CD4+ T helper 1 cells facilitate regression of murine Lyme carditis

Animal models of Lyme carditis. Understanding how to study a complex disease

Lyme carditis, a well-established manifestation of Lyme disease, has been studied in animal models to improve understanding of its pathogenesis. This review synthesizes existing literature on these models and associated disease mechanisms. Searches in MEDLINE, Embase, BIOSIS, and Web of Science yielded 53 articles (47 mice models and 6 other animal models). Key findings include: 1) Onset of carditis correlates with spirochete localization in the heart; 2) Carditis occurs within 10 days of infection, progressing to peak inflammation within 30 days; 3) Infiltrates were predominantly composed of Mac-1+ macrophages and were associated with increases in TNF-α, IL-1 and IL-12 cytokines; 4) Resolution of inflammation was primarily mediated by lymphocytes; 5) Immune system is a double-edged sword: it can play a role in the progression and severity of carditis, but can also have a protective effect. Animal models offer valuable insights into the evolution and pathophysiologic mechanisms of Lyme carditis.

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 PD-1/PD-L1 pathway is induced during Borrelia burgdorferi infection and inhibits T cell joint infiltration without compromising bacterial clearance

The Lyme disease bacterial pathogen, Borrelia burgdorferi, establishes a long-term infection inside its mammalian hosts. Despite the continued presence of the bacteria in animal models of disease, inflammation is transitory and resolves spontaneously. T cells with limited effector functions and the inability to become activated by antigen, termed exhausted T cells, are present in many long-term infections. These exhausted T cells mediate a balance between pathogen clearance and preventing tissue damage resulting from excess inflammation. Exhausted T cells express a variety of immunoinhibitory molecules, including the molecule PD-1. Following B. burgdorferi infection, we found that PD-1 and its ligand PD-L1 are significantly upregulated on CD4+ T cells and antigen presenting cell subsets, respectively. Using mice deficient in PD-1, we found that the PD-1/PD-L1 pathway did not impact bacterial clearance but did impact T cell expansion and accumulation in the ankle joint and popliteal lymph nodes without affecting B cell populations or antibody production, suggesting that the PD-1/PD-L1 pathway may play a role in shaping the T cell populations present in affected tissues.

CD4 T cell responses in persistent Borrelia burgdorferi infection

Infection of mice with Borrelia burgdorferi (Bb), a tick-transmitted spirochete and the pathogen that causes Lyme disease in humans, triggers CD4 T cell activation in secondary lymphoid tissues, from which they disseminate into various infected tissues. Despite their activation and the appearance of CD4 T cell-dependent antibody responses, Bb establishes persistent infection in natural Bb reservoir hosts in the absence of overt disease, raising the question of the effectiveness of the anti-Bb T cell responses. Reviewing the existing literature, we propose that CD4 T cells might constitute a host cell target of Bb-mediated immune evasion, rendering these cells ineffective in orchestrating effective inflammatory responses and in supporting highly functional Bb-specific antibody induction. Supporting the induction of more effective CD4 T cell responses may help overcome Bb persistence.

Sphingomyelinases in a journey to combat arthropod-borne pathogen transmission

Ixodes scapularis ticks feed on humans and other vertebrate hosts and transmit several pathogens of public health concern. Tick saliva is a complex mixture of bioactive proteins, lipids and immunomodulators, such as I. scapularis sphingomyelinase (IsSMase)-like protein, an ortholog of dermonecrotoxin SMase D found in the venom of Loxosceles spp. of spiders. IsSMase modulates the host immune response towards Th2, which suppresses Th1-mediated cytokines to facilitate pathogen transmission. Arboviruses utilize exosomes for their transmission from tick to the vertebrate host, and exosomes derived from tick saliva/salivary glands suppress C-X-C motif chemokine ligand 12 and interleukin-8 immune response(s) in human skin to delay wound healing and repair processes. IsSMase affects also viral replication and exosome biogenesis, thereby inhibiting tick-to-vertebrate host transmission of pathogenic exosomes. In this review, we elaborate on exosomes and their biogenesis as potential candidates for developing novel control measure(s) to combat tick-borne diseases. Such targets could help with the development of an efficient anti-tick vaccine for preventing the transmission of tick-borne pathogens.

