Acquired resistance to Borrelia burgdorferi infection in the rabbit. Comparison between outer surface protein A vaccine- and infection-derived immunity

New Zealand White Rabbits Effectively Clear Borrelia burgdorferi B31 despite the Bacterium's Functional vlsE Antigenic Variation System

Borrelia burgdorferi is a tick-borne bacterium responsible for approximately 300,000 annual cases of Lyme disease (LD) in the United States, with increasing incidences in other parts of the world. The debilitating nature of LD is mainly attributed to the ability of B. burgdorferi to persist in patients for many years despite strong anti-Borrelia antibody responses. Antimicrobial treatment of persistent infection is challenging. Similar to infection of humans, B. burgdorferi establishes long-term infection in various experimental animal models except for New Zealand White (NZW) rabbits, which clear the spirochete within 4 to 12 weeks. LD spirochetes have a highly evolved antigenic variation vls system, on the lp28-1 plasmid, where gene conversion results in surface expression of the antigenically variable VlsE protein. VlsE is required for B. burgdorferi to establish persistent infection by continually evading otherwise potent antibodies. Since the clearance of B. burgdorferi is mediated by humoral immunity in NZW rabbits, the previously reported results that LD spirochetes lose lp28-1 during rabbit infection could potentially explain the failure of B. burgdorferi to persist. However, the present study unequivocally disproves that previous finding by demonstrating that LD spirochetes retain the vls system. However, despite the vls system being fully functional, the spirochete fails to evade anti-Borrelia antibodies of NZW rabbits. In addition to being protective against homologous and heterologous challenges, the rabbit antibodies significantly ameliorate LD-induced arthritis in persistently infected mice. Overall, the current data indicate that NZW rabbits develop a protective antibody repertoire, whose specificities, once defined, will identify potential candidates for a much-anticipated LD vaccine.

Evidence for strain-specific immunity in patients treated for early lyme disease

Lyme disease, caused by Borrelia burgdorferi, is the most commonly reported vector-borne disease in the United States. Many patients treated for early Lyme disease incur another infection in subsequent years, suggesting that previous exposure to B. burgdorferi may not elicit a protective immune response. However, identical strains are almost never detected from patients who have been infected multiple times, suggesting that B. burgdorferi exposure may elicit strain-specific immunity. Probabilistic and simulation models assuming biologically realistic data derived from patients in the northeastern United States suggest that patients treated for early Lyme disease develop protective immunity that is strain specific and lasts for at least 6 years.

Temporal analysis of the antigenic composition of Borrelia burgdorferi during infection in rabbit skin

The numbers of host-adapted Borrelia burgdorferi (HAB) organisms in rabbit skin were assessed by real-time PCR over the first 3 weeks of infection. Maximal numbers were found at day 11, while spirochete numbers decreased by more than 30-fold by day 21. The antigenic composition of HAB in skin biopsy samples was determined by use of a procedure termed hydrophobic antigen tissue Triton extraction. Immune sera from rabbits, sera from chronically infected mice, and monospecific antiserum to the antigenic variation protein, VlsE, were used to probe parallel two-dimensional immunoblots representing each time point. Individual proteins were identified using either specific antisera or by matching protein spots to mass spectrometry-identified protein spots from in vitro-cultivated Borrelia. There were significant changes in the relative expression of a variety of known and previously unrecognized HAB antigens during the 21-day period. OspC and the outer membrane proteins OspA and OspB were prominent at the earliest time point, day 5, when the antigenic variation protein VlsE was barely detected. OspA and OspB were not detected after day 5. OspC was not detected after day 9. VlsE was the most prominent antigen from day 7 through day 21. BmpA, ErpN, ErpP, LA7, OppA-2, DbpA, and an unidentified 15-kDa protein were also detected from day 7 through day 21. Immunoblot analysis using monospecific anti-VlsE revealed the presence of prominent distinct VlsE lower forms in HAB at days 9, 11, and 14; however, these lower forms were no longer detected at day 21. This marked diminution in VlsE lower forms paralleled the clearance of the spirochete from skin.

Antigenic composition of Borrelia burgdorferi during infection of SCID mice

The general concept that during infection of mice the Borrelia burgdorferi surface protein composition differs profoundly from that of tick-borne or in vitro-cultivated spirochetes is well established. Specific knowledge concerning the differences is limited because the small numbers of spirochetes present in tissue have not been amenable to direct compositional analysis. In this report we describe novel means for studying the antigenic composition of host-adapted Borrelia (HAB). The detergent Triton X-114 was used to extract the detergent-phase HAB proteins from mouse ears, ankles, knees, and hearts. Immunoblot analysis revealed a profile distinct from that of in vitro-cultivated Borrelia (IVCB). OspA and OspB were not found in the tissues of SCID mice 17 days after infection. The amounts of antigenic variation protein VlsE and the relative amounts of its transcripts were markedly increased in ear, ankle, and knee tissues but not in heart tissue. VlsE existed as isoforms having both different unit sizes and discrete lower molecular masses. The hydrophobic smaller forms of VlsE were also found in IVCB. The amounts of the surface protein (OspC) and the decorin binding protein (DbpA) were increased in ear, ankle, knee, and heart tissues, as were the relative amounts of their transcripts. Along with these findings regarding VlsE, OspC, and DbpA, two-dimensional immunoblot analysis with immune sera also revealed additional details of the antigenic composition of HAB extracted from ear, heart, and joint tissues. A variety of novel antigens, including antigens with molecular masses of 65 and 30 kDa, were found to be upregulated in mouse tissues. Extraction of hydrophobic B. burgdorferi antigens from tissue provides a powerful tool for determining the antigenic composition of HAB.

