Comparative ultrastructural characterization of African horse sickness virus-infected mammalian and insect cells reveals a novel potential virus release mechanism from insect cells

摘要

African horse sickness virus (AHSV) is an arbovirus capable of successfully replicating in both itsmammalian host and insect vector. Where mammalian cells show a severe cytopathic effect (CPE)following AHSV infection, insect cells display no CPE. These differences in cell death could belinked to the method of viral release, i.e. lytic or non-lytic, that predominates in a specific cell type.Active release of AHSV, or any related orbivirus, has, however, not yet been documented from insectcells. We applied an integrated microscopy approach to compare the nanomechanical andmorphological response of mammalian and insect cells to AHSV infection. Atomic force microscopyrevealed plasma membrane destabilization, integrity loss and structural deformation of the entiresurface of infected mammalian cells. Infected insect cells, in contrast, showed no morphologicaldifferences from mock-infected cells other than an increased incidence of circular cavities presenton the cell surface. Transmission electron microscopy imaging identified a novel large vesicle-likecompartment within infected insect cells, not present in mammalian cells, containing viral proteinsand virus particles. Extracellular clusters of aggregated virus particles were visualized adjacent toinfected insect cells with intact plasma membranes. We propose that foreign material isaccumulated within these vesicles and that their subsequent fusion with the cell membrane releasesentrapped viruses, thereby facilitating a non-lytic virus release mechanism different from thebudding previously observed in mammalian cells. This insect cell-specific defence mechanismcontributes to the lack of cell damage observed in AHSV-infected insect cells.