Streptococcus pneumoniae, a gram-positive bacteria, is the most common cause of community-acquired pneumonia. It is a common cause of septic shock with multiple organ dysfunction syndrome (MODS) resulting in significant mortality. Gram-positive mouse models of sepsis with MODS are required to examine mechanisms of immune responses in severe sepsis. To assess whether lung infection due to S. pneumoniae in a nonventilated mouse model can induce multiple organ dysfunction. S. pneumoniae, SPN 15814 strain, harvested at log phase, was injected intratracheally in C57BL/6 mice at OD 600 between 0.35 and 0.63. A dose of bacteria at OD 600 = 0.63 conferred approximately 30% mortality in 36 h. Lung pneumonia was assessed by histology, lung myeloperoxidase activity, and lung bacterial load; intestinal epithelial barrier integrity was assessed by measuring blood-to-lumen clearance of Cr-EDTA; renal function was assessed by measuring plasma creatinine and urea; and myocardiac function was assessed using an isolated perfused mouse heart model. S. pneumoniae-induced pneumonia resulted in neutrophil infiltration into the lungs and increased lung bacterial load. Although relatively few bacteria gained access to the blood stream, the pneumonia was accompanied by increased intestinal epithelial barrier permeability, increased plasma creatinine, and decreased cardiac output and stroke volume. These data clearly show that intratracheal S. pneumoniae induced not only pneumonia but also MODS, despite the fact that few organisms gain access to the blood stream. This model can be used as a good gram-positive model of sepsis and MODS for further studies.

To investigate the potential role of the local expression of alternative complement factor B (hBf) in human sepsis, we examined the induction of Bf gene expression in human peripheral blood monocytes (PBMCs) from patients with septic shock and the mechanisms of hBf gene regulation by tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and lipopolysaccharide (LPS) in human monocytes. PBMCs from septic shock patients showed increased hBf mRNA expression when compared with control patients. Costimulation with TNF-alpha and IFN-gamma or stimulation with LPS demonstrated a time- and dose-dependent induction of hBf mRNA expression in human PBMCs. A region of the hBf promoter between -735 and +128 bp was found to mediate IFN-gamma, TNF-alpha, and LPS responsiveness as well as the synergistic effect of IFN-gamma/TNF-alpha on hBf promoter activity. Site-directed mutagenesis of a IFN-gamma-activation site (GAS) cis element (-90 to -82 bp) abrogated IFN-gamma responsiveness. Mutagenesis of a nuclear factor (NF)-kappaB cis element at -466 to -456 bp abrogated TNF-alpha and LPS responsiveness of the Bf promoter. Thus hBf gene expression is induced in PBMCs from septic shock patients, and the induction of hBf by IFN-gamma, TNF-alpha, and LPS is through GAS and NF-kappaB cis-binding sites on the hBf promoter. Furthermore, activated protein C (APC) inhibited LPS-stimulated hBf promoter activity and protein expression in human monocytes suggesting that the beneficial effect of APC therapy in sepsis may in part be due to inhibition of complement induction and/or activation via the alternative pathway.