Borrelia burgdorferi-induced inflammation facilitates spirochete adaptation and variable major protein-like sequence locus recombination

YebC regulates variable surface antigen VlsE expression and is required for host immune evasion in Borrelia burgdorferi

Borrelia burgdorferi, the Lyme disease pathogen causes persistent infection by evading the host immune response. Differential expression of the surface-exposed lipoprotein VlsE that undergoes antigenic variation is a key immune evasion strategy employed by B. burgdorferi. Most studies focused on the mechanism of VlsE antigen variation, but little is known about VlsE regulation and factor(s) that regulates differential vlsE expression. In this study, we investigated BB0025, a putative YebC family transcriptional regulator (and hence designated BB0025 as YebC of B. burgdorferi herein). We constructed yebC mutant and complemented strain in an infectious strain of B. burgdorferi. The yebC mutant could infect immunocompromised SCID mice but not immunocompetent mice, suggesting that YebC plays an important role in evading host adaptive immunity. RNA-seq analyses identified vlsE as one of the genes whose expression was most affected by YebC. Quantitative RT-PCR and Western blot analyses confirmed that vlsE expression was dependent on YebC. In vitro, YebC and VlsE were co-regulated in response to growth temperature. In mice, both yebC and vlsE were inversely expressed with ospC in response to the host adaptive immune response. Furthermore, EMSA proved that YebC directly binds to the vlsE promoter, suggesting a direct transcriptional control. These data demonstrate that YebC is a new regulator that modulates expression of vlsE and other genes important for spirochetal infection and immune evasion in the mammalian host.

Immune escape strategies of Borrelia burgdorferi

The borrelial resurge demonstrates that Borrelia burgdorferi is a persistent health problem. This spirochete is responsible for a global public health concern called Lyme disease. B. burgdorferi faces diverse environmental conditions of its vector and host during its life cycle. To circumvent the host immune system is a prominent feature of B. burgdorferi. To date, numerous studies have reported on the various mechanisms used by this pathogen to evade the host defense mechanisms. This current review attempts to consolidate this information to describe the immunological and molecular methods used by B. burgdorferi for its survival.

Host Immune Evasion by Lyme and Relapsing Fever Borreliae: Findings to Lead Future Studies for Borrelia miyamotoi

The emerging pathogen, Borrelia miyamotoi, is a relapsing fever spirochete vectored by the same species of Ixodes ticks that carry the causative agents of Lyme disease in the US, Europe, and Asia. Symptoms caused by infection with B. miyamotoi are similar to a relapsing fever infection. However, B. miyamotoi has adapted to different vectors and reservoirs, which could result in unique physiology, including immune evasion mechanisms. Lyme Borrelia utilize a combination of Ixodes-produced inhibitors and native proteins [i.e., factor H-binding proteins (FHBPs)/complement regulator-acquiring surface proteins, p43, BBK32, BGA66, BGA71, CD59-like protein] to inhibit complement, while some relapsing fever spirochetes use C4b-binding protein and likely Ornithodoros-produced inhibitors. To evade the humoral response, Borrelia utilize antigenic variation of either outer surface proteins (Osps) and the Vmp-like sequences (Vls) system (Lyme borreliae) or variable membrane proteins (Vmps, relapsing fever borreliae). B. miyamotoi possesses putative FHBPs and antigenic variation of Vmps has been demonstrated. This review summarizes and compares the common mechanisms utilized by Lyme and relapsing fever spirochetes, as well as the current state of understanding immune evasion by B. miyamotoi.

vls Antigenic Variation Systems of Lyme Disease Borrelia: Eluding Host Immunity through both Random, Segmental Gene Conversion and Framework Heterogeneity

