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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Research Article Inflammation Pulmonology

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 4

Analysis of bDNA associated with RBCs.

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Analysis of bDNA associated with RBCs. (A) RBCs were incubated with Legi...
(A) RBCs were incubated with Legionella sp. followed by 16S rRNA gene amplicon sequencing on the RBCs. RBC-associated DNA was dominated by Legionella-classified amplicons (97.5%). (B) RBC-associated bDNA was quantified by qPCR of the 16S rRNA gene. Human RBCs had a greater quantity of bDNA than did negative control specimens, and RBCs from patients with sepsis had more bDNA than did RBCs from healthy volunteers. n = 27 healthy donors and n = 64 patients with sepsis. (C) RBC-associated bDNA contained a greater diversity of bacterial taxa than did negative control specimens. Negative control specimens included ddH2O, AE buffer, AE buffer run through DNA isolation columns, and DNA-free water. (D) Bacterial taxa detected in RBCs (both in health and sepsis) were distinct from those of negative control specimens and distinct from each other. (E) Abundance rank analysis demonstrated the influence of some contaminant taxa on RBC taxa (e.g., Comamonadaceae) as well as distinct taxa within RBC specimens not detected in negative control specimens. (F) Direct comparison of prominent bacterial families across negative controls and RBC from healthy individuals and patients with sepsis. (G) Among patients with sepsis, the acute inflammatory cytokine IL-6 was positively correlated with RBC-bound bDNA diversity. Unadjusted association of plasma IL-6 with community richness, the Shannon index, and community dominance are shown. When adjusted for the Acute Physiology and Chronic Health Evaluation (APACHE) score and vasopressor use, the association remained significant. Adjusted for the APACHE score: P = 0.039, P = 0.012, and P = 0.024 for richness, the Shannon index, and community dominance, respectively. Adjusted for vasopressor use: P = 0.04, P = 0.006, and P = 0.013 for richness, the Shannon index, and community dominance, respectively. n = 20 healthy controls; n = 51 patients with sepsis (C–G).