Immunoperoxidase labeling of subacute sclerosing panencephalitis virus in hamster acute encephalitis

A hamster neuroadapted strain of subacute sclerosing panencephalitis (SSPE) virus induces in the newborn animal an acute encephalitis with ultrastructural features similar to those observed earlier in measles encephalitis and characteristic of a productive viral infection. The direct immunoperoxidase technique, using labeled SSPE gamma-globulin, was applied to formaldehyde-fixed thick sections. These were either chopped after perfusion of the animal or cryocut after quick freezing of the tissue and then fixed. The latter procedure showed good correlation with light microscopic immunoperoxidase or fluorescent antibody staining on paired thin cryostat sections, whereas the former procedure resulted in easier handling of the sections and better ultrastructural preservation, especially when the lysine-periodate-formaldehyde fixative was used. Under electron microscopy the plasma membrane of the nerve cells was often labeled on its inner side in areas where nucleocapsids accumulate to form buds. The membrane antigen appeared to be more focal than in productive SSPE infection in vitro. Within the cytoplasm, most of the tubular inclusions were stained with the label located on the external granular coat of the nucleocapsid. Nonstructural antigen was also detected in the rough endoplasmic reticulum membrane (often on the side of a tubular inclusion), in the cytoplasmic matrix, and sometimes in the nucleus and on the nuclear membrane of giant cells. It thus seems that SSPE gamma-globulin reacts with viral proteins close to the site of synthesis. Because of the high specificity and reproducibility of this method for the detection of intracellular viral antigens, its use is recommended for further studies of conventional and nonconventional viral central nervous system diseases in which an immune response is present.