Granulocyte‐Macrophage Colony‐Stimulating Factor Induces Activation and Restores Respiratory Burst Activity in Monocytes from Septic Patients

Agrawal

et al. 2008

Mol Med

The development of immunosuppression during polymicrobial sepsis is associated with the failure of dendritic cells (DC) to promote the polarization of T helper (Th) cells toward a protective Th1 type. The aim of the study was to test potential immunomodulatory approaches to restore the capacity of splenic DC to secrete interleukin (IL) 12 that represents the key cytokine in Th1 cell polarization. Murine polymicrobial sepsis was induced by cecal ligation and puncture (CLP). Splenic DC were isolated at different time points after CLP or sham operation, and stimulated with bacterial components in the presence or absence of neutralizing anti-IL-10 antibodies, murine interferon (IFN) γ, and/or granulocyte macrophage colony-stimulating factor (GM-CSF). DC from septic mice showed an impaired capacity to release the pro-inflammatory and Th1-promoting cytokines tumor necrosis factor α, IFN-γ, and IL-12 in response to bacterial stimuli, but secreted IL-10. Endogenous IL-10 was not responsible for the impaired IL-12 secretion. Up to 6 h after CLP, the combined treatment of DC from septic mice with IFN-γ and GM-CSF increased the secretion of IL-12. Later, DC from septic mice responded to IFN-γ and GM-CSF with increased expression of the co-stimulatory molecule CD86, while IL-12 secretion was no more enhanced. In contrast, splenic macrophages from septic mice during late sepsis responded to GM-CSF with increased cytokine release. Thus, therapy of sepsis with IFN-γ/GM-CSF might be sufficient to restore the activity of macrophages, but fails to restore DC function adequate for the development of a protective Th1-like immune response.

Section: Discussionmentioning

confidence: 99%

Diversity of Interferon γ and Granulocyte-Macrophage Colony-Stimulating Factor in Restoring Immune Dysfunction of Dendritic Cells and Macrophages During Polymicrobial Sepsis

Agrawal

et al. 2008

Mol Med

American Journal of Physiology-Lung Cellular and Molecular Phys

“…Short-term treatment with GM-CSF has been shown to counteract impaired innate immune function due to a variety of insults. Ex vivo exposure to GM-CSF has restored function in monocytes harvested from humans with septic shock (36) or from immunosuppressed liver transplant recipients (37). In a rat model of hemorrhagic shock, GM-CSF treatment in vivo has corrected tissue macrophage dysfunction (17).…”

Section: Discussionmentioning

confidence: 99%

GM-CSF and the impaired pulmonary innate immune response following hyperoxic stress

Baleeiro¹,

Christensen²,

Morris³

et al. 2006

We have previously demonstrated that mice exposed to sublethal hyperoxia (an atmosphere of Ͼ95% oxygen for 4 days, followed by return to room air) have significantly impaired pulmonary innate immune response. Alveolar macrophages (AM) from hyperoxia-exposed mice exhibit significantly diminished antimicrobial activity and markedly reduced production of inflammatory cytokines in response to stimulation with LPS compared with AM from control mice in normoxia. As a consequence of these defects, mice exposed to sublethal hyperoxia are more susceptible to lethal pneumonia with Klebsiella pneumoniae than control mice. Granulocyte/macrophage colony-stimulating factor (GM-CSF) is a growth factor produced by normal pulmonary alveolar epithelial cells that is critically involved in maintenance of normal AM function. We now report that sublethal hyperoxia in vivo leads to greatly reduced alveolar epithelial cell GM-CSF expression. Systemic treatment of mice with recombinant murine GM-CSF during hyperoxia exposure preserved AM function, as indicated by cell surface Toll-like receptor 4 expression and by inflammatory cytokine secretion following stimulation with LPS ex vivo. Treatment of hyperoxic mice with GM-CSF significantly reduced lung bacterial burden following intratracheal inoculation with K. pneumoniae, returning lung bacterial colony-forming units to the level of normoxic controls. These data point to a critical role for continuous GM-CSF activity in the lung in maintenance of normal AM function and demonstrate that lung injury due to hyperoxic stress results in significant impairment in pulmonary innate immunity through suppression of alveolar epithelial cell GM-CSF expression.

The Journal of Immunology

“…Because it is known that monocytes of sepsis patients often show a desensitized phenotype (6,20), we elucidated the underlying mechanism. An attenuated respiratory burst in monocytes/macrophages has been described in response to IL-4, causing LPS-receptor (CD14) and TLR-4 downregulation (24).…”

Section: Discussionmentioning

confidence: 99%

“…Because it is known that monocytes of sepsis patients often show a desensitized phenotype (6,20), we elucidated the molecular mechanisms attenuating the oxidative burst in septic monocytes. We took into consideration that PMA activates the NADPH oxidase by phosphorylating p47 phagocyte oxidase, consequently causing its translocation to the phagosome, and in turn allowing the assembly of the functional O 2 .…”

Section: Desensitized Monocytes/macrophages Derived From Septic Patientsmentioning

confidence: 99%

Activation-Induced Depletion of Protein Kinase Cα Provokes Desensitization of Monocytes/Macrophages in Sepsis

Knethen

Tautenhahn

Lindemann

et al. 2005

Sepsis accounts for the majority of fatal casualties in critically ill patients, because extensive research failed to significantly improve appropriate therapy strategies. Thus, understanding molecular mechanisms initiating the septic phenotype is important. Symptoms of septic disease are often associated with monocyte/macrophage desensitization. In this study, we provide evidence that a desensitized cellular phenotype is characterized by an attenuated oxidative burst. Inhibition of the oxidative burst and depletion of protein kinase Cα (PKCα) were correlated in septic patients. To prove that PKCα down-regulation indeed attenuated the oxidative burst, we set up a cell culture model to mimic desensitized monocytes/macrophages. We show that LPS/IFN-γ-treatment of RAW264.7 and U937 cells lowered PKCα expression and went on to confirm these data in primary human monocyte-derived macrophages. To establish a role of PKCα in cellular desensitization, we overexpressed PKCα in RAW264.7 and U937 cells and tested for phorbolester-elicited superoxide formation following LPS/IFN-γ-pretreatment. Inhibition of the oxidative burst, i.e., cellular desensitization, was clearly reversed in cells overexpressing PKCα, pointing to PKCα as the major transmitter in eliciting the oxidative burst in monocytes/macrophages. However, PKCα inactivation by transfecting a catalytically inactive PKCα mutant attenuated superoxide formation. We suggest that depletion of PKCα in monocytes from septic patients contributes to cellular desensitization, giving rise to clinical symptoms of sepsis.