Detection of anti-Borrelia burgdorferi antibody responses with the borreliacidal antibody test, indirect fluorescent-antibody assay performed by flow cytometry, and western immunoblotting

Evaluation of OspA vaccination-induced serological correlates of protection against Lyme borreliosis in a mouse model

BACKGROUND

For clinical development of a novel multivalent OspA vaccine against Lyme borreliosis, serological assays are required which can be used to establish immune correlates of protection against infection with Borrelia.

METHODS

Four assays (an OspA IgG ELISA, a competitive inhibition (CI) ELISA, a Borrelia surface-binding (SB) assay and a Borrelia killing assay) were used to evaluate the correlation between immune responses induced by rOspA 1/2 (a chimeric immunogen containing protective epitopes from OspA serotypes 1 and 2), and protective immunity against infection by B. burgdorferi s.s. (OspA-1) and B. afzelii (OspA-2). Mice were immunized with OspA 1/2 doses ranging from 0.3 ng to 100 ng, to induce a range of OspA antibody titers, and exposed to needle challenge with B. burgdorferi s.s. or tick challenge with B. afzelii. Receiver operator characteristics (ROC) curves were constructed for each assay, and the area under the curve (AUC), sensitivity, specificity and Youden Index were calculated. Potential cutoff antibody titers which could be used as correlates of vaccine-induced protection were derived from the maximum Youden Index.

RESULTS

Immunization with OspA-1/2 provided dose-dependent protection against infection with B. burgdorferi s.s. and B. afzelii. Antibody responses detected by all four assays were highly significantly correlated with protection from infection by either B. burgdorferi s.s. (p<0.0001 to 0.0062) or B. afzelii (p<0.0001). ROC analyses of the diagnostic effectiveness of each assay showed the AUC to range between 0.95 and 0.79, demonstrating that all assays distinguish well between infected and non-infected animals. Based on sensitivity, specificity and AUC, the OspA IgG ELISA and SB assays best discriminated between infected and non-infected animals.

CONCLUSIONS

All four assays differentiate well between Borrelia-infected and non-infected animals. The relatively simple, high throughput IgG ELISA would be suitable to establish immune correlates of protection for the novel OspA vaccine in clinical trials.

Cyclooxygenase-1 orchestrates germinal center formation and antibody class-switch via regulation of IL-17

The cyclooxygenase (COX) enzymes are known modulators of innate immune cell function; however, their contributions to adaptive immunity are relatively unknown. We investigated the roles of COX-1 and COX-2 in the humoral immune response to infection with the Lyme disease pathogen Borrelia burgdorferi. We report that in vitro, murine B cells constitutively expressed COX-1 and up-regulated expression of both COX-1 and COX-2 as well as their products PGE(2), PGF(2alpha), and thromboxane B(2) and their receptors following stimulation with B. burgdorferi or anti-CD40. In vitro inhibition of COX-1 and/or COX-2 in murine B cells resulted in decreased eicosanoid production and altered Ab production. Importantly, infection of mice lacking COX-1, but not COX-2, activity resulted in a defect in Ig class-switching and a lack of Borrelia-specific IgG production. This defect correlated with decreased germinal center formation and IL-6 and IL-17 production, and it could be partially recovered by restoration of IL-6, but fully recovered by IL-17. Furthermore, sera from COX-1 inhibitor-treated mice were dramatically less effective in killing B. burgdorferi, but borreliacidal activity was restored in COX-1 inhibitor-treated mice administered IL-17. We conclude that IL-17 plays a role in Ab production and Ig class-switching in response to infection and that COX-1 is a critical, previously unrecognized regulator of this response.

