Lyme arthritis resolution with antiserum to a 37-kilodalton Borrelia burgdorferi protein

Antigen-Specific CD4 T Cell and B Cell Responses to Borrelia burgdorferi

Long-lived T-dependent B cell responses fail to develop during persistent infection of mice with Borrelia burgdorferi, the causative agent of Lyme disease, raising questions about the induction and/or functionality of anti-B. burgdorferi adaptive immune responses. Yet, a lack of reagents has limited investigations into B. burgdorferi-specific T and B cells. We attempted two approaches to track B. burgdorferi-induced CD4 T cells. First, a B. burgdorferi mutant was generated with an influenza hemagglutinin (HA) peptide, HA111-119, inserted into the B. burgdorferi arthritis-related protein (Arp) locus. Although this B. burgdorferi arp::HA strain remained infectious, peptide-specific TCR transgenic CD4 T cells in vitro, or adoptively transferred into B. burgdorferi arp::HA-infected BALB/c mice, did not clonally expand above those of recipients infected with the parental B. burgdorferi strain or a B. burgdorferi mutant containing an irrelevant peptide. Some expansion, however, occurred in B. burgdorferi arp::HA-infected BALB/c SCID mice. Second, a (to our knowledge) newly identified I-Ab-restricted CD4 T cell epitope, Arp152-166, was used to generate Arp MHC class II tetramers. Flow cytometry showed small numbers of Arp-specific CD4 T cells emerging in mice infected with B. burgdorferi but not with Arp-deficient Borrelia afzelii. Although up to 30% of Arp-specific CD4 T cells were ICOS+PD-1+CXCR5+BCL6+ T follicular helper cells, their numbers declined after day 12, before germinal centers (GCs) are prominent. Although some Arp-specific B cells, identified using fluorochrome-labeled rArp proteins, had the phenotype of GC B cells, their frequencies did not correlate with anti-Arp serum IgG. The data suggest a failure not in the induction, but in the maintenance of GC T follicular helper and/or B cells to B. burgdorferi.

The Borrelia burgdorferi VlsE Lipoprotein Prevents Antibody Binding to an Arthritis-Related Surface Antigen

Arp is an immunogenic protein of the Lyme disease spirochete Borrelia burgdorferi and contributes to joint inflammation during infection. Despite Arp eliciting a strong humoral response, antibodies fail to clear the infection. Given previous evidence of immune avoidance mediated by the antigenically variable lipoprotein of B. burgdorferi, VlsE, we use passive immunization assays to examine whether VlsE protects the pathogen from anti-Arp antibodies. The results show that spirochetes are only able to successfully infect passively immunized mice when VlsE is expressed. Subsequent immunofluorescence assays reveal that VlsE prevents binding of Arp-specific antibodies, thereby providing an explanation for the failure of Arp antisera to clear the infection. The results also show that the shielding effect of VlsE is not universal for all B. burgdorferi cell-surface antigens. The findings reported here represent a direct demonstration of VlsE-mediated protection of a specific B. burgdorferi surface antigen through a possible epitope-shielding mechanism.

Lone and Bankhead report that the antigenically variable VlsE protein of the Lyme disease agent Borrelia burgdorferi can prevent antibody binding to a surface antigen of the pathogen. They show that protection is likely via an epitope-shielding mechanism, thus expanding the current role of VlsE in immune evasion.

Plasmid diversity and phylogenetic consistency in the Lyme disease agent Borrelia burgdorferi

Background

Bacteria from the genus Borrelia are known to harbor numerous linear and circular plasmids. We report here a comparative analysis of the nucleotide sequences of 236 plasmids present in fourteen independent isolates of the Lyme disease agent B. burgdorferi.

Results

We have sequenced the genomes of 14 B. burgdorferi sensu stricto isolates that carry a total of 236 plasmids. These individual isolates carry between seven and 23 plasmids. Their chromosomes, the cp26 and cp32 circular plasmids, as well as the lp54 linear plasmid, are quite evolutionarily stable; however, the remaining plasmids have undergone numerous non-homologous and often duplicative recombination events. We identify 32 different putative plasmid compatibility types among the 236 plasmids, of which 15 are (usually) circular and 17 are linear. Because of past rearrangements, any given gene, even though it might be universally present in these isolates, is often found on different linear plasmid compatibility types in different isolates. For example, the arp gene and the vls cassette region are present on plasmids of four and five different compatibility types, respectively, in different isolates. A majority of the plasmid types have more than one organizationally different subtype, and the number of such variants ranges from one to eight among the 18 linear plasmid types. In spite of this substantial organizational diversity, the plasmids are not so variable that every isolate has a novel version of every plasmid (i.e., there appears to be a limited number of extant plasmid subtypes).

Conclusions

Although there have been many past recombination events, both homologous and nonhomologous, among the plasmids, particular organizational variants of these plasmids correlate with particular chromosomal genotypes, suggesting that there has not been rapid horizontal transfer of whole linear plasmids among B. burgdorferi lineages. We argue that plasmid rearrangements are essentially non-revertable and are present at a frequency of only about 0.65% that of single nucleotide changes, making rearrangement-derived novel junctions (mosaic boundaries) ideal phylogenetic markers in the study of B. burgdorferi population structure and plasmid evolution and exchange.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3553-5) contains supplementary material, which is available to authorized users.

