A key mechanism for immune evasion and persistent infection by the Lyme disease spirochete, Borrelia burgdorferi, is antigenic variation of the VlsE surface protein. Despite the presence of a substantial number of additional proteins residing on the bacterial surface, VlsE is the only antigen that exhibits ongoing variation of its exposed epitopes. Recent work in our lab has identified a VlsE-mediated immune avoidance system that allows non-VlsE surface antigens to escape the killing effects of host antibodies. Moreover, we have identified the Arp lipoprotein as one such surface antigen that benefits from VlsE-mediated immune protection. Despite this important evidence, certain functional and mechanistic aspects involved in this system are still unknown. Our long-term goals are to determine the mechanism and overall implications of surface antigen protection promoted by the VlsE lipoprotein during host infection by B. burgdorferi. The objective of this application is to decipher the functional details of factors involved in VlsE-mediated immune avoidance, and identify any additional B. burgdorferi surface antigens that are shielded by VlsE. Based on published studies and preliminary findings, our central hypothesis is that VlsE exists establishes protein-protein interactions with Arp and other proteins on the B. burgdorferi cell surface. Additionally, we hypothesize that the presence of VlsE functions to dampen the antibody response to Arp. The rationale for the proposed research is that identifying the functional details of this system will provide the knowledge required to design downstream studies targeted at dissecting the overall mechanism. Together, the proposed research is relevant to NIH?s mission that pertains to developing fundamental knowledge that will potentially help to reduce the burdens of human illness and disability. Guided by preliminary findings, our hypotheses will be tested by pursuing two specific aims: 1) Determine whether VlsE directly interacts with Arp and other B. burgdorferi cell surface proteins; and 2) Determine whether the presence of VlsE modulates the antibody response to Arp. Under the first aim, a specialized in vivo crosslinking/elution technique will be used to detect protein-protein interactions between mutant VlsE and Arp, and to identify novel VlsE binding partners. Under the second aim, qRT-PCR will be utilized to quantitate the relative arp expression levels during host infection by a VlsE-deficient clone compared to a wild type control, and anti-Arp antibody titers in mice infected with clones expressing or lacking VlsE will be assessed by ELISA. The proposed work is innovative, because it utilizes a new VlsE/Arp over-expresser clone to analyze potential VlsE-Arp interactions, and uses the Arp lipoprotein as a readout for VlsE protection assays. Overall, these studies will significantly advance our knowledge of immune evasion by B. burgdorferi, and provide more useful strategies to prevent and treat Lyme disease in humans.
The proposed studies are of an important area of Lyme disease research that has potential applicability to understanding immune evasion and persistence by Borrelia burgdorferi and other Lyme disease-causing Borrelia species. The proposed research has relevance to public health because the resulting discoveries have the potential to fundamentally advance the field of B. burgdorferi immune evasion, and may have broad implications for antigenic variation systems in other animal and human pathogens. Thus, the findings are ultimately expected to be applicable to the health of human beings.
