Are alterations of lymphocyte subpopulations in polymicrobial sepsis and DHEA treatment mediated by the tumour necrosis factor (TNF)-alpha receptor (TNF-RI)? A study in TNF-RI (TNF-RI(-/-)) knock-out rodents

Effect of dehydroepiandrosterone on the immune function of mice in vivo and in vitro

Dehydroepiandrosterone (DHEA) has anti-inflammatory, anti-oxidant and immune-regulating properties, while the mechanism of DHEA actions remains unclear. The present study aims to investigate the effect and possible mechanism of DHEA on immune function of mice in vivo and in vitro. In vivo, a lipopolysaccharide (LPS)-induced experimental inflammation model was constructed to analyze the regulation of DHEA on anti-oxidative and immune function in ICR mice; In vitro, the effects of DHEA on the biological functions of lymphocytes and macrophages were studied. The results showed that DHEA increased the activity of total antioxidant capacity and superoxide dismutase, while it decreased the level of reactive oxygen species in LPS-induced mice. Meanwhile, DHEA increased the proportion of T lymphocytes and decreased that of B lymphocytes in primary cultured spleen lymphocytes, and markedly enhanced the Th1/Th2 ratio in spleen T lymphocytes. Furthermore, DHEA significantly increased the Th1 type cytokine (IL-2 and IFN-α) and decreased the Th2 type cytokine (IL-4 and IL-10) levels in LPS-induced mice or in primary cultured spleen T lymphocytes. In addition, DHEA improved the phagocytic ability, enhanced the NO production and increased the iNOS activity in peritoneal macrophages. Our data indicates that DHEA increases the macrophages function via improving NO content and up-regulating TNF-α expression levels; and it evoked a Th1 immuno-response and repressed a Th2 immuno-response through promoting a shift in Th1/Th2 balance toward Th1-dominant immunity in vivo and in vitro. These results provide substantial evidence on the mechanism of DHEA-mediated immune function and the efficient protection against infectious and inflammatory response in animals and humans.

TNFR1 absence protects against memory deficit induced by sepsis possibly through over-expression of hippocampal BDNF

The involvement of TNF-α type 1 receptor (TNFR1) in memory deficits induced by sepsis was explored by using TNFR1 knockout (KO) mice. We reported that wild type (WT) mice presented memory deficits in the novel object recognition test 10 days after sepsis induced by cecum ligation and perforation (CLP). These deficits were not observed in TNFR1 KO mice. The involvement of serum and brain cytokines TNF-α, IL-1β, IL-6, IFN-γ and IL-10 was then investigated. TNFR1 KO mice had higher serum levels of TNF-α and IL-1β, and brain levels of TNF-α than WT mice. After CLP, the brain levels of TNF-α, IL-1β, IL-6 and IFN-γ increased in both WT and KO mice. Our next step was to determine the expression of inflammatory cytokines, BDNF and TrKb in the hippocampus. The absence of TNFR1 in mice subjected to polymicrobial sepsis resulted in higher BDNF expression in the hippocampus. In conclusion, after CLP, memory is preserved in the absence of TNFR1. This finding was associated with increased BDNF expression in the hippocampus.

DHEA-dependent and organ-specific regulation of TNF-alpha mRNA expression in a murine polymicrobial sepsis and trauma model

Introduction

Dehydroepiandrosterone (DHEA) improves survival after trauma and sepsis, while mechanisms of action are not yet fully understood. Therefore, we investigated the influence of DHEA on local cytokine expression in a two-hit model.

Methods

Male NMRI mice were subjected to femur fracture/hemorrhagic shock and subsequent sepsis. Sham-operated animals were used as controls. DHEA (25 mg/kg) or vehicle was administered daily. Mortality rate, activity and body temperature were determined daily after sepsis induction. TNF-α, IL-1β and IL-10 mRNA expression pattern were investigated in lung and liver tissue after 48 and 96 hours.

Results

DHEA treatment resulted in a significantly reduced mortality rate and improvements in the clinical status. On cytokine level, only TNF-α was significantly reduced in the cecal ligation and puncture (CLP)-vehicle group in both tissues after 48 hours. This suppression could be restored by DHEA administration. In contrast, after 96 hours, TNF-α was up-regulated in the CLP-vehicle group while remaining moderate by DHEA treatment in liver tissue.

