Analysis of<i>Borrelia burgdorferi</i><i>vlsE</i>Gene Expression and Recombination in the Tick Vector

Indest, Karl J.; Howell, Jerrilyn K.; Jacobs, Mary B.; Scholl-Meeker, Dorothy; Norris, Steven J.; Philipp, Mario T.

doi:10.1128/iai.69.11.7083-7090.2001

Cited by 77 publications

(93 citation statements)

References 34 publications

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“…It was reported by Ohnishi and de Silva (31) that B. burgdorferi in ticks inoculated by feeding on infected mice contained vlsE sequence variants that either arose within the ticks or were selected during the second feeding. However, vlsE recombination was not detected in recent studies in which ticks were inoculated with B. burgdorferi clone 5A3 by capillary feeding (32). Thus the recombination mechanism appears to be up-regulated in mammalian tissues as compared with either the arthropod or in vitro culture environments.…”

Section: Resultsmentioning

confidence: 84%

Crystal Structure of Lyme Disease Variable Surface Antigen VlsE of Borrelia burgdorferi

Eicken¹,

Sharma²,

Klabunde³

et al. 2002

Journal of Biological Chemistry

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132

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VlsE is an outer surface lipoprotein of Borrelia burgdorferi that undergoes antigenic variation through an elaborate gene conversion mechanism and is thought to play a major role in the immune response to the Lyme disease borellia. The crystal structure of recombinant variant protein VlsE1 at 2.3-Å resolution reveals that the six variable regions form loop structures that constitute most of the membrane distal surface of VlsE, covering the predominantly ␣-helical, invariant regions of the protein. The surface localization of the variable amino acid segments appears to protect the conserved regions from interaction with antibodies and hence may contribute to immune evasion.Lyme disease is a multistage, tick-borne infection that is endemic to regions of the United States, Europe, and Asia (1). The causative bacteria are a family of closely related spirochetes, including Borrelia burgdorferi, Borrelia garinii, and Borrelia afzelii, and are transmitted from one mammal to another by Ixodes ticks. Lyme disease borrelia cause persistent infections and chronic neurologic, cardiovascular, and arthralgic manifestations that can last for months to years in humans and other mammals if not treated successfully, indicating that the spirochetes can effectively evade the host's immune defenses.The mechanisms of immune evasion are not well understood at this time but are thought to include at least one form of antigenic variation. The variable major protein (VMP)-like sequence (vls) 1 locus of B. burgdorferi (2) is a complex antigenic variation system that in many ways resembles the more thoroughly characterized variable major protein system of relapsing fever borrelia (3). The vls locus of B. burgdorferi B31 consists of the expression site vlsE and a contiguous set of 15 vls silent cassettes. The exact function of the 35-kDa surfaceexposed lipoprotein VlsE is unknown; however, it is thought that the vls system may play an important role in mammalian infection because loss of the encoding linear plasmid lp28-1 results in reduced infectivity (4, 5).

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Section: Resultsmentioning

confidence: 84%

Crystal Structure of Lyme Disease Variable Surface Antigen VlsE of Borrelia burgdorferi

Eicken¹,

Sharma²,

Klabunde³

et al. 2002

Journal of Biological Chemistry

Self Cite

132

154

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“…This result suggested that vlsE recombination may be stimulated during nymphal feeding or that the vlsE locus may be subjected to different selective forces within unfed and partially fed nymphs. In a related study, Indest et al (15) used capillary feeding to introduce a clonal population of spirochetes with a single vlsE allele into ticks (15). When capillaryinfected nymphs were tested, only the original allele was detected, indicating that vlsE recombination did not occur within capillary-infected nymphs (15).…”

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confidence: 99%

“…A few studies have focused on vlsE alleles within infected nymphal ticks (15,24). Individual wild ticks carry spirochete populations with multiple vlsE alleles, which may be indicative of recombination within the tick or the tick acquiring a heter-ogeneous population from the vertebrate host (16).…”

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confidence: 99%

Genetic Variation at thevlsELocus ofBorrelia burgdorferiwithin Ticks and Mice over the Course of a Single Transmission Cycle

