FIG. 1.

Freeze-fracture electron microscopy of T. pallidum following incubation in sera from infected and curatively treated rabbits with various degrees of immunity to challenge reinfection. T. pallidum was incubated for 16 h in the absence of complement with serum from a rabbit susceptible to challenge reinfection (A), a rabbit showing partial protection against challenge reinfection (B), and a rabbit completely immune to challenge reinfection (C). Arrows show nonaggregated (A and B) and aggregated (B and C) TROMPs. Bar, 0.1 μm.