Role of IL-17, transforming growth factor-beta, and IL-6 in the development of arthritis and production of anti-outer surface protein A borreliacidal antibodies in Borrelia-vaccinated and -challenged mice

We showed recently that the adaptive immune events leading to the development of arthritis in Borrelia burgdorferi isolate 297-vaccinated and Borrelia bissettii-challenged mice involve IL-17. Here, we show in Borrelia-vaccinated and -challenged mice that two cytokines known to induce the production of IL-17, IL-6 and transforming growth factor (TGF)-beta, are also involved in the development of arthritis. Vaccinated and challenged mice administered either anti-TGF-beta or anti-IL-6 antibodies developed histopathologic changes of the hind paws similar to or greater than untreated control mice. By contrast, simultaneous blockage of these cytokines reduced the severity of arthritis in Borrelia-vaccinated and -challenged mice. Moreover, administration of anti-IL-17 antibodies to these dual-antibody-treated mice completely prevented the development of histopathologic changes of the ankle joints, significantly reduced edema of the hind paws, and prevented the production of anti-outer surface protein A borreliacidal antibodies. These findings demonstrate a role for the combined effects of IL-17, IL-6, and TGF-beta in the adaptive immune events leading to the development of Borrelia-induced arthritis.

Inhibition of interleukin-17 prevents the development of arthritis in vaccinated mice challenged with Borrelia burgdorferi

We showed that Borrelia burgdorferi-vaccinated interferon gamma-deficient (IFN-gamma(0)) mice challenged with the Lyme spirochete developed a prominent chronic severe destructive osteoarthropathy. The immune response underlying the development of the severe destructive arthritis involves interleukin-17 (IL-17). Treatment of vaccinated IFN-gamma(0) mice challenged with B. burgdorferi with anti-IL-17 antibody delayed the onset of swelling of the hind paws but, more importantly, inhibited the development of arthritis. Histopathologic examination confirmed that treatment with anti-IL-17 antibody prevented the destructive arthropathy seen in vaccinated and challenged IFN-gamma(0) mice. Similar preventive results were obtained when vaccinated and challenged IFN-gamma(0) mice were treated with anti-IL-17 receptor antibody or sequentially with anti-IL-17 antibody followed by anti-IL-17 receptor antibody. By contrast, treatment of vaccinated and challenged IFN-gamma(0) mice with recombinant IL-17 (rIL-17) did not alter the development and progression of arthritis found in vaccinated and challenged IFN-gamma(0) mice without treatment with rIL-17. Therapeutic intervention may be a realistic approach to prevent arthritis, especially if IL-17 is involved in the perpetuation of chronic or intermittent arthritis.

Laboratory testing for suspected Lyme disease

Laboratory testing for B. burgdorferi infection is intended to substantiate a physician's clinical judgment of whether a patient has Lyme disease or not. Cultivation of B. burgdorferi from a patient's skin or blood is the gold standard for demonstration of active infection, but it is expensive and lacks clinical sensitivity. Detection of spirochetal DNA in clinical samples by PCR has better sensitivity, but PCR for B. burgdorferi has not yet been standardized for more routine diagnostic testing. Detection of antibodies to B. burgdorferi is the most practical and common approach for laboratory work-up of a case of suspected Lyme disease. Serologic assays fall short of 100% sensitivity and specificity, however, and examination of a single specimen in time does not discriminate between previous and ongoing infection. Because of a background false positivity even among healthy populations of nonendemic regions, serologic testing is recommended only when there is at least a one in five chance, in the physician's estimation, that the patient has active Lyme disease. The pretest likelihood of the disease is determined by the physician in the context of epidemiologic and clinical facts of the case. This estimate can serve to reassure patients who are at low risk of B. burgdorferi infection but are seeking a Lyme test for complaints of a more nonspecific nature. Although new subunit serologic assays based on recombinant proteins are becoming available commercially, the longstanding two-test approach, in which a positive or indeterminate result with a standardized, sensitive ELISA test is followed by verification with a more specific Western blot assay, still provides the physician with a reasonably accurate and reliable assessment of the presence of antibodies to B. burgdorferi. More recent challenges for serologic testing are seropositivity in the population as the result of immunization with the Lyme disease vaccine and the emergence of new Borrelia species that cause Lyme disease-like illnesses.

