Active and passive immunity against Borrelia burgdorferi decorin binding protein A (DbpA) protects against infection

Abstract

Borrelia burgdorferi, the spirochete that causes Lyme disease, binds decorin, a collagen-associated extracellular matrix proteoglycan found in the skin (the site of entry for the spirochete) and in many other tissues. Two borrelial adhesins that recognize this proteoglycan, decorin binding proteins A and B (DbpA and DbpB, respectively), have recently been identified. Infection of mice by low-dose B. burgdorferi challenge elicited antibodies against DbpA and DbpB that were sustained at high levels, suggesting that these antigens are expressed in vivo. Scanning immunoelectron microscopy showed that DbpA was surface accessible on intact borreliae. Passive administration of DbpA antiserum protected mice from infection following challenge with heterologous B. burgdorferi sensu stricto isolates, even when serum administration was delayed for up to 4 days after challenge. DbpA is the first antigen target identified that is capable of mediating immune resolution of early, localized B. burgdorferi infections. DbpA immunization also protected mice from B. burgdorferi challenge; DbpB immunization was much less effective. DbpA antiserum inhibited in vitro growth of many B. burgdorferi sensu lato isolates of diverse geographic, phylogenetic, and clinical origins. In combination, these findings support a role for DbpA in the immunoprophylaxis of Lyme disease and suggest that DbpA vaccines have the potential to eliminate early-stage B. burgdorferi infections.

FIG. 1

Diagrammatic representation of the recombinant Dbp immunogens evaluated for vaccine efficacy. All proteins included the complete DbpA or DbpB coding sequence following Cys at the site of the presumed posttranslational processing. Lpp1:DbpA₂₉₇ is a fusion of this mature DbpA protein sequence to a modified lpp leader peptide. Fusions of DbpA and DbpB to a (His)₆ tag were made within, or in place of, their respective leader peptides. Lpp2:DbpA_N40His has both a N-terminal lpp leader and a C-terminal (His)₆ fusion.

FIG. 2

Detection of surface-directed antibody labeling by scanning immunoelectron microscopy. B. burgdorferi B31 was incubated in BSKII plus mouse anti-DbpA (A and B), mouse anti-OspA (C), or normal mouse serum (D) prior to labeling of bound antibodies with goat anti-mouse IgG plus IgM-conjugated colloidal gold particles. Typical electron micrographs for these samples are shown except for panel B, which represents spirochetes with atypically heavy anti-DbpA labeling. Bars, 0.2 μm.

FIG. 3

Early antibody responses to DbpA and OspA elicited by low-dose challenge. Multilane immunoblot showing antibodies reactive with DbpA and OspA at weeks 2, 4, and 8 postchallenge (lanes 4 to 12) in sera pooled from mice infected by challenge with 10², 10³, or 10⁴ B. burgdorferi (B.b.) B31 spirochetes. Lanes: 1, anti-DbpA MAb, 1.0 μg/ml; 2, anti-OspA MAb, 0.2 μg/ml; 3, normal mouse serum. Samples for SDS-PAGE were 2 μg of purified Lpp1:DbpA₂₉₇ or OspA_B31.

FIG. 4

Relative levels of IgG antibodies to DbpA, DbpB, and other selected borrelial antigens during chronic infection of mice. Sera were collected for a 1-year period from mice infected by challenge with 10² B31. Sera were pooled at each time point, and end point titers of IgG specific for each of four recombinant borrelial antigens were determined by ELISA. E. coli MBP, the fusion partner for recombinant P39, was used as a negative control protein.