Fig. 4. Possible beneficial and detrimental effects of neutrophils during respiratory viral infections.

Neutrophils infiltrating the lungs during viral infections can aid the ongoing antiviral response by contributing to the production of antiviral cytokines and chemokines, as well as producing antimicrobial peptides. As phagocytes, neutrophils can clear pathogens and debris. These functions can aid in viral control/clearance as well as resolution of inflammation. An excess of activated neutrophils can contribute to lung tissue damage by excessive production of MPO, NE, MMPs, oxidative burst, and NETs, exacerbating disease severity.