoint of three weeks. Five out-of 
eight Sterne-infected mice had high bacterial counts in the brain, while no bacteria were recovered from the brains of DLF/EF-infected mice. Microscopic examination of brain tissue from mice infected with the Sterne strain showed thickening of the meninges, an influx of inflammatory cells and substantial hemorrhaging. In addition, Gram stain revealed the presence of numerous bacilli in both the meninges and the parenchyma. The brains of mice that were infected with the DLF/EF strain did not show any signs of infection over the course of the experiment and exhibited normal brain architecture. The absence of clinical symptoms in DLF/EF-infected mice 10864898 could partially be due to reduced virulence of this strain in vivo. Therefore, we performed additional in vitro experiments to assess whether anthrax toxins contribute directly to the penetration of brain endothelium. Compared to the parent strain, the toxin deficient strain exhibited a 7080