CD4+ T cells promote antibody production but not sustained affinity maturation during Borrelia burgdorferi infection

CD4 T cells are crucial for enhancing B cell-mediated immunity, supporting the induction of high-affinity, class-switched antibody responses, long-lived plasma cells, and memory B cells. Previous studies showed that the immune response to Borrelia burgdorferi appears to lack robust T-dependent B cell responses, as neither long-lived plasma cells nor memory B cells form for months after infection, and nonswitched IgM antibodies are produced continuously during this chronic disease. These data prompted us to evaluate the induction and functionality of B. burgdorferi infection-induced CD4 T(FH) cells. We report that CD4 T cells were effectively primed and T(FH) cells induced after B. burgdorferi infection. These CD4 T cells contributed to the control of B. burgdorferi burden and supported the induction of B. burgdorferi-specific IgG responses. However, while affinity maturation of antibodies against a prototypic T-dependent B. burgdorferi protein, Arthritis-related protein (Arp), were initiated, these increases were reversed later, coinciding with the previously observed involution of germinal centers. The cessation of affinity maturation was not due to the appearance of inhibitory or exhausted CD4 T cells or a strong induction of regulatory T cells. In vitro T-B cocultures demonstrated that T cells isolated from B. burgdorferi-infected but not B. burgdorferi-immunized mice supported the rapid differentiation of B cells into antibody-secreting plasma cells rather than continued proliferation, mirroring the induction of rapid short-lived instead of long-lived T-dependent antibody responses in vivo. The data further suggest that B. burgdorferi infection drives the humoral response away from protective, high-affinity, and long-lived antibody responses and toward the rapid induction of strongly induced, short-lived antibodies of limited efficacy.

Presence of Arp specifically contributes to joint tissue edema associated with early-onset Lyme arthritis

Antiserum to the Borrelia burgdorferi arthritis-related protein, Arp, has been shown to prevent or reduce arthritis in immunodeficient mice. To directly investigate the requirement for this lipoprotein in the generation of Lyme arthritis, we utilized targeted deletion to generate a B. burgdorferi clone that lacked only the arp gene locus. Infection of Lyme disease-susceptible C3H/HeN mice with the arp deletion mutant demonstrated significantly reduced tibiotarsal joint swelling during the first 6 weeks of infection compared to a wild-type control. The severity of joint swelling was restored to wild-type levels in mice infected with an arp mutant clone complemented in cis. Interestingly, the reduced swelling of joint tissues exhibited by mice infected with the arp deletion mutant did not directly correspond to reduced underlying arthritis. Histopathology data at 2 weeks postinfection showed some reduction in arthritis severity caused by the arp mutant clone; however, by 8 weeks, no significant difference was observed between joint tissues infected by the wild-type or arp mutant clones. The spirochete load in the joint tissues of mice infected with the arp mutant was found to be greater than that exhibited by the wild-type control. Our findings demonstrate that this lipoprotein contributes to the generation of early-onset joint swelling and suggests that arp expression has a negative secondary effect on total spirochete numbers in joint tissues.

Influence of arthritis-related protein (BBF01) on infectivity of Borrelia burgdorferi B31

Background

Lyme borreliosis, caused by tick-borne Borrelia burgdorferi, is a multi-phasic, multi-system disease in humans. Similar to humans, C3H mice develop arthritis and carditis, with resolution and periodic bouts of recurrence over the course of persistent infection. Borrelia burgdorferi arthritis-related protein (Arp/BBF01), a highly conserved protein among B. burgdorferi s.s. isolates, has been shown to be antigenic in humans with Lyme borreliosis, and a target for antibody-mediated disease resolution in the mouse model.

Results

A mutant strain of B. burgdorferi s.s. deficient of the arp gene and a complemented version of that mutant were created and examined for phenotypic effects in mice compared to wild-type B. burgdorferi. Deletion of arp did not abolish infectivity, but did result in a higher infectious dose compared to wild-type B. burgdorferi, which was restored by complementation. Spirochete burdens in tissues of C3H-scid mice were lower when infected with the arp mutant, compared to wild-type, but arthritis was equally severe. Spirochete burdens were also lower in C3H mice infected with the arp mutant, but disease was markedly reduced. Ticks that fed upon infected C3H mice were able to acquire infection with both wild-type and arp mutant spirochetes. Arp mutant spirochetes were marginally able to be transmitted to naïve hosts by infected ticks.

Conclusion

These results indicated that deletion of BBF01/arp did not abrogate, but diminished infectivity and limited spirochete burdens in tissues of both immunocompetent and immunodeficient hosts, and attenuated, but did not abolish the ability of ticks to acquire or transmit infection.

Analysis of an ordered, comprehensive STM mutant library in infectious Borrelia burgdorferi: insights into the genes required for mouse infectivity

The identification of genes important in the pathogenesis of Lyme disease Borrelia has been hampered by exceedingly low transformation rates in low-passage, infectious organisms. Using the infectious, moderately transformable B. burgdorferi derivative 5A18NP1 and signature-tagged versions of the Himar1 transposon vector pGKT, we have constructed a defined transposon library for the efficient genome-wide investigation of genes required for wild-type pathogenesis, in vitro growth, physiology, morphology, and plasmid replication. To facilitate analysis, the insertion sites of 4,479 transposon mutants were determined by sequencing. The transposon insertions were widely distributed across the entire B. burgdorferi genome, with an average of 2.68 unique insertion sites per kb DNA. The 10 linear plasmids and 9 circular plasmids had insertions in 33 to 100 percent of their predicted genes. In contrast, only 35% of genes in the 910 kb linear chromosome had incapacitating insertions; therefore, the remaining 601 chromosomal genes may represent essential gene candidates. In initial signature-tagged mutagenesis (STM) analyses, 434 mutants were examined at multiple tissue sites for infectivity in mice using a semi-quantitative, Luminex-based DNA detection method. Examples of genes found to be important in mouse infectivity included those involved in motility, chemotaxis, the phosphoenolpyruvate phosphotransferase system, and other transporters, as well as putative plasmid maintenance genes. Availability of this ordered STM library and a high-throughput screening method is expected to lead to efficient assessment of the roles of B. burgdorferi genes in the infectious cycle and pathogenesis of Lyme disease.

