The damaging action of cellular immunity in flavivirus infections of mice.

The development of acute infections caused by different flaviviruses was studied in immunosuppressed inbred and non-inbred mice. Cyclophosphamide treatment of challenged animals resulted in an increase of the mean survival time by 24--144 hours in some but not all virus-mouse strain combinations. The transient protective action of cyclophosphamide was not due to suppression of the reproduction of tick-borne encephalitis (TBE) or dengue 2 (D2) virus in the brains of mice. In TBE or D2 infections of immunosuppressed mice the clinical signs of central nervous system lesions seemed to be associated with the development of cellular immunity measured by the splenobyte migration inhibition test. The transfer of sensitized splenocytes in immunosuppressed animals, challenged with TBE or D2 virus, shortened the incubation period. These results suggest that cellular immunity may have a damaging effect in acute flavivirus infections in mice, and also that the immunopathological response varies considerably in different strains of inbred mice.