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.
SUMMARY Treponema denticola is an anaerobic spirochete whose abundance in the subgingival crevice correlates with the development and severity of periodontal disease. T. denticola’s ability to survive and thrive in the hostile environment of the periodontal pocket is due, at least in part, to its ability to bind factor H (FH), a negative regulator of the alternative complement pathway. The FH binding protein of T. denticola has been identified as FhbB and its atomic structure has been determined. The interaction of FH with T. denticola is unique in that FH bound to the cell surface is cleaved by the T. denticola protease, dentilisin. It has been postulated that FH cleavage by T. denticola leads to immune dysregulation in periodontal pockets. In this study, we conduct a comparative assessment of the sequence, properties, structure, and ligand binding kinetics of the FhbB proteins of strains 33521 and 35405. The biological outcome of the interaction of these strains with FH could differ significantly as 33521 lacks dentilisin activity. The data presented here offer insight into our understanding of the interactions of T. denticola with the host and its potential to influence disease progression.
OspC is produced by all species of the Borrelia burgdorferi sensu lato complex and is required for infectivity in mammals. To test the hypothesis that the conserved C-terminal motif (C10) of OspC is required for function in vivo, a mutant Borrelia burgdorferi strain (B31∷ospCΔC10) was created in which ospC was replaced with an ospC gene lacking the C10 motif. The ability of the mutant to infect mice was investigated using tick transmission and needle inoculation. Infectivity was assessed by cultivation, qRT-PCR, and measurement of IgG antibody responses. B31∷ospCΔC10 retained the ability to infect mice by both needle and tick challenge and was competent to survive in ticks after exposure to the blood meal. To determine if recombinant OspC protein lacking the C-terminal 10 amino acid residues (rOspCΔC10) can bind plasminogen, the only known mammalian derived ligand for OspC, binding analyses were performed. Deletion of the C10 motif resulted in a statistically significant decrease in plasminogen binding. Although deletion of the C10 motif influenced plasminogen binding, it can be concluded that the C10 motif is not required for OspC to carry out its critical in vivo functions in tick to mouse transmission.
Borrelia burgdorferiOspC is an outer membrane lipoprotein required for the establishment of infection in mammals. Due to its universal distribution among B. burgdorferi sensu lato strains and high antigenicity, it is being explored for the development of a next-generation Lyme disease vaccine. An understanding of the surface presentation of OspC will facilitate efforts to maximize its potential as a vaccine candidate. OspC forms homodimers at the cell surface, and it has been hypothesized that it may also form oligomeric arrays. Here, we employ site-directed mutagenesis to test the hypothesis that interdimeric disulfide bonds at cysteine 130 (C130) mediate oligomerization. B. burgdorferi B31 ospC was replaced with a C130A substitution mutant to yield strain B31::ospC(C130A). Recombinant protein was also generated. Disulfide-bond-dependent oligomer formation was demonstrated and determined to be dependent on C130. Oligomerization was not required for in vivo function, as B31::ospC(C130A) retained infectivity and disseminated normally. The total IgG response and the induced isotype pattern were similar between mice infected with untransformed B31 and those infected with the B31::ospC(C130A) strain. These data indicate that the immune response to OspC is not significantly altered by formation of OspC oligomers, a finding that has significant implications in Lyme disease vaccine design. (2,3,9,21,25,31). B. burgdorferi is maintained in an enzootic cycle involving Ixodes ticks and reservoir mammals and birds (4, 5, 18). As the spirochetes transit between ticks and reservoir hosts, differential gene expression aids in adaptation to the radically different environments. OspC, a 21-kDa plasmid-encoded lipoprotein, is upregulated in ticks concurrent with the blood meal and is expressed at a high level during the first weeks of infection in mammals (6,17,19,32,40,42,43). OspC is required to establish infection but not for persistence (20,(46)(47)(48)(49). The function of OspC has not yet been clearly defined (37). It has been hypothesized that ligand binding domain 1 (LBD1) of OspC binds a small ligand and that this interaction is required for the establishment of infection in mammals (13). OspC also binds other ligands, including Salp15 (a tick-derived protein with immunomodulatory activity) and plasminogen, by unknown mechanisms (1,10,22,23,29,38). Lyme borreliosis is an emerging infectious disease in North America and Europe caused by the spirochetes Borrelia burgdorferi, Borrelia garinii, and Borrelia afzeliiOspC is predominantly helical and forms a homodimer tethered to the outer membrane by an N-terminal tripalmitoyl-Sglyceryl-cysteine moiety (8,11,16,17,24,27,52). Residues lining the dimeric interface are conserved, while the remainder of OspC is variable in sequence. More than 30 phylogenetically distinct types of OspC have been defined (4, 11, 51). It has been hypothesized that OspC and its relapsing fever Borrelia ortholog (Vsp) form arrays in the outer membrane (30, 52).OspC is a candidate for a next-generation...
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