Genome stability of Lyme disease spirochetes: comparative genomics of Borrelia burgdorferi plasmids

Lyme disease is the most common tick-borne human illness in North America. In order to understand the molecular pathogenesis, natural diversity, population structure and epizootic spread of the North American Lyme agent, Borrelia burgdorferi sensu stricto, a much better understanding of the natural diversity of its genome will be required. Towards this end we present a comparative analysis of the nucleotide sequences of the numerous plasmids of B. burgdorferi isolates B31, N40, JD1 and 297. These strains were chosen because they include the three most commonly studied laboratory strains, and because they represent different major genetic lineages and so are informative regarding the genetic diversity and evolution of this organism. A unique feature of Borrelia genomes is that they carry a large number of linear and circular plasmids, and this work shows that strains N40, JD1, 297 and B31 carry related but non-identical sets of 16, 20, 19 and 21 plasmids, respectively, that comprise 33–40% of their genomes. We deduce that there are at least 28 plasmid compatibility types among the four strains. The B. burgdorferi ∼900 Kbp linear chromosomes are evolutionarily exceptionally stable, except for a short ≤20 Kbp plasmid-like section at the right end. A few of the plasmids, including the linear lp54 and circular cp26, are also very stable. We show here that the other plasmids, especially the linear ones, are considerably more variable. Nearly all of the linear plasmids have undergone one or more substantial inter-plasmid rearrangements since their last common ancestor. In spite of these rearrangements and differences in plasmid contents, the overall gene complement of the different isolates has remained relatively constant.

Lymphoadenopathy during lyme borreliosis is caused by spirochete migration-induced specific B cell activation

Lymphadenopathy is a hallmark of acute infection with Borrelia burgdorferi, a tick-borne spirochete and causative agent of Lyme borreliosis, but the underlying causes and the functional consequences of this lymph node enlargement have not been revealed. The present study demonstrates that extracellular, live spirochetes accumulate in the cortical areas of lymph nodes following infection of mice with either host-adapted, or tick-borne B. burgdorferi and that they, but not inactivated spirochetes, drive the lymphadenopathy. The ensuing lymph node response is characterized by strong, rapid extrafollicular B cell proliferation and differentiation to plasma cells, as assessed by immunohistochemistry, flow cytometry and ELISPOT analysis, while germinal center reactions were not consistently observed. The extrafollicular nature of this B cell response and its strongly IgM-skewed isotype profile bear the hallmarks of a T-independent response. The induced B cell response does appear, however, to be largely antigen-specific. Use of a cocktail of recombinant, in vivo-expressed B. burgdorferi-antigens revealed the robust induction of borrelia-specific antibody-secreting cells by ELISPOT. Furthermore, nearly a quarter of hybridomas generated from regional lymph nodes during acute infection showed reactivity against a small number of recombinant Borrelia-antigens. Finally, neither the quality nor the magnitude of the B cell responses was altered in mice lacking the Toll-like receptor adaptor molecule MyD88. Together, these findings suggest a novel evasion strategy for B. burgdorferi: subversion of the quality of a strongly induced, potentially protective borrelia-specific antibody response via B. burdorferi's accumulation in lymph nodes.

Characterization of unique regions of Borrelia burgdorferi surface-located membrane protein 1

The pathogen of Lyme disease, Borrelia burgdorferi, produces a putative surface protein termed "surface-located membrane protein 1" (Lmp1). Lmp1 has been shown previously to assist the microbe in evasion of host-acquired immune defenses and in the establishment of persistent infection of mammals. Here, we show that Lmp1 is an integral membrane protein with surface-exposed N-terminal, middle, and C-terminal regions. During murine infection, antibodies recognizing these three protein regions were produced. Separate immunization of mice with each of the discrete regions exerted differential effects on spirochete survival during infection. Notably, antibodies against the C-terminal region primarily interfered with B. burgdorferi persistence in the joints, while antibodies specific to the N-terminal region predominantly affected pathogen levels in the heart, including the development of carditis. Genetic reconstitution of lmp1 deletion mutants with the lmp1 N-terminal region significantly enhanced its ability to resist the bactericidal effects of immune sera and also was observed to increase pathogen survival in vivo. Taken together, the combined data suggest that the N-terminal region of Lmp1 plays a distinct role in spirochete survival and other parts of the protein are related to specific functions corresponding to pathogen persistence and tropism during infection that is displayed in an organ-specific manner. The findings reported here underscore the fact that surface-exposed regions of Lmp1 could potentially serve as vaccine targets or antigenic regions that could alter the course of natural Lyme disease.

Borrelia burgdorferi complement regulator-acquiring surface protein 2 does not contribute to complement resistance or host infectivity

Borrelia burgdorferi, the pathogen of Lyme disease, cycles in nature through Ixodes ticks and mammalian hosts. At least five Complement Regulator-Acquiring Surface Proteins (BbCRASPs) are produced by B. burgdorferi, which are thought to assist spirochetes in host immune evasion. Recent studies established that BbCRASP-2 is preferentially expressed in mammals, and elicits robust antibody response in infected hosts, including humans. We show that BbCRASP-2 is ubiquitously expressed in diverse murine tissues, but not in ticks, reinforcing a role of BbCRASP-2 in conferring B. burgdorferi defense against persistent host immune threats, such as complement. BbCRASP-2 immunization, however, fails to protect mice from B. burgdorferi infection and does not modify disease, as reflected by the development of arthritis. An infectious BbCRASP-2 mutant was generated, therefore, to examine the precise role of the gene product in spirochete infectivity. Similar to wild type B. burgdorferi, BbCRASP-2 mutants remain insensitive to complement-mediated killing in vitro, retain full murine infectivity and induce arthritis. Quantitative RT-PCR assessment indicates that survivability of BbCRASP-2-deficient B. burgdorferi is not due to altered expression of other BbCRASPs. Together, these results suggest that the function of a selectively expressed B. burgdorferi gene, BbCRASP-2, is not essential for complement resistance or infectivity in the murine host.

The failure of immune response evasion by linear plasmid 28-1-deficient Borrelia burgdorferi is attributable to persistent expression of an outer surface protein

Infectivity and persistence by Borrelia burgdorferi, the etiologic agent of Lyme disease, rely stringently on regulatory events. Among these is the downregulation of lipoprotein antigen expression, exemplified by outer surface protein C (OspC), at the advent of specific immunity in the mammalian host. B. burgdorferi spirochetes that lack the linear plasmid 28-1 (lp28-1) succumb to the host's immune response. We thus explored the notion that these two phenomena were related--that lp28-1(-) organisms fail to downregulate ospC and thus are cleared following the appearance of anti-OspC antibody in the murine host. The lp-28-1(-) isolate and a wild-type (wt) isolate bearing the complete set of plasmids were grown in dialysis membrane chambers that were implanted into rat peritoneal cavities. Analysis of mRNA and protein from these cultures showed that OspC expression levels by lp28-1(-) organisms are abnormally high in vivo. A time course analysis of ospC expression in tissues following infection indicates also that temporal diminution of the dominant antigen OspC is impaired in lp28-1(-) spirochetes. Finally, passive transfer of monoclonal OspC-specific antibody into SCID mice 8 days postinfection cleared lp28-1(-) spirochetes, yet the wt organisms persisted in a majority of animals. These findings indicate that incomplete repression of OspC by lp28-1(-) organisms renders them susceptible to immune-mediated clearance. The lp28-1 plasmid must harbor one or more genes involved in OspC downregulation.

