Background. West Nile virus (WNV) is an emerging cause of meningitis and encephalitis in the United States. Although severe neuroinvasive disease and death can occur in rare instances, the majority of infected individuals remain asymptomatic or present with a range of clinical manifestations associated with West Nile fever.
Methods. To better understand the interindividual variability associated with the majority of WNV infections, we evaluated the association of cytokine/chemokine production and outcome of infection among 115 WNV-positive US blood donors identified in 2008–2011. All subjects self-reported symptoms as having occurred during the 2 weeks following blood donation, using a standardized questionnaire.
Results. We discovered that, prior to seroconversion, an early potent, largely type I interferon–mediated response correlated with development of a greater number of symptoms in WNV-infected individuals. Interestingly, individuals who developed fewer symptoms had not only a more modest type I interferon response initially, but also a protracted cytokine response after seroconversion, marked by the production of monocyte and T-cell–associated chemokines.
Conclusions. Collectively, our data suggest that, although an early type I interferon response appears to be crucial to control WNV infection, successful immunity may require a modest early response that is maintained during the course of infection.