Sensitive and highly specific radioimmunoprecipitation and gel electrophoresis-fluorography were used to monitor the serum IgG response of experimentally infected rabbits against key protein antigens of Treponema pallidum. The sera from six rabbits challenged intradermally (ID) and six intratesticularly (IT) with T pallidum were examined over a period of four months. A specific antibody response to most treponemal surface proteins (including those ligands implicated as mediating host-cell-surface adherence) developed by about day 20 after inoculation. Maximum antibody concentrations against most of these immunogens were detected by day 50 in all animals irrespective of the route of inoculation. Differences as well as similarities in the IgG response to infection were observed among selected rabbits. Furthermore, the antibody reactivity of each animal was comparable to that of human sera from patients with secondary syphilis. Antibody directed against treponemal outer envelope proteins was detected by preferential agglutination of washed radiolabelled organisms with protein A-bearing Staphylococcus aureus in the presence of syphilitic rabbit sera.
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