Antigenic Variation in Treponema pallidum
Arturo Centurion-Lara
from: Pathogenic Treponema: Molecular and Cellular Biology (Edited by: Justin D. Radolf and Sheila A. Lukehart). Caister Academic Press, U.K. (2006)
Abstract
The pathogenic treponemes include three subspecies of Treponema pallidum (T. pallidum), T. carateum, T. paraluiscuniculi, and the unclassified Fribourg-Blanc (simian) isolate. These treponemes are antigenically highly related, cause persistent infections in their respective hosts, and induce similar histopathological changes and immune responses. The host immune response is able clear the great majority of spirochetes from early active lesions, however, some organisms escape immune clearance and cause chronic infections. Several mechanisms, including antigenic variation, have been proposed to explain the ability of T. pallidum to disseminate and evade the immune response of the host. One member of the tpr gene family, tprK, undergoes extensive sequence diversification during infection, and its encoded protein induces an active immune response. The variable portions of the protein are antibody epitopes, and variation of these epitope sequences would potentially allow T. pallidum to avoid the immune response or, alternatively, to adapt to the changing micro-environments posed by dissemination to different tissue sites. We describe in this chapter a non-reciprocal gene conversion-like mechanism for the generation of tprK diversity in Treponema pallidum subsp pallidum, in which new variants are created by unidirectional exchange between donor sites and the tprK expression site. This mechanism of antigenic variation is likely to be shared by all members of this group of pathogenic treponemes and is likely to contribute to the persistence of treponemal infections read more ...
