A live vaccine against tick-borne encephalitis; integrated studies, H. Histopathology of mice peripherally immunized with E5 "14" virus and challenged with virulent virus.

Histopathological changes in the central nervous and lymphoid systems were semiquantitatively analyzed in subadult mice (M) peripherally immunized with the live, highly attenuated E5 "14" virus from the tick-born encephalitis (TE) complex and in immunized M subjected to virulent challenge. The E5 "14" clone possesses an exceedingly restricted neuroinvasivity. A study of the sc marker, refined and extended by microscopic examinations seems to present a more relevant approach for comparative investigations on TE virus virulence. Morphological findings in immunized M given immunosuppressive doses of cyclophosphamide (CPA) suggest that the high efficiency of live vaccines may be related to the prolonged antigenic stimulation.