Electron microscopy examination of parental virus-infected or DNA of MDV △UL28-transfected CEF cells. A CEF cells were infected with parental virus or transfected with DNA of MDV △UL28, and fixed at 3 days post-infection/transfection. The electron microscopic examination indicated that mature and immature virions were formed. The mature virions were marked with a red arrow, while immature virions were marked with a black arrow; B CEF cells were transfected with DNA of MDV △UL28, and fixed at 3 days post-transfection. The electron microscopic examination revealed that immature capsids were formed and marked with a black arrow. The scale bar is 500 nm.