Peptide Antigen for Diagnostics

Notes From:

Arnaboldi PM, Seedarnee R, Sambir M, Callister SM, Imparato JA, Dattwyler RJ. An outer surface protein C (OspC) peptide derived from Borrelia burgdorferi sensu strico as a target for the serodiagnosis of early Lyme disease. Clin Vaccine Immunol. 2013 Jan 30.

Current CDC guidelines for the serodiagnosis of Lyme disease mandate a two tier analysis for improved accuracy, as current IgM and IgG serological assays lack sufficient specificity and/or are insensitive for the detection of antibody present at the time that many patients with early Lyme disease seek initial medical care. The first tier assay is an ELISA, typically utilizing lysates of whole-Borrelia as the target, which if positive or equivocal, is followed by a western blot containing several whole Borrelia proteins. Some of the whole protein antigens present in both whole cell ELISAs and in western blot assays contain epitopes that are cross-reactive with epitopes found in antigens of other bacteria. Because of the need to maintain a reasonable balance between specificity and sensitivity, current laboratory tests fail to serodiagnose early Lyme disease approximately 50% of the time.

OspC is a Borrelia surface protein required for transmission of the bacteria from the midgut of tick into the human host. It is a protein of significant diagnostic value because it is required for entry into the mammalian host, and therefore, will always present during infection and is expressed during the initiation of infection. However, the OspC protein is not highly conserved, containing numerous subtypes that have significant sequence variability. Furthermore, some previous studies using whole recombinant OspC as a serodiagnostic for Lyme disease demonstrated a high level of cross-reactivity within negative disease control samples, though cross-reactivity was not often seen in normal control serum.

In the present study we mapped linear epitopes within the OspC protein to identify highly-conserved regions lacking cross-reactivity with antigens from other bacteria. We have generated an antigenic peptide (OspC1) that binds to antibody from early Lyme disease patients with high specificity. OspC1 outperformed a previously identified peptide antigen from OspC (PepC10) in an ELISA-based immunoassay, and is a potential target for inclusion into a sensitive multi-peptide serological assay for the diagnosis of early Lyme disease.

An elegant analysis by Barbour, et.al. demonstrated that an effective diagnostic serological assay for the detection of early Borrelia infection would require a minimum of five distinct antigens to attain an appropriate level of both specificity and sensitivity that would be unaffected by antigenic variation.

We identified 3 potential epitopes for further analysis. Of the three peptide epitopes identified, OspC1, a 20AA peptide from the N-terminal region of OspC, was the only peptide that was both highly conserved among the different OspC types and capable of distinguishing between individual Lyme disease patient sera and healthy control sera.

As a target for a serological diagnostic assay, OspC1 has a number of desirable attributes: it is derived from a principal virulence factor that is required for mammalian infection, it is expressed very early in infection increasing the likelihood of an immune response being mounted against it, it is highly conserved among different OspC genotypes, and it identified a significant majority of patients with early disease. Our data suggest that OspC1 should be considered a viable candidate for testing in a multi-peptide diagnostic assay.

An assay containing 5 or more specific peptide antigens, derived from multiple B. burgdorferi proteins, would markedly improve upon currently available technologies in both specificity and sensitivity, and represent a potentially viable standalone laboratory test for all phases of Lyme disease diagnosis, especially early disease.

Conflict of Interest Statement: R.J.D. is a shareholder in Biopeptides, Corp. P.M.A. and M.S. have research appointments with Biopeptides, Corp. The peptides OspC1 and OspC30 are protected under U.S. provisional patent application No. 61/705,344, filed by Biopeptides, Corp., and could serve as a future source of funding. S.M.C., R.S., and J.A.I. have no conflicts.