Persistence of Borrelia burgdorferi following antibiotic treatment in mice

The effectiveness of antibiotic treatment was examined in a mouse model of Lyme borreliosis. Mice were treated with ceftriaxone or saline solution for 1 month, commencing during the early (3 weeks) or chronic (4 months) stages of infection with Borrelia burgdorferi. Tissues from mice were tested for infection by culture, PCR, xenodiagnosis, and transplantation of allografts at 1 and 3 months after completion of treatment. In addition, tissues were examined for the presence of spirochetes by immunohistochemistry. In contrast to saline solution-treated mice, mice treated with antibiotic were consistently culture negative, but tissues from some of the mice remained PCR positive, and spirochetes could be visualized in collagen-rich tissues. Furthermore, when some of the antibiotic-treated mice were fed on by Ixodes scapularis ticks (xenodiagnosis), spirochetes were acquired by the ticks, as determined based upon PCR results, and ticks from those cohorts transmitted spirochetes to naïve SCID mice, which became PCR positive but culture negative. Results indicated that following antibiotic treatment, mice remained infected with nondividing but infectious spirochetes, particularly when antibiotic treatment was commenced during the chronic stage of infection.

Borrelia burgdorferi basic membrane proteins A and B participate in the genesis of Lyme arthritis

Lyme arthritis results from colonization of joints by Borrelia burgdorferi and the ensuing host response. Using gene array–based differential analysis of B. burgdorferi gene expression and quantitative reverse trancription-polymerase chain reaction, we identified two paralogous spirochete genes, bmpA and bmpB, that are preferentially up-regulated in mouse joints compared with other organs. Transfer of affinity-purified antibodies against either BmpA or BmpB into B. burgdorferi–infected mice selectively reduced spirochete numbers and inflammation in the joints. B. burgdorferi lacking bmpA/B were therefore generated to further explore the role of these proteins in the pathogenesis of Lyme disease. B. burgdorferi lacking bmpA/B were infectious in mice, but unable to persist in the joints, and they failed to induce severe arthritis. Complementation of the mutant spirochetes with a wild-type copy of the bmpA and bmpB genes partially restored the original phenotype. These data delineate a role for differentially produced B. burgdorferi antigens in spirochete colonization of mouse joints, and suggest new strategies for the treatment of Lyme arthritis.

Constitutive expression of outer surface protein C diminishes the ability of Borrelia burgdorferi to evade specific humoral immunity

The Lyme disease spirochete Borrelia burgdorferi reduces the expression of outer surface protein C (OspC) in response to the development of an anti-OspC humoral response, leading to the hypothesis that the ability to repress OspC expression is critical for the pathogen to proceed to chronic infection. B. burgdorferi was genetically modified to constitutively express OspC by introducing an extra ospC copy fused with the borrelial flagellar gene (flaB) promoter. Such a genetic modification did not reduce infectivity or pathogenicity in severe combined immunodeficiency mice but resulted in clearance of infection by passively transferred OspC antibody. Spirochetes with constitutive ospC expression were unable to establish chronic infections in immunocompetent mice unless they had undergone very destructive mutations in the introduced ospC copy. Two escape mutants were identified; one had all 7 bp deleted between the putative ribosome-binding site and the start codon, ATG, causing a failure in translational initiation, and the other mutant had an insertion of 2 bp between nucleotides 315 and 316, resulting in a nonsense mutation at codon 108. Thus, the ability of B. burgdorferi to repress ospC expression during mammalian infection allows the pathogen to avoid clearance and to preserve the integrity of the important gene for subsequent utilization during its enzootic life cycle.

Antibody-mediated disease remission in the mouse model of lyme borreliosis

In the mouse model of Lyme borreliosis, the host immune response during infection with Borrelia burgdorferi results in the remission of carditis and arthritis, as well as global reduction of spirochete numbers in tissues, without elimination of infection. These events were recapitulated by passive transfer of immune serum from infected immunocompetent mice or T-cell-deficient mice to severe combined immunodeficient (SCID) mice. Previous studies have shown that immune serum is reactive against arthritis-related protein (Arp) and that Arp antiserum induces arthritis remission. However, although immune serum from T-cell-deficient mice induced disease remission, it was not reactive against Arp, suggesting that antibody to another antigen may be responsible. T-cell-deficient mouse immune serum was reactive to decorin binding protein A (DbpA). Therefore, DbpA antiserum was tested to determine its ability to induce disease remission in SCID mice. Antisera to Arp or DbpA induced both carditis and arthritis remission but did not significantly reduce spirochete numbers in tissues, based upon quantitative flaB DNA analysis, nor did treatment affect RNA levels of several genes, including arp and dbpA. Immunohistochemical labeling of spirochetes in hearts and joints during disease remission induced by adoptive transfer of lymphocytes, passive transfer of immune serum, or passive transfer of DbpA antiserum revealed that such treatment resulted in elimination of spirochetes from heart base and synovium but not vascular walls, tendons, or ligaments. These results suggest that Arp and DbpA antibodies may be active as disease-resolving components in immune serum but antibody against other antigens may be involved in reductions of spirochetes in tissues.

