Long-term persistence of cell-mediated and humoral immune response in specifically resistant mice given live attenuated langat (E5 "14") virus.

In a long-term experiment, the features of humoral and cell-mediated immunity (CMI) were investigated in mice given intravenously (i.v.) a single dose of live attenuated Langat (E5 "14") virus of the tick-borne encephalitis (TBE) complex. The inapparent infection induced in mice specific resistance against challenge with virulent TBE virus, CMI was assayed by the capillary method of murine splenic lymphocyte migrarion inhibition (LMI) in the presence of partially purified TBE vurus. Significant LMI values were observed as early as 4 days after inoculation (p.i.), persisting for at least 15 months. Specific virus neutralizing (VN) antibodies were detected in the pooled serum of mice on the 4th day p.i. by a VN test potentiated with monospecific anti-mouse IgG serum. For the whole experimental period, significant antibody levels were found in the immunized mice which also displayed a complete resistance against 1000 s.c. LD50 of the virulent virus. Organ cultures of brain and spleen from these mice did not yield infections virus.