Relationship between Treponemal Immobilizing Antibodies and Acquired Immunity in Experimental Syphilis

Summary Measurement of circulating “immobilizing antibody” has proved to be a poor measure of the resistance of immune rabbits to challenge infection with three strains of Treponema pallidum. Crude correlation between the results of the immobilization test and the resistance to challenge was demonstrated only when challenge shortly followed termination of the immunizing infection. Strain 20A may be a more sensitive antigen than the Nichols strain of Treponema pallidum in the demonstration of the immobilization phenomenon. The in vitro immobilization test failed to demonstrate strain differences among three strains of T. pallidum. The mechanism of acquired immunity in syphilis is still poorly understood.