Targeting the “Rising DAMP” during a Francisella tularensis Infection

Abstract

Antibiotic efficacy is greatly enhanced the earlier it is administered following infection with a bacterial pathogen. However, in a clinical setting antibiotic treatment usually commences following the onset of symptoms, which in some cases (e.g., biothreat agents) may be too late. In a BALB/c murine intranasal model of infection for Francisella tularensis SCHU S4 infection, we demonstrate during a time course experiment that proinflammatory cytokines and the damage-associated molecular pattern HMGB1 were not significantly elevated above naive levels in tissue or sera until 72 h postinfection. HMGB1 was identified as a potential therapeutic target that could extend the window of opportunity for the treatment of tularemia with antibiotics. Antibodies to HMGB1 were administered in conjunction with a delayed/suboptimal levofloxacin treatment of F. tularensis. We found in the intranasal model of infection that treatment with anti-HMGB1 antibody, compared to an isotype IgY control antibody, conferred a significant survival benefit and decreased bacterial loads in the spleen and liver but not the lung (primary loci of infection) 4 days into infection. We also observed an increase in the production of gamma interferon in all tested organs. These data demonstrate that treatment with anti-HMGB1 antibody is beneficial in enhancing the effectiveness of current antibiotics in treating tularemia. Strategies of this type, involving antibiotics in combination with immunomodulatory drugs, are likely to be essential for the development of a postexposure therapeutic for intracellular pathogens.

Mitogen-activated protein kinases (MAPKs) are modulated during Francisella tularensis infection, but inhibition of extracellular-signal-regulated kinases (ERKs) is of limited therapeutic benefit

“…It is well documented that an inflammatory response is essential for pathogen clearance, although it is also clear that pro-inflammatory responses contribute to the tissue damage and pathology seen during infection [6]. Indeed, the overactive immune response seen late during Francisella infection has been hypothesised to be one of the main contributors of detrimental outcome [7, 37]. Therefore, in this context, the modulation of the immune response achieved through inhibition of ERK with PD0325901 could be beneficial to survival of the host following infection.…”

“…The ERK inhibitor could be used in this context to indirectly reduce systemic spread, whilst a bactericidal antibiotic directly kills the bacteria that remain within the lung. An analogous therapeutic strategy has already been shown to be beneficial in our laboratory for the treatment of the fully virulent SCHUS4 strain of F. tularensis , whereby inhibition of HMGB1, combined with levofloxacin use, significantly increased survival of infected mice compared to controls [7]. In addition, related approaches involving the administration of an antibiotic and an immunodulating therapy have been reported for other bacterial pathogens as well as in the treatment of sepsis [38].…”

“…Indeed, it is now well documented that an overactive immune response can be more damaging to the host than the progression of infection by the pathogen [6]. This fine balance is illustrated when a host is infected via the inhalational route with the Gram-negative facultative intracellular bacterium Francisella tularensis , where there is an initial suppression of pro-inflammatory cytokines followed by a “cytokine storm” prior to death [7]. …”

“FoxP3 Hunting” during Infection with Francisella Tularensis

“…FoxP3 cells were identified in the lung, liver and spleen using immunohistochemistry. The data presented here indicates that in the murine lung, the site ofinfection, there is an initial increase in FoxP3 regulatory cells around lesions and these significantly decrease at d4 and d5 p.i, which interestingly correlates with a decrease in the anti-inflammatory cytokine TGF-ã nd coincides with the "cytokine storm" associated with F. tularensis infection (15). A similar pattern was seen in healthy tissue in the spleen, with FoxP3 cell being significantly reduced at d5 p.i, and this was further confirmed via image analysis software of the spleen.…”

The Impact of “Omic” and Imaging Technologies on Assessing the Host Immune Response to Biodefence Agents

“…Flow cytometry bead-based assays have the potential to aid our understanding of potential protective mechanisms of novel immunotherapeutics by assessing cytokine responses. These assays have been used in studies investigating the effects of IFN-therapy in mice during B. pseudomallei infection [103] and to understand changes occurring as a result of treatment with an HMGB1-antibody antibiotic combination therapy [104]. This study showed that treated mice had significantly higher IFN-levels which correlated with survival.…”