Spirochetes that cause Lyme borreliosis (also called Lyme disease) possess the vls locus, encoding an elaborate antigenic variation system. This locus contains the expression site vlsE as well as a contiguous array of vls silent cassettes, which contain variations of the central cassette region of vlsE. The locus is present on one of the many linear plasmids in the organism, e.g. plasmid lp28-1 in the strain Borrelia burgdorferi B31. Changes in the sequence of vlsE occur continuously during mammalian infection and consist of random, segmental, unidirectional recombination events between the silent cassettes and the cassette region of vlsE. These gene conversion events do not occur during in vitro culture or the tick portion of the infection cycle of B. burgdorferi or the other related Borrelia species that cause Lyme disease. The mechanism of recombination is largely unknown, but requires the RuvAB Holliday junction branch migrase. Other features of the vls locus also appear to be required, including cis locations of vlsE and the silent cassettes and high G+C content and GC skew. The vls system is required for long-term survival of Lyme Borrelia in infected mammals and represents an important mechanism of immune evasion. In addition to sequence variation, immune selection also results in significant heterogeneity in the sequence of the surface lipoprotein VlsE. Despite antigenic variation, VlsE generates a robust antibody response, and both full-length VlsE and the C6 peptide (corresponding to invariant region 6) are widely used in immunodiagnostic tests for Lyme disease.

Epitope-Specific Evolution of Human B Cell Responses to Borrelia burgdorferi VlsE Protein from Early to Late Stages of Lyme Disease

Most immunogenic proteins of Borrelia burgdorferi, the causative agent of Lyme disease, are known or expected to contain multiple B cell epitopes. However, the kinetics of the development of human B cell responses toward the various epitopes of individual proteins during the course of Lyme disease has not been examined. Using the highly immunogenic VlsE as a model Ag, we investigated the evolution of humoral immune responses toward its immunodominant sequences in 90 patients with a range of early to late manifestations of Lyme disease. The results demonstrate the existence of asynchronous, independently developing, Ab responses against the two major immunogenic regions of the VlsE molecule in the human host. Despite their strong immunogenicity, the target epitopes were inaccessible to Abs on intact spirochetes, suggesting a lack of direct immunoprotective effect. These observations document the association of immune reactivity toward specific VlsE sequences with different phases of Lyme disease, demonstrating the potential use of detailed epitope mapping of Ags for staging of the infection, and offer insights regarding the pathogen's possible immune evasion mechanisms.

Vesicular stomatitis virus infects resident cells of the central nervous system and induces replication-dependent inflammatory responses

Vesicular stomatitis virus (VSV) infection of mice via intranasal administration results in a severe encephalitis with rapid activation and proliferation of microglia and astrocytes. We have recently shown that these glial cells express RIG-I and MDA5, cytosolic pattern recognition receptors for viral RNA. However, it is unclear whether VSV can replicate in glial cells or if such replication is required for their inflammatory responses. Here we demonstrate that primary microglia and astrocytes are permissive for VSV infection and limited productive replication. Importantly, we show that viral replication is required for robust inflammatory mediator production by these cells. Finally, we have confirmed that in vivo VSV administration can result in viral infection of glial cells in situ. These results suggest that viral replication within resident glial cells might play an important role in CNS inflammation following infection with VSV and possibly other neurotropic nonsegmented negative-strand RNA viruses.

Toll-like receptors 1 and 2 heterodimers alter Borrelia burgdorferi gene expression in mice and ticks

Borrelia burgdorferi, the agent of Lyme disease, is recognized by Toll-like receptor (TLR) 1 and 2 heterodimers. Microarray analysis of in vivo B. burgdorferi gene expression in murine skin showed that several genes were altered in TLR1/2-deficient animals compared with wild-type mice. For example, expression of bbe21 (a gene involved in B. burgdorferi lp25 plasmid maintenance) and bb0665 (a gene encoding a glycosyl transferase) were higher in TLR1/2-deficient mice than in control animals. In contrast, messenger RNA levels for bb0731 (a spoJ-like gene) and bba74 (a gene encoding a periplasmic protein) were lower in TLR1/2-deficient mice than in wild-type animals. The expression profiles of some of these genes were altered similarly in B. burgdorferi-infected ticks fed on control or TLR1/2-deficient mice. Quantitative reverse-transcription polymerase chain reaction analysis supported the microarray analysis and suggested that spirochete gene expression is altered by the milieu created by specific host TLRs, both in the murine host and in the arthropod vector.

