Cell-mediated immunity in experimental syphilis in rabbits.

The development of cell-mediated immunity was studied in rabbits: a) experimentally injected with T. pallidum, and b) artificially immunized with nonviable T. pallidum. The macrophage migration inhibition test (MMI test) using ultrasonicate of T. pallidum as antigen was employed to demonstrate this type of immunologic response. Lymphocytes of syphilitic rabbits were found to exert a pronounced inhibitory effect upon macrophage migration as early as one month after infection; between the fourth and sixth month, a transient decrease of this capacity occurred, followed by a slow but steady increase during the next two years, i.e. until the end of the observation period. In rabbits in which the infection had been controlled by penicillin treatment in the fifth month, no increase but gradual diminution of this capacity was observed. In the group of rabbits artificially immunized with nonviable T. pallidum, the MMI response appeared very shortly after commencement of the immunization and persisted for about nine months after completion of the immunization procedure. Only a crude correlation could be established between levels of the MMI response of the immunized animals and their resistance to infection with T. pallidum.