OspE-related, OspF-related, and Elp lipoproteins are immunogenic in baboons experimentally infected with Borrelia burgdorferi and in human lyme disease patients

Abstract

Presently, the rhesus macaque is the only nonhuman primate animal model utilized for the study of Lyme disease. While this animal model closely mimics human disease, rhesus macaques can harbor the herpes B virus, which is often lethal to humans; macaques also do not express the full complement of immunoglobulin G (IgG) subclasses found in humans. Conversely, baboons contain the full complement of IgG subclasses and do not harbor the herpes B virus. For these reasons, baboons have been increasingly utilized as the basis for models of infectious diseases and studies assessing the safety and immunogenicity of new vaccines. Here we analyzed the capability of baboons to become infected with Borrelia burgdorferi, the agent of Lyme disease. Combined culture and PCR analyses of tick- and syringe-infected animals indicated that baboons are a sufficient host for B. burgdorferi. Analysis of the antibody responses in infected baboons over a 48-week period revealed that antibodies are generated early during infection against many borrelial antigens, including the various OspE, OspF, and Elp paralogs that are encoded on the ubiquitous 32-kb circular plasmids (cp32s). By using the baboon sera generated by experimental infection it was determined that a combination of two cp32-encoded lipoproteins, OspE and ElpB1, resulted in highly specific and sensitive detection of B. burgdorferi infection. An expanded analysis, which included 39 different human Lyme disease patients, revealed that a combination of the OspE and ElpB1 lipoproteins could be the basis for a new serodiagnostic assay for Lyme disease. Importantly, this novel serodiagnostic test would be useful independent of prior OspA vaccination status.

FIG. 1.

Identification of an erythematous lesion on baboon TI-2 at the site of feeding by a tick infected with B. burgdorferi strain B31-CDC. (A) The lesion observed on a tick-infected baboon (TI-2) where B. burgdorferi B31-CDC-infected ticks were placed. (B) The absence of lesion or inflammation on baboon NC-1 where uninfected ticks were placed. The bars represent 2 cm, and arrows indicate the site of tick attachment.

FIG. 2.

Antibody response of baboons to OspE-related, OspF-related, and Elp proteins. ELISAs to determine combined IgM and IgG antibody titers were performed with sera from TI-1 (A), TI-2 (B), SI-1 (C), and SI-2 (D) baboons from 6 to 48 weeks p.i. Reciprocal antibody endpoint titers were determined as described in Materials and Methods. Asterisks indicate that the titer was greater than 1:51,200.

FIG. 3.

Comparison of baboon reactivity to B. burgdorferi WCL and a combination of the OspE and ElpB1 proteins. Combined IgM and IgG ELISA OD₄₀₅ values were measured by using sera from NC-1 (A), NC-2 (B), TI-1 (C), TI-2 (D), SI-1 (E), and SI-2 (F) baboons during the 48 weeks of analysis to compare the seroreactivity to OspE and ElpB1 and WCL as indicated in Materials and Methods. Values displayed are mean OD₄₀₅ values. Asterisks indicate that the mean OD₄₀₅ for OspE and ElpB1 was significantly higher than the mean OD₄₀₅ for WCL (P < 0.001).