Passage through Ixodes scapularis ticks enhances the virulence of a weakly pathogenic isolate of Borrelia burgdorferi

Lyme disease is the most common tick-borne illness in the United States. In this paper we explore the contribution of Ixodes scapularis ticks to the pathogenicity of Borrelia burgdorferi in mice. Previously we demonstrated that an isolate of B. burgdorferi sensu stricto (designated N40), passaged 75 times in vitro (N40-75), was infectious but was no longer able to cause arthritis and carditis in C3H mice. We now show that N40-75 spirochetes can readily colonize I. scapularis and multiply during tick engorgement. Remarkably, tick-transmitted N40-75 spirochetes cause disease in mice. N40-75 spirochetes isolated from these animals also retained their pathogenicity when subsequently administered to mice via syringe inoculation. Array analysis revealed that several genes associated with virulence, including bba25, bba65, bba66, bbj09, and bbk32, had higher expression levels in the tick-passaged N40-75 spirochete. These data suggest that transmission of a high-passage attenuated isolate of B. burgdorferi by the arthropod vector results in the generation of spirochetes that have enhanced pathogenesis in mice.

Detailed analysis of sequence changes occurring during vlsE antigenic variation in the mouse model of Borrelia burgdorferi infection

Lyme disease Borrelia can infect humans and animals for months to years, despite the presence of an active host immune response. The vls antigenic variation system, which expresses the surface-exposed lipoprotein VlsE, plays a major role in B. burgdorferi immune evasion. Gene conversion between vls silent cassettes and the vlsE expression site occurs at high frequency during mammalian infection, resulting in sequence variation in the VlsE product. In this study, we examined vlsE sequence variation in B. burgdorferi B31 during mouse infection by analyzing 1,399 clones isolated from bladder, heart, joint, ear, and skin tissues of mice infected for 4 to 365 days. The median number of codon changes increased progressively in C3H/HeN mice from 4 to 28 days post infection, and no clones retained the parental vlsE sequence at 28 days. In contrast, the decrease in the number of clones with the parental vlsE sequence and the increase in the number of sequence changes occurred more gradually in severe combined immunodeficiency (SCID) mice. Clones containing a stop codon were isolated, indicating that continuous expression of full-length VlsE is not required for survival in vivo; also, these clones continued to undergo vlsE recombination. Analysis of clones with apparent single recombination events indicated that recombinations into vlsE are nonselective with regard to the silent cassette utilized, as well as the length and location of the recombination event. Sequence changes as small as one base pair were common. Fifteen percent of recovered vlsE variants contained “template-independent” sequence changes, which clustered in the variable regions of vlsE. We hypothesize that the increased frequency and complexity of vlsE sequence changes observed in clones recovered from immunocompetent mice (as compared with SCID mice) is due to rapid clearance of relatively invariant clones by variable region-specific anti-VlsE antibody responses.

Lyme borreliosis is the most common vector-transmitted infection in Europe and North America, and is caused by the spirochete Borrelia burgdorferi and other closely related Borrelia species. Lyme disease Borrelia have an elaborate mechanism for varying the sequence of VlsE, a surface-localized, immunogenic lipoprotein. This antigenic variation is thought to be important in immune evasion and thus in the ability of Lyme disease Borrelia to cause long-term infection. In this study, we examined 1,399 B. burgdorferi clones isolated from infected immunocompetent and immunodeficient mice to gain a better understanding of the rate and variety of VlsE sequence changes that occur during infection. We determined that clones with few or no VlsE sequence changes are rapidly cleared in mice with active immune responses, whereas clones with many VlsE changes persist. The vls antigenic variation system can utilize any of the 15 silent cassette sequences as sequence “donors,” and does not exhibit obvious preferences in the location of changes within the vlsE cassette region or the types of VlsE sequence variations found in different tissues, such as in joints or in the heart. Our findings provide further evidence that the vls locus represents a remarkably robust recombination system and immune evasion mechanism.

