Active immunization with Escherichia coli-expressed recombinant
outer surface protein C (
OspC) of Borrelia burgdorferi has been demonstrated to confer protection against a tick-transmitted
infection on laboratory animals. A previous study in this laboratory showed that
OspC antibody raised against a denatured immunogen isolated from B. burgdorferi cells failed to provide protective immunity. Therefore, to determine whether the protective
epitope of the recombinant
antigen was sensitive to denaturation, recombinant
OspC preparations were subjected to heat and chemical treatments prior to animal immunization. Following seroconversion to
OspC, the animals were challenged with an infectious dose of B. burgdorferi B31 by
tick bite. Whereas mice immunized with a soluble, nondenatured form continued to show protection rates close to 100%, mice that had been immunized with denatured
antigen were not protected. Furthermore, mice that were immunized with an insoluble (rather than a soluble), nondenatured form of the recombinant
OspC showed a protection rate of only 40%. Protective
epitope localization experiments showed that either the amino or the carboxy end of the
recombinant protein was required to react with a protective
OspC-specific
monoclonal antibody. The data from these experiments demonstrate that a conformational organization of the
protein is essential for the protective capability of the strain B31
OspC immunogen.