Association of linear plasmid 28-1 with an arthritic phenotype of Borrelia burgdorferi

Borrelia burgdorferi, the Lyme disease spirochete, has a genome comprised of a linear chromosome and up to 21 plasmids. Loss of plasmids is associated with decreased infectivity and pathogenicity. Sixteen transformants were generated by transforming the noninfectious clone 5A13 with the recombinant plasmid pBBE22. The transformants were classified into nine groups based on plasmid content analysis. An infectivity study revealed that all nine transformants examined, each of which represented one of the plasmid patterns, were infectious in mice with severe combined immunodeficiency (SCID) regardless of their genomic compositions. Tissue bacterial quantification revealed that the loss of plasmids significantly reduced the spirochete burden in the heart and joint tissues, not in the skin, suggesting virulence factors may be tissue specific. Four transformants containing lp28-1 induced severe arthritis in SCID mice, in contrast to the five transformants lacking lp28-1. These pathogenicity studies associated lp28-1 with an arthritic phenotype and further studies may identify factors that contribute to arthritic pathology.

Differential detection of five mouse-infecting helicobacter species by multiplex PCR

Several species of helicobacter have been isolated from laboratory mice, including H. bilis, H. hepaticus, H. muridarum, H. rodentium, and H. typhlonius, which appear to be the most common. The most widely used published method for molecular detection of these agents is PCR amplification of a conserved region of 16S rRNA, but differential speciation requires restriction enzyme digestion of the amplicons. This study was undertaken to determine PCR conditions that would simultaneously and specifically identify each of the five common species without restriction enzyme analyses. First, we designed novel and specific PCR primers for H. bilis, H. hepaticus, H. muridarum, H. rodentium, and H. typhlonius, using sequences from the heterologous regions of 16S rRNA. Because of comigration of amplified products, we next identified P17, an H. bilis-specific protein; P25, an H. hepaticus-specific protein; and P30, an H. muridarum-specific protein by screening genomic DNA expression libraries of each species. Primers were designed from these three genes, plus newly designed, species-specific 16S rRNA primers for H. rodentium and H. typhlonius that could be utilized for a five-plex PCR. The sizes of the amplicons from H. bilis, H. hepaticus, H. muridarum, H. rodentium, and H. typhlonius were 435, 705, 807, 191, and 122 bp, respectively, allowing simultaneous detection and effective discrimination among species.

Human Lyme arthritis and the immunoglobulin G antibody response to the 37-kilodalton arthritis-related protein of Borrelia burgdorferi

In Borrelia burgdorferi-infected C3H-scid mice, antiserum to a differentially expressed, 37-kDa spirochetal outer-surface protein, termed arthritis-related protein (Arp), has been shown to prevent or reduce the severity of arthritis. In this study, we determined the immunoglobulin G (IgG) antibody responses to this spirochetal protein in single serum samples from 124 antibiotic-treated human patients with early or late manifestations of Lyme disease and in serial serum samples from 20 historic, untreated patients who were followed longitudinally from early infection through the period of arthritis. These 20 patients were representative of the spectrum of the severity and duration of Lyme arthritis. Among the 124 antibiotic-treated patients, 53% with culture-proven erythema migrans (EM) had IgG responses to recombinant glutathione S-transferase (GST)-Arp, as did 59% of the patients with facial palsy and 68% of those with Lyme arthritis. In addition, 75 to 80% of the 20 past, untreated patients had reactivity with this protein when EM was present, during initial episodes of joint pain, or during the maximal period of arthritis. There was no association at any of these three time points between GST-Arp antibody levels and the severity of the maximal attack of arthritis or the total duration of arthritis. Thus, after the first several weeks of infection, 60 to 80% of patients had IgG antibody responses to GST-Arp, but this response did not correlate with the severity or duration of Lyme arthritis.

Relative contributions of innate and acquired host responses to bacterial control and arthritis development in Lyme disease

TLR2(-/-)/scid double-mutant mice were infected with B. burgdorferi to assess the relative importance of acquired and innate host defenses. Although spirochete levels at 4 weeks were lower in TLR2(-/-) mice than in TLR2(-/-)/scid mice, the increased arthritis severity of TLR2 (Toll-like receptor 2)-deficient mice was reduced by the presence of the scid mutation.

Research opportunities on human neuroborreliosis

A workshop, sponsored by the National Institutes of Health, was convened in September 2001 to evaluate the current knowledge in neurological Lyme disease. The meeting was centered into discussion of both clinical and basic aspects of the disease. Participants included researchers from the fields of infectious diseases, neurology, rheumatology, autoimmunity and basic immunology, largely but not exclusively focused on Lyme disease. This report summarizes the presentations made at the meeting.

The plasmids of Borrelia burgdorferi: essential genetic elements of a pathogen

The spirochete Borrelia burgdorferi, the causative agent of Lyme disease, has an unusual genome comprised of a linear chromosome and the largest plasmid complement of any characterized bacterium. Certain plasmid-encoded elements are required for virulence and viability, both in vitro and in vivo. The genetic tools to manipulate B. burgdorferi are sufficiently developed for precise molecular genetic investigations. B. burgdorferi now represents a prime system with which to address basic questions of plasmid biology and plasmid contributions to bacterial virulence and disease pathogenesis.

Borrelia burgdorferi changes its surface antigenic expression in response to host immune responses

The Lyme disease spirochete, Borrelia burgdorferi, causes persistent mammalian infection despite the development of vigorous immune responses against the pathogen. To examine spirochetal phenotypes that dominate in the hostile immune environment, the mRNA transcripts of four prototypic surface lipoproteins, decorin-binding protein A (DbpA), outer surface protein C (OspC), BBF01, and VlsE, were analyzed by quantitative reverse transcription-PCR under various immune conditions. We demonstrate that B. burgdorferi changes its surface antigenic expression in response to immune attack. dbpA expression was unchanged while the spirochetes decreased ospC expression by 446 times and increased BBF01 and vlsE expression up to 20 and 32 times, respectively, under the influence of immune pressure generated in immunocompetent mice during infection. This change in antigenic expression could be induced by passively immunizing infected severe combined immunodeficiency mice with specific Borrelia antisera or OspC antibody and appears to allow B. burgdorferi to resist immune attack.