Tick-host-pathogen interactions in Lyme borreliosis

Borrelia burgdorferi, the spirochetal agent of Lyme borreliosis, is predominantly transmitted by Ixodes ticks. Spirochetes have developed many strategies to adapt to the different environments that are present in the arthropod vector and the vertebrate host. This review focuses on B. burgdorferi genes that are preferentially expressed in the tick and the vertebrate host, and describes how selected gene products facilitate spirochete survival throughout the enzootic life cycle. Interestingly, B. burgdorferi also enhances expression of specific Ixodes scapularis genes, such as TROSPA and salp15. The importance of these genes and their products for B. burgdorferi survival within the tick, and during the transmission process, will also be reviewed. Moreover, we discuss how such vector molecules could be used to develop vector-antigen-based vaccines to prevent the transmission of B. burgdorferi and, potentially, other arthropod-borne microbes.

Antigenicity and recombination of VlsE, the antigenic variation protein of Borrelia burgdorferi, in rabbits, a host putatively resistant to long-term infection with this spirochete

Borrelia burgdorferi, the Lyme disease pathogen, employs several immune-evasive strategies to survive in mammals. Unlike mice, major reservoir hosts for B. burgdorferi, rabbits are considered to be nonpermissive hosts for persistent infection. Antigenic variation of the VlsE molecule is a probable evasion strategy known to function in mice. The invariable region 6 (IR6) and carboxyl-terminal domain (Ct) of VlsE elicit dominant antibody responses that are not protective, perhaps to function as decoy epitopes that protect the spirochete. We sought to determine if either of these characteristics of VlsE differed in rabbit infection, contributing to its reputed nonpermissiveness. VlsE recombination was observed in rabbits that were given inoculations with either cultured or host-adapted spirochetes. Early observations showed a lack of anti-C6 (a peptide encompassing the IR6 region) response in most rabbits, so the anti-Ct and anti-C6 responses were monitored for 98 weeks. Anti-C6 antibody appeared as late as 20 weeks postinoculation, and the anti-Ct response, evident within the first 2 weeks, oscillated for prolonged periods of time. These observations, together with the recovery of cultivable spirochetes from tissue of one animal at 98 weeks postinoculation, challenge the notion that the rabbit cannot harbour a long-term B. burgdorferi infection.

Evolving models of Lyme disease spirochete gene regulation

The spirochete Borrelia burgdorferi, the causative agent of Lyme disease (Lyme borreliosis), is well-adapted to maintain a natural cycle of alternately infecting vertebrates and blood-sucking ticks. During this cycle, B. burgdorferi interacts with a broad spectrum of vertebrate and arthropod tissues, acquires nutrients in diverse environments and evades killing by vertebrate and tick immune systems. The bacterium also senses when situations occur that necessitate transmission between hosts, such as when an infected tick is taking a blood meal from a potential host. To accurately accomplish the requirements necessary for survival in nature, B. burgdorferi must be keenly aware of its surroundings and respond accordingly. In this review, we trace studies performed to elucidate regulatory mechanisms employed by B. burgdorferi to control gene expression, and the development of models or "paradigms" to explain experimental results. Through comparisons of five borrelial gene families, it is readily apparent that each is controlled through a distinct mechanism. Furthermore, those results indicate that current models of interpreting in vitro data cannot accurately predict all aspects of B. burgdorferi environmental sensing and gene regulation in vivo.

Control of Borrelia burgdorferi-specific CD4+-T-cell effector function by interleukin-12- and T-cell receptor-induced p38 mitogen-activated protein kinase activity

Infection with Borrelia burgdorferi, the causative agent of Lyme disease, results in a Th1 response and proinflammatory cytokine production. Mice deficient for MKK3, an upstream activator of p38 mitogen-activated protein (MAP) kinase, develop a lower Th1 response and exhibit an impaired ability to produce proinflammatory cytokines upon infection with the spirochete. We investigated the contribution of p38 MAP kinase activity in gamma interferon (IFN-gamma) production in CD4+ T cells in response to specific antigen through T-cell receptor (TCR)- and interleukin-12 (IL-12)-mediated signals. The specific inhibition of p38 MAP kinase in T cells and the administration of a pharmacological inhibitor of the kinase during the course of infection with the spirochete resulted in reduced levels of IFN-gamma in the sera of infected mice. Our results also demonstrate that although p38 MAP kinase activity is not required for the differentiation of B. burgdorferi-specific CD4+ T cells, the production of IFN-gamma by Th1 effector cells is regulated by the kinase. Both TCR engagement and IL-12 induced the production of the Th1 cytokine through the activation of the p38 MAP kinase pathway. Thus, the inhibition of this pathway in vitro resulted in decreased levels of IFN-gamma during restimulation of B. burgdorferi-specific T cells in response to anti-CD3 and IL-12 stimulation. These results clarify the specific contribution of the p38 MAP kinase in the overall immune response to the spirochete and its role in the effector function of B. burgdorferi-specific T cells.

