Combined fluorescent-antibody and electron microscopy study of Marek's disease virus-infected cell culture

Duck embryo fibroblast (DEF) and chicken embryo fibroblast (CEF) cultures infected with Marek's disease virus were studied by combined fluorescent antibody and electron microscopy techniques. In both DEF and CEF cultures, cells containing immunofluorescent (IF) antigen also contained herpesvirus particles; conversely, cells lacking this antigen lacked herpesvirus particles. Two morphologically distinct IF antigens were detected in the cytoplasm. (i) A granular antigen in the perinuclear region was brightly stained with the conjugated antibody. This antigen was composed of a granular mass of osmiophilic material and did not contain virions. (ii) A diffuse antigen, present throughout the cytoplasm of infected cells, was less brightly stained. The area of the cell with the highest concentration of this antigen contained small vesicles, folded membranes, and fine electron-dense granules. Naked virions were occasionally seen in these areas. A diffuse nuclear IF antigen was occasionally seen in infected cells. This antigen was often separated from the nuclear membrane and the nucleolus by a clear margin. The intranuclear IF antigen was composed of a fine granular aggregate and naked herpesvirus particles which were randomly distributed throughout the nucleus. Viral capsids in antibody-treated cells were coated with fine filamentous material.