Acquired resistance of hamsters to challenge with homologous and heterologous virulent treponemes.

Hamsters infected with Treponema pallidum Nichols (venereal syphilis), T. pallidum Bosnia A (endemic syphilis), or T. pertenue (frambesia, or yaws) developed substantial resistance to homologous reinfection. Hamsters infected for 10 weeks developed no lesions, and their lymph nodes contained fewer treponemes after reinfection with the same strain. The degree of cross-resistance among the treponemes correlated well with pathological changes occurring in infected hamsters and with the persistence of treponemal antigen during primary infection. Only hamsters infected with T. pallidum Bosnia A developed substantial resistance to heterologous reinfection. These animals also had extensive chronic skin lesions and lymph nodes containing measurable numbers of treponemes. Frambesial hamsters had less extensive lesions and were resistant to T. pallidum Nichols and, to a lesser extent, to T. pallidum Bosnia A. Hamsters infected with T. pallidum Nichols developed no cutaneous lesions and were resistant only to reinfection with T. pertenue. Confirmation of these results was obtained in normal hamsters infused with syphilitic (Nichols or Bosnia A) or frambesial immune cells and challenged with homologous or heterologous treponemes.