| First Author | Hotz MJ | Year | 2018 |
| Journal | Am J Respir Crit Care Med | Volume | 197 |
| Issue | 4 | Pages | 470-480 |
| PubMed ID | 29053005 | Mgi Jnum | J:331022 |
| Mgi Id | MGI:6869948 | Doi | 10.1164/rccm.201706-1161OC |
| Citation | Hotz MJ, et al. (2018) Red Blood Cells Homeostatically Bind Mitochondrial DNA through TLR9 to Maintain Quiescence and to Prevent Lung Injury. Am J Respir Crit Care Med 197(4):470-480 |
| abstractText | RATIONALE: Potentially hazardous CpG-containing cell-free mitochondrial DNA (cf-mtDNA) is routinely released into the circulation and is associated with morbidity and mortality in critically ill patients. How the body avoids inappropriate innate immune activation by cf-mtDNA remains unknown. Because red blood cells (RBCs) modulate innate immune responses by scavenging chemokines, we hypothesized that RBCs may attenuate CpG-induced lung inflammation through direct scavenging of CpG-containing DNA. OBJECTIVES: To determine the mechanisms of CpG-DNA binding to RBCs and the effects of RBC-mediated DNA scavenging on lung inflammation. METHODS: mtDNA on murine RBCs was measured under basal conditions and after systemic inflammation. mtDNA content on human RBCs from healthy control subjects and trauma patients was measured. Toll-like receptor 9 (TLR9) expression on RBCs and TLR9-dependent binding of CpG-DNA to RBCs were determined. A murine model of RBC transfusion after CpG-DNA-induced lung injury was used to investigate the role of RBC-mediated DNA scavenging in mitigating lung injury in vivo. MEASUREMENTS AND MAIN RESULTS: Under basal conditions, RBCs bind CpG-DNA. The plasma-to-RBC mtDNA ratio is low in naive mice and in healthy volunteers but increases after systemic inflammation, demonstrating that the majority of cf-mtDNA is RBC-bound under homeostatic conditions and that the unbound fraction increases during inflammation. RBCs express TLR9 and bind CpG-DNA through TLR9. Loss of TLR9-dependent RBC-mediated CpG-DNA scavenging increased lung injury in vivo. CONCLUSIONS: RBCs homeostatically bind mtDNA, and RBC-mediated DNA scavenging is essential in mitigating lung injury after CpG-DNA. Our data suggest a role for RBCs in regulating lung inflammation during disease states where cf-mtDNA is elevated, such as sepsis and trauma. |
