Single-cell analyses reveal SARS-CoV-2 interference with intrinsic immune response in the human gut
Authors: Triana Sergio , Metz Zumaran Camila , Ramirez Carlos , Kee Carmon , Doldan Patricio , Shahraz Mohammed , Schraivogel Daniel , Gschwind Andreas R. , Steinmetz Lars M. , Herrmann Carl , Alexandrov Theodore , Boulant Steeve , Stanifer Megan L. 
Published: October 2020

Objective

Exacerbated pro-inflammatory immune response contributes to COVID-19 pathology. Despite the evidence about SARS-CoV-2 infecting the human gut, little is known about the importance of the enteric phase of SARS-CoV-2 for the viral lifecycle and for the development of COVID-19-associated pathologies. Similarly, it remains unknown whether the innate immune response triggered in this organ to combat viral infection is similar or distinct compared to the one triggered in other organs.

Design

We exploited human ileum- and colon-derived organoids as a non-transformed culture model supporting SARS-CoV-2 infection. We characterized the replication kinetics of SARS-CoV-2 in intestinal epithelial cells and correlated the expression of the viral receptor ACE2 with infection. We performed conventional and targeted single-cell transcriptomics and multiplex single-molecule RNA fluorescence in situ hybridization and used IFN-reporter bioassays to characterize the response of primary human intestinal epithelial cells to SARS-CoV-2 infection.

Results

We identified a subpopulation of enterocytes as the prime target of SARS-CoV-2. We found the lack of positive correlation between susceptibility to infection and the expression of ACE2 and revealed that SARS-CoV-2 downregulates ACE2 expression upon infection. Infected cells activated strong proinflammatory programs and produced interferon, while expression of interferon-stimulated genes was limited to bystander cells due to SARS-CoV-2 suppressing the autocrine action of interferon in infected cells.

Conclusion

Our findings reveal that SARS-CoV-2 curtails the immune response in primary human intestinal epithelial cells to promote its replication and spread and this highlights the gut as a proinflammatory reservoir that should be considered to fully understand SARS-CoV-2 pathogenesis.

Significance of the study

What is already known about this subject?

COVID-19 patients have gastrointestinal symptoms which likely correlates with SARS-CoV-2 infection of the intestinal epithelium

SARS-CoV-2 replicates in human intestinal epithelial cells.

Intestinal organoids are a good model to study SARS-CoV-2 infection of the gastrointestinal tract

There is a limited interferon response in human lung epithelial cells upon SARS-CoV-2 infection.

What are the new findings?

A specific subpopulation of enterocytes are the prime targets of SARS-CoV-2 infection of the human gut.

There is a lack of correlation between ACE2 expression and susceptibility to SARS-CoV-2 infection. SARS-CoV-2 downregulates ACE2 expression upon infection.

Human intestinal epithelium cells produce interferon upon SARS-CoV-2 infection.

Interferon acts in a paracrine manner to induce interferon stimulated genes that control viral infection only in bystander cells.

SARS-CoV-2 actively blocks interferon signaling in infected cells.

How might it impact on clinical practice in the foreseeable future?

The absence of correlation between ACE2 levels and susceptibility suggest that medications influencing ACE2 levels (e.g. high blood pressure drugs) will not make patients more susceptible to SARS-CoV-2 infection.

The restricted cell tropism and the distinct immune response mounted by the GI tract, suggests that specific cellular restriction/replication factors and organ specific intrinsic innate immune pathways can represent unique therapeutic targets to treat COVD-19 patients by considering which organ is most infected/impacted by SARS-CoV-2.

The strong pro-inflammatory signal mounted by the intestinal epithelium can fuel the systemic inflammation observed in COVID-19 patients and is likely participating in the lung specific pathology.