OUTER SURFACE PROTEIN-C (OSPC), BUT NOT P39, IS A PROTECTIVE IMMUNOGEN AGAINST A TICK-TRANSMITTED BORRELIA-BURGDORFERI CHALLENGE - EVIDENCEFOR A CONFORMATIONAL PROTECTIVE EPITOPE IN OSPC

Outbred mice were immunized with the soluble fraction of a crude Esche richia coli lysate containing either recombinant outer surface protein C (OspC) or P39 of Borrelia burgdorferi B31 (low passage). Following seroconversion, the mice were challenged with an infections dose of B. burgdorferi B31 via the natural transmission mode of tick bite. Three mice immunized with P39 were not protected; however, all 12 of the re combinant OspC-immunized mice were protected from infection as assayed by culture and serology. Although OspC has been shown to be a protect ive immunogen against challenge with in vitro-cultured borrelia admini stered by needle, this study is the first to demonstrate OspC effectiv eness against tick-borne spirochetes. Following feeding, all ticks sti ll harbored B. burgdorferi, suggesting that the mechanism of protectio n is not linked to destruction of the infectious spirochete within the tick. In a separate experiment, groups of four mice were immunized wi th protein fractions from B. burgdorferi B31 purified by preparative g el electrophoresis in an attempt to identify potential protective anti gens. Many of these mice developed high-titer-antibody responses again st OspC, but curiously the mice were susceptible to B. burgdorferi inf ection via tick bite. These results suggest that the protective epitop e(s) on OspC is heat sensitive/conformational, a finding which has imp lications in vaccine development.