Distinct bacterial dissemination and disease outcome in mice subcutaneously infected withBorrelia burgdorferiin the midline of the back and the footpad

Subcutaneous inoculation of mice with Borrelia burgdorferi, the causative agent of Lyme disease, results in established infection and the development of acute arthritis and carditis, hallmarks of human disease. Because conflicting results may originate from the site of subcutaneous inoculation, we addressed the dissemination capacity of spirochetes injected in the shoulder region versus the footpad. Spirochetes inoculated in the footpad disseminated to a lesser extent to distant organs, such as the ear and the heart. This resulted in distinct degrees of joint and cardiac inflammation at the peak of the disease. The differences eventually leveled out. These results suggest that caution must be exercised in the interpretation of results obtained with routes of inoculation that do not closely represent the natural site of infection.

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.

Molecualar survival strategies of the Lyme disease spirochete Borrelia burgdorferi

Lyme disease is a tick-transmitted disease caused by the spirochete Borrelia burgdorferi. The bacterium adopts different strategies for its survival inside the immunocompetent host from the time of infection until dissemination in different parts of body tissues. The success of this spirochete depends on its ability to colonise the host tissues and counteract the host's defence mechanisms. During this process borrelia seems to maintain its vitality to ensure long-term survival in the host. Borrelia's proteins are encoded by plasmid and chromosomal genes. These genes are differentially regulated and expressed by different environmental factors in ticks as well as in the mammalian host during infection. In addition, antigenic diversity enables the spirochete to escape host defence mechanisms and maintain infection. In this review we focus on the differential expression of proteins and genes, and further molecular mechanisms used by borrelia to maintain its survival in the host. In light of these pathogenetic mechanisms, further studies on spirochete host interaction are needed to understand the complex interplay that finally lead to host autoimmunity.

BBK32, a fibronectin binding MSCRAMM from Borrelia burgdorferi, contains a disordered region that undergoes a conformational change on ligand binding

BBK32 is a fibronectin-binding lipoprotein on Borrelia burgdorferi, the causative agent of Lyme disease. Analysis using secondary structure prediction programs suggested that BBK32 is composed of two domains, an N-terminal segment lacking well defined secondary structure and a C-terminal segment composed largely of alpha-helices. Analysis of purified recombinant forms of the two domains by circular dichroism spectroscopy, gel permeation chromatography, and intrinsic viscosity determination were consistent with an N-terminal-extended, unstructured segment and a C-terminal globular domain in BBK32. Solid phase binding experiments suggest that the unstructured N-terminal domain binds fibronectin. Analysis of changes in circular dichroism spectra of the N-terminal segment of BBK32 upon binding of the N-terminal domain of fibronectin revealed an increase in beta-sheet content in the complex. Hence, BBK32, which belongs to a different family of proteins and shows no overall sequence similarity with the fibronectin binding MSCRAMMs (microbial surface components recognizing adhesive matrix molecules) of Gram-positive bacteria, binds fibronectin by a mechanism that is reminiscent of the "tandem beta-zipper" previously demonstrated for the fibronectin binding of streptococcal adhesins.

