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Updated: Dec 6, 2025
Quantification of Monocyte Chemotactic Activity In Vivo and Characterization of Blood Monocyte Derived Macrophages
Published on: August 12, 2019
Monocyte exocytosis of mitochondrial danger-associated molecular patterns in sepsis suppresses neutrophil chemotaxis
Barbora Konecna1, Jinbong Park, Woon-Yong Kwon
1From the Institute of Molecular Biomedicine (B.K., B.V.), Comenius University, Bratislava, Slovakia; Department of Surgery (J.P., W.H., H.I.K., M.B.Y., L.E.O., K.I., C.J.H.), Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachussets; Department of Emergency Medicine (W-.Y.K.), Seoul National University College of Medicine Seoul, Korea; College of Nursing (Q.Z.), Harbin Medical School, Daqing, China; and Departments of Biology and Biological Engineering (M.B.Y.), Massachusetts Institute of Technology, Boston, Massachussets.
Background:
Trauma and sepsis both increase the risk for secondary infections. Injury mobilizes mitochondrial (MT) danger-associated molecular patterns (mtDAMPs) directly from cellular necrosis. It is unknown, however, whether sepsis can cause active MT release and whether mtDAMPs released by sepsis might affect innate immunity.
Methods:
Mitochondrial release from human monocytes (Mo) was studied after LPS stimulation using electron microscopy and using fluorescent video-microscopy of adherent Mo using Mito-Tracker Green (MTG) dye. Release of MTG+ microparticles was studied using flow cytometry after bacterial stimulation by size exclusion chromatography of supernatants with polymerase chain reaction (PCR) for mitochondrial DNA (mtDNA). Human neutrophil (PMN), chemotaxis, and respiratory burst were studied after PMN incubation with mtDNA.
Results:
LPS caused Mo to release mtDAMPs. Electron microscopy showed microparticles containing MT. mtDNA was present both in microvesicles and exosomes as shown by PCR of the relevant size exclusion chromatography bands. In functional studies, PMN incubation with mtDNA suppressed chemotaxis in a dose-dependent manner, which was reversed by chloroquine, suggesting an endosomal, toll-like receptor-9-dependent mechanism. In contrast, PMN respiratory burst was unaffected by mtDNA.
Conclusion:
In addition to passive release of mtDAMPs by traumatic cellular disruption, inflammatory and infectious stimuli cause active mtDAMP release via microparticles. mtDNA thus released can have effects on PMN that may suppress antimicrobial function. mtDAMP-mediated "feed-forward" mechanisms may modulate immune responses and potentially be generalizable to other forms of inflammation. Where they cause immune dysfunction the effects can be mitigated if the pathways by which the mtDAMPs act are defined. In this case, the endosomal inhibitor chloroquine is benign and well tolerated. Thus, it may warrant study as a prophylactic antiinfective after injury or prior sepsis.
Insights
Sepsis actively releases mitochondrial danger signals that can impair neutrophil antimicrobial function. Chloroquine may mitigate these effects, suggesting a potential prophylactic anti-infective strategy.
Area of Science:
- Immunology
- Cell Biology
- Molecular Medicine
Background:
- Trauma and sepsis elevate secondary infection risk.
- Injury causes passive release of mitochondrial danger-associated molecular patterns (mtDAMPs).
- Sepsis-induced active mtDAMP release and its impact on innate immunity remain unclear.
Purpose of the Study:
- Investigate active mitochondrial release by sepsis.
- Determine if sepsis-derived mtDAMPs affect innate immunity.
- Explore therapeutic interventions for sepsis-induced immune dysfunction.
Main Methods:
- Studied mitochondrial release from human monocytes (Mo) after LPS stimulation using microscopy.
- Analyzed microparticle release and mitochondrial DNA (mtDNA) via flow cytometry and PCR.
- Assessed human neutrophil (PMN) chemotaxis and respiratory burst after mtDNA incubation.
Main Results:
- LPS stimulation induced active mtDAMP release from Mo via microparticles.
- mtDNA was detected in microvesicles and exosomes.
- Neutrophil chemotaxis was suppressed by mtDNA in a dose-dependent manner, reversible by chloroquine.
Conclusions:
- Inflammatory stimuli actively release mtDAMPs via microparticles, beyond passive release from injury.
- Released mtDNA can suppress neutrophil antimicrobial function.
- Chloroquine may mitigate mtDAMP-induced immune dysfunction, warranting study as a prophylactic anti-infective.
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