Immune Response to Borrelia: Lessons from Lyme Disease Spirochetes

The mammalian host responds to infection with Borrelia spirochetes through a highly orchestrated immune defense involving innate and adaptive effector functions aimed toward limiting pathogen burdens, minimizing tissue injury, and preventing subsequent reinfection. The evolutionary adaptation of Borrelia spirochetes to their reservoir mammalian hosts may allow for its persistence despite this immune defense. This review summarizes our current understanding of the host immune response to B. burgdorferi sensu lato, the most widely studied Borrelia spp. and etiologic agent of Lyme borreliosis. Pertinent literature will be reviewed with emphasis on in vitro, ex vivo and animal studies that influenced our understanding of both the earliest responses to B. burgdorferi as it enters the mammalian host and those that evolve as spirochetes disseminate and establish infection in multiple tissues. Our focus is on the immune response of inbred mice, the most commonly studied animal model of B. burgdorferi infection and surrogate for one of this pathogen's principle natural reservoir hosts, the white-footed deer mouse. Comparison will be made to the immune responses of humans with Lyme borreliosis. Our goal is to provide an understanding of the dynamics of the mammalian immune response during infection with B. burgdorferi and its relation to the outcomes in reservoir (mouse) and non-reservoir (human) hosts.

Chagas' cardiomyopathy and Lyme carditis: Lessons learned from two infectious diseases affecting the heart

Chagas' disease and Lyme disease are two endemic, vector-borne zoonotic infectious diseases that impact multiple organ systems, including the heart. Chagas' cardiomyopathy is a progressive process that can evolve into a dilated cardiomyopathy and heart failure several decades after the acute infection; in contrast, although early-disseminated Lyme carditis has been relatively well characterized, the sequelae of Lyme disease on the heart are less well-defined. A century of research on Chagas' cardiomyopathy has generated compelling data for pathophysiological models, evaluated the efficacy of therapy in large randomized controlled trials, and explored the social determinants of health impacting preventative measures. Recognizing the commonalities between Chagas' disease and Lyme disease, we speculate on whether some of the lessons learned from Chagas' cardiomyopathy may be applicable to Lyme carditis.

Protozoan Parasite Babesia microti Subverts Adaptive Immunity and Enhances Lyme Disease Severity

Lyme disease is the most prominent tick-borne disease in the United States. Co-infections with the tick-transmitted pathogens Babesia microti and Borrelia burgdorferi sensu stricto are becoming a serious health problem. B. burgdorferi is an extracellular spirochete that causes Lyme disease while B. microti is a protozoan that infects erythrocytes and causes babesiosis. Testing of donated blood for Babesia species is not currently mandatory due to unavailability of an FDA approved test. Transmission of this protozoan by blood transfusion often results in high morbidity and mortality in recipients. Infection of C3H/HeJ mice with B. burgdorferi and B. microti individually results in inflammatory Lyme disease and display of human babesiosis-like symptoms, respectively. Here we use this mouse model to provide a detailed investigation of the reciprocal influence of the two pathogens on each other during co-infection. We show that B. burgdorferi infection attenuates parasitemia in mice while B. microti subverts the splenic immune response, such that a marked decrease in splenic B and T cells, reduction in antibody levels and diminished functional humoral immunity, as determined by spirochete opsonophagocytosis, are observed in co-infected mice compared to only B. burgdorferi infected mice. Furthermore, immunosuppression by B. microti in co-infected mice showed an association with enhanced Lyme disease manifestations. This study demonstrates the effect of only simultaneous infection by B. burgdorferi and B. microti on each pathogen, immune response and on disease manifestations with respect to infection by the spirochete and the parasite. In our future studies, we will examine the overall effects of sequential infection by these pathogens on host immune responses and disease outcomes.

Molecular identification of tick-borne pathogens in asymptomatic individuals with human immunodeficiency virus type 1 (HIV-1) infection: a retrospective study

Background

The studies on the occurrence and diversity of tick-borne infections in HIV-infected individuals have been few, and the subject has been relatively neglected when compared with other common infections associated with HIV. In HIV-positive patients in whom a serological diagnostics is complicated due to reduced positive predictive value, a method where the microorganism is detected directly is of great value. Therefore, we performed a molecular study to ascertain the prevalence and incidence of tick-borne infections in HIV-infected persons in Poland, an endemic area for Ixodes ricinus ticks.

