Extracellular Vesicles Released by Picornavirus-Infected Cells Modify Antiviral Immune Cell Responses.

Naked viruses of the family Picornaviridae commonly spread via lysis of infected cells. Recent studies indicate that, prior to cell lysis, naked viruses are packaged and released inside extracellular vesicles (EVs). This has been considered a pro-viral mechanism because EV membranes protect enclosed virions from neutralizing antibodies. Here, we explored whether immune cells can respond to picornavirus-induced EVs. Using two different picornaviruses, we demonstrate that EVs from virus-infected cells stimulate human immune cells to produce the antiviral cytokine type I IFN and chemotactic cytokine IP-10. Virus-containing EVs trigger higher cytokine levels than similar amounts of naked virus. Monocytes are the predominant cell type to interact with and respond to virus-induced EVs. By blocking virion-receptor interactions we demonstrate that both EV-enclosed virions and additional host/virus components in EVs aid in immune cell stimulation. This EV-induced response may provide protection prior to lytic virus release and development of the humoral immune response. We further demonstrate that EV-enclosed viruses, in contrast to naked virus, cannot be opsonized by neutralizing antibodies. This prevents enhanced uptake of EV-enclosed virus and ensuing pro-inflammatory cytokine production by immune cells needed for viral clearance. This work underscores the role of virus-induced EVs in host antiviral responses to picornavirus infections.