Functional properties of Borrelia burgdorferi recA

Functions of the Borrelia burgdorferi RecA protein were investigated in Escherichia coli recA null mutants. Complementation with B. burgdorferi recA increased survival of E. coli recA mutants by 3 orders of magnitude at a UV dose of 2,000 microJ/cm(2). The viability at this UV dose was about 10% that provided by the homologous recA gene. Expression of B. burgdorferi recA resulted in survival of E. coli at levels of mitomycin C that were lethal to noncomplemented hosts. B. burgdorferi RecA was as effective as E. coli RecA in mediating homologous recombination in E. coli. Furthermore, E. coli lambda phage lysogens complemented with B. burgdorferi recA produced phage even in the absence of UV irradiation. The level of phage induction was 55-fold higher than the level in cells complemented with the homologous recA gene, suggesting that B. burgdorferi RecA may possess an enhanced coprotease activity. This study indicates that B. burgdorferi RecA mediates the same functions in E. coli as the homologous E. coli protein mediates. However, the rapid loss of viability and the absence of induction in recA expression after UV irradiation in B. burgdorferi suggest that recA is not involved in the repair of UV-induced damage in B. burgdorferi. The primary role of RecA in B. burgdorferi is likely to be a role in some aspect of recombination.

Adaptation of Borrelia burgdorferi in the tick and the mammalian host

Borrelia burgdorferi, the causative agent of Lyme disease, shows a great ability to adapt to different environments, including the arthropod vector, and the mammalian host. The success of these microorganisms to survive in nature and complete their enzootic cycle depends on the regulation of genes that are essential to their survival in the different environments. This review describes the current knowledge of gene expression by B. burgdorferi in the tick and the mammalian host. The functions of the differentially regulated gene products as well as the factors that influence their expression are discussed. A thorough understanding of the changes in gene expression and the function of the differentially expressed antigens during the life cycle of the spirochete will allow a better control of this prevalent infection and the design of new, second generation vaccines to prevent infection with the spirochete.

Molecular methods for ehrlichiosis and Lyme disease

This article reviews molecular techniques that have been developed and are effective in the clinical laboratory for the emerging tick-borne infections, ehrlichiosis and Lyme disease.

Coevolution of markers of innate and adaptive immunity in skin and peripheral blood of patients with erythema migrans

We used multiparameter flow cytometry to characterize leukocyte immunophenotypes and cytokines in skin and peripheral blood of patients with erythema migrans (EM). Dermal leukocytes and cytokines were assessed in fluids aspirated from epidermal suction blisters raised over EM lesions and skin of uninfected controls. Compared with corresponding peripheral blood, EM infiltrates were enriched for T cells, monocytes/macrophages, and dendritic cells (DCs), contained lower proportions of neutrophils, and were virtually devoid of B cells. Enhanced expression of CD14 and HLA-DR by lesional neutrophils and macrophages indicated that these innate effector cells were highly activated. Staining for CD45RO and CD27 revealed that lesional T lymphocytes were predominantly Ag-experienced cells; furthermore, a subset of circulating T cells also appeared to be neosensitized. Lesional DC subsets, CD11c(+) (monocytoid) and CD11c(-) (plasmacytoid), expressed activation/maturation surface markers. Patients with multiple EM lesions had greater symptom scores and higher serum levels of IFN-alpha, TNF-alpha, and IL-2 than patients with solitary EM. IL-6 and IFN-gamma were the predominant cytokines in EM lesions; however, greater levels of both mediators were detected in blister fluids from patients with isolated EM. Circulating monocytes displayed significant increases in surface expression of Toll-like receptor (TLR)1 and TLR2, while CD11c(+) DCs showed increased expression of TLR2 and TLR4; lesional macrophages and CD11c(+) and CD11c(-) DCs exhibited increases in expression of all three TLRs. These results demonstrate that Borrelia burgdorferi triggers innate and adaptive responses during early Lyme disease and emphasize the interdependence of these two arms of the immune response in the efforts of the host to contain spirochetal infection.