The fur homologue in Borrelia burgdorferi

Borrelia burgdorferi contains a gene that codes for a Fur homologue. The function of this Fur protein is unknown; however, spirochetes grown at 23 or 35 degrees C expressed fur as determined by reverse transcriptase PCR. The fur gene (BB0647) was cloned and overexpressed as a His-Fur fusion protein in Escherichia coli. The fusion protein was purified by zinc-chelate chromatography, and the N-terminal His tag was removed to generate recombinant Fur for use in mobility shift studies. Fur bound DNA containing the E. coli Fur box sequence (GATAATGATAATCATTATC) or Bacillus subtilis Per box sequence (TTATAAT-ATTATAA) with an apparent Kd of approximately 20 nM. Fur also bound the upstream sequences of three Borrelia genes: BB0646 (gene encoding a hydrolase of the alpha/beta-fold family), BB0647 (fur), and BB0690 (napA). Addition of metal ions was not required. Binding activity was greatly decreased by either exposure to oxidizing agents (H2O2, t-butyl hydroperoxide, cumene hydroperoxide, or diamide) or by addition of Zn2+. B. burgdorferi NapA is a homologue of Dps. Dps functions in E. coli to protect DNA against damage during periods of redox stress. Fur may function in B. burgdorferi as a repressor and regulate oxidative stress genes. Additional genes (10 chromosomal and 15 plasmid) that may be Fur regulated were identified by in silico analysis.

Effects of Helicobacter pylori infection on gastric inflammation and local cytokine production in histamine-deficient (histidine decarboxylase knock-out) mice

Helicobacter pylori infection in humans causes gastritis. The infection elicits a complex immune response in which the activation of mast cells and histamine release is of particular importance. Histamine further promotes the immune response and stimulates gastric acid secretion. The inflammatory effects of H. pylori can be studied in intragastrically infected mice. The aim of this study was to compare the local cytokine responses of histamine-deficient, histidine decarboxylase knock-out (HDC KO) and wild-type (WT) mice following H. pylori infection.

METHODS

H. pylori was administered intragastrically to HDC KO and WT mice. The animals were infected three times in a 1-week-period and were sacrificed 8 weeks after the first intervention. The local TNF-alpha, IL-6 and IL-10 cytokine levels in gastric mucosal specimens were determined by ELISA. Gastric mucosa sections were also analysed for histological signs of inflammation. To investigate the antibody response following H. pylori infection, the total anti-H. pylori IgG and the ratio of IgG1/IgG2a isotypes were determined in the serum by ELISA.

RESULTS

H. pylori induced considerable cytokine production in the infected groups. The TNF-alpha and IL-6 levels were significantly higher in the WT mice than in the HDC KO mice, whereas the IL-10 levels did not differ between the groups. Anti-H. pylori IgG was detected only in the infected groups and the titre was higher in the WT mice. A higher IgG1/IgG2a ratio was observed in the H. pylori infected HDC KO group. Histological analysis revealed that the grades of inflammation were less severe in the infected HDC KO animals.

CONCLUSIONS

The results suggest that H. pylori induces lower TNF-alpha and IL-6 secretion in the gastric mucosa in the HDC KO mice than in the WT animals, while the levels of induction of IL-10 were similar. The imbalance between Th1/Th2 is less pronounced in the HDC KO mice, which might explain the milder inflammation in the gastric mucosa. These results provide further information on the role of histamine in the pathomechanism of H. pylori-induced gastritis.

Quantitative analysis of Borrelia burgdorferi gene expression in naturally (tick) infected mouse strains

Adaptation of Borrelia burgdorferi in the vector and vertebrate host is mediated by mechanisms that regulate differential expression of outer surface lipoproteins (Osps). In this study, real time PCR was applied to quantify tissue-specific expression of four linear plasmid (lp54)-encoded (ospA, zs7.a36, zs7.a66 zs7.a68) and one circular plasmid (cp26)-encoded (ospC) gene from B. burgdorferi sensu stricto, in a natural setting of tick-infected immunodeficient (C.B-17 SCID) and immunocompetent (BALB/c and AKR/OlaHsd) mice for up to 120 days post-infection (p.i.). Early during infection (day 30 p.i.) high numbers of spirochetes were found in the heart and joint, but not the ear and spleen tissues of disease-susceptible SCID mice. In disease-susceptible AKR mice spirochetes colonized the ear and joint tissues, but were undetectable in tissues of disease-resistant BALB/c mice. Later in infection (day 120 p.i.), spirochetes had expanded (approximately 1,000-fold) in all SCID tissues tested but were undetectable in AKR and BALB/c mice. Of the five genes analyzed, only zs7.a36 transcripts were detected in various tissues of all infected mouse strains, though at differing levels, whereas ospC transcripts were only found in tissue specimens of SCID mice. Furthermore, gene expression of ospC and zs7.a36 appears to be differentially regulated in distinct organs of individual mice. In contrast, transcripts for ospA, zs7.a66, and zs7.a68 were not detected in any of the mouse strains, independent of their immune status and/or the severity of their infection/inflammatory responses. Late during infection (day 120 p.i.), transcription of zs7.a36 and ospC was down-regulated in the tissues of SCID mice despite expansion of spirochetes. This type of quantitative analysis may be helpful to further disclose principles of pathogenesis of Lyme borreliosis and to design strategies for its therapeutic treatment.

Elucidation of Lyme arthritis

Before the first description of Lyme arthritis in 1976, patients with this disease were often thought to have juvenile or adult rheumatoid arthritis. It is now known that Lyme arthritis is caused by a tick-borne spirochete that disseminates to joints, where it induces marked pro-inflammatory responses. In most patients, the arthritis resolves with antibiotic treatment. However, in the United States, about 10% of patients with Lyme arthritis develop persistent synovitis, which lasts for months or even several years after the apparent eradication of the spirochete from the joint with antibiotic therapy. The elucidation of Lyme arthritis, from acute infection to chronic synovitis, might help in our understanding not only of this entity, but also of other forms of chronic inflammatory arthritis, including rheumatoid arthritis.

