Fig. 1

EBV infection promotes VM formation in vitro and in vivo. a (Left) Morphologies of EBV-infected NPC cells and their parental cells grown in conventional 2D culture plates. Cells are mixed with the sheet-like and thread-like cell types, and the latter were outlined with yellow lines. Scale bars = 100 μm. (Right) Quantification of the sheet-like and thread-like cell types in EBV-infected NPC cells and their parental cells. More than 100 cells were counted in randomly chosen fields. Mean ± SD, n = 5, ***p < 0.001 (two-tailed unpaired t-test). b Images (left) and quantification (right) of tube formation in EBV-infected NPC cells and their parental cells. Images were taken 12 h after seeding on Matrigel. Scale bars = 100 μm. Tubes were counted under a microscope with 200× magnification in randomly chosen fields. Mean ± SD, n = 5, * p < 0.05 (two-tailed Mann–Whitney test). c EBV-infected NPC cells displayed tubular networks and channels in 3D Matrigel, as observed by scanning electron microscopy. Scale bars = 100  μm (left panel), scale bars = 10 μm (right locally enlarged images). d CNE2 and CNE2-EBV cells were subcutaneously injected into nude mice, and images were taken 20 days post-implantation. e Growth curves of xenograft tumors formed by CNE2 and CNE2-EBV cells. Mean ± SD, n = 4, two-tailed Mann–Whitney test. f The presence of VM in CNE2-EBV xenografts but not in control CNE2 xenografts. Pink arrows indicate VM channels (PAS⁺/mCD31⁻), which are formed by tumor cells (as stained by EBER) and containing red blood cells (stained by H&E; red arrows); brown arrows indicate typical blood vessels with brown mCD31⁺ staining. White scale bars = 100 μm, black scale bars = 10 μm. (Left) Quantification of PAS⁺/mCD31⁻ channels determined by microscopy with 400× magnification in randomly chosen fields. Mean ± SD, n = 5, ***p = 0.0002 (two-tailed unpaired t-test)