Measles antigen distribution in brains of chronically infected hamsters. An immunoperoxidase study of experimental subacute sclerosing panencephalitis.

Weanling (21-day old) hamsters were inoculated intracerebrally with hamster-adapted, HBS strain of subacute sclerosing panencephalitis virus and studied between days 6 and 51 of infection with light microscopic immunofluorescent and ultrastructural immunoperoxidase methods. Characteristic measles fuzzy nucleocapsids developed and persisted in brain cell cytoplasm while smooth nucleocapsids developed in both nucleus and cytoplasm. Measles virus antigens appeared not only in relation to nucleocapsid but also in cytoplasm and along the inner aspect of cytoplasmic membranes of brain cells including neuronal dendrites. No budding virions were seen. Focal concentrations of bound hamster IgG occurred within foci of infected cells during the chronic infection. These studies show that in hamsters, persistent central nervous system measles infection is due to morphologically identifiable virus structures even when the host serologic response is active. The finding of viral antigens within the cytoplasmic membrane along with focal collections of hamster IgG in the same areas suggests that a "blocking factor," possibly antibody, protects infected cells from immune surveillance and destruction.