Immunogenicity of Borrelia burgdorferi arthritis-related protein

Immunization against arthritis-related protein (Arp) elicits antibody in mice that resolves arthritis but is not protective against challenge with Borrelia burgdorferi. In mice immunized against Arp, an unrelated 37-kDa protein (P37-42), outer surface protein A (OspA), or glutathione S-transferase (GT) and then challenged by syringe or tick, only OspA conferred protection. Passive transfer of Arp antiserum into infected SCID mice induced arthritis resolution, but antisera to P37-42, OspA, GT, or six overlapping Arp peptide fragments did not. Results suggest that the arthritis-resolving immunogenicity is specific to Arp, but the relevant epitopes may be conformational.

Borrelia burgdorferi population dynamics and prototype gene expression during infection of immunocompetent and immunodeficient mice

The population dynamics of Borrelia burgdorferi were quantified by real-time PCR targeting the flaB gene in skin (inoculation site, noninoculation site, and ear), heart (heart base and ventricle), quadriceps muscle, and the tibiotarsal joint at 1, 2, 4, 6, and 8 weeks after intradermal inoculation in C3H and C3H-scid mice. In addition, RNA transcription was assessed for several prototype genes, including flaB, ospA, ospC, dbpA, arp, vlsE, fbp, oppA-2, and p37-42. Spirochete numbers were equivalent in C3H and C3H-scid mice at 1 or 2 weeks and then declined in C3H mice, but they continued to rise and then plateaued in C3H-scid mice. Gene transcription was likewise higher in C3H-scid mice than in C3H mice, particularly at 4 or more weeks of infection. Gene transcription showed variation among tissues, with the highest levels of transcription in heart and joint tissue, which are sites of inflammation.

Adaptation of Borrelia burgdorferi in the vector and vertebrate host

Borrelia burgdorferi sensu lato is the causative agent of Lyme disease, which afflicts both humans and some domestic animals. B. burgdorferi, a highly evolved extracellular pathogen, uses several strategies to survive in a complex enzootic cycle involving a diverse range of hosts. This review focuses on the unique adaptive features of B. burgdorferi, which are central to establishing a successful spirochetal infection within arthropod and vertebrate hosts. We also discuss the regulatory mechanisms linked with the development of molecular adaptation of spirochetes within different host environments.

Humoral immune response associated with lyme borreliosis in nonhuman primates: analysis by immunoblotting and enzyme-linked immunosorbent assay with sonicates or recombinant proteins

The immune response to Borrelia burgdorferi, the causative agent of Lyme disease, is complex. We studied the immunoglobulin M (IgM) and IgG antibody response to N40Br, a sensu stricto strain, in the rhesus macaque(nonhuman primate [NHP]) model of infection to identify the spirochetal protein targets of specific antibody. Antigens used in enzyme-linked immunosorbent assays were whole-cell sonicates of the spirochete and recombinant proteins of B. burgdorferi. Immunoblotting with a commercially available strip and subsequent quantitative densitometry of the bands were also used. Sera from four different groups of NHPs were used: immunocompetent, transiently immunosuppressed, extended immunosuppressed, and uninfected. In immunocompetent and transiently immunosuppressed NHPs, there was a strong IgM and IgG response. Major proteins for the early IgM response were P39 and P41 and recombinant BmpA and OspC. Major proteins for the later IgG response were P39, P41, P18, P60, P66, and recombinant BmpA and DbpA. There was no significant response in the NHPs to recombinant OspA or to Arp, a 37-kDa protein that elicits an antibody response during infection in mice. Most antibody responses, except for that to DbpA, were markedly diminished by prolonged dexamethasone treatment. This study supports the hypothesis that recombinant proteins may provide a useful adjunct to current diagnostic testing for Lyme borreliosis.

Borrelia burgdorferi population kinetics and selected gene expression at the host-vector interface

By using real-time quantitative PCR, the population dynamics and gene transcription of Borrelia burgdorferi were examined in ticks and skin of mice during acquisition of the infection from mice by ticks and during transmission of the infection from ticks to mice. Population dynamics were determined by using a flaB DNA target. A quantitative analysis of flaB, ospA, ospC, dbpA, and arp transcription was also performed. The results revealed that both uninfected larval and nymphal Ixodes scapularis ticks acquired B. burgdorferi as early as 1 day after attachment and that the sizes of spirochete populations within ticks increased during feeding. In addition, all gene targets revealed that there was RNA transcription during feeding. Similar events occurred within infected nymphal ticks feeding on uninfected hosts. Transmission from infected nymphal ticks to mice could be detected within 1 day after attachment. Analysis of skin during the first 3 days after attachment of infected ticks revealed rising numbers of spirochetes but minimal gene transcription. In contrast, the skin of mice with established infections revealed static populations of spirochetes and active but stable transcription of flaB, ospC, dbpA, and arp. There were consistent reductions in the number of spirochetes in the skin at the tick attachment sites compared to the number of spirochetes in the skin at nontick sites, but there were no differences in gene expression between tick and nontick skin sites. Evidence of ospA transcription in skin could be found 1 day after tick attachment but not thereafter.

Cloning and expression of a Helicobacter bilis immunoreactive protein

In an effort to identify immunoreactive Helicobacter bilis antigens with potential for serodiagnosis, sera from mice experimentally infected with H. bilis were used to screen an H. bilis genomic DNA expression library. Among 17 immunoreactive clones, several contained sequences that encoded a predicted 167-kDa protein (P167). Five overlapping P167 peptides (P167A to P167E) of approximately 40 kDa each were generated and tested. Immune sera reacted with fragments P167C and P167D at dilutions of 1:1,600 and 1:6,400, respectively, and reacted with an H. bilis membrane extract at a dilution of 1:800 in an enzyme-linked immunosorbent assay. Sera from mice experimentally infected with H. hepaticus did not react with P167C and P167D. Sera from mice naturally infected with H. bilis but not sera from mice naturally infected with H. hepaticus reacted with P167C and P167D. Hyperimmune sera against P167C peptide reacted with recombinant P167C and with a 120-kDa band in H. bilis lysates but did not react with a protein of the same size on immunoblots prepared from H. hepaticus, H. muridarum, or unrelated Borrelia burgdorferi and Campylobacter jejuni whole-cell lysates. Nevertheless, the P167A, P167B, P167C, and P167D primers, but not the P167E primers, amplified DNA from H. hepaticus, and all five primer sets amplified DNA from H. muridarum. These results suggest that P167 is an immunodominant, H. bilis-specific antigen that may have potential for use in serodiagnosis.

