Susceptibility of rabbits to Treponema pallidum after infection with Mycobacterium bovis.

Rabbits stimulated with Mycobacterium bovis (strain BCG) one month before challenge with Treponema pallidum (Nichols) did not show any modification in their development of syphilitic lesions. A second infection with BCG given at the same time and at the same intradermal site as the T. pallidum challenge also failed to protect the rabbits against syphilis. Thus the non-specific activation of cell-mediated immunity by BCG does not appear to protect rabbits against T. pallidum infection even when both activation and challenge take place in the dermis. The role of the macrophage in syphilis remains obscure.