Experimental In Vivo Sepsis Models to Monitor Immune Cell Apoptosis and Survival in Laboratory Mice

Absence of pro-survival A1 has no impact on inflammatory cell survival in vivo during acute lung inflammation and peritonitis

Inflammation is a natural defence mechanism of the body to protect against pathogens. It is induced by immune cells, such as macrophages and neutrophils, which are rapidly recruited to the site of infection, mediating host defence. The processes for eliminating inflammatory cells after pathogen clearance are critical in preventing sustained inflammation, which can instigate diverse pathologies. During chronic inflammation, the excessive and uncontrollable activity of the immune system can cause extensive tissue damage. New therapies aimed at preventing this over-activity of the immune system could have major clinical benefits. Here, we investigated the role of the pro-survival Bcl-2 family member A1 in the survival of inflammatory cells under normal and inflammatory conditions using murine models of lung and peritoneal inflammation. Despite the robust upregulation of A1 protein levels in wild-type cells upon induction of inflammation, the survival of inflammatory cells was not impacted in A1-deficient mice compared to wild-type controls. These findings indicate that A1 does not play a major role in immune cell homoeostasis during inflammation and therefore does not constitute an attractive therapeutic target for such morbidities.

Evaluation of Pseudomonas aeruginosa pathogenesis and therapeutics in military-relevant animal infection models

Modern combat-related injuries are often associated with acute polytrauma. As a consequence of severe combat-related injuries, a dysregulated immune response results in serious infectious complications. The gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that often causes life-threatening bloodstream, lung, bone, urinary tract, and wound infections following combat-related injuries. The rise in the number of multidrug-resistant P. aeruginosa strains has elevated its importance to civilian clinicians and military medicine. Development of novel therapeutics and treatment options for P. aeruginosa infections is urgently needed. During the process of drug discovery and therapeutic testing, in vivo testing in animal models is a critical step in the bench-to-bedside approach, and required for Food and Drug Administration approval. Here, we review current and past literature with a focus on combat injury-relevant animal models often used to understand infection development, the interplay between P. aeruginosa and the host, and evaluation of novel treatments. Specifically, this review focuses on the following animal infection models: wound, burn, bone, lung, urinary tract, foreign body, and sepsis.

Circulating BiP/Grp78 is a novel prognostic marker for sepsis-mediated immune cell death

Sepsis remains to be a major contributor to mortality in ICUs, and immune suppression caused by immune cell apoptosis determines the overall patient survival. However, diagnosis of sepsis-induced lymphopenia remains problematic with no accurate prognostic techniques or biomarkers for cell death available. Developing reliable prognostic tools for sepsis-mediated cell death is not only important for identifying patients at increased risk of immune suppression but also to monitor treatment progress of currently trialed immunotherapy strategies. We have previously shown an important role for endoplasmic reticulum stress (ER stress) in inducing sepsis-mediated cell death and here report on the identification of a secreted form of the ER chaperone BiP (immunoglobulin binding protein) as a novel circulating prognostic biomarker for immune cell death and ER stress during sepsis. Using biochemical purification and mass spectrometry coupled with an established in vitro sepsis cell death assay, we identified BiP/Grp78 as a factor secreted by lipopolysaccharide-activated macrophages that is capable of inducing cell death in target cells. Quantitative ELISA analysis showed significantly elevated levels of circulating BiP in mice undergoing polymicrobial sepsis, which was absent in Bim^-/- mice that are protected from sepsis-induced lymphopenia. Using blood serum from human sepsis patients, we could detect a significant difference in levels of secreted BiP in sepsis patients compared to nonseptic controls, suggesting that secreted circulating BiP could indeed be used as a prognostic marker that is directly correlative to immune cell death during sepsis.

