English: Tomographic reconstruction showing a few virus particles that budded from a naturally HTLV-1 infected CD4+ T cell (PBMC) into the synaptic cleft. Most of the virions are not attached to a cell membrane. The particles are characterized by an electron-dense core surrounded by a less dense area and enveloped by the electron-dense viral membrane. The average diameter of HTLV-1 particles derived from naturally HTLV-1 infected CD4+ T-cell (PBMC) was 105.2 +/− 21.8 nm (SD). A slice through the entire tomogram is shown in Figure 3E. The sample was fixed with PFA/glutaraldehyde, embedded in Agar 100 resin, post-fixed with OsO4 and stained with lead citrate. The tomogram was calculated from a tilt series of 141 images (tilt range −70° to +70°, 1° increment). The images were recorded with a 2k×2k Gatan CCD camera (pixel size 1.21 nm) at an under focus of −0.2 µm with an FEI Tecnai F30 FEG-TEM (300 kV) in Boulder, Colorado using the software SerialEM. The reconstruction was calculated using the software IMOD. The tomogram represents a volume with an area of 1.70×2.24 µm2 and a thickness of 176 nm.