Late Breaking Abstract - SARS-CoV-2 induces hyperinflammation in human macrophages via TLR4

Background: Exaggerated inflammation significantly contributes to pulmonary failure and death in COVID-19. Objective: To study the role of Toll-like receptors 3 (TLR3), TLR4 and TLR7/9 in human macrophages infected with SARS-CoV-2. Methods: THP-1 derived human macrophages were challenged with the Spike protein ectodomain (SARS-CoV-2-ECD), or infected with viable SARS-CoV-2, including wildtype (WT), as well as B.1.1.7, B.1351 and B.1.1.7-E484K variants. Inhibitors of SARS-CoV-2 entry and of specific TLR signaling cascades were used to delineate the inflammatory circuits. Results: Human macrophages showed a marked time- and concentration-dependent inflammatory response when exposed to SARS-CoV-2-ECD, or to viable SARS-CoV-2 WT. TLR4-specific inhibition with TAK-242 suppressed the expression of inflammatory TLR4-NF-κB dependent cytokines >50%, whereas inhibition of TLR3 and TLR7/9 pathways did not lead to an attenuated response. Importantly, inhibition of TLR4 suppressed the exaggerated inflammatory response also in human macrophages infected with variants of concern B.1.1.7, B.1.351 and B.1.1.7-E484K (Fig. A-D). Conclusion: SARS-CoV-2 induces a hyperinflammatory response in human macrophages through Spike protein-dependent activation of TLR4. TLR4 constitutes a novel important target to counteract COVID-19 associated morbidity and death. erj;58/suppl_65/OA4110/F1 F1 F1