# Regnase-1-mediated regulation of neutrophils modulates SARS-CoV-2 pneumonia

## TL;DR

Reduced Regnase-1 in neutrophils improves resistance to SARS-CoV-2 infection by dampening harmful immune responses.

## Contribution

Regnase-1 is identified as a novel regulator of neutrophil function and antiviral immunity during SARS-CoV-2 infection.

## Key findings

- Reduced Regnase-1 expression in neutrophils enhances resistance to SARS-CoV-2 MA10 infection.
- Regnase-1 suppresses Tsc22d3, a negative regulator of interferon signaling, contributing to immune dysregulation.
- A specific neutrophil subset with interferon-stimulated gene signatures is decreased in Regnase-1+/– mice.

## Abstract

The innate immune response to viral infection needs to be tightly regulated to ensure effective pathogen clearance while avoiding excessive immune activation. During SARS-CoV-2 infection, however, the immune system often fails to elicit appropriate responses, resulting in cytokine-release syndrome in patients with COVID-19. In this study, we show that reduced expression of Regnase-1, an RNase that negatively regulates immune cell activation, confers resistance to infection with the mouse-adapted SARS-CoV-2 MA10 strain. In Regnase-1+/– mice, altered neutrophil function contributed to the amelioration of MA10-induced pneumonia. Single-cell RNA sequencing of lung tissue during MA10 infection revealed four distinct neutrophil subsets, and among these, a subset characterized by an interferon-stimulated gene (ISG) signature was decreased in Regnase-1+/– mice. Furthermore, Regnase-1+/– neutrophils exhibited reduced ISG expression without corresponding changes in proinflammatory gene expression. Regnase-1 was found to repress the expression of Tsc22d3, a gene involved in the negative regulation of interferon responses, through its 3′ untranslated region. Collectively, these findings suggest that Regnase-1 attenuates resistance to SARS-CoV-2 MA10 infection by promoting excessive interferon responses in neutrophils.

Significant progress has been made in understanding the pathophysiology of SARS-CoV-2 infection. However, the mechanisms by which innate immune cells are activated to eliminate viruses while restraining hyperinflammation remain unclear. Antiviral innate immune responses are regulated by multiple checkpoints that balance effective inflammatory activity with the prevention of cytokine release syndrome. In this study, we demonstrate that the expression level of Regnase-1, a posttranscriptional regulator of immune cells, determines resistance to infection with the mouse-adapted SARS-CoV-2 MA10 strain. Reduced Regnase-1 expression in neutrophils significantly enhances resistance to viral infection. A decreased representation of a neutrophil subset characterized by a robust interferon-stimulated gene signature is associated with the attenuation of excessive inflammation. These excessive interferon responses may contribute to increased mortality from a lethal dose of the MA10 strain. Regnase-1 suppresses the expression of Tsc22d3, a negative regulator of IFN signaling. This implicates Regnase-1 in the dysregulation of immune reactions during infection. Our findings identify Regnase-1 as a novel regulator of neutrophil function and antiviral immunity, which modulates disease severity and pulmonary inflammation.