Antigenic variation of TprK V regions abrogates specific antibody binding in syphilis

Area of Science:

• Microbiology
• Immunology
• Genetics

Background:

• The syphilis spirochete, *Treponema pallidum* subsp. *pallidum*, exhibits antigenic variation in the seven variable (V) regions of its *tprK* gene.
• This genetic variability within *T. pallidum* strains necessitates methods to isolate and study specific *tprK* sequences.

Purpose of the Study:

• To investigate the antibody response to specific *TprK* variants of *Treponema pallidum*.
• To determine if *TprK* variants contribute to immune evasion and chronic infection by *T. pallidum*.

Main Methods:

• Generation of *T. pallidum* clones expressing single, unique *tprK* sequences.
• Infection of rabbits with distinct *T. pallidum* clones or the parent strain.
• Immunoassay analysis of rabbit sera for antibody reactivity against synthetic peptides representing *TprK* V regions.

Main Results:

• Infection with the parent strain induced broad antibody responses against multiple V regions.
• Rabbits infected with specific clones developed antibodies primarily against the V regions of the infecting clone, with rare cross-reactivity.
• Antibody responses were highly specific to the V regions of the infecting *tprK* variant.

Conclusions:

• The V regions of *TprK* elicit a variant-specific antibody response.
• This immune response specificity supports the hypothesis that *TprK* variants facilitate immune evasion.
• Antigenic variation in *TprK* likely contributes to the persistence of *T. pallidum* and the establishment of chronic syphilis infections.