The bat-CoV RaTG13 (red), bat-like CoV Rs3367 (green) and SARS-CoV-2 (blue) ORF8 homologues, superposed on the SARS-CoV-2 ORF8 template (7JTL yellow). Only Cα atoms are shown for clarity d) Superposition of CoV ORF8 homology models. c) Individual monomers from 7MX9 (black), 7JTL (cyan), and 7JX6 (magenta) are superposed, and loop regions between β2-β3, β3-β4, β4-β5, and β7-β8 are indicated with dotted circles. Surface representations highlight the closed shape of 7MX9 relative to 7JTL. Chain A (transparent) of 7JTL and 7MX9 were aligned to show the change in the relative orientation of chain B within the dimer. b) Superposition of the ORF8 structure determined here (gray), and the previously deposited structure 7JTL (cyan). Intra- and inter-molecular disulfide bridges are shown as sticks, and regions with missing electron density (residues 63-77) are shown as dashed lines. The sequence recognized by α-ORF8 antibodies (residues 41-90) (83) is highlighted in red and indicated. a) Crystal structure of the SARS-CoV-2 ORF8 dimer. Lastly, the team performed a custom-made enzyme-linked immunosorbent assay (ELISA) to detect ORF8 antibodies in the convalescent plasma of COVID-19 patients.Ĭrystal structure of SARS-CoV-2 ORF8 and related CoV homologues. They investigated the capacity of neutralizing antibodies in patient sera to neutralize the ORF8-induced effect. The team performed ribonucleic acid (RNA) sequencing to further characterize the pro-inflammatory response of the ORF8 treated DCs. They also analyzed the cytokine and chemokine fingerprints of DCs exposed to ORF8 during the DC differentiation process.
For multiplex analysis of cytokines, the researchers collected supernatant from differentiated DCs of several donors in the presence or absence of ORF8 protein. They escalated the dose of ORF8 protein to investigate the upregulation of the DC maturation markers, the cluster of differentiation 40 (CD40), and CD80.įurther, the team used immune precipitation (IP) to investigate ORF8 interaction with the DC marker, DC-SIGN. To this end, the team differentiated monocytes to moDCs with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) in the presence or absence of ORF8 in different concentrations. They aimed to define the function of ORF8 as an immune modulator and virulence factor and analyzed if ORF8 could influence the differentiation process of DCs.įurther, they investigated whether ORF8 directly triggered the differentiation of monocytes to DCs. They isolated purified ORF8 from HEK293 cells transfected with the ORF8 plasmid. In the present study, researchers aimed to study the DCs-ORF8 interaction and its contribution to the cytokine storm observed in COVID-19 patients. However, studies demonstrating function and interactions between DCs and ORF8 are sparse. Studies have shown its value as an early diagnostic marker of SARS-CoV-2 infection. SARS-CoV-2 ORF8 gene is different from the ORF8 gene of SARS-CoV and Middle Eastern respiratory syndrome coronavirus (MERS-CoV). Notably, the cytokine storm drives the severity and magnitude of acute respiratory distress syndrome (ARDS), the most common cause of death in COVID-19 patients. The DCs activate T and B cells to suppress disease progression, failure of which could lead to a second innate immune response characterized by the quick onset of widespread inflammation, often referred to as the cytokine storm. The DCs are antigen-presenting cells of the host’s innate immune system that infiltrate the human lungs after a pathogenic infection and differentiate into monocyte-derived DCs (moDCs) to help clear viral infections, including coronavirus disease 2019 (COVID-19). Study: The unique ORF8 protein from SARS-CoV-2 binds to human dendritic cells and induces a hyper-inflammatory cytokine storm. In a recent study posted to the bioRxiv* pre-print server, researchers examined how the interaction of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) open reading frame 8 (ORF8) protein with host dendritic cells (DCs) induced cytokine storm. By Neha Mathur Reviewed by Danielle Ellis, B.Sc.
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