Neutrophils in viral infections: Current concepts and caveats

Neutrophils are the first immune cell population recruited to sites of infection, including viral infections, and exhibit both protective and pathologic functions. In antibacterial and antifungal immunity, the role of neutrophils is well defined. However, in antiviral immunity, much less is known. Conventional wisdom suggests that neutrophils enhance antiviral defenses, yet evidence for that is limited. Interaction with other immune cell populations, virus internalization and killing, the release of cytokines, chemokines, and antimicrobial components are all mechanisms by which neutrophils can contribute to pathogen clearance. NET formation, extensively studied during bacterial infection, can further mediate antiviral defense by trapping and inactivating virus. In the present review, we discuss the current understanding of the complex role of neutrophil immunity in viral infections and disease pathogenesis and the potential mechanisms identified to date. We pinpoint the importance of a finely tuned neutrophilic response for achieving effective immune protection while avoiding detrimental tissue damage that can form the basis for the development of novel therapeutics.