Enhanced Protective Immunogenicity of Homodimeric Borrelia burgdorferi Outer Surface Protein C

Abstract

Lyme borreliosis is caused by tick-transmitted spirochetes of the Borrelia burgdorferi sensu lato group and is the most common vector-borne disease in the United States and Europe. Outer surface protein C (OspC) is a 23-kDa outer surface lipoprotein expressed during spirochete transmission from the tick to the vertebrate host. In a previous study, we found that immunization with a recombinant disulfidebridged dimeric form of OspC (D-OspC) stimulates increased antibody responses relative to immunization with commonly employed monomeric OspC. Here, we report that mice immunized with dimeric OspC proteins also exhibited enhanced protection against infection with the cognate B. burgdorferi strain. Mice were protected by four immunizations containing as little as 100 ng of dimeric OspC, suggesting that this form of the protein can induce protective immunity within a dose range reasonable for a human or veterinary vaccine. In contrast, monomeric OspC was only partially protective at much higher doses. IgG subclass analysis revealed that D-OspCimmunized animals mainly possessed anti-OspC-IgG1. In contrast, infected animals develop anti-OspC restricted to the IgG3 isotype. A subset of antibodies generated by dimeric OspC immunization did not recognize the monomeric variant, indicating that unique epitopes exist on the dimeric form. Moreover, monoclonal antibodies that recognized only dimeric OspC protected mice from B. burgdorferi challenge, whereas another monoclonal that recognized both immunogens was not protective. These studies suggest that this dimeric OspC presents distinctive epitopes that generate antibodies protective against B. burgdorferi infection and could be a useful vaccine component.

Epitope mapping of Borrelia burgdorferi OspC protein in homodimeric fold

“…The tertiary and/or quaternary structure of OspC and related epitopes accessibility seems to play a crucial part in borrelia dissemination and protectiveness of elicited antibodies. It has been proposed earlier, that only non‐denatured protein is able to elicit protective antibodies . The importance of preserved tertiary structure also supports the results of experiments with GST‐tag, enhancing the folding, fused to recombinant OspC.…”

“…The ability to form dimers was confirmed by size exclusion chromatography (Supporting Information). To exclude the possibility that the spontaneous disulphide‐dependent dimers or oligomers are formed through the formation of bonds between cysteines C130 and C130' the non‐reducing SDS‐PAGE was performed. Only the minor fraction of purified OspC was oxidised, and the dimeric form wasn't abolished [Fig.…”

Analysis of the antigenic determinants of the OspC protein of the Lyme disease spirochetes: Evidence that the C10 motif is not immunodominant or required to elicit bactericidal antibody responses

“…The minor differences could indicate that the C10 motif is either weakly immunogenic or that it may contribute directly or indirectly to the presentation of a conformationally defined epitope. Several studies have provided evidence for the existence of conformational epitopes in OspC [23,26,49].…”

“…OspC variants or “OspC types”of OspC are differentiated by letter designations [21,22]. While OspC is a protective antigen [23,24], due to its variation, protection is generally strain specific [25,26]. The narrow protection provided by any one given OspC type protein suggests that the protective epitopes of OspC reside within variable regions of the protein [27,28].…”

Immunization of mice with Borrelia burgdorferi lp54 gene encoded recombinant proteins does not provide protection against tick transmitted infectious challenge

“…Several candidate proteins have been identified that fit this criteria and have been evaluated for protective capability following immunization in experimental animals [6]. Most have shown little or no immunizing protection against tick bite challenge with the exception of OspC which has shown the best potential as a protective immunogen [7][8][9][10]. However, doubts have arisen that with OspC strain heterogeneity, cross protection from different B. burgdorferi strains would be limited.…”