Type I IFN regulates neutrophils responses to murine beta-coronavirus infection

Abstract

Introduction: Type I IFNs play a critical role in the immune response to viral infections. Suppressed type I IFN levels are predictive of severe SARS-CoV-2 infections. Given the critical role of neutrophils in viral-mediated lung injury, we investigated how type I IFNs regulated neutrophil responses during pulmonary coronaviral infections.

Methods: IFNAR-/- and C57BL/6 (WT) mice were infected with 2,500PFU of murine beta-coronavirus (MHV-1) and survival determined. At day 3 post infection, cellular recruitment, cytokine profiles and markers of lung injury were evaluated. Neutrophils were evaluated for activation markers, ROS generation and NET formation.

Results: All IFNAR-/- mice succumbed within 5 days versus 100% survival for WT mice. IFNAR-/- mice had higher pulmonary levels of GM-CSF (p=0.0079) and 3-fold more recruited neutrophils (p=0.0159) and monocytes (p=0.016). IFNAR-/- lung neutrophils had significantly lower TLR3, TLR4, TLR7, TLR9, CD88, CXCR2, CD69 (p<0.05 for all) but increased levels of PDL-1. IFNAR-/- neutrophils isolated during infection showed significantly decreased ROS and NETs compared to WT.

Conclusion:IFNAR-/- mice are highly susceptible to MHV-1, displaying elevated neutrophil recruitment with lower frequency of activation markers, reduced ROS and NETs, and increased expression of PDL-1. Our findings demonstrate mechanisms by which inadequate type I IFN levels subvert critical aspects of neutrophil responses during severe viral respiratory infections.