Entry of HSV-1 into axons of explanted human DRG. Coverslips with explanted DRG cultures in situ were infected with the clinical isolate CW1 of HSV-1, fixed at 1.5 h p.i., and processed for electron microscopy. Areas containing mid- and distal regions of axons were sectioned and examined. (A) Enveloped virion (arrow) adherent to the plasma membrane of an axonal varicosity. The inset shows an enlargement of the viral particle. (B) Extracellular virion (arrow), viral particle (short arrow) bound to the axonal plasma membrane, and unenveloped capsid (arrowhead) inside the axon. The inset shows an enlargement of the adherent viral particle. (C) Unenveloped capsid (arrowhead) in an axon, subjacent to the axonal plasma membrane. The inset shows an enlargement of the unenveloped capsid. Bars, 200 nm.