Neutrophils in respiratory syncytial virus infection: more trouble than they’re worth?
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Lower respiratory tract infections by respiratory syncytial virus (RSV) impose a large burden of disease on infants, the immunocompromised, and the elderly. In RSV infection-induced bronchiolitis, the lungs are flooded with neutrophils. Whether neutrophils contribute to the control of viral replication in RSV infection, or only exacerbate immunopathology, remains an open question. Traditionally, neutrophils were only thought to contribute to the elimination of extracellular bacteria and fungi. However, the classical view of neutrophils as unsophisticated microbe killers is obsolete. Neutrophils are increasingly recognised as important contributors to innate and adaptive immunity with a plethora of regulatory functions. Neutrophils stimulate, polarise, as well as suppress T cell responses, promote antibody production, support NK cell homeostasis, and contribute to the resolution of inflammation. Neutrophil extracellular traps (NETs) are imbued not only with antibacterial and antifungal, but also with antiviral activity. Even the classical neutrophil effector mechanisms, i.e. phagocytosis and degranulation, can be brought to bear against viral infection. Moreover, neutrophils are well equipped to detect viruses. Thus, striking new roles for neutrophils in immunity have emerged. This review examines the recent literature on the possible contributions of neutrophils to antiviral defence, in particular against RSV.