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Crit Care Med. 2009 Jun;37(6):2000-9. doi: 10.1097/CCM.0b013e3181a001ae.

Monocyte activation by necrotic cells is promoted by mitochondrial proteins and formyl peptide receptors.

Author information

1
Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Dorothy M Davis Heart and Lung Research Institute, The Ohio State University Medical Center, Columbus, OH, USA. elliott.crouser@osumc.edu

Abstract

OBJECTIVE:

Necrotic cells evoke potent innate immune responses through unclear mechanisms. The mitochondrial fraction of the cell retains constituents of its bacterial ancestors, including N-formyl peptides, which are potentially immunogenic. Thus, we hypothesized that the mitochondrial fraction of the cell, particularly N-formyl peptides, contributes significantly to the activation of monocytes by necrotic cells.

DESIGN:

Human peripheral blood monocytes were incubated with necrotic cell fractions and mitochondrial proteins to investigate their potential for immune cell activation.

SETTING:

University Medical Center Research Laboratory.

SUBJECTS:

Healthy human adults served as blood donors.

MEASUREMENTS AND MAIN RESULTS:

Human blood monocyte activation was measured after treatment with cytosolic, nuclear and mitochondrial fractions of necrotic HepG2 cells or necrotic HepG2 cells depleted of N-formyl peptides [Rho(0) cells]. The specific role of the high affinity formyl peptide receptor (FPR) was then tested using specific pharmacologic inhibitors and RNA silencing. The capacity of mitochondrial N-formyl peptides to activate monocytes was confirmed using a synthetic peptide conforming to the N-terminus of mitochondrial nicotinamide adenine dinucleotide subunit 6. The results demonstrated that mitochondrial cell fractions most potently activated monocytes, and interleukin (IL)-8 was selectively released at low-protein concentrations. Mitochondria from Rho(0) cells induced minimal monocyte IL-8 release, and specific pharmacologic inhibitors and RNA-silencing confirmed that FPR contributes significantly to monocyte IL-8 responses to both necrotic cells and mitochondrial proteins. N-formyl peptides alone did not induce monocyte IL-8 release; whereas, the combination of mitochondrial N-formyl peptides and mitochondrial transcription factor A (TFAM) dramatically increased IL-8 release from monocytes. Likewise, high mobility group box 1, the nuclear homolog of TFAM, did not induce monocyte IL-8 release unless combined with mitochondrial N-formyl peptides.

CONCLUSIONS:

Interactions between mitochondrial N-formyl peptides and FPR in the presence of other mitochondrial antigens (e.g., TFAM) contributes significantly to the activation of monocytes by necrotic cells.

PMID:
19384205
PMCID:
PMC2743203
DOI:
10.1097/CCM.0b013e3181a001ae
[Indexed for MEDLINE]
Free PMC Article

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