Subacute sclerosing panencephalitis virus in immunosuppressed adult hamster

A hamster-adapted subacute sclerosing panencephalitis agent (HBS virus) produced a subclinical, nonlethal, and cell-associated encephalitis after intracerebral inoculation of adult hamsters. When adult hamsters were immunosuppressed by intraperitoneal injections of rabbit origin anti-hamster lymphocyte serum for varying periods of time before and after intracerebral challenge with HBS virus, more than 50 per cent died in all experiments. Large titers of cell-free virus developed acutely in all animals and were maintained in continuously immunosuppressed hamsters, all but one of which died within 21 days. When animals were given transient anti-hamster lymphocyte serum treatment, those surviving for 21 to 54 days always displayed serum measles antibodies, and, from such animals, highly cell-associated virus could often be isolated from the brain. In such animals and in some others from which no virus could be isolated, the presence of measles antigen or inclusion cell pathology was noted in the brain. The neuropathology was characterized early by focal necrosis; small, multinucleated, ependymal giant cells; and minimal inflammatory reactions. Chronically, it was represented by mild perivascular inflammation, plasma cell accumulations, and inclusion-bearing cells. These studies indicate that it is the host immune response, rather than intrinsic central nervous system resistance to virus infection, which changes with age and thereby increases the chance of survival. The results suggest that antibodies modify the virus, making it more cell-associated or defective and thus enhancing its persistence in the immune host.