Kupffer cell depletion reduces hepatic inflammation and apoptosis but decreases survival in abdominal sepsis.

OBJECTIVE: During abdominal sepsis, the activation of hepatic Kupffer cells (KC) and its consequences are of central interest. This study evaluates the impact of selective KC depletion on hepatic microcirculation, cytokine release, and systemic alterations in the colon ascendens stent peritonitis (CASP), a model of polymicrobial abdominal sepsis. METHODS: For KC depletion clodronate liposomes were injected 24 h before CASP surgery in female C57BL/6N mice. Three and 12 h after CASP, in-vivo fluorescence microscopy of the liver was performed. Analysis of hepatocellular apoptosis was conducted by immunohistochemistry. In addition, levels of tumor necrosis factor (TNF), IL-6, and IL-10 in the liver, lungs, spleen, and plasma were determined, and bacteriology and survival analysis were performed. RESULTS: CASP led to significant sinusoidal perfusion failure, increased leukocyte recruitment, hepatocellular apoptosis and increased levels of TNF, IL-6, and IL-10 in the liver and plasma. KC depletion before CASP significantly reduced leukocyte recruitment to the liver and hepatocellular apoptosis. IL-10 secretion decreased dramatically in the liver and plasma of KC-depleted septic mice. In contrast, TNF levels were clearly elevated after clodronate treatment. In the lung and spleen, a compensatory upregulation of IL-10 could be detected after KC depletion. Clodronate treatment resulted in a significant reduction in survival. CONCLUSION: The results indicate that KC depletion is locally protective in polymicrobial abdominal sepsis, as it reduces hepatic inflammation and apoptosis. These effects could be observed in the presence of clearly elevated TNF levels. However, the lack of IL-10 in KC-depleted mice resulted in a detrimental systemic proinflammation.

Selective depletion of alveolar macrophages in polymicrobial sepsis increases lung injury, bacterial load and mortality but does not affect cytokine release.

BACKGROUND: Resident tissue macrophages exert important functions during severe systemic infection and contribute to changes in local as well as systemic immune responses. Alveolar macrophages (AM) play a crucial role in airway diseases and in the defense against microorganisms invading the body via the bronchopulmonary tract. It has been postulated that AM are involved in the development of acute local disorders as a consequence of extrapulmonary stimuli like pancreatitis, peritonitis, or trauma. OBJECTIVE: The aim of this study was to analyze the local and systemic role of AM during sepsis using selective AM depletion in the murine colon ascendens stent peritonitis (CASP) model of polymicrobial sepsis. METHODS: 48 h prior to CASP surgery, AM of female C57BL/6 mice were selectively depleted by intratracheal application of clodronate liposomes (Lipo-clod). For control purposes, phosphate-buffered saline (PBS) liposomes (Lipo-PBS) were used. RESULTS: CASP led to significantly elevated levels of local and systemic cytokines independent of the presence of AM. In contrast, levels of gut-derived bacteria in bronchoalveolar lavage and lung of septic mice were significantly higher in Lipo-clod-treated animals compared to Lipo-PBS-treated animals. After CASP-induced sepsis, local barrier dysfunction in the lung was detected; AM depletion resulted in severely enhanced development of acute lung injury. Consequently, Lipo-clod-treated animals showed strongly reduced survival rates after CASP. CONCLUSIONS: Contrarily to other macrophage populations, AM do not significantly contribute to local and systemic cytokine release during polymicrobial abdominal sepsis. AM have important protective functions for local clearance of gut-derived bacteria and attenuation of lung injury.

Detrimental role of CC chemokine receptor 4 in murine polymicrobial sepsis.

CC chemokine receptor 4 (CCR4) and its two ligands, CCL17 and CCL22, are critically involved in different immune processes. In models of lipopolysaccharide-induced shock, CCR4-deficient (CCR4(-/-)) mice showed improved survival rates associated with attenuated proinflammatory cytokine release. Using CCR4(-/-) mice with a C57BL/6 background, this study describes for the first time the role of CCR4 in a murine model of polymicrobial abdominal sepsis, the colon ascendens stent peritonitis (CASP). CASP-induced sepsis led to a massive downregulation of CCR4 in lymphoid and nonlymphoid tissues, whereas the expression of CCL17 and CCL22 was independent of the presence of CCR4. After CASP, CCR4(-/-) animals showed a strongly enhanced bacterial clearance in several organs but not in the peritoneal lavage fluid and the blood. In addition, significantly reduced levels of proinflammatory cytokines/chemokines were measured in organ supernatants as well as in the sera of CCR4(-/-) mice. CCR4 deficiency consequently resulted in an attenuated severity of systemic sepsis and a strongly improved survival rate after CASP or CASP with intervention. Thus, our data provide clear evidence that CCR4 plays a strictly detrimental role in the course of polymicrobial sepsis.

The vagal nerve as a link between the nervous and immune system in the instance of polymicrobial sepsis.

BACKGROUND: The role of the vagal nerve in the autonomic nervous system is widely well known. Recently, an additional function was revealed serving as a connector between the nervous and immune system. This connection is called the "cholinergic inflammatory pathway." Through stimulation of the acetylcholine receptors located upon the macrophages, the "unspecific" immune system can be directly influenced. METHODS: The vagal nerve was completely transected directly posterior to its passage through the diaphragm. The effect of complete vagotomy was analyzed using a murine model of polymicrobial peritonitis (colon ascendens stent peritonitis, CASP). Survival and clinical course of vagotomized or sham-operated mice were analyzed in the CASP model. RESULTS: After CASP surgery, vagotomy led to a significantly increased mortality (64.7%) in comparison to sham-vagotomized animals (34%). No difference in the bacterial load of various tissues (lung, liver, spleen, blood, lavage fluid, and kidney) from septic animals with or without vagotomy was observed. Vagotomized animals reveal elevated serum cytokine levels (TNF, IL-6, IL-10, and MCP-1) 20 h after the induction of polymicrobial peritonitis. CONCLUSION: The vagal nerve is therefore an important modulator of the immune system.