Analysis of Borrelia burgdorferi gene expression during life cycle phases of the tick vector Ixodes scapularis

Borrelia burgdorferi exists in nature via an enzootic cycle whereby the organism must adapt to the diverse environmental conditions provided inside the arthropod transmission vector and the mammalian reservoir hosts. B. burgdorferi genes shown to be regulated by temperature, pH and/or cell density during the organism's growth in culture medium were assayed for expression during various stages of the tick feeding cycle by reverse transcription-polymerase chain reaction (RT-PCR). ospA, ospC, flaB, erpA/I/N, erpB/J/O, rev and mlpA, were transcriptionally active following the larval and nymphal stages of feeding as determined by qualitative RT-PCR. During tick resting periods between feedings, ospC, mlpA and rev transcription were undetectable, in contrast to ospA, flaB, erpA/I/N and erpB/J/O. bba64, a gene induced by environmental changes in culture and expressed during mammalian infection, was not detectable during any of the tick life cycle phases. Quantitative PCR to determine B. burgdorferi genome equivalents in these tick samples using DNA co-purified with the RNA allowed an estimation of gene expression relative to the numbers of B. burgdorferi present in the ticks. Although the spirochete totals varied widely between individual tick pools of fed, replete nymphs, the relative expression ratios between individual target genes following a nymphal feed were comparable. Similarly, borrelial gene transcription from the larval feeding and the nymphal feeding were observed and compared. These findings analogize B. burgdorferi gene expression observed by environmental stimuli in vitro with the transcriptional activity occurring during the organism's infectious cycle within the tick.

Conformational nature of the Borrelia burgdorferi decorin binding protein A epitopes that elicit protective antibodies

Decorin binding protein A (DbpA) has been shown by several laboratories to be a protective antigen for the prevention of experimental Borrelia burgdorferi infection in the mouse model of Lyme borreliosis. However, different recombinant forms of the antigen having either lipidated amino termini, approximating the natural secretion and posttranslational processing, or nonprocessed cytosolic forms have elicited disparate levels of protection in the mouse model. We have now used the unique functional properties of this molecule to investigate the structural requirements needed to elicit a protective immune response. Genetic and physicochemical alterations to DbpA showed that the ability to bind to the ligand decorin is indicative of a potent immunogen but is not conclusive. By mutating the two carboxy-terminal nonconserved cysteines of DbpA from B. burgdorferi strain N40, we have determined that the stability afforded by the putative disulfide bond is essential for the generation of protective antibodies. This mutated protein was more sensitive to thermal denaturation and proteolysis, suggesting that it is in a less ordered state. Immunization with DbpA that was thermally denatured and functionally inactivated stimulated an immune response that was not protective and lacked bactericidal antibodies. Antibodies against conformationally altered forms of DbpA also failed to kill heterologous B. garinii and B. afzelii strains. Additionally, nonsecreted recombinant forms of DbpA(N40) were found to be inferior to secreted lipoprotein DbpA(N40) in terms of functional activity and antigenic potency. These data suggest that elicitation of a bactericidal and protective immune response to DbpA requires a properly folded conformation for the production of functional antibodies.

Lyme disease

Lyme disease is the most common tick-borne disease in the United States, and the number of reported cases has increased steadily since 1992. Coinfection of ticks with Borrelia burgdorferi and Ehrlichia phagocytophila did not appear to affect the transmission of the other agent. Serologic evidence of exposure to Babesia microti did not significantly impact the clinical course of Lyme disease. Two clinical studies indicated that the long-term outcome of Lyme disease is good. Results are pending of chronic Lyme disease studies funded by the US National Institutes of Health. A better understanding of the pathogenesis of Lyme disease provided clues about possible mechanisms for persistent symptoms. Use of the current method of diagnosis by the two-step approach has proven to be reliable, but new methods are under investigation. Treatment guidelines were published recently. OspA vaccination of children aged 2 to 5 years was shown to be safe and immunogenic.

Gamma interferon is not required for arthritis resistance in the murine Lyme disease model

Lyme arthritis is the most common complication following infection of human individuals with Borrelia burgdorferi sensu stricto. In mice, B. burgdorferi infection leads to arthritis of the tibiotarsal joints. Arthritis severity in mice is under host genetic control, as BALB/c mice developed mild arthritis but C3H/He mice developed severe disease following B. burgdorferi infection. To study the role of gamma interferon (IFN-gamma) in arthritogenesis, targeted mutant mice lacking the IFN-gamma receptor (IFN-gammaR) were infected by inoculation with B. burgdorferi. IFN-gammaR(-/-) and parental 129/SvEv mice developed mild arthritis of similar severity, as determined both by weekly tibiotarsal joint measurements and histopathology at 2 and 5 weeks postinfection. Both strains of mice had the same spirochetal burden in the joints, suggesting that the IFN-gammaR(-/-) mice were not impaired in controlling spirochetal expansion in vivo. The wild-type mice mounted a Th1 response, with a predominance of CD4(+) IFN-gamma(+) T cells observed by flow cytometry. In contrast, the IFN-gammaR(-/-) mice mounted a Th2 response, with a predominance of CD4(+) IL-4(+) T cells. As expected given their cytokine profile, the IFN-gammaR(-/-) mice produced fewer CD8(+) IFN-gamma(+) and MAC-1(+) IL-12(+) cells and less immunoglobulin G2a (IgG2a) than their wild-type counterparts. These results strongly suggest that IFN-gamma is not required for arthritis resistance or as part of an effective immune response against B. burgdorferi.

Dissociation of infectivity and pathogenicity in Borrelia burgdorferi

Clonal Borrelia burgdorferi N40 (cN40) passaged 75 times in vitro (N40-75) infects mice but does not cause disease. N40-75 passaged 45 times further in vitro (N40-120) was no longer infectious and lacked genes encoded on linear plasmids 38 and 28-1, among other differences. These data suggest that B. burgdorferi cN40, N40-75, and N40-120 have distinct phenotypes that can be used to dissect the genetic elements responsible for pathogenicity and infectivity.