Novel surface proteins in the pathogenesis and diagnosis of Lyme disease

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Lyme disease is caused by an infection with the spirochete Borrelia burgdorferi. Transmitted between mammal reservoirs by the bite of an Ixodes tick, the pathogen exists in a complex life cycle that requires long-term persistence in arthropod and mammal hosts. The mechanisms responsible for persistence and the pathogenesis of Lyme disease are not well understood, but may involve interactions between bacterial surface proteins and the host. Previous experiments have shown that differential gene expression of surface proteins assists the pathogen in adaptation and persistence in a new host. Most B. burgdorferi surface proteins have no homology to known proteins, making the identification of virulence factors difficult. Gene expression analyses can be used to identify potentially important gene products for further study, based on the conditions under which they are expressed.

To this end, the B. burgdorferi in vivo transcriptome of selected potential surface proteins was analyzed to identify promising targets for further study. Based on these analyses and other observations from the literature, the lipoproteins BbCRASP-2 and BBK07 were selected for further characterization. My hypothesis is that these proteins are important for B. burgdorferi virulence and persistence in the murine host. The surface exposure of each protein was assessed, as well as a detailed transcriptional profile of each gene. Using specific antibody-mediated interference and gene inactivation, I show that neither BbCRASP-2 nor BBK07 is essential for infectivity or pathogenesis in the murine model of Lyme disease. My results also indicate that BBK07 is a novel immunodominant antigen of B. burgdorferi that could be used as a serodiagnostic marker for human Lyme disease. Using a peptide library, the most immunodominant epitopes of BBK07 were identified, and shown to improve the diagnostic accuracy over that of the full-length recombinant BBK07. Finally, I show that BBK07-based diagnosis was sensitive even in the early stages of Lyme disease, and that the addition of BBK07 epitopes to current serodiagnostic assays could improve their sensitivity.