Pathogen-Induced Apoptotic Neutrophils Express Heat Shock Proteins and Elicit Activation of Human Macrophages

Abstract

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.

MicroRNA-155 Regulates Inflammatory Cytokine Production in Tumor-associated Macrophages via Targeting C/EBPβ

“…Human peripheral blood mononuclear cell (PBMC) were isolated from buffy coats derived from healthy donors by Ficoll density gradient centrifugation as described previously (24). The cells were incubated in DMEM alone at 4 × 10 6 /well in 24-well plates for 1.5 h, then washed and cultured in DMEM containing 10% human AB serum for 16 h to remove residual lymphocytes.…”

“…The cell lysates were extracted as previously described (24). Equal amounts of cellular proteins were separated by 10% SDS-PAGE, immunoblotted with mouse anti-human C/EBP mAb, and visualized with a commercial ECL kit (Pierce, Rockford, IL).…”

From regulation of dying cell engulfment to development of anti-cancer therapy

“…68 This observation may explain how macrophages balance pro-and anti-inflammatory responses in an in vivo situation where apoptotic cells are associated with inflammation and infection. 75 Indeed, macrophages reconcile two opposing responses: avoidance of unnecessary inflammatory responses to dying cells and the need for an appropriate response to pathogens. It is conceivable that macrophages engaging apoptotic cells suppress in a cell autonomous way their own inflammatory responses, but will nevertheless still allow newly recruited macrophages to function independently by responding normally to pathogens or pro-inflammatory stimuli.…”

“…75,79 These discrepancies may be explained by the activation or differentiation state of macrophages (discussed above), the source and activation state of target cells, the type of cell death stimuli, and the presence of TLR ligands resulting in differential recognition mechanisms and immunological consequences. Some bridging molecules, such as surfactant proteins A and D, have a dual function depending on binding orientation and on the receptor system that is triggered.…”

Peritumoral stromal neutrophils are essential for c-Met-elicited metastasis in human hepatocellular carcinoma

“…46 Equal amounts of cellular proteins were separated by 10% SDS-PAGE, immunoblotted with Abs against AKT, p38, JNK, Erk1/ 2, phospho-AKT, phospho-p38, phospho-JNK, phospho-Erk1/ 2, phospho-IkB (Cell signaling Technology), and Actin (Boster), and then visualized with an ECL kit (Thermo Fisher Scientific).…”