Immunity to syphilis: passive transfer in rabbits using serial doses of immune serum

The influence of prolonged treatment with serial doses of immune serum initiated either 2 or 48 h before intracutaneous challenge with Treponema pallidum on the subsequent appearance and development of lesions was studied. Whereas treatment with large doses of immune serum initiated 48 h before treponemal challenge caused a delay of 9 to 20 days in the onset of lesions and marked suppression of lesion development. Treatment initiated 2 h before treponemal challenge failed to delay the onset of lesions and only moderately suppressed their development. Lesion development was suppressed as long as treatment was continued. The significance of the results is discussed.