The ontogeny of the
IgG response in rabbits with experimental
syphilis to individual
polypeptides of Treponema pallidum, Nichols strain, was examined. The
polypeptides of motile, virulent T. pallidum, purified from host tissue by
Percoll density gradient centrifugation, were separated on SDS-
polyacrylamide gels and were electrophoretically transferred to a solid-phase matrix of
nitrocellulose for
antigen analysis. Serum from rabbits early in
infection at day 3 post-
infection showed a weak but detectable
IgG response to two
polypeptides of 60,000 and 46,000 m.w. This was followed on days 11, 17, and 19 by an apparent quantitative increase in antibody to other treponemal
protein antigens. By day 19, 21 of the 22 detectable
polypeptides could be identified. A similar set of
antigens was detected by serum from patients with human secondary and early
latent syphilis. A close correlation was found between the presence of
IgG antibody to T. pallidum
polypeptides at day 9 and 1, 4.5, 13.5, and 17 mo post-
infection and the immune status of the rabbit to symptomatic
reinfection. Serum from rabbits that were partially immune to challenge at day 9 detected three
polypeptides of 60,000, 46,000, and 36,000 daltons. By 1 mo post-
infection, at a time when a more complete immunity had developed, the number of detectable
antigens increased to 21
polypeptides ranging in m.w. from 94,000 to 14,400 daltons.
IgG antibody to 22 treponemal
antigens persisted in animals that were solidly immune to symptomatic
reinfection at 3, 4.5, 13.5, and 17 mo post-
infection. Serum neutralizing activity was not demonstrable at day 9 or 1 mo post-
infection, however, but was present at 3, 4.5, 13.5, and 17 mo. The results suggest that after intratesticular challenge a vigorous
IgG response to T. pallidum
polypeptides can be detected. The potential role of humoral immune mechanisms in the development and maintenance of immunity is discussed.