Tuft Cells Modulate Macrophage Response Following Lung Viral Infection

ABSTRACT The hyperinflammatory response is a major cause of disease severity and death in patients infected by influenza or SARS- CoV-2. In severe cases dysregulated macrophage responses contribute to the progression of acute respiratory distress syndrome (ARDS). Nevertheless, how macrophages are activated remains largely unknown, especially in COVID-19 lungs. Intriguingly, we and others found that the immune sensing tuft cells are ectopically present in the alveolar region (parenchyma) following infection by H1N1 (PR8) virus with unclarified functions. Our preliminary data show that these tuft cells are derived from ectopic basal cells (also known as pod cells) in the parenchyma. More importantly, tuft cell reduction and ablation result in reduced macrophage accumulation, improved survival rate and better recovery, accompanied by the decreased level of Il-25. Pharmacological inhibition of Notch signaling reduces the numbers of ectopic tuft cells in PR8-infected lungs. These findings lead to the hypothesis that tuft cells enhance macrophage accumulation through Il-25 and that reducing tuft cell derivation through Notch inhibition attenuates excessive macrophage responses and improves lung function. We formulate two specific aims to further test the hypothesis. Aim1: To determine whether tuft cells modulate macrophage responses through Il-25 upon infection with influenza or SARS-CoV-2. We will also use a novel R26hACE2 mouse line to build the first targeted SARS-CoV-2 infection model. Aim 2: To test the hypothesis that Notch inhibition reduces tuft cell derivation from pod cells and attenuates macrophage responses in virus-infected lungs. In this aim, we will delete Rbpjk in pod cells and use a novel Notch decoy to inhibit Notch signaling. Together this project will provide the first mechanistic insights into the role played by tuft cells in driving dysregulated macrophage responses in virus-infected lungs. It will also offer new approaches to reduce tuft cell differentiation and attenuate hyperinflammation.