Toll-Like Receptors -2, -3, -4 and -7 Expression Patterns in the Liver of a CLP-Induced Sepsis Mouse Model

Objective: To investigate the expression of toll-like receptors (TLRs) in the liver of septic mouse model. Materials and methods: For this study seventy-two C57BL/6J mice were utilized. Sepsis was induced by cecal ligation and puncture (CLP) in the mice of the three septic (S) groups (euthanized at 24 hours, 48 hours and 72 hours). Sham (laparotomy)- operated mice constituted the control (C) groups (euthanized at 24, 48 and 72 hours). Blood samples were drawn and liver tissues were extracted and examined histologically. The expression of TLRs 2, 3, 4 and 7 was assessed via immunohistochemistry (IHC) and qrt-PCR (quantitative- Polymerase Chain Reaction). Results: Liver function tests were elevated in all S-groups in contrast to their time-equivalent control groups (S24 versus C24, S48 versus C48 and S72 versus C72) (p < 0.05). Liver histology displayed progressive deterioration in the septic groups. IHC and qrt-PCR both showed an increased expression of all TLRs in the septic mice in comparison to their analogous control ones (p < 0.05). Analysis of livers and intestines of the septic animals proved that all TLRs were significantly expressed in higher levels in the intestinal tissues at 24h and 48h (p < 0.05) except for TLR 3 in S48 (p > 0.05); whereas at 72 hours only TLR 4 levels were significantly elevated in the intestine (p < 0.05). Conclusion: TLRs seem to be expressed in significant levels in the livers of septic rodents, indicating that they have a possible role in the pathophysiology of liver damage in septic conditions.

Expression of Toll-like receptors (TLRs) in the lungs of an experimental sepsis mouse model

Background

Sepsis is a condition characterized by high mortality rates and often accompanied by multiple-organ dysfunction. During sepsis, respiratory system may be affected and possibly result in acute respiratory distress syndrome (ARDS). Toll-like receptors (TLRs), as a first line defense against invading pathogens, seem to be highly expressed in septic states. Therefore, expression of TLRs in the lungs of a sepsis animal model could indicate the involvement of the respiratory system and appear as a severity index of the clinical course.

Materials and methods

A total of 72 C57BL/6J mice, aged 12–14 weeks, were studied. The animals were divided into 3 sepsis (S) groups (24h, 48h and 72h) and 3 control (C) groups (24h, 48h and 72h), each consisting of 12 mice. The S-groups were subjected to cecal ligation and puncture (CLP) while the C-groups had a sham operation performed. Blood samples were drawn from all groups. Total blood count analysis was performed along with the measurement of certain biochemical markers. Additionally, lung tissues were harvested and the expression of TLRs, namely TLR 2, TLR 3, TLR 4 and TLR 7 were evaluated by means of immunofluorescence (IF) and qRT-PCR (quantitative-Polymerase Chain Reaction). Statistical analysis was performed by using one-way ANOVA followed by student t-test. Results were considered statistically significant when p<0.05.

Results

WBCs and lymphocytes were decreased in all S-groups compared to the corresponding C-groups (p<0.05), while RBCs showed a gradual decline in S-groups with the lowest levels appearing in the S72 group. Only, monocytes were higher in S-groups, especially between S48-C48 (p<0.05) and S72-C72 (p<0.05). Creatinine, IL-10 and IL-6 levels were significantly increased in the S-groups compared to the corresponding C-groups (S24 vs C24, S48 vs C48 and S72 vs C72, p<0.05). IF showed that expression of TLRs 2, 3, 4 and 7 was increased in all S-groups compared to the time-adjusted C-groups (p<0.05). Similarly, qRT-PCR revealed that expression of all TLRs was higher in all S-groups compared to their respective C-groups in both lungs and intestine (p<0.05). Comparing lung and intestinal tissues from S-groups, TLRs 2 and 4 were found increased in the lung at 24, 48 and 72 hours (p<0.05), whereas TLR 3 was higher in the intestine at all time points examined (p<0.05). Finally, TLR 7 levels were significantly higher in the intestinal tissues at 24 hours (p<0.0001), while lungs predominated at 48 hours (p<0.0001).

Conclusion

TLRs seem to be highly expressed in the lungs of septic mice, therefore suggesting a potential role in the pathogenesis of ARDS during sepsis. While more studies need to be conducted in order to completely understand the underlying mechanisms, TLRs may represent a promising target for establishing novel therapeutic strategies in the treatment of sepsis.