Canine borreliosis

A guild of organisms carried by the same vector (Ixodes ticks) in Lyme-endemic areas may be confounding the understanding of Lyme disease in dogs. A new diagnostic method, the C6 peptide test for Lyme, and serology and PCR testing for Ehrlichia, Babesia, and Bartonella species will help to sort out seroprevalence and symptomatology caused by exposure to these agents or by coinfections. In addition, Rickettsia, Leptospira, Mycoplasma species, and more could be involved in dogs diagnosed with a "doxycycline-responsive" disease. The author does not recommend treating asymptomatic Borrelia carrier dogs, but does recommend screening them for proteinuria and for exposure to other agents. A positive Lyme titer is a marker of exposure to Ixodes ticks and the agents they carry. The risk/benefit of vaccination will be understood better as the symptomatology and immunopathogenesis of Lyme disease are defined. Meanwhile, tick control is highly recommended for all dogs in Lyme-endemic areas.

Host-adapted Borrelia burgdorferi in mice expresses OspA during inflammation

Antibody responses to outer surface protein A (OspA) of Borrelia burgdorferi may occur during periods of arthritis late in the clinical course of untreated Lyme disease. These antibody responses are paradoxical, given the conclusive evidence demonstrating that B. burgdorferi transmitted to the mammalian host expresses little or no OspA. The parallel occurrence of OspA antibodies and arthritic episodes suggests that OspA expression is upregulated during infection with B. burgdorferi. We hypothesized that this was due to the inflammatory environment caused by the immune response to the spirochete. To test our hypothesis, we adapted an in vivo model that mimics the host-pathogen interaction. Dialysis chambers containing B. burgdorferi were implanted into the peritoneal cavities of mice in the presence or absence of zymosan, a yeast cell wall extract that induces inflammation. Spirochetes were harvested 2 days later, and OspA expression was assessed at the protein and transcription level by Western blotting and real-time reverse transcription-PCR, respectively. Flow cytometry was also utilized to evaluate OspA protein expression on individual spirochetes. B. burgdorferi maintained in an inflammatory in vivo environment show an increased OspA expression relative to B. burgdorferi kept under normal in vivo conditions. Furthermore, host-adapted B. burgdorferi with a low OspA phenotype upregulates OspA expression when transferred to an inflammatory in vivo environment. The results obtained by these techniques uniformly identify inflammation as a mediator of in vivo OspA expression in host-adapted B. burgdorferi, providing insights into the behavior of live spirochetes in the mammalian host.

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.

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.

Geographical and seasonal correlation of multiple sclerosis to sporadic schizophrenia

BACKGROUND: Clusters by season and locality reveal a striking epidemiological overlap between sporadic schizophrenia and multiple sclerosis (MS). As the birth excesses of those individuals who later in life develop schizophrenia mirror the seasonal distribution of Ixodid ticks, a meta analysis has been performed between all neuropsychiatric birth excesses including MS and the epidemiology of spirochaetal infectious diseases. RESULTS: The prevalence of MS and schizophrenic birth excesses entirely spares the tropical belt where human treponematoses are endemic, whereas in more temperate climates infection rates of Borrelia garinii in ticks collected from seabirds match the global geographic distribution of MS. If the seasonal fluctuations of Lyme borreliosis in Europe are taken into account, the birth excesses of MS and those of schizophrenia are nine months apart, reflecting the activity of Ixodes ricinus at the time of embryonic implantation and birth. In America, this nine months' shift between MS and schizophrenic births is also reflected by the periodicity of Borrelia burgdorferi transmitting Ixodes pacificus ticks along the West Coast and the periodicity of Ixodes scapularis along the East Coast. With respect to Ixodid tick activity, amongst the neuropsychiatric birth excesses only amyotrophic lateral sclerosis (ALS) shows a similar seasonal trend. CONCLUSION: It cannot be excluded at present that maternal infection by Borrelia burgdorferi poses a risk to the unborn. The seasonal and geographical overlap between schizophrenia, MS and neuroborreliosis rather emphasises a causal relation that derives from exposure to a flagellar virulence factor at conception and delivery. It is hoped that the pathogenic correlation of spirochaetal virulence to temperature and heat shock proteins (HSP) might encourage a new direction of research in molecular epidemiology.

