BORRELIA-BURGDORFERI STRAIN-SPECIFIC OSP C-MEDIATED IMMUNITY IN MICE

Antibodies to the outer surface proteins (Osps) A, B, and C of the spi rochete Borrelia burgdorferi can prevent infection in animal models of Lyme borreliosis. We have previously demonstrated that immune serum f rom mice infected with B. burgdorferi N40 can also prevent challenge i nfection and induce disease regression in infected mice. The antigens targeted by protective and disease-modulating antibodies are presently unknown, but they do not include Osp A or Osp B. Because Osp C antibo dies are present in immune mouse serum, we investigated the ability of hyperimmune serum to recombinant Osp C (N40) to protect mice against challenge infection with N40 spirochetes. In both active and passive i mmunization studies, Osp C (N40) antiserum failed to protect mice from challenge infection with cultured organisms. Mice actively immunized with recombinant Osp C (N40) were susceptible to tick-borne challenge infection, and nymphal ticks remained infected after feeding on Osp C- hyperimmunized mice. In contrast, similar immunization studies perform ed with Osp C (PKo) antiserum prevented challenge infection of mice wi th a clone of PKo spirochetes pathogenic for mice. Both Osp C (N40) an d Osp C (PKo) antisera showed minimal in vitro borreliacidal activity, and immunofluorescence studies localized Osp C beneath the outer memb rane of both N40 and PKo spirochetes. We conclude that Osp C antibody- mediated immunity is strain specific and propose that differences in O sp C surface expression by spirochetes in vivo may account for strain- specific immunity.