et al. 2003

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The Lyme disease spirochete, Borrelia burgdorferi, causes a persistent infection in the vertebrate host even though infected animals mount an active immune response against the spirochete. One strategy used by the spirochete to evade vertebrate host immunity is to vary the structure and expression of outer membrane antigens. The vlsE locus represents the best-studied example of antigenic variation in B. burgdorferi. During vertebrate host infection, recombination between the active vlsE locus and silent, partial vlsE copies leads to gene conversion events and the generation of novel alleles at the expression site. In the present study, we followed a population of B. burgdorferi organisms moving through vertebrate host and tick stages to complete one transmission cycle. The major goal of the study was to determine if the vlsE locus was subject to different selective pressure and/or recombination frequency at different stages of the spirochete's life cycle. We report here that the vlsE genetic diversity generated within the rodent host was maintained through the larval and nymphal tick stages. Therefore, naturally infected ticks are likely to transmit spirochete populations with multiple vlsE alleles into naive vertebrate hosts. Although vlsE genetic diversity in mice was maintained through tick stages, the dominant vlsE alleles were different between tick stages as well as between individual ticks. We propose that population-level bottlenecks experienced by spirochetes, especially during the larvalto-nymphal molt, are responsible for individual infected ticks harboring different dominant vlsE alleles. Although vlsE genetic diversity is maintained through tick stages, the VlsE protein is unlikely to be of functional importance in the vector, because the protein was expressed by very few (<1%) bacteria in the vector.

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“…The resulting recombination leads to changes in the sequence of the expression cassette but no alterations in the sequences of the silent cassettes (53). vlsE variation has been shown to occur within 4 days of experimental infection of mice with B. burgdorferi B31 and continues throughout the course of infection but has not been observed in vitro or in the tick vector (21,53,54). The conservation of vls sequences in other strains and species of Borrelia indicate that the vls locus is important for the life cycle of Lyme disease agents (23,25,49).…”

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Effects of vlsE Complementation on the Infectivity of Borrelia burgdorferi Lacking the Linear Plasmid lp28-1

2004

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The loss of linear plasmid lp28-1, which contains the vls antigenic variation locus, is associated with reduced infectivity of Borrelia burgdorferi in immunocompetent mice. The recombinant shuttle vector pBBE22, which includes the virulence determinant BBE22 from lp25 and restores infectivity to readily transformable B. burgdorferi lacking lp25 and lp56, was used to determine the effect of trans expression of vlsE on virulence. Spirochetes lacking lp28-1 were complemented with the plasmid pBBE22:vlsE, containing both BBE22 and vlsE. VlsE protein produced by this construct was expressed and surface accessible in in vitro-cultured B. burgdorferi, as determined by surface proteolysis and immunoblot analysis. Clones lacking lp25 but containing lp28-1 and either pBBE22 or pBBE22:vlsE were reisolated consistently from immunocompetent mice 8 weeks after infection. In contrast, a clone lacking both lp25 and lp28-1 and complemented with pBBE22:vlsE was isolated from only a single tissue of one of six C3H/HeN mice 8 weeks postinfection. These results indicate that either an intact vls antigenic variation locus or another determinant on lp28-1 is required to restore complete infectivity. In addition, an isogenic clone that retained lp28-1 was complemented with the vlsE shuttle plasmid and was examined for vlsE sequence variation and infectivity. Sequence variation was not observed for the shuttle plasmid, indicating that the cis arrangement of vlsE and the vls silent cassettes in lp28-1 facilitate vlsE gene conversion. Lack of vlsE sequence variation on the shuttle plasmid thus did not result in clearance of the trans-complemented strain in immunocompetent mice under the conditions tested.Lyme borreliosis, the most prevalent vector-borne disease in the United States, is a chronic infection caused by Borrelia burgdorferi and other members of the genus Borrelia (6). Spirochetes are transmitted to mammalian hosts by Ixodes ticks, leading to the development of an annular rash called erythema migrans at the site of inoculation and progressing to a multisystemic infection with neurological, arthritic, and cardiac manifestations (45). As infection advances and Borrelia disseminate into deeper tissues in the host, a strong immune response is elicited towards the pathogen, including the development of Borrelia-specific antibodies (7,8,11,14,17). Though an active immune response develops early during infection, Borrelia is able to escape clearance and persist for months to years. Elucidation of the mechanisms of immune evasion may lead to a better understanding of the pathobiology of Lyme disease.The vls (Vmp-like sequence) locus of B. burgdorferi B31 is on the linear plasmid lp28-1, a plasmid associated with infectivity in the mouse model (26, 27, 42, 52). The vls locus consists of an expression site (vlsE) and 15 unexpressed (silent) vls cassettes. The silent cassettes have high homology to the central cassette region of vlsE. Within the cassettes, there are six variable regions interspersed between highly conserved regions (52). ...

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Analysis ofBorrelia burgdorferivlsEGene Expression and Recombination in the Tick Vector

Cited by 77 publications

References 34 publications

Crystal Structure of Lyme Disease Variable Surface Antigen VlsE of Borrelia burgdorferi

Crystal Structure of Lyme Disease Variable Surface Antigen VlsE of Borrelia burgdorferi

Genetic Variation at thevlsELocus ofBorrelia burgdorferiwithin Ticks and Mice over the Course of a Single Transmission Cycle

Effects of vlsE Complementation on the Infectivity of Borrelia burgdorferi Lacking the Linear Plasmid lp28-1

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