Viral Antigen in Rat Embryo in Culture Infected with the H-1 Virus Isolated from Transplantable Human Tumors: Cytochemical Studies

The infection of rat embryo cells with H-1 virus was followed, with Coon's method used for staining with fluorescent antibodies. After a period of 12 hours the stain revealed a diffuse fluorescence that occupied the nucleus except for areas corresponding to the nucleoli. The stained nuclei increased in number during the subsequent 16, 20, and 24 hours corresponding to the log phase of viral growth. On the 2d day after inoculation, when the viral growth curve had reached a plateau, a homogeneous type of fluorescent antibody stain was present in nuclei. Some cells contained granular or diffuse stain in the cytoplasm. At this stage acridine stain showed nuclear structural changes and homogeneous nuclei of DNA-like material. Treatment with pepsin and nucleases indicated the presence in the homogeneous nuclei of a deoxyribonucleoprotein resistant to DNase. Phase microscopy also showed nuclear alteration. By the 3d day, when the viral antigen was present in most of the cells, inclusion bodies and cytopathic effect were present. These changes were followed by the release of hemagglutinating virus.