Borrelia burgdorferi spirochetes that harbor only a portion of the lp28-1 plasmid elicit antibody responses detectable with the C6 test for Lyme disease

Laboratory Diagnosis of Lyme Borreliosis

Lyme borreliosis is caused by a growing list of related, yet distinct, spirochetes with complex biology and sophisticated immune evasion mechanisms. It may result in a range of clinical manifestations involving different organ systems, and can lead to persistent sequelae in a subset of cases. The pathogenesis of Lyme borreliosis is incompletely understood, and laboratory diagnosis, the focus of this review, requires considerable understanding to interpret the results correctly. Direct detection of the infectious agent is usually not possible or practical, necessitating a continued reliance on serologic testing. Still, some important advances have been made in the area of diagnostics, and there are many promising ideas for future assay development. This review summarizes the state of the art in laboratory diagnostics for Lyme borreliosis, provides guidance in test selection and interpretation, and highlights future directions.

Antigenic Variation in Bacterial Pathogens

Antigenic variation is a strategy used by a broad diversity of microbial pathogens to persist within the mammalian host. Whereas viruses make use of a minimal proofreading capacity combined with large amounts of progeny to use random mutation for variant generation, antigenically variant bacteria have evolved mechanisms which use a stable genome, which aids in protecting the fitness of the progeny. Here, three well-characterized and highly antigenically variant bacterial pathogens are discussed: Anaplasma, Borrelia, and Neisseria. These three pathogens display a variety of mechanisms used to create the structural and antigenic variation needed for immune escape and long-term persistence. Intrahost antigenic variation is the focus; however, the role of these immune escape mechanisms at the population level is also presented.

Single-tier testing with the C6 peptide ELISA kit compared with two-tier testing for Lyme disease

For the diagnosis of Lyme disease, the 2-tier serologic testing protocol for Lyme disease has a number of shortcomings including low sensitivity in early disease; increased cost, time, and labor; and subjectivity in the interpretation of immunoblots. In this study, the diagnostic accuracy of a single-tier commercial C6 ELISA kit was compared with 2-tier testing. The results showed that the C6 ELISA was significantly more sensitive than 2-tier testing with sensitivities of 66.5% (95% confidence interval [CI] 61.7-71.1) and 35.2% (95% CI 30.6-40.1), respectively (P < 0.001) in 403 sera from patients with erythema migrans. The C6 ELISA had sensitivity statistically comparable to 2-tier testing in sera from Lyme disease patients with early neurologic manifestations (88.6% versus 77.3%, P = 0.13) or arthritis (98.3% versus 95.6%, P = 0.38). The specificities of C6 ELISA and 2-tier testing in over 2200 blood donors, patients with other conditions, and Lyme disease vaccine recipients were found to be 98.9% and 99.5%, respectively (P < 0.05, 95% CI surrounding the 0.6 percentage point difference of 0.04 to 1.15). In conclusion, using a reference standard of 2-tier testing, the C6 ELISA as a single-step serodiagnostic test provided increased sensitivity in early Lyme disease with comparable sensitivity in later manifestations of Lyme disease. The C6 ELISA had slightly decreased specificity. Future studies should evaluate the performance of the C6 ELISA compared with 2-tier testing in routine clinical practice.

Effect of Borrelia burgdorferi genotype on the sensitivity of C6 and 2-tier testing in North American patients with culture-confirmed Lyme disease

BACKGROUND

A potential concern with any serologic test to detect antibodies to Borrelia burgdorferi is whether the epitopes incorporated in the test provide sufficient cross-reactivity to detect infection with all of the pathogenic strains of the species. This is a particular concern for the C6 test, which is based on reactivity to a single peptide.

METHODS

C6 testing and 2-tier testing were performed on acute-phase serum samples obtained from >158 patients with erythema migrans for whom the genotype of the borrelial isolate was defined on the basis of an analysis of the 16S-23S ribosomal DNA spacer region and/or on the genetic variation of the outer surface protein C gene (ospC). The sonicated whole cell-based enzyme-linked immunosorbent assay, the immunoblots used in the 2-tier testing, and the C6 assay all used antigens from B. burgdorferi sensu stricto strain B31.

RESULTS

The sensitivity of C6 testing (69.5%) was greater than that of 2-tier testing (38.9%) (P<.001); the difference in sensitivity, however, was statistically significant only for patients infected with 2 of the 3 ribosomal spacer type-defined genotypes. The lower sensitivity of 2-tier testing was attributable to the low sensitivity of the immunoblot tests, rather than the first-tier enzyme-linked immunosorbent assay. There was also a trend for the sensitivity of 2-tier testing to vary according to the ospC genotype for the 14 genotypes represented in the study (P=.07); this relationship was not observed with C6 testing.

