Scientists have shown for the first time that exosomes from tick cells can aid transmission of viral proteins and genetic material from arthropod to vertebrate host cells, according to research published on January 4, 2018 in PLOS Pathogens. The open-access article is titled “Exosomes Serve As Novel Modes of Tick-Borne Flavivirus Transmission from Arthropod to Human Cells and Facilitates Dissemination of Viral RNA and Proteins to the Vertebrate Neuronal Cells.” When ticks (Ixodes scapularis species; commonly known as deer ticks) bite humans or other vertebrates, they can transmit dangerous, brain-infecting viruses in the Flaviviridae viral family, such as tick-borne encephalitis virus (TBEV). However, the mechanisms underlying transmission of Flaviviridae from tick to vertebrate host are poorly understood. Previous studies have shown that some other pathogens use exosomes--tiny, membrane-bound spheres released from cells--to facilitate transmission and infection. Dr. Hameeda Sultana of Old Dominion University, Virginia, and colleagues hypothesized that tick-borne Flaviviridae viruses may use similar techniques. To investigate this hypothesis, the researchers infected cells from an Ixodes scapularis-derived cell line (ISE6) with tick-borne Langat virus (LGTV), which is closely related to TBEV but safer for laboratory work. Using cryo-electron microscopy, they showed that infected tick cells indeed produced exosomes, and further investigation showed that these contained LGTV RNA and proteins. Additional experiments using human and vertebrate cell lines revealed more about the role of exosomes in LGTV transmission. LGTV-carrying tick exosomes were able to infect keratinocytes, cells found at the outermost layer of human skin and human blood endothelial cells.
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