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Downregulation of proinflammatory cytokine release in whole blood from septic patients
W Ertel1, J P Kremer, J Kenney
1Department of Surgery, University Hospital Zurich, Switzerland.
Abstract:
Using animal models or healthy volunteers, injection of lipopolysaccharide (LPS) or bacteria causes activation of macrophages with excessive synthesis and secretion of proinflammatory cytokines. Although these models mimic the effects of LPS in the host, they may represent more of an experimental expression of endotoxemia than natural infection itself. Therefore, as an ex vivo model of sepsis, whole blood from 15 patients with severe sepsis and 20 control patients without infection was stimulated with LPS to study the kinetics of mRNA expression and release of proinflammatory cytokines, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta, and IL-6. Stimulation of whole blood with 1 microgram/mL LPS resulted in a maximum increase of cytokine secretion in the control group, while a marked (P < .01) depression of TNF-alpha, IL-1 beta, and IL-6 release was observed in the septic group, which persisted up to 10 days after study enrollment. While IL-1 beta mRNA expression was similar in peripheral blood mononuclear cells (PBMCs) harvested from LPS-stimulated whole blood in septic and control patients, the half-life and consequently the expression of TNF-alpha and IL-6 mRNA were strongly reduced in the septic group. These data indicate a downregulatory mechanism of cytokine release in whole blood from patients with severe sepsis that occurs on different levels. Although excessive secretion of proinflammatory cytokines has been considered deleterious for the host, the reduced capacity of PBMCs in whole blood from septic patients to synthesize and secrete proinflammatory cytokines to an inflammatory stimulus may result in immunodeficiency, because these cytokines in low concentrations are involved in the upregulation of essential cellular and humoral immune functions.
Insights
Severe sepsis patients show reduced cytokine release and mRNA expression in response to lipopolysaccharide (LPS). This suggests a downregulatory mechanism potentially leading to immunodeficiency, despite previous beliefs about excessive cytokine secretion.
Area of Science:
- Immunology
- Sepsis Pathophysiology
- Cytokine Biology
Background:
- Lipopolysaccharide (LPS) injection in animal models and healthy volunteers activates macrophages, leading to excessive pro-inflammatory cytokine release.
- Existing models may not accurately reflect natural infection, prompting the need for ex vivo sepsis models.
Purpose of the Study:
- To investigate the kinetics of mRNA expression and cytokine release in whole blood from severe sepsis patients stimulated with LPS.
- To compare cytokine responses between patients with severe sepsis and healthy controls.
Main Methods:
- Whole blood from 15 severe sepsis patients and 20 controls was stimulated ex vivo with 1 microgram/mL LPS.
- Kinetics of mRNA expression and release of TNF-alpha, IL-1 beta, and IL-6 were analyzed.
- mRNA half-life and expression levels in peripheral blood mononuclear cells (PBMCs) were assessed.
Main Results:
- Control group showed maximum cytokine secretion upon LPS stimulation.
- Septic group exhibited a marked depression (P < .01) in TNF-alpha, IL-1 beta, and IL-6 release, persisting for up to 10 days.
- While IL-1 beta mRNA expression was similar, TNF-alpha and IL-6 mRNA half-life and expression were reduced in septic patients.
Conclusions:
- Severe sepsis involves a downregulatory mechanism affecting cytokine release at multiple levels.
- Reduced cytokine synthesis and secretion capacity in septic patients may lead to immunodeficiency.
- Pro-inflammatory cytokines are crucial for immune function upregulation, even at low concentrations.