CONCLUSIONS

Lack of sensitivity of the C6 test because of strain diversity seems less likely to be a limitation of this serologic test, compared with 2-tier testing in North American patients with early Lyme disease.

BBK07, a dominant in vivo antigen of Borrelia burgdorferi, is a potential marker for serodiagnosis of Lyme disease

One of the recently identified Borrelia burgdorferi immunogens, BBK07, is characterized for its expression in the spirochete infection cycle and evaluated for its potential use as a serodiagnostic marker for Lyme disease. We show that the BBK07 gene is expressed at extremely low levels in vitro and in ticks but is dramatically induced by spirochetes once introduced into the host and is highly expressed throughout mammalian infection. In contrast, the expression of BBK12, a paralog of BBK07 with 87% amino acid identity, although expressed in vitro, remained undetectable in vivo throughout murine infection and in ticks. BBK07 is localized in the outer membrane, and the amino-terminal domain of the antigen is exposed on the microbial surface. A truncated BBK07 protein representing the amino-terminal domain is able to effectively detect antibodies to B. burgdorferi, both in experimentally infected mice and in humans. Further characterization of the immunodominant antigens of B. burgdorferi, such as BBK07, could contribute to the development of novel serodiagnostic markers for detection of Lyme disease.

Evaluation of the recombinant VlsE-based liaison chemiluminescence immunoassay for detection of Borrelia burgdorferi and diagnosis of Lyme disease

Recent efforts to improve the serologic diagnosis of Lyme disease have included the use of a synthetic peptide (C6) that reproduces the sequence of invariable region 6 of VlsE, the variable surface antigen of Borrelia burgdorferi. In the present study, the diagnostic performance of DiaSorin's recombinant VlsE-based chemiluminescence immunoassay in 1,947 human serum samples was evaluated. Sensitivity was determined using two serum panels from the CDC. For panel I, we observed sensitivities of 68.4% and 75.6% for subjects with early, localized (n=19) or disseminated (n=41) disease, respectively. For panel II, we observed sensitivities of 61.5% and 100% for subjects with early (n=26) or late-stage (n=11) disease, respectively. We observed a specificity of 99.5% for healthy donors (n=600) living either in regions of the United States where the disease is endemic or in regions where it is not endemic. Overall, specificity among 207 potentially cross-reactive sera from subjects who had other spirochetal infections, nonspirochetal infections including bacterial and viral infections, or autoimmune or neurologic disease; who were positive for rheumatoid factor or anti-mouse antibodies; or who had been previously vaccinated for Lyme disease was 93.7%. In a direct comparison of 1,038 prospectively collected samples for Lyme disease testing we observed a relative sensitivity of 70%, a relative specificity of 99.1%, and an overall agreement of 97.1% between the DiaSorin recombinant VlsE chemiluminescence immunoassay and the Immunetics peptide-based C6 enzyme-linked immunosorbent assay.

Borrelia burgdorferi VlsE antigen for the serological diagnosis of Lyme borreliosis

In this study, raising and development of antibody response to Borrelia burgdorferi infection in 66 Italian patients suffering from culture-confirmed Lyme borreliosis erythema migrans (EM) was investigated. Sixty-two of 66 cultures obtained from biopsies were identified as B. afzelii by PCR. A total of 175 serially collected serum samples were tested by using two different sets of commercial assays: Enzygnost Lyme link VlsE/IgG and Enzygnost Borreliosis IgM (DADE Behring, Marburg, Germany) and LIAISON Borrelia IgG and IgM (Diasorin, Saluggia, Italy). Considering only samples obtained at first presentation when EM was clinically evident, 49/66 patients (72.4%) were IgG or IgM positive by Enzygnost, whereas 33/66 (50.0%) patients were IgG or IgM positive by LIAISON. Taking into account the follow-up period, eight patients sero-converted for IgG or IgM by Enzygnost and four by LIAISON. Similar and very good specificity values were obtained by all methods. Testing sera obtained from blood donors (n = 300) and from patients suffering from some of the most common biological conditions possibly resulting in false-positive reactivity in Lyme disease serology (n = 100) showed that Enzygnost Lyme link VlsE/IgG was the more specific (98.3%), followed by LIAISON Borrelia IgG (96.5%), and considering IgM tests, Enzygnost Borreliosis IgM showed to be 95.3%% specific, whereas the LIAISON Borrelia IgM was 92.8% specific. Recombinant VlsE antigens obtained from all three B.burgdorferi genospecies pathogenic to humans (included in Enzygnost Lyme link VlsE/IgG) greatly improved serodiagnosis of Lyme disease.