Antigenic variation plays a vital role in the pathogenesis of many infectious agents, most notably bacteria and protozoa that cause chronic infections. Borrelia burgdorferi and related organisms cause Lyme disease, a multistage, systemic infection that is transmitted by Ixodes ticks and has dermatologic, neurologic, arthralgic, and constitutional manifestations in humans and other animals. Lyme disease Borrelia have an elaborate antigenic variation system consisting of vlsE, a gene expressing a surface-exposed lipoprotein, and a series of vls silent cassettes, which serve as the source of sequences for random, segmental gene conversion events that change the sequence of the central cassette region of vlsE. It has been established that vlsE expression and variation are required for persistence of infection and immune evasion, yet the mechanisms that govern this biologically important process are poorly understood. In this project, several approaches will be used to address these questions.
In Specific Aim 1, a newly developed tissue explant model system will be optimized and utilized to study vlsE recombination. The effects of environmental conditions on vlsE expression and variation will be analyzed by quantitative polymerase chain reaction (qPCR) and sequence specific PCR.
Specific Aim 2 involves the systematic screening and characterization of trans-acting factors (e.g. proteins) that affect vlsE recombination and expression. A transposon mutant library will be used to screen for genes important in vlsE variation and regulation, and in vitro expression libraries will be employed to screen for factors that regulate vlsE expression and variation.
In Specific Aim 3, the roles of cis-acting elements (vls-associated DNA sequences) in vlsE recombination and functional activities will be examined using a combination of bioinformatic analysis of sequences, comparison of the properties of divergent vls systems, and mutagenic analysis of DNA sequences thought to be important in VlsE sequence variation and function. These studies will define the importance and mechanistic properties of VlsE in the immune evasion, persistent infection, and pathogenesis of Lyme disease Borrelia.

Public Health Relevance

Lyme disease is the most prevalent tick-borne infection in North America and Eurasia and can cause long-term infections that affect the skin, joints, heart, and central nervous system. The bacterium that causes Lyme disease (Borrelia burgdorferi) remains hidden from the immune system by constantly changing a surface protein called VlsE. This project studies the mechanisms Borrelia burgdorferi uses to change VlsE. Understanding these mechanisms will help us to discover ways to prevent Lyme disease and to inhibit the organism's ability to cause persistent infection and debilitating symptoms.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Bacterial Pathogenesis Study Section (BACP)
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Breen, Joseph J
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University of Texas Health Science Center Houston
Schools of Medicine
United States
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Edmondson, Diane G; Prabhakaran, Sabitha; Norris, Steven J et al. (2017) Enhanced Protective Immunogenicity of Homodimeric Borrelia burgdorferi Outer Surface Protein C. Clin Vaccine Immunol 24:
Norris, Steven J (2014) vls Antigenic Variation Systems of Lyme Disease Borrelia: Eluding Host Immunity through both Random, Segmental Gene Conversion and Framework Heterogeneity. Microbiol Spectr 2:
Magnarelli, Louis A; Williams, Scott C; Norris, Steven J et al. (2013) Serum antibodies to Borrelia burgdorferi, Anaplasma phagocytophilum, and Babesia microti in recaptured white-footed mice. J Wildl Dis 49:294-302
Magnarelli, Louis A; Norris, Steven J; Fikrig, Erol (2012) Serum antibodies to whole-cell and recombinant antigens of Borrelia burgdorferi in cottontail rabbits. J Wildl Dis 48:12-20
Norris, Steven J (2012) How do lyme borrelia organisms cause disease? The quest for virulence determinants(). Open Neurol J 6:119-23
Norris, Steven J; Howell, Jerrilyn K; Odeh, Evelyn A et al. (2011) High-throughput plasmid content analysis of Borrelia burgdorferi B31 by using Luminex multiplex technology. Appl Environ Microbiol 77:1483-92
Coutte, Loïc; Botkin, Douglas J; Gao, Lihui et al. (2009) Detailed analysis of sequence changes occurring during vlsE antigenic variation in the mouse model of Borrelia burgdorferi infection. PLoS Pathog 5:e1000293
Lin, Tao; Gao, Lihui; Edmondson, Diane G et al. (2009) Central role of the Holliday junction helicase RuvAB in vlsE recombination and infectivity of Borrelia burgdorferi. PLoS Pathog 5:e1000679
Embers, Monica E; Liang, Fang Ting; Howell, Jerrilyn K et al. (2007) Antigenicity and recombination of VlsE, the antigenic variation protein of Borrelia burgdorferi, in rabbits, a host putatively resistant to long-term infection with this spirochete. FEMS Immunol Med Microbiol 50:421-9
Norris, Steven J (2006) Antigenic variation with a twist--the Borrelia story. Mol Microbiol 60:1319-22

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