The incidence of infectious syphilis has doubled in the United States since 2000, and has increased dramatically in Western Europe and in China during that time. In addition to serious clinical sequelae in adults, congenital syphilis is responsible for a high proportion of fetal and neonatal morbidity and mortality in developing countries. Syphilis is a chronic sexually transmitted infection which, untreated, lasts for many decades. When our laboratory discovered sequence variation in seven discrete regions (termed V regions) of TprK, a putative surface- exposed protein of Treponema pallidum, we hypothesized that this represents an antigenic variation system, leading to immune evasion and contributing to the chronic nature of syphilis infection. Syphilis is transmissible by sexual contact only during the early (primary and secondary) stages, however, so what is the evolutionary advantage of decades-long persistence? Antigenic variation must impart another advantage to the bacterium. We now hypothesize that the major advantage of TprK antigenic variation by T. pallidum lies in the prolongation of the infectious stages: longer duration of the primary chancre, immune escape to permit development of secondary lesions, and longer duration of secondary lesions. Immune clearance of T. pallidum from early lesions occurs via phagocytosis of opsonized T. pallidum by activated macrophages, so organisms persisting in these lesions must be able to evade this immune activity to delay lesion resolution. This is consistent with our earlier finding that treponemes persisting in lesions following initial immune clearance in vivo are resistant to opsonophagocytosis. In this renewal application, we propose to focus on the early stages of syphilis infection in the rabbit model and to define, at the molecular and functional level, the role of TprK V region variation in immune escape. Specifically, we propose the following aims: 1) Define the mechanism(s) by which specific anti-TprK antibodies contribute to the clearance of T. pallidum from healing primary lesions;2) Identify the epitopes recognized by functional anti- TprK antibodies;3) Determine whether new variants comprise the treponemes seen in secondary lesions;4) Investigate whether variant-specific antibodies are induced by new variant TprK antigens;and 5) Determine the role of interferon-3 in development of new TprK variants. These studies will elucidate the mechanisms by which TprK antigenic variation contributes to immune evasion by T. pallidum and leads to long duration of the infectious stages of syphilis.

Public Health Relevance

Syphilis is an important and common disease. This grant application will study how the bacterium that causes syphilis, Treponema pallidum, evades the immune response of the infected host to prolong the period of infectivity. We will study a protein called TprK that is thought to be exposed on the surface of the bacterial cell. TprK undergoes changes in its sequence which inhibits the ability of antibodies to bind it, thus enabling the bacterium to escape from host immunity.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Host Interactions with Bacterial Pathogens Study Section (HIBP)
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Hiltke, Thomas J
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University of Washington
Internal Medicine/Medicine
Schools of Medicine
United States
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Molini, Barbara J; Tantalo, Lauren C; Sahi, Sharon K et al. (2016) Macrolide Resistance in Treponema pallidum Correlates With 23S rDNA Mutations in Recently Isolated Clinical Strains. Sex Transm Dis 43:579-83
Giacani, Lorenzo; Brandt, Stephanie L; Ke, Wujian et al. (2015) Transcription of TP0126, Treponema pallidum putative OmpW homolog, is regulated by the length of a homopolymeric guanosine repeat. Infect Immun 83:2275-89
Reid, Tara B; Molini, Barbara J; Fernandez, Mark C et al. (2014) Antigenic variation of TprK facilitates development of secondary syphilis. Infect Immun 82:4959-67
Giacani, Lorenzo; Lukehart, Sheila A (2014) The endemic treponematoses. Clin Microbiol Rev 27:89-115
Cameron, Caroline E; Lukehart, Sheila A (2014) Current status of syphilis vaccine development: need, challenges, prospects. Vaccine 32:1602-9
Lukehart, Sheila A; Giacani, Lorenzo (2014) When is syphilis not syphilis? Or is it? Sex Transm Dis 41:554-5
Centurion-Lara, Arturo; Giacani, Lorenzo; Godornes, Charmie et al. (2013) Fine analysis of genetic diversity of the tpr gene family among treponemal species, subspecies and strains. PLoS Negl Trop Dis 7:e2222
Grimes, Matthew; Sahi, Sharon K; Godornes, B Charmie et al. (2012) Two mutations associated with macrolide resistance in Treponema pallidum: increasing prevalence and correlation with molecular strain type in Seattle, Washington. Sex Transm Dis 39:954-8
Giacani, Lorenzo; Chattopadhyay, Sujay; Centurion-Lara, Arturo et al. (2012) Footprint of positive selection in Treponema pallidum subsp. pallidum genome sequences suggests adaptive microevolution of the syphilis pathogen. PLoS Negl Trop Dis 6:e1698
Giacani, Lorenzo; Brandt, Stephanie L; Puray-Chavez, Maritza et al. (2012) Comparative investigation of the genomic regions involved in antigenic variation of the TprK antigen among treponemal species, subspecies, and strains. J Bacteriol 194:4208-25

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