Figure 3.

Serum from mice immunized with VLP-CspZ-Y207A/Y211A had more robust levels of bactericidal activity than VLP- or VLP-CspZ-vaccinated mice. Serum collected five C3H/HeN mice at 42 days post inoculation of virus-like particle (“VLP”), CspZ (“CspZ”), VLP-CspZ (“VLP-CspZ-WT”), or VLP-CspZ-Y207A/Y211A (“VLP-CspZ-Y207A/Y211A”) was mixed at indicated dilutions with guinea pig complement and 5 × 10⁵ cells/mL Borrelia burgdorferi strain B31-A3. The serum collected from three C3H/HeN mice at 42 days post inoculation of PBS was also included as negative control. Surviving spirochetes were quantified using dark-field microscopy after 24-h of incubation. (A) The survival percentage was derived from the proportion of serum-treated to untreated B. burgdorferi. Data shown are the mean ± SEM of survival percentage derived from three fields under the microscope for each sample. (B) The 50% borreliacidal titer of each serum sample, representing the dilution rate of the serum that effectively killed 50% of spirochetes, was obtained from the cure-fitting in Panel (A) (see Materials and Methods). Data shown are the mean ± SEM of borreliacidal titers of each serum sample derived from five CspZ, VLP-CspZ, or VLP-CspZ-Y207A/Y211A mice per group. The 50% borreliacidal titers of the serum samples from PBS- or VLP-inoculated mice were not detectable (“ND”) as those serum samples displayed no bactericidal activity. Statistical significances (p < 0.05) of differences in bactericidal titers relative to CspZ-immunized mice were determined using a t-test and are indicated (“*”).