Red blood cells capture and deliver bacterial DNA to drive host responses during polymicrobial sepsis
L.K. Metthew Lam, … , Robert P. Dickson, Nilam S. Mangalmurti
L.K. Metthew Lam, … , Robert P. Dickson, Nilam S. Mangalmurti
Published December 12, 2024
Citation Information: J Clin Invest. 2025;135(4):e182127. https://doi.org/10.1172/JCI182127.
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Red blood cells capture and deliver bacterial DNA to drive host responses during polymicrobial sepsis

Abstract

Red blood cells (RBCs), traditionally recognized for their role in transporting oxygen, play a pivotal role in the body’s immune response by expressing TLR9 and scavenging excess host cell-free DNA. DNA capture by RBCs leads to accelerated RBC clearance and triggers inflammation. Whether RBCs can also acquire microbial DNA during infections is unknown. Murine RBCs acquire microbial DNA in vitro, and bacterial DNA–induced (bDNA-induced) macrophage activation was augmented by WT, but not Tlr9-deleted, RBCs. In a mouse model of polymicrobial sepsis, RBC-bound bDNA was elevated in WT mice but not in erythroid Tlr9–deleted mice. Plasma cytokine analysis in these mice revealed distinct sepsis clusters characterized by persistent hypothermia and hyperinflammation in the most severely affected mice. RBC Tlr9 deletion attenuated plasma and tissue IL-6 production in the most severely affected group. Parallel findings in humans confirmed that RBCs from patients with sepsis harbored more bDNA than did RBCs from healthy individuals. Further analysis through 16S sequencing of RBC-bound DNA illustrated distinct microbial communities, with RBC-bound DNA composition correlating with plasma IL-6 in patients with sepsis. Collectively, these findings unveil RBCs as overlooked reservoirs and couriers of microbial DNA, capable of influencing host inflammatory responses in sepsis.

Authors

L.K. Metthew Lam, Nathan J. Klingensmith, Layal Sayegh, Emily Oatman, Joshua S. Jose, Christopher V. Cosgriff, Kaitlyn A. Eckart, John McGinniss, Piyush Ranjan, Matthew Lanza, Nadir Yehya, Nuala J. Meyer, Robert P. Dickson, Nilam S. Mangalmurti

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Figure 1

RBCs from WT but not Erytlr9–/– mice acquire microbial DNA and demonstrate morphologic changes during sepsis.

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RBCs from WT but not Erytlr9–/– mice acquire microbial DNA and demonstra...
Erytlr9–/– mice and their WT littermates were injected with CS or D5W and monitored for 24 hours. (A) Weight change and differences between groups were analyzed by 1-way ANOVA with Šidák’s multiple-comparison test. ****P < 0.0001 for WT D5W versus WT CS and Erytlr9–/– D5W versus Erytlr9–/– CS, WT CS versus Erytlr9–/– CS = NS. n = 20–30 mice per group. (B) For temperature profiles of injected mice, 88°F was the lower limit of detection. ANOVA with Šidák’s multiple-comparison analysis, ***P = 0.002 between CS-injected groups at 2 hours, **P = 0.005 between Erytlr9–/– D5W and Erytlr9–/– CS. n = 9–20 mice per group. (C) Hypothermic state of the mice by strain at 24 hours. P = 0.035, by χ2 test. (D) Kaplan-Meier survival with log-rank comparison. P = 0.031 between all groups; P = 0.08 for WT CS-injected versus Erytlr9–/– CS-injected mice. (E) RBC-associated 16S rRNA gene expression on murine RBCs was quantified 6 hours following CS-induced sepsis. One-way Kruskal-Wallis test with Dunn’s multiple-comparison test. n = 3–11. *P = 0.042 WT D5W versus WT CS; *P = 0.044 WT CS versus Erytlr9–/– CS. (F) RBCs from WT or Erytlr9–/– mice 24 hours after D5W or CS injection. Inset shows echinocytic RBCs observed in the WT CS-injected mice. Original magnification, ×40. (G) RBC score (number of echinocytes and altered RBCs/high-power field [hpf]). *P = 0.013, WT D5W versus WT CS. n = 8–14 from 3 independent studies. (H) Cell-free hemoglobin 24 hours after CS injection. Differences between groups were measured using 1-way ANOVA with Šidák’s multiple-comparison test. *P = 0.044 for WT CS versus Erytlr9–/– CS; P = NS for all other comparisons.