Figure 7.

BBI39 is immunogenic by oral immunization and induces borreliacidal antibody responses. A, Serological response in mice immunized orally with recombinant Escherichia coli expressing BBI39. Mice were immunized orally with live recombinant E. coli expressing BBI39. Blood samples were collected on days 0, 12, 28, and 49, and antibody levels were measured by enzyme-linked immunosorbent assay (ELISA) using 1:100 serum dilutions. The average of triplicate readings per mouse/per group was determined, and the error bar indicates standard deviation. B, Immunoglobulin G (IgG) isotypes for orally immunized BBI39 antibodies. BBI39 antibodies measured by ELISA were subtyped into IgG1 (black bars) and IgG2a (gray bars). C, In vitro bacteriostatic activities of BBI39 antibodies. Spirochetes were incubated with normal mouse serum (NMS), OspA antibodies (positive control), FlaB antibodies (negative control), and BBI39 antibodies in the absence of active complement. The sensitivity of spirochetes to the bactericidal effects of the antibodies was assessed by a regrowth assay after 48 hours of antibody incubation. Growth of the spirochetes was determined by dark-field microscopy every 24 hours. BBI39 antisera showed significant difference in borreliacidal activities compared with that of normal mouse serum or FlaB antibodies (*P < .001).