Anti-tumor necrosis factor-alpha therapy during murine Klebsiella pneumoniae bacteremia: increased mortality in the absence of liver injury.

Klebsiella pneumoniae is a leading cause of gram-negative bacterial pneumonia, often resulting in bacteremia concurrent with the localized pulmonary infection. The beneficial role of tumor necrosis factor (TNF)-alpha during pulmonary infection has been well documented; however, consequences of TNF-alpha production during systemic bacterial infection are controversial. A murine model of K. pneumoniae was developed to address this important issue. Liver-associated TNF-alpha mRNA was induced within 30 min after intravenous bacterial inoculation and remained elevated through 6 h before returning to near-baseline at 24 h postinfection. Intravenous K. pneumoniae infection induced liver cellular injury that was completely ablated when mice were pretreated with a neutralizing anti-TNF-alpha antibody. Interestingly, this reduction in liver injury failed to translate into improved survival. Mice receiving anti-TNF-alpha continued to succumb to the infection even out to day 10 postinfection. Bacterial clearance after TNF-alpha neutralization was significantly impaired at later time points during infection. Correlating with impaired bacterial clearance was diminished production of liver-associated MIP-2, MIP-1alpha, MCP-1, and interferon-gamma. Further evidence of diminished antibacterial immune responses was noted when the activational status of splenic natural killer cells in anti-TNF-alpha-treated mice was examined 24 h postinfection. Natural killer cells displayed decreased CD69 expression. Combined, these data indicate that the beneficial effects of TNF-alpha during systemic K. pneumoniae infection outweigh the detrimental effects of TNF-alpha-mediated hepatocyte cellular injury. Anti-TNF-alpha therapy, although preventing liver injury during blood-borne bacterial infection, results in a dampened anti-bacterial host response, resulting in decreased bacterial clearance and overall survival

Increased Mortality and Dysregulated Cytokine Production in Tumor Necrosis Factor Receptor 1-Deficient Mice following Systemic Klebsiella pneumoniae Infection

A significant clinical complication of pulmonary infections with Klebsiella pneumoniae is peripheral blood dissemination, resulting in a systemic infection concurrent with the localized pulmonary infection. In this context, little is known about the role of tumor necrosis factor receptor 1 (TNFR1)-mediated innate immune responses during systemic Klebsiella infections. Mice lacking TNFR1 were significantly more susceptible to Klebsiella-induced mortality following intravenous inoculation. Bacterial clearance was impaired in TNFR1-deficient mice at early times following infection. Unexpectedly, bacterial burdens at the onset of mortality (days 2 to 3 postinfection) were not higher in mice lacking TNFR1. However, elevated production of liver-associated proinflammatory cytokines (interleukin-12, tumor necrosis factor alpha [TNF-α[, and gamma interferon [IFN-γ]) and chemokines (MIP-1α, MIP-2, and MCP-1) was observed within the first 24 h of infection. Additionally, excessive plasma-associated IFN-γ was also observed late in the course of infection (day 3). Spleen cells from day-3 infected TNFR1-deficient mice secreted markedly enhanced levels of IFN-γ when cultured in vitro. Additionally, there was a marked increase in the total number of activated lymphocyte subsets as indicated by CD69 upregulation. A notable exception was the sharp decrease in the frequency of splenic NK T cells in infected TNFR1 knockout (KO) mice. Anti-TNF-α therapy in TNFR1 KO mice significantly reduced chemokine production and liver injury. Combined, these data indicate a dysregulated antibacterial host response following intravenous Klebsiella infection in the absence of TNFR1 signaling, resulting in heightened cytokine production and hyperactivation of specific splenic lymphocyte subsets