Anti-Tumor Necrosis Factor-?? Therapy During Murine Klebsiella pneumoniae Bacteremia: Increased Mortality in the Absence of Liver Injury

Abstract

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.

β 2 -Microglobulin-Dependent Bacterial Clearance and Survival during Murine Klebsiella pneumoniae Bacteremia

“…These studies indicated that IFN-␥ is a critical mediator for the resolution of localized, pulmonary gram-negative pneumonia, whereas resolution of systemic, blood-borne gram-negative bacterial infections is independent of IFN-␥ secretion (16). In contrast, in our murine model of Klebsiella bacteremia, mice receiving antitumor necrosis factor alpha (anti-TNF-␣) treatment displayed increased mortality that correlated with impaired bacterial clearance (13,15). These studies, however, did not address the cellular source of these cytokines induced during Klebsiella bacteremia.…”

“…Survival following infection was then observed over the course of 10 days. As we have previously reported (13,15,16), this dose of K. pneumoniae results in a mortality rate of 50% in wild-type animals, with the majority of death occurring within 2 to 4 days of infection. Interestingly, ␤2-m KO mice were significantly more susceptible to K. pneumoniae infection, with 90% of the infected animals succumbing by day 5 postinfection (Fig.…”

“…Inability to clear blood-borne bacteria can lead to a state of overwhelming bacteremia, which can culminate in multiple organ dysfunction syndrome and increased mortality. We have previously reported on the requirements for the proinflammatory cytokines TNF-␣ and IFN-␥ during Klebsiella bacteremia; however, these studies did not address the cellular source of these and other requisite cytokines (13,15,16). Here we report on the critical importance of ␤2-m expression for survival during blood-borne Klebsiella infection.…”

“…At designated time points, mice were euthanized by inhalation of CO 2 . The liver was perfused with 2 to 3 ml phosphate-buffered saline-5 mM EDTA and removed for analyses as previously described (13,15,16). Briefly, liver or spleen was homogenized using a tissue homogenizer (Biospec Products, Bartlesville, OK) in 1 ml phosphatebuffered saline.…”

Modeling Klebsiella pneumoniae Pathogenesis by Infection of the Wax Moth Galleria mellonella

“…K. pneumoniae is an important cause of community-acquired pneumonia in individuals with impaired pulmonary defenses and is a major pathogen in nosocomial pneumonia (19,20). Results obtained using the mouse model of Klebsiella pneumonia highlight the fact that the clearance of the pathogen is primarily dependent upon a vigorous innate immune response (21)(22)(23)(24)(25)(26)(27)(28). Furthermore, stimulation of this response enhances bacterial clearance and prolongs animal survival (29)(30)(31)(32).…”