Mature virions are attached to filaments inside reovirus inclusion and immunogold labeling of LAMP-1 in uninfected and reovirus-infected HBMECs. (A and B) HBMECs were adsorbed with reovirus T1L M1-P208S at an MOI of 1 PFU/cell and processed at 18 hpi by high-pressure freezing, freeze substitution, ultra-thin sectioning, and TEM. (A) High-magnification view of a VI showing virions and filaments (arrows). The inset on the left shows a mature virion attached to a filament (arrow). The inset on the right shows an empty viral particle with no filaments. (B) The histogram depicts quantification of mature virions and empty viral particles attached to filaments in VIs and SOs as detected by TEM of infected cells. A total of 889 virions and 117 empty capsids in VIs and 332 virions in SOs were included in the quantification. Scale bars, 100 nm for main field, 80 nm for insets. (C and D) HBMECs were adsorbed with reovirus T1L M1-P208S at an MOI of 1 PFU/cell and cryosectioned using the Tokuyasu method at 18 hpi. Sections were immunogold labeled for LAMP-1 using secondary antibodies conjugated with 10-nm gold particles. (C) Lysosome-like structures labeled for LAMP-1 (arrows) in uninfected cells. (D) In reovirus-infected cells, LAMP-1 labeling was apparent in the membrane of SOs and MCs (arrows) adjacent to VIs. V, virion. Scale bars, 200 nm.