J Korean Med Sci.  2020 Sep;35(38):e343. 10.3346/jkms.2020.35.e343.

COVID-19 Patients Upregulate Toll-like Receptor 4-mediated Inflammatory Signaling That Mimics Bacterial Sepsis

  • 1Division of Infectious Diseases, Department of Internal Medicine, Chungnam National University School of Medicine, Daejeon, Korea
  • 2School of Biological Sciences and Technology, Chonnam National University, Gwangju, Korea
  • 3Department of Microbiology, Chungnam National University School of Medicine, Daejeon, Korea
  • 4Infection Control Convergence Research Center, Chungnam National University School of Medicine, Daejeon, Korea
  • 5Division of Pulmonary and Critical Care, Department of Internal Medicine, Chungnam National University School of Medicine, Daejeon, Korea


Observational studies of the ongoing coronavirus disease 2019 (COVID-19) outbreak suggest that a ‘cytokine storm’ is involved in the pathogenesis of severe illness. However, the molecular mechanisms underlying the altered pathological inflammation in COVID-19 are largely unknown. We report here that toll-like receptor (TLR) 4-mediated inflammatory signaling molecules are upregulated in peripheral blood mononuclear cells (PBMCs) from COVID-19 patients, compared with healthy controls (HC).
A total of 48 subjects including 28 COVID-19 patients (8 severe/critical vs. 20 mild/ moderate cases) admitted to Chungnam National University Hospital, and age/sex-matched 20 HC were enrolled in this study. PBMCs from the subjects were processed for nCounter Human Immunology gene expression assay to analyze the immune related transcriptome profiles. Recombinant proteins of severe acute respiratory syndrome coronavirus-2 (SARSCoV-2) were used to stimulate the PBMCs and monocyte-derived macrophages, and real-time polymerase chain reaction was performed to quantify the mRNA expressions of the proinflammatory cytokines/chemokines.
Among the most highly increased inflammatory mediators in severe/critically ill patients, S100A9, an alarmin and TLR4 ligand, was found as a noteworthy biomarker, because it inversely correlated with the serum albumin levels. We also observed that recombinant S2 and nucleocapsid proteins of SARS-CoV2 significantly increased proinflammatory cytokines/chemokines and S100A9 in human primary PBMCs.
These data support a link between TLR4 signaling and pathological inflammation during COVID-19 and contribute to develop therapeutic approaches through targeting TLR4-mediated inflammation.


SARS-CoV-2; Inflammation; Cytokines; S100A9
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