Homologous and heterologous Borrelia burgdorferi challenge of infection-derived immune rabbits using host-adapted organisms

We have recently found that strain B31 infection-immune rabbits are completely protected against homologous challenge with large numbers (>10(6)) of host-adapted Borrelia burgdorferi (HAB) (E. S. Shang, C. I. Champion, X. Wu, J. T. Skare, D. B. Blanco, J. N. Miller, and M. A. Lovett, Infect. Immun. 68:4189-4199, 2000). In this study, we have extended these findings to determine whether B31 strain infection-immune rabbits are also protected against heterologous HAB challenge. Infection-immune rabbits challenged with large numbers (>10(6)) of homologous HAB strain B31 were completely protected from erythema migrans (EM) and skin and disseminated infection. In contrast, infection-immune rabbits challenged with heterologous HAB strains N40 and Sh-2-82 were completely susceptible to EM and skin and disseminated infection; challenge with strain 297 also resulted in EM and infection of the skin and viscera, but clearance of infection occurred 3 weeks postchallenge. These findings confirm that immunity elicited in rabbits by B31 strain infection confers complete protection against large-dose homologous HAB challenge but not against a heterologous strain.

Comparison of protection in rabbits against host-adapted and cultivated Borrelia burgdorferi following infection-derived immunity or immunization with outer membrane vesicles or outer surface protein A

In this study, infection-derived immunity in the rabbit model of Lyme disease was compared to immunity following immunization with purified outer membrane vesicles (OMV) isolated from Borrelia burgdorferi and recombinant outer surface protein A (OspA). Immunization of rabbits with OMV isolated from virulent strain B31 and its avirulent derivative B313 (lacking OspA and DbpA) conferred highly significant protection against intradermal injection with 6 x 10(4) in vitro-cultivated virulent B. burgdorferi. This is the first demonstration of protective immunogenicity induced by OMV. While immunization with OspA and avirulent B31 OMV provided far less protection against this challenge, rabbits with infection-derived immunity were completely protected. Protection against host-adapted B. burgdorferi was assessed by implantation of skin biopsies taken from rabbit erythema migrans (a uniquely rich source of B. burgdorferi in vertebrate tissue) containing up to 10(8) spirochetes. While all of the OMV- and OspA-immunized rabbits were fully susceptible to skin and disseminated infection, rabbits with infection-derived immunity were completely protected. Analysis of the antibody responses to outer membrane proteins, including DbpA, OspA, and OspC, suggests that the remarkable protection exhibited by the infection-immune rabbits is due to antibodies directed at antigens unique to or markedly up-regulated in host-adapted B. burgdorferi.

Pediatric immunization for the future. Lyme disease vaccine and beyond

This article highlights some of the exciting new developments in pediatric immunization. Starting with the newly licensed Lyme disease vaccine, which is not yet approved for children younger than 15 years of age, the article discusses potential vaccines for severe allergy and cocaine abuse and stresses some of the new techniques in needleless vaccination, including the edible plant technology.

Evaluation of whole-cell and OspC enzyme-linked immunosorbent assays for discrimination of early lyme borreliosis from OspA vaccination

A recombinant Lyme borreliosis vaccine consisting of outer surface protein A (OspA) is commercially available for vaccination of humans against infection with Borrelia burgdorferi. Vaccination with OspA induces an antibody response that makes serologic interpretation of infection with B. burgdorferi difficult, especially by screening tests based on whole-cell preparations of B. burgdorferi. We show that an enzyme-linked immunosorbent assay with B. burgdorferi sensu stricto 50772, which lacks the plasmid encoding OspA and OspB, or a full-length recombinant OspC protein can identify patients infected with B. burgdorferi. We found that 69 and 65% of serum samples from patients with case-defined early Lyme borreliosis had anti-B. burgdorferi sensu stricto 50772 and anti-OspC reactivities, respectively. In addition, little or no reactivity was detected with sera obtained from individuals vaccinated with OspA. Unfortunately, 51 and 33% of sera from healthy patients and sera from patients with other illnesses were also reactive against B. burgdorferi sensu stricto 50772 and OspC, respectively. Although these assays can discriminate B. burgdorferi infection from vaccination with OspA, their lack of specificity highlights the necessity for confirming equivocal or positive reactivities with more specific serodiagnostic tests.

