In the present study, immunomodulatory responses of
a DNA vaccine constructed by fusing Treponema pallidum (Tp)
glycerophosphodiester phosphodiesterase (Gpd) to
interleukin-2 (IL-2) and using
chitosan (CS) nanoparticles as vectors were investigated. New Zealand white rabbits were immunized by intramuscular inoculation of control DNAs, Tp Gpd
DNA vaccine, or Gpd-IL-2 fusion
DNA vaccine, which were vectored by CS nanoparticles. Levels of the anti-Gpd
antibodies and levels of
IL-2 and
interferon-γ in rabbits were increased upon inoculation of Gpd-IL-2 fusion
DNA vaccine, when compared with the inoculation with Gpd
DNA vaccine, with CS vectoring increasing the effects. The Gpd-IL-2 fusion
DNA vaccine efficiently enhanced the
antigen-specific lymphocyte proliferative response. When the rabbits were challenged intradermally with 10(5) Tp (Nichols) spirochetes, the Gpd-IL-2 fusion
DNA vaccine conferred better protection than the Gpd
DNA vaccine (P < 0.05), as characterized by lower detectable amounts of dark field positive lesions (17.5%), lower ulcerative lesion scores (15%), and faster recovery. Individuals treated with the Tp Gpd-IL-2 fusion
DNA vaccine vectored by CS nanoparticles had the lowest amounts of dark field positive lesions (10%) and ulcerations (5%) observed and the fastest recovery (42 days). These results indicate that the Gpd-IL-2 fusion
DNA vaccine vectored by CS nanoparticles can efficiently induce Th1-dominant immune responses, improve protective efficacy against Tp
spirochete infection, and effectively attenuate development of syphilitic lesions.