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Exposure to bacteria or viruses can change innate immune cells in a way that impacts future immune responses. This exposure results in epigenetic rewiring that either enhances or weakens immune responses to a secondary challenge. One primary mechanism of innate immune cell function is through toll-like receptors (TLRs) that sense a variety of bacterial and viral molecules and cause immune activation. SARS-CoV-2 Envelope protein (E protein) is critical for viral assembly and has been shown to mediate innate immune activation, through engagement of TLR2. Due to its ability to induce inflammation, E protein could play a role in inflammatory disease pathology seen during severe COVID-19. In this study, we determined the secretome of chemokines, cytokines and growth factors from monocytes in response to E protein stimulation and compared this response with other viral antigens and TLR agonists. Next, to investigate if E protein stimulation would modify response to secondary challenge, we performed a primary stimulation of monocytes with E protein followed by secondary stimulation with lipopolysaccharide (LPS) on monocyte-derived macrophages (MDM) 1 week later. Reduced expression of CCL3, CCL4, CCL5, CXCL10 TNF-A, and IL-12 upon secondary LPS or autologous E protein stimulation were statistically reflecting a more tolerant MDM state that is imprinted after E protein exposure. Finally, we demonstrated that immunizing neonatal mice with SARS-CoV-2 E protein induced proinflammatory cytokine secretion and lung tissue inflammation pathology and demonstrated a long-term impact on immune cell function and secondary response to LPS. Thus, SARS-CoV-2 E protein induces macrophage proinflammatory networks that lead to tissue inflammation, but also induce a more tolerant state after return to a resting state that could impact the ability to respond to secondary infection. Further understanding of the molecular pathways that drive this immune activation and tolerance could identify treatment targets to restore immunity after SARS-CoV-2 infection.
Pierce, Stephen; McLennan, Rebecca; Khanal, Santosh; Menden, Heather; Sampath, Venkatesh; and Bradley, Todd, "SARS-CoV-2 Envelope Protein Tolerizes Macrophage Response to Secondary Inflammatory Stimuli" (2023). Research at Children's Mercy Month 2023. 5.