Conclusions

The improved outcome after DHEA treatment and trauma is coherent with restoration of TNF-α in liver and lung after 48 hours and a counter-regulatory attenuation of TNF-α in liver after 96 hours. Thus, DHEA seems to act, time and organ dependent, as a potent modulator of TNF-α expression.

Depletion of NK cells in a murine polytrauma model is associated with improved outcome and a modulation of the inflammatory response

Sepsis and associated diseases such as systemic inflammatory response syndrome and multiple organ dysfunction syndrome represent common posttraumatic complications on intensive care units induced by a variety of body defense mechanisms. Natural killer (NK) cells are part of the innate immune system. They are thought to play an important role in the development of such syndromes by interplay with other immune cell types and subsequent activation of the inflammatory cascade. To test this hypothesis, NK cells were depleted by administration of antimouse asialo-GM1 antibody in a murine polytrauma model consisting of femur fracture, hemorrhagic shock, and subsequent sepsis. Mortality and immune parameters such as cytokine expression in lung and liver, lymphocyte phenotyping, lymphocyte apoptosis, and organ pathology were determined 96 h after sepsis induction. Survival values showed 50% in the control sepsis group and 100% after NK cell depletion. Thus, NK cell depletion resulted in 50% mortality reduction. Furthermore, we found reductions in the inflammatory response, represented by IL-6 expression in liver, and a decrease in infiltrating neutrophils in the liver and lung. In addition, lymphocyte apoptosis in spleen was decreased by depletion of NK cells. Taken together, these data demonstrate that NK cells contribute to the pathogenetic pathways in a murine polytrauma model. One main mechanism of action seems to be the induction of systemic inflammatory events. Thus, depletion of NK cells results in attenuated inflammation and an overall improvement in outcome. Therefore, NK cells can be considered as important targets for therapeutic strategies.

Effects of changing strategies of fracture fixation on immunologic changes and systemic complications after multiple trauma: damage control orthopedic surgery

In the treatment of polytrauma patients, multiple studies have shown how the timing and the type of the initial surgery of long bone fractures influence the incidence of systemic complications. Database analyses documented that unduly long surgical procedures undertaken early after trauma increase the risk of acute respiratory distress syndrome (ARDS), especially when femoral shaft fractures are stabilized. Animal research and prospective clinical studies also support the fact that the type of stabilization of a femoral shaft fracture may influence the systemic response to trauma. Reamed intramedullary reaming and nailing for a femoral shaft fracture is associated with an increased risk of pulmonary fat embolization from the medullary canal. This can result in pulmonary compromise if certain cofactors are also present. Modified reamers have been developed to reduce this side effect. The mediating effects are immunologic changes, varying according to the magnitude of the surgical procedure. Pro-inflammatory markers (e.g., Interleukins) may be used to assess the inflammatory response to injury as well as the magnitude of surgery and the systemic impact induced by surgery. Serum levels of such markers can be used clinically to tailor the amount of surgery that is performed to the clinical condition of the patient. The potentially negative impact of excessive surgery in high-risk patients can be avoided by using a new grading system for the assessment of the clinical status of the injured patient. Most recently, a large prospective randomized multicenter study has documented that this grading system is effective for identifying these borderline patients, and that in the borderline patient a staged surgical approach, such as temporary femoral stabilization with an external fixator, reduces the incidence of systemic complications. This work has changed the surgical management of multiply injured patients toward an approach that is tailored to the clinical condition of the patient, as indicated by well-defined clinical parameters as well as objective measurements of serum cytokine levels.

The hypothalamic-pituitary-adrenal axis in critical illness

The hypothalamic-pituitary-adrenal response to stress is a dynamic process. The homeostatic corrections that have emerged in the course of human evolution to cope with the catastrophic events during critical illness involve a complex multisystem endeavor. Although the repertoire of endocrine changes has been probed in some detail, discerning the vulnerabilities and failures of this system is far more challenging. One of the most controversially debated topics in the current literature is the characterization and optimal treatment of allegedly inadequate adaptations of the hypothalamic-pituitary-adrenal axis during critical illness. This outline attempts to touch briefly some of the debated issues, stir the discussion, and thereby contribute to resolving the dispute.