Lyme disease is caused by spirochetes that have been grouped into three different genospecies, Borrelia burgdorferi, B. afzelii, and B. garinii. Interestingly, all three genospecies seem to populate different niches in the mammalian host during infection. For example, B. burgdorferi and B. afzelii are commonly associated with disease involving the heart, joints, and skin, while B. garinii often causes central nervous system abnormalities. It was recently shown that both B. burgdorferi and B. afzelii bind host serum complement inhibitor factor H on their cell surface, which possibly enhances their resistance to serum. By contrast, most B. garinii isolates do not bind factor H and are killed by mammalian serum. This observation has led to the suggestion that B. garinii organisms persistently infect the central nervous system because it is an environment limited in cytotoxic complement. Recently, several B. burgdorferi outer surface lipoproteins (Osp) were identified by us and others that can bind factor H in vitro. The factor H binding proteins that are most relevant include a family of lipoproteins related to OspE as well as a borrelial surface lipoprotein designated CspA. Consistent with their ability to bind factor H, all of these surface lipoproteins have been shown to enhance serum resistance. We and others have previously reported that expressing the B. burgdorferi strain 297 OspE protein in a serum sensitive B. garinii strain results in increased resistance to serum-mediated killing. We also have shown that mutating the cspA gene in a virulent strain of B. burgdorferi results in a mutant that is exquisitely sensitive to serum-mediated killing. Furthermore, we also have recently shown that CspA expression is required for B. burgdorferi to survive in the midgut of ticks as they engorge on mammalian blood. The combined observations are consistent with our hypothesis that CspA and the OspE surface lipoproteins are integral to serum resistance in B. burgdorferi. To directly examine this underlying hypothesis and further examine the mechanistic role played by these proteins in transmission of B. burgdorferi from the tick to mammal, we propose the following two Specific Aims.
In Specific Aim 1 we will use several novel strains we recently generated to examine the role of CspA in virulence and disease pathogenesis using the mouse model of Lyme disease.
In Specific Aim 2 we will examine a strain that lacks expression of the OspE-related lipoproteins in both wild type B. burgdorferi and in our CspA mutant strain to better assess their role(s) in serum resistance and Lyme disease pathogenesis during the borrelial enzootic cycle. Finally, in the revised proposal we have included more mechanism-based studies to determine if factor H binding to CspA and OspE actually enhances degradation of C3b to iC3b on the surface of this organism, which is the current dogma in the field. Since our last submission, we have generated interesting data indicating that factor H binding proteins may not enhance generation of iC3b on the surface of B. burgdorferi after all, and we will examine this observation in more detail in our revised Aim 2.

Public Health Relevance

The combined studies could result in the identification of new mechanisms that allow Lyme disease bacteria to evade the initial host immune surveillance system after infection. Information derived from the proposed studies could be used to generate a new vaccine or disease modulating therapeutic for Lyme disease. Given that Lyme disease is the most prevalent tick-borne infection in the United States, unique insight from the proposed studies that could lead to a new vaccine strategy for Lyme disease could greatly benefit overall public health in the United States and abroad.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21AI085310-02
Application #
8075005
Study Section
Special Emphasis Panel (ZRG1-IDM-A (80))
Program Officer
Breen, Joseph J
Project Start
2010-05-24
Project End
2013-04-30
Budget Start
2011-05-01
Budget End
2013-04-30
Support Year
2
Fiscal Year
2011
Total Cost
$181,405
Indirect Cost
Name
University of Oklahoma Health Sciences Center
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
878648294
City
Oklahoma City
State
OK
Country
United States
Zip Code
73117
Kenedy, Melisha R; Luthra, Amit; Anand, Arvind et al. (2014) Structural modeling and physicochemical characterization provide evidence that P66 forms a ?-barrel in the Borrelia burgdorferi outer membrane. J Bacteriol 196:859-72
Lenhart, Tiffany R; Kenedy, Melisha R; Yang, Xiuli et al. (2012) BB0324 and BB0028 are constituents of the Borrelia burgdorferi ?-barrel assembly machine (BAM) complex. BMC Microbiol 12:60
Kenedy, Melisha R; Lenhart, Tiffany R; Akins, Darrin R (2012) The role of Borrelia burgdorferi outer surface proteins. FEMS Immunol Med Microbiol 66:1-19
Kenedy, Melisha R; Akins, Darrin R (2011) The OspE-related proteins inhibit complement deposition and enhance serum resistance of Borrelia burgdorferi, the lyme disease spirochete. Infect Immun 79:1451-7
Caimano, Melissa J; Kenedy, Melisha R; Kairu, Toru et al. (2011) The hybrid histidine kinase Hk1 is part of a two-component system that is essential for survival of Borrelia burgdorferi in feeding Ixodes scapularis ticks. Infect Immun 79:3117-30