Inhibition of the production of anti-OspA borreliacidal antibody with T cells from hamsters vaccinated against Borrelia burgdorferi

The serious morbidity associated with Lyme borreliosis has focused considerable effort on the development of a comprehensive vaccine for protection against infection with Borrelia burgdorferi. Induction of borreliacidal antibody by vaccination or infection has been shown to correlate with protection of humans and animals against infection with the Lyme spirochete. In this report, we showed that high levels of borreliacidal antibody (titer of 1,280) were produced in vitro when T and B cells from hamsters 14 days after vaccination were incubated with macrophages and B. burgdorferi. By contrast, T and B cells from hamsters 7 or 21 days after vaccination failed to initiate production of borreliacidal activity. Furthermore, the T cells from hamsters 7 or 21 days after vaccination inhibited the in vitro production of borreliacidal antibody when cocultured with T and B cells obtained from hamsters 14 days after vaccination. When cell-free supernatants from the suspensions of T and B cells from hamsters 14 days after vaccination were absorbed with recombinant OspA, they lost nearly all borreliacidal activity. The removal of anti-OspA antibody resulted in a decrease in borreliacidal titer from 1,280 to less than 4. These results demonstrate that T cells from vaccinated animals can prevent a sustained production of protective borreliacidal antibody.

Interpretation criteria for standardized Western blots for three European species of Borrelia burgdorferi sensu lato

Western blots (WBs; immunoblots) are a widely used tool for the serodiagnosis of Lyme borreliosis, but so far, no defined criteria for performance, analysis, and interpretation have been established in Europe. For the current study WBs were produced with strains PKa2 (Borrelia burgdorferi sensu stricto), PKo (Borrelia afzelii), and PBi (Borrelia garinii). To improve resolution we used gels of 17 cm in length. In a first step, 13 immunodominant proteins were identified with monoclonal antibodies. Then, the apparent molecular masses of all visually distinguishable bands were determined densitometrically. Approximately 40 bands of between 14 and 100 kDa were differentiated for each strain. From a study with 330 serum samples (from 189 patients with Lyme borreliosis and 141 controls), all observed bands were documented. To establish criteria for a positive WB result, the discriminating ability of a series of band combinations (interpretation rules) were evaluated separately for each strain (for immunoglobulin G [IgG] WB, > 40 combinations; for IgM WB, > 15 combinations). The following interpretation criteria resulting in specificities of greater than 96% were recommended: for IgG WB, at least one band of p83/100, p58, p56, OspC, p21, and p17a for PKa2; at least two bands of p83/100, p58, p43, p39, p30, OspC, p21, p17, and p14 for PKo; and at least one band of p83/100, p39, OspC, p21, and p17b for PBi; for IgM WB, at least one band of p39, OspC, and p17a or a strong p41 band for PKa2; at least one band of p39, OspC, and p17 or a strong p41 band for PKo; and at least one band of p39 and OspC or a strong p41 band for PBi. The overall sensitivity was the highest for PKo WB, followed by PBi and PKa2 WB, in decreasing order. Standardization of WB assays is necessary for comparison of results from different laboratories.

Sensitivity and specificity of the borreliacidal-antibody test during early Lyme disease: a "gold standard"?

The serodiagnosis of early Lyme disease has been plagued with problems of sensitivity and specificity. We found that the flow-cytometric borreliacidal-antibody test had a sensitivity of 72% for the detection of patients with early Lyme disease. By contrast, the sensitivity of the enzyme immunofluorescence assay was 28%. The enhanced sensitivity of the borreliacidal-antibody test was due to the use of Borrelia burgdorferi 50772, which lacks OspA and OspB. When B. burgdorferi 297, which expresses both OspA and OspB, was used, the sensitivity of the borreliacidal-antibody test was 15%. Our results also showed that the borreliacidal-antibody test was specific. No borreliacidal activity was detected in normal sera or in sera from patients with mononucleosis, rheumatoid factor, or syphilis. These results demonstrate that the flow-cytometric borreliacidal-antibody test may be the laboratory "gold standard" for the serodiagnosis of Lyme disease.