DBPA, BUT NOT OSPA, IS EXPRESSED BY BORRELIA-BURGDORFERI DURING SPIROCHETEMIA AND IS A TARGET FOR PROTECTIVE ANTIBODIES

DbpA is a target for antibodies that protect mice against infection by cultured Borrelia burgdorferi. Infected mice exhibit early and sustai ned humoral responses to DbpA and DbpB, suggesting that these proteins are expressed in vivo. Many antigens expressed in mammals by B. burgd orferi are repressed in vitro at lower growth temperatures, and we hav e now extended these observations to include DbpA and DbpB. To confirm that the protective antigen DbpA is expressed in vivo and to address the question of its accessibility to antibodies during infection, we e xamined B. burgdorferi in blood samples from mice following cutaneous inoculation. B. burgdorferi was visualized by dark-field microscopy in plasma samples from spirochetemic mice, and an indirect immunofluores cence assay showed that these spirochetes were DbpA positive and OspA negative. We developed an ex vivo borreliacidal assay to show that hyp erimmune antiserum against DbpA, but not OspA, killed these plasma-der ived spirochetes, demonstrating that DbpA is accessible to antibodies during this phase of infection. Blood transferred from spirochetemic d onor mice readily established B. burgdorferi infection in naive recipi ent mice or mice hyperimmunized with OspA, while mice hyperimmunized w ith DbpA showed significant protection against challenge,vith host-ada pted spirochetes. Antiserum from persistently infected mice had borrel iacidal activity against both cultured and plasma derived spirochetes, and adsorption of this serum with DbpA substantially depleted this ki lling activity. Our observations show that immunization with DbpA bloc ks B. burgdorferi dissemination from the site of cutaneous inoculation and suggest that DbpA antibodies may contribute to control of persist ent infection.