Cloning and molecular characterization of plasmid-encoded antigens of Borrelia burgdorferi

Thirteen independent clones that encode Borrelia burgdorferi antigens utilizing antiserum from infection-immune rabbits were identified. The serum was adsorbed against noninfectious B. burgdorferi B31 to enrich for antibodies directed against either infection-associated antigens of B. burgdorferi B31 or proteins preferentially expressed during mammalian infection. The adsorption efficiency of the immune rabbit serum (IRS) was assessed by Western immunoblot analysis with protein lysates derived from infectious and noninfectious B. burgdorferi B31. The adsorbed IRS was used to screen a B. burgdorferi expression library to identify immunoreactive phage clones. Clones were then expressed in Escherichia coli and subsequently analyzed by Western blotting to determine the molecular mass of the recombinant B. burgdorferi antigens. Southern blot analysis of the 13 clones indicated that 10 contained sequences unique to infectious B. burgdorferi. Nucleotide sequence analysis indicated that the 13 clones were composed of 9 distinct genetic loci and that all of the genes identified were plasmid encoded. Five of the clones carried B. burgdorferi genes previously identified, including those encoding decorin binding proteins A and B (dbpAB), a rev homologue present on the 9-kb circular plasmid (cp9), a rev homologue from the 32-kb circular plasmid (cp32-6), erpM, and erpX. Additionally, four previously uncharacterized loci with no known homologues were identified. One of these unique clones encoded a 451-amino-acid lipoprotein with 21 consecutive, invariant 9-amino-acid repeats near the amino terminus that we have designated VraA (for "virulent strain-associated repetitive antigen A"). Since all the antigens identified are recognized by serum from infection immune rabbits, these antigens represent potential vaccine candidates and, based on the identification of dbpAB in this screen, may also be involved in pathogenic processes operative in Lyme borreliosis.

Lyme disease prevention and vaccine prophylaxis

OBJECTIVE

To provide a comprehensive review of the epidemiology, diagnosis, and prevention of Lyme disease with a focus on the Lyme disease vaccine.

DATA SOURCE

A computerized search of MEDLINE (January 1996-December 1998) was used to identify articles regarding Lyme disease, Borrelia burgdorferi, epidemiology, prevention, and vaccine.

DATA SYNTHESIS

Lyme disease is a condition caused by infection with B. burgdorferi. The organism is carried by certain species of Ixodes ticks and is the most common tick-borne disease in the US. In patients with clinical manifestations of Lyme disease, various pharmacotherapeutic approaches have proven effective in treatment of the clinical features. Prevention strategies exist; however, their application is sometimes difficult. A vaccine for the prevention of Lyme disease is available, and another is being considered for approval. The recombinant outer surface protein A (OspA) vaccines to prevent Lyme disease are immunogenic and have an acceptable adverse effect profile. These vaccines are highly efficacious for the prevention of Lyme disease.

CONCLUSIONS

Lyme disease is the most common tick-borne disease in the US. The infection, caused by B. burgdorferi, results in dermatologic, neurologic, cardiovascular, and musculoskeletal manifestations. Until recently, tick bite prevention strategies were the only means of decreasing the risk of acquiring the infection. The OspA vaccines are efficacious for the prevention of infection. Although universal immunization with these vaccines is unlikely, the availability of effective vaccines represents an important tool for the prevention of Lyme disease in endemic regions of the US.

A new animal model for studying Lyme disease spirochetes in a mammalian host-adapted state

There is now substantial evidence that Borrelia burgdorferi, the Lyme disease spirochete, undergoes major alterations in antigenic composition as it cycles between its arthropod and mammalian hosts. In this report, we cultivated B. burgdorferi 297 within dialysis membrane chambers implanted into the peritoneal cavities of rats to induce antigenic changes similar to those which occur during mammalian infection. Chamber-grown spirochetes, which remained fully virulent, did not express either outer surface protein A or Lp6.6, lipoproteins known to be downregulated after mammalian infection. However, they did, express p21, a well characterized outer surface protein E homologue, which is selectively expressed during infection. SDS-PAGE, two-dimensional gel electrophoresis, and immunoblot analysis revealed that chamber-grown borreliae also expressed uncharacterized proteins not expressed by in vitro-cultivated spirochetes; reactivity with sera from mice chronically infected with B. burgdorferi 297 confirmed that many of these novel proteins are selectively expressed during experimental murine infection. Finally, we used differential display RT-PCR to identify transcripts of other differentially expressed B. burgdorferi genes. One gene (2.9-7lpB) identified with this technique belongs to a family of genes located on homologous 32- and 18-kb circular plasmids. The lipoprotein encoded by 2.9-7lpB was shown to be selectively expressed by chamber-grown spirochetes and by spirochetes during experimental infection. Cultivation of B. burgdorferi in rat peritoneal implants represents a novel system for studying Lyme disease spirochetes in a mammalian host-adapted state.

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.