SARS-CoV-2–associated ssRNAs activate inflammation and immunity via TLR7/8
Valentina Salvi, … , Silvano Sozzani, Daniela Bosisio
Valentina Salvi, … , Silvano Sozzani, Daniela Bosisio
Published August 6, 2021
Citation Information: JCI Insight. 2021;6(18):e150542. https://doi.org/10.1172/jci.insight.150542.
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Research Article Immunology

SARS-CoV-2–associated ssRNAs activate inflammation and immunity via TLR7/8

Abstract

The inflammatory and IFN pathways of innate immunity play a key role in the resistance and pathogenesis of coronavirus disease 2019 (COVID-19). Innate sensors and SARS-CoV-2–associated molecular patterns (SAMPs) remain to be completely defined. Here, we identified single-stranded RNA (ssRNA) fragments from the SARS-CoV-2 genome as direct activators of endosomal TLR7/8 and MyD88 pathway. The same sequences induced human DC activation in terms of phenotype and function, such as IFN and cytokine production and Th1 polarization. A bioinformatic scan of the viral genome identified several hundreds of fragments potentially activating TLR7/8, suggesting that products of virus endosomal processing potently activate the IFN and inflammatory responses downstream of these receptors. In vivo, SAMPs induced MyD88-dependent lung inflammation characterized by accumulation of proinflammatory and cytotoxic mediators and immune cell infiltration, as well as splenic DC phenotypical maturation. These results identified TLR7/8 as a crucial cellular sensor of ssRNAs encoded by SARS-CoV-2 involved in host resistance and the disease pathogenesis of COVID-19.

Authors

Valentina Salvi, Hoang Oanh Nguyen, Francesca Sozio, Tiziana Schioppa, Carolina Gaudenzi, Mattia Laffranchi, Patrizia Scapini, Mauro Passari, Ilaria Barbazza, Laura Tiberio, Nicola Tamassia, Cecilia Garlanda, Annalisa Del Prete, Marco A. Cassatella, Alberto Mantovani, Silvano Sozzani, Daniela Bosisio

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Figure 2

SAMP-activated DCs trigger T cell proliferation and functional activation.

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SAMP-activated DCs trigger T cell proliferation and functional activatio...
(A) moDCs were stimulated with vehicle (-) or with SCV2-RNA or the A-to-U–replaced SCV2-RNA-A (both at 5 μg/mL) for 24 hours. Activated moDCs were cocultured for 6 days with CFSE-stained allogenic naive CD4+ T cells or CD8+ T cells at the indicated DC/T cell ratio. Alloreactive T cell proliferation was assessed by measuring CellTrace-CFSE dye loss by flow cytometry. Data are expressed as mean ± SEM (n = 3) of the percentage of proliferating T cells. (B) moDCs stimulated as in A were cocultured for 6 days with allogenic naive CD4+ T cells (DC/T cell ratio 1:20). Intracellular IFN-γ and IL-4 were evaluated by FACS analysis. Left, dot plots from 1 representative experiment out of 4 are shown. Right, bar graphs from 4 independent experiments. Data are expressed as mean ± SEM of the percentage of IFN-γ–producing cells. (C) moDCs activated as in A were cocultured for 6 days with allogenic CD8+ T cells (DC/T cell ratio 1:10). IFN-γ production was evaluated by ELISA in cell-free supernatants and intracellular granzyme B (GrB) by FACS analysis. Data are expressed as mean ± SEM (n = 3). (A–C) *P < 0.05 versus (-) by 1-way ANOVA with Dunnett’s post hoc test.