Piñeros YSS, et al. - Researchers evaluated possible intracellular antiviral activity by eosinophils, based on initial murine investigations. They labeled respiratory syncytial virus and influenza virus with a fluorescent lipophilic dye so they could follow eosinophil-virus interaction. Both viruses quickly adhered to human eosinophils and were internalized and inactivated (95% in ≤ 2 hours), echoed by a lower replication in epithelial cells. With increasing severity of asthma, a reduction of up to 75% was evident in the capacity of eosinophils to capture virus. In vitro and in vivo, activation of eosinophils by virus was evident; in vivo, this was found to be associated with virus-induced loss of asthma control. This previously unrecognized and potentially reduced antiviral property provides a new perception to eosinophils in asthma. An imbalance between protective and cytotoxic properties by eosinophils is suggested by this, which could underlie asthma exacerbations.