Antibody profiling of canine IgG responses to the OspC protein of the Lyme disease spirochetes supports a multivalent approach in vaccine and diagnostic assay development.

OspC performs essential functions during the enzootic cycle of the Lyme disease (LD) spirochetes. In this study, the specificity of antibody (Ab) responses to OspC was profiled to define the antigenic determinants during infection and after vaccination. Several OspC variants or 'types' were screened with serum from SNAP4Dx C6 positive dogs and with serum from rabbits hyperimmunized with OspC proteins. The OspC type-specific nature of the Ab response revealed that variable domains of OspC are immunodominant during infection and upon vaccination. To assess the potential of OspC to elicit Ab in the context of a bacterin vaccine, OspC production in strains cultivated in vitro was assessed. Immunoblot and indirect immunofluorescent antibody analyses demonstrated that production is low and that only a subset of cells actively produces OspC in vitro, raising questions about the potential of bacterin vaccines to stimulate significant anti-OspC Ab responses. The specificity of the OspC Ab response in experimentally infected mice over time was assessed to determine if domains shielded in the OspC homodimer become accessible and stimulate Ab production as infection progresses. The results demonstrate that the OspC Ab response remains focused on surface exposed variable regions of the protein throughout infection. In contrast to some earlier studies, it is concluded that conserved domains of OspC, including the C7 or C10 domain, do not elicit significant Ab responses during infection or upon vaccination. Collectively, the results indicate that OspC diversity must be considered in vaccine design and in the interpretation of diagnostic assays that employ OspC as a diagnostic antigen.