Per se, intravenously-infected S100A8/A9-/- mice generated immune responses in the thoracic cavity that were similarly observed following natural and subcutaneous infection, with thoracic cavity cell numbers being increased (Fig 6D) and significantly higher levels of CXCL-2 (Fig 6F) and elastase (Fig 6H) within the pleural lavage of S100A8/A9-/- animals, whereas the concentrations of CXCL-1 (Fig 6E) and CXCL-5 (Fig 6G) were comparable between WT and S100A8/A9-/- mice. This evidence concerns the gene CXCL2 and infection.