Murine model for study of cell-mediated immunity: protection against death from fully virulent Francisella tularensis infection.

To assess cell-mediated immunity in terms of host protection, an experimental model was developed in which passively transferred spleen cells from immunized AKR/J mice enabled nonimmume syngeneic recipients to survive an otherwise fatal infection with fully virulent Francisella tularensis. Donor immunization was achieved by administering live attenuted tularemia vaccine and, subsequently, the virulent streptomycin-sensitive SCHU S4 strain of F. tularensis. At selected intervals after immunization, donor spleen cells were transferred to streptomycin-treated recipients challenged subcutaneously, intravenously, or intraperitoneally with 25 to 50 minimal lethal doses of virulent streptomycin-resistant F. tularensis SCHU S5. The protection afforded by immune spleen cells was maximal (essentially 100%) 12 days after the SCHU S4 secondary immunization.