An immunopathologic component in experimental togavirus encephalitis

The effects of immune manipulation upon survival and histopathology in two experimental group B togavirus encephalitides were studied in inbred mice. The median survival time 8 days after intracerebral injection of Langat virus increased to 10 days with an immunosuppressive course of cyclophosphamide, with concomitant reduction in the inflammatory response. Adoptive immunization with immune lymphoid cells or serum also tended to prolong Langat virus survival while increasing inflammation. Survival following intracerebral West Nile virus (7 days) was unaffected by immunosuppression or adoptive transfer, although suppression was associated with less severe CNS lesions, and immune serum with less necrosis. These findings indicate that the immune response may be both protective and pathology-inducing in some togarvirus encephalitides. The differences in host response to these two related agents suggest caution in generalizing about the role of the immune response in viral infections.