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Pathogen-Induced Apoptotic Neutrophils Express Heat Shock Proteins and Elicit Activation of Human Macrophages
Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology . Linköping University, Faculty of Health Sciences.
Department of Biochemistry, College of Life Sciences, Sun Yatsen (Zhongshan) University, Guangzhou, China.
Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology . Linköping University, Faculty of Health Sciences.
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2004 (English)In: Journal of immunology, ISSN 0022-1767 (print) 1550-6606 (online), Vol. 173, no 10, 6319-6326 p.Article in journal (Refereed) Published
Abstract [en]

Ingestion of aged or irradiated apoptotic neutrophils actively suppresses stimulation of macrophages (MΦ). Many bacterial pathogens can also provoke apoptosis in neutrophils, but little is known about how such apoptotic cells influence MΦ activation. We found that neutrophils undergoing apoptosis induced by UV irradiation, Escherichia coli, or Staphylococcus aureus could either stimulate or inhibit MΦ activation. In contrast to MΦ that had ingested irradiated apoptotic neutrophils, MΦ that had phagocytosed bacteria-induced apoptotic neutrophils exhibited markedly increased production of the proinflammatory cytokine TNF-α, but not the anti-inflammatory cytokine TGF-β. Moreover, ingestion of bacteria, but not UV-induced apoptotic neutrophils, caused increased expression of FcγRI on MΦ, and this effect was not provoked directly by bacteria associated with the apoptotic neutrophils. Instead, we found that a link between pathogen-induced apoptotic neutrophils and up-regulation of the heat shock proteins HSP60 and HSP70, and we also observed that recombinant HSP60 and HSP70 potentiated LPS-stimulated production of TNF-α in MΦ. The opposing macrophage responses to neutrophils undergoing apoptosis induced in different ways may represent a novel mechanism that regulates the extent of the immune response to invading microbes in two steps: first by aiding the functions of MΦ at an early stage of infection, and subsequently by deactivating those cells through removal of uninfected apoptotic neutrophils. HSP induction in neutrophils may provide the danger signals required to generate a more effective macrophage response.

Place, publisher, year, edition, pages
2004. Vol. 173, no 10, 6319-6326 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-14006OAI: diva2:22442
Available from: 2006-09-27 Created: 2006-09-27 Last updated: 2009-06-09
In thesis
1. Microbe-induced apoptosis in phagocytic cells and its role in innate immunity
Open this publication in new window or tab >>Microbe-induced apoptosis in phagocytic cells and its role in innate immunity
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Apoptosis, or programmed cell death, is a controlled process by which aged or damages cells are eliminated in multicellular organisms. Neutrophils, short-lived phagocytes of the innate immune system, are highly equipped effectors that can sense, locate, ingest and kill bacterial pathogens. Inflammatory mediators and the presence of bacterial products at the foci of infection regulate the function and life span of these cells. Modulation of neutrophil apoptosis and the subsequent clearance by scavenger cells, such as macrophages, is part of a balanced inflammatory process leading to resolution of inflammation. Many pathogens are capable of modulating host cell apoptosis, and thereby influence the progression of disease. Hence, this thesis was aiming at elucidating mechanisms involved in pathogen- and host-modulated apoptosis and its contribution to the inflammatory process.

We found that different routes of bacterial entry, i.e. through invasion or by receptor-mediated phagocytosis, triggered different signaling pathways within phagocytes. Invasion of virulent Salmonella caused apoptosis, a process requiring activation of the Rho GTPases Rac1 and Cdc42. On the other hand, phagocytosis of the non-invasive Salmonella inhibited apoptosis despite similar intracellular survival as the invasive bacteria. Protection against phagocytosis-induced apoptosis was regulated by tyrosine- and PI3-kinase-dependent activation of AKT (also called PKB for protein kinase B). Furthermore, inhibiting the intraphagosomal production of reactive oxygen species (ROS) in neutrophils during phagocytosis of E. coli decreased apoptosis below spontaneous apoptosis, further indicating that both pro- and anti-apoptotic pathways are triggered by receptor-mediated phagocytosis.

Type 1 fimbria-expressing E. coli adhering to neutrophils resisted ingestion, and induced a ROS-dependent apoptosis by a cooperative effect of the FimH adhesin and LPS. To explore how compartmentalization of ROS during neutrophil activation was involved in modulating apoptosis, we evaluated the stability of lysosomes. In contrast to phagocytosis of E. coli, the adhesive strain induced intracellular non-phagosomal ROS production which triggered early permeabilization and release of lysosomal enzymes to the cytosol. Cathepsin B and/or L were responsible for targeting of the pro-apoptotic Bcl-2 protein Bid, thereby inducing mitochondrial damage, and apoptosis. These data propose a novel pathway for ROS-induced apoptosis in human neutrophils, where the location of the ROS rather than production per se is important.

Moreover, we found that pathogen-induced apoptotic neutrophils, in contrast to uninfected apoptotic neutrophils, activated blood-monocyte derived macrophages to increase their FcγRI surface expression and to produce large quantities of the pro-inflammatory cytokine TNF-α. This demonstrates that during the early phase of infection, pathogen-induced neutrophil apoptosis will help local macrophages to gain control over the microbes. Furthermore, we suggest that heat shock protein 60 and 70 represent a stress signal that enables macrophages to distinguish between, and react differently to, uninfected and inflammatory apoptotic neutrophils.

Place, publisher, year, edition, pages
Institutionen för molekylär och klinisk medicin, 2006
Linköping University Medical Dissertations, ISSN 0345-0082 ; 956
apoptosis, cell death, inflammation, innate immunity, microbiology, neutrophil, macrophage, phagocyte
National Category
Microbiology in the medical area
urn:nbn:se:liu:diva-7445 (URN)91-85523-11-9 (ISBN)
Public defence
2006-09-28, Linden, Campus US, Linköpings Universitet, Linköping, 13:00 (English)
Available from: 2006-09-27 Created: 2006-09-27

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