Seasonal correlation of sporadic schizophrenia to Ixodes ticks and Lyme borreliosis

BACKGROUND: Being born in winter and spring is considered one of the most robust epidemiological risk factors for schizophrenia. The aetiology and exact timing of this birth excess, however, has remained elusive so far. Since during phylogeny, Borrelia DNA has led to multiple germ-line mutations within the CB1 candidate gene for schizophrenia, a meta analysis has been performed of all papers on schizophrenic birth excesses with no less than 3000 cases each. All published numerical data were then plotted against the seasonal distributions of Ixodes ticks worldwide. RESULTS: In the United States, Europe and Japan the birth excesses of those individuals who later in life develop schizophrenia mirror the seasonal distribution of Ixodes ticks nine months earlier at the time of conception. South of the Wallace Line, which limits the spread of Ixodes ticks and Borrelia burgdorferi into Australia, seasonal trends are less significant, and in Singapore, being non-endemic for Ixodes ticks and Lyme disease, schizophrenic birth excesses are absent. CONCLUSION: At present, it cannot be excluded that prenatal infection by B. burgdorferi is harmful to the implanting human blastocyst. The epidemiological clustering of sporadic schizophrenia by season and locality rather emphasises the risk to the unborn of developing a congenital, yet preventable brain disorder later in life.

Borrelia burgdorferi induces inflammatory mediator production by murine microglia

Lyme disease has been associated with damaging inflammation within the central nervous system. In the present study, we demonstrate that Borrelia burgdorferi is a significant stimulus for the production of IL-6, TNF-alpha, and PGE(2) by microglia. This effect is associated with induction of NF-kappaB, and increased expression of Toll-like receptor 2 and CD14, receptors known to underlie spirochete activation of other immune cell types. These studies identify microglia as a previously unappreciated source of inflammatory mediator production following challenge with B. burgdorferi. Such production may play an important role during the development of Lyme neuroborreliosis.

Host-pathogen interactions and the pathogenesis of murine Lyme disease

Lyme disease results from persistent infection with the spirochete Borrelia burgdorferi. A combination of bacterial factors and host factors contributes to the development of inflammatory disease. Studies from the past year have provided insight into both sides of this host-pathogen interplay. We now have a better appreciation of the bacterial genes and products that are involved in pathology and the components of the host response that participate in disease development.

Murine Lyme arthritis development mediated by p38 mitogen-activated protein kinase activity

Borrelia burgdorferi, the Lyme disease agent, causes joint inflammation in an experimental murine model. Inflammation occurs, in part, due to the ability of B. burgdorferi to induce the production of proinflammatory cytokines and a strong CD4(+) T helper type 1 response. The mechanisms by which spirochetes induce these responses are not completely known, although transcription factors, such as NF-kappa B in phagocytic cells, initiate the proinflammatory cytokine burst. We show here that the mitogen-activated protein (MAP) kinase of 38 kDa (p38 MAP kinase) is involved in the proinflammatory cytokine production elicited by B. burgdorferi Ags in phagocytic cells and the development of murine Lyme arthritis. B. burgdorferi Ags activated p38 MAP kinase in vitro, and the use of a specific inhibitor repressed the spirochete-induced production of TNF-alpha. The infection of mice that are deficient for a specific upstream activator of the kinase, MAP kinase kinase 3, resulted in diminished proinflammatory cytokine production and the development of arthritis, without compromising the ability of CD4(+) T cells to respond to borrelial Ags or the production of specific Abs. Overall, these data indicated that the p38 MAP kinase pathway plays an important role in B. burgdorferi-elicited inflammation and point to potential new therapeutic approaches to the treatment of inflammation induced by the spirochete.

Salp15, an ixodes scapularis salivary protein, inhibits CD4(+) T cell activation

Tick saliva has pleiotropic properties that facilitate persistence of the arthropod upon the host. We now describe a feeding-inducible protein in Ixodes scapularis saliva, Salp15, that inhibits CD4(+) T cell activation. The mechanism involves the repression of calcium fluxes triggered by TCR ligation and results in lower production of interleukin-2. Salp15 also inhibits the development of CD4(+) T cell-mediated immune responses in vivo, demonstrating the functional importance of this protein. Salp15 provides a molecular basis for understanding the immunosuppressive activity of I. scapularis saliva and vector-host interactions.