Immunization with Treponema pallidum outer membrane vesicles induces high-tilter complement-dependent treponemicidal activity and aggregation of T-pallidum rare outer membrane proteins (TROMPs)

The purpose of this study was to determine whether immunization with purifi ed outer membrane vesicles (OMV) from Treponema pallidum (T.p.) could elici t Abs capable of killing this organism. It is well established that the imm unization of rabbits or mice with killed T.p. or with recombinant T.p. Ags has failed to generate serum killing activity comparable with that of infec tion-derived immunity, Because of the small amount of T.p, OMV obtainable, a single mouse was immunized with purified OMV, The mouse anti-OMV serum an d infection-derived immune rabbit serum (IRS) were compared by reactivities on two-dimensional T.p. immunoblots and by the T.p. immobilization test, a complement-dependent killing assay, Whereas IRS detected >40 Ags, the anti -OMV serum identified only 6 Ags corresponding to proteins identified previ ously in the outer membrane, T.p. immobilization testing showed that IRS ha d a 100% killing titer of 1:44 and a 50% killing titer of 1:662, By compari son, the mouse anti-OMV serum had a significantly greater 100% killing tite r of 1:1,408 and a 50% killing titer of 1:16,896, Absorption of the anti-OM V serum to remove Ab against outer membrane-associated lipoproteins did not change the 100% killing titer, Freeze-fracture analysis of T.p. incubated in IRS or anti-OMV serum showed that T.p. rare membrane-spanning outer memb rane proteins were aggregated. This is the first demonstration of high-tite r killing Abs resulting from immunization with defined T.p. molecules; our study indicates that the targets for these Abs are T.p. rare outer membrane proteins.