Endemic syphilis: passive transfer of resistance with serum and cells in hamsters.

Serum or spleen cells from hamsters immune to infection with Treponema pallidum strain Bosnia A conferred partial protection against syphilitic infection by the same strain on recipient hamsters. Cutaneous lesions did not develop, and in the lymph nodes the average weight and number of treponemes detected were significantly lower than in normal and control hamsters. Treatment of the immune spleen cells with antithymocyte serum and complement abolished their ability to transfer resistance. This is the first direct evidence that thymus-derived cells are involved in resistance to syphilitic infection.