Immunochemical characterization and purification of Treponema pallidum antigen TpD expressed by Escherichia coli K12.

The immunochemical properties of the Treponema pallidum antigen TpD, as expressed by Escherichia coli K12, was investigated by crossed immunoelectrophoresis in which an affinity-purified antibody to this antigen was used. Two immunologically cross-reacting components of TpD with different mobility were demonstrated. Affinity-purified antibodies were used in obtaining purified TpD and in determining the cellular localization of TpD in T. pallidum by immunoelectron microscopy. TpD was localized on the surface of methanol-fixed T. pallidum. Twenty sera from patients with secondary syphilis and 20 sera from nonsyphilitics were examined in crossed immunoelectrophoresis. All sera from patients with secondary syphilis and none from nonsyphilitics contained antibodies to the TpD components. Because TpD seems to be surface associated and a major immunogen during infection with T. pallidum, this antigen might be useful for development of a vaccine against syphilis and for development of improved methods for serodiagnosis of syphilis.