Abstract
The ability of Treponema pallidum, the syphilis spirochete to colonize various tissues requires the presence of surface-exposed adhesins that have been difficult to identify due to the inability to culture and genetically manipulate T. pallidum. Using a Borrelia burgdorferi-based heterologous system and gain-in-function approach, we show for the first time that a highly immunogenic lipoprotein TP0435 can be differentially processed into multiple isoforms with one variant stochastically displayed on the spirochete surface. TP0435 was previously believed to be exclusively located in T. pallidum periplasm. Furthermore, non-adherent B. burgdorferi strain expressing TP0435 acquires the ability to bind to a variety of host cells including placental cells and exhibits slow opsonophagocytosis in vitro similar to poor ex vivo phagocytosis of T. pallidum by host macrophages reported previously. This phenomenon of production of both surface and periplasmic immunogenic lipoprotein isoforms has possible implications in immune evasion of the obligate pathogen T. pallidum during infection.
Highlights
Syphilis is a chronic, systemic, sexually transmitted disease that still affects millions of people worldwide
We show here that TP0435 is stochastically expressed on the surface of both B. burgdorferi and T. pallidum and this lipoprotein facilitates binding of the spirochetes to mammalian epithelial, glioma and placental cell lines
TP0435 is recognized by secondary syphilis patient serum on B. burgdorferi surface by Indirect Fluorescent Antibody (IFA) test
Summary
Systemic, sexually transmitted disease that still affects millions of people worldwide. Lyme disease-causing Borrelia burgdorferi and T. pallidum are structurally and physiologically related spirochetal pathogens that express different lipoproteins. B. burgdorferi can be grown in complex medium in vitro and genetically manipulated[30,31,32] and its genome (1.52 Mb) consists of a linear chromosome and numerous endogenous linear and circular plasmids[33] encoding the majority of ~132 lipoproteins responsible for survival and colonization of tick vector and various hosts. We used two high passage, poorly adherent, non-infectious B. burgdorferi strains (B314 and B31HP), which have lost different endogenous plasmids[34] to investigate the role of highly expressed and immunogenic TP0435. We selected TP0435 ( known as the 17 kD lipoprotein or Tpp17) for expression and to determine function of T. pallidum lipoprotein(s) using B. burgdorferi because of our interest in studying adherence mechanism of spirochetes. We show here that TP0435 is stochastically expressed on the surface of both B. burgdorferi and T. pallidum and this lipoprotein facilitates binding of the spirochetes to mammalian epithelial, glioma and placental cell lines
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