Methods

Genomic DNA was isolated from whole blood of tested patients. Detection of tick-borne pathogens was performed by amplification and sequencing of different loci. Molecular and phylogenetic analyses of obtained nucleotide sequences were performed. Serum samples were analyzed for antibodies against tick-borne pathogens by using commercial tests in all patients.

Results

Among 148 studied blood samples from HIV-infected patients, two cases (1.4%) of infection with tick-borne pathogen were reported. No symptoms of tick-borne infection were observed in these cases. In one case a patient was infected with Anaplasma phagocytophilum – the agent of human granulocytic anaplasmosis (HGA) and in the other with Borrelia garinii.

Conclusions

Our study revealed the first case of HIV positive patient infected with A. phagocytophilum. Asymptomatic tick-borne infection can occur in HIV-positive patients. The detailed history of tick bites, especially in endemic tick areas, should be considered as part of anamnesis in routine clinical care of HIV-positive patients.

Sleeper cells: the stringent response and persistence in the Borreliella (Borrelia) burgdorferi enzootic cycle

Infections with tick-transmitted Borreliella (Borrelia) burgdorferi, the cause of Lyme disease, represent an increasingly large public health problem in North America and Europe. The ability of these spirochetes to maintain themselves for extended periods of time in their tick vectors and vertebrate reservoirs is crucial for continuance of the enzootic cycle as well as for the increasing exposure of humans to them. The stringent response mediated by the alarmone (p)ppGpp has been determined to be a master regulator in B. burgdorferi. It modulates the expression of identified and unidentified open reading frames needed to deal with and overcome the many nutritional stresses and other challenges faced by the spirochete in ticks and animal reservoirs. The metabolic and morphologic changes resulting from activation of the stringent response in B. burgdorferi may also be involved in the recently described non-genetic phenotypic phenomenon of tolerance to otherwise lethal doses of antimicrobials and to other antimicrobial activities. It may thus constitute a linchpin in multiple aspects of infections with Lyme disease borrelia, providing a link between the micro-ecological challenges of its enzootic life-cycle and long-term residence in the tissues of its animal reservoirs, with the evolutionary side effect of potential persistence in incidental human hosts.

Diet-Induced Obesity Does Not Alter Tigecycline Treatment Efficacy in Murine Lyme Disease

Obese individuals more frequently suffer from infections, as a result of increased susceptibility to a number of bacterial pathogens. Furthermore, obesity can alter antibiotic treatment efficacy due to changes in drug pharmacokinetics which can result in under-dosing. However, studies on the treatment of bacterial infections in the context of obesity are scarce. To address this research gap, we assessed efficacy of antibiotic treatment in diet-induced obese mice infected with the Lyme disease pathogen, Borrelia burgdorferi. Diet-induced obese C3H/HeN mice and normal-weight controls were infected with B. burgdorferi, and treated during the acute phase of infection with two doses of tigecycline, adjusted to the weights of diet-induced obese and normal-weight mice. Antibiotic treatment efficacy was assessed 1 month after the treatment by cultivating bacteria from tissues, measuring severity of Lyme carditis, and quantifying bacterial DNA clearance in ten tissues. In addition, B. burgdorferi-specific IgG production was monitored throughout the experiment. Tigecycline treatment was ineffective in reducing B. burgdorferi DNA copies in brain. However, diet-induced obesity did not affect antibiotic-dependent bacterial DNA clearance in any tissues, regardless of the tigecycline dose used for treatment. Production of B. burgdorferi-specific IgGs was delayed and attenuated in mock-treated diet-induced obese mice compared to mock-treated normal-weight animals, but did not differ among experimental groups following antibiotic treatment. No carditis or cultivatable B. burgdorferi were detected in any antibiotic-treated group. In conclusion, obesity was associated with attenuated and delayed humoral immune responses to B. burgdorferi, but did not affect efficacy of antibiotic treatment.

Borrelia burgdorferi Manipulates Innate and Adaptive Immunity to Establish Persistence in Rodent Reservoir Hosts

Borrelia burgdorferi sensu lato species complex is capable of establishing persistent infections in a wide variety of species, particularly rodents. Infection is asymptomatic or mild in most reservoir host species, indicating successful co-evolution of the pathogen with its natural hosts. However, infected humans and other incidental hosts can develop Lyme disease, a serious inflammatory syndrome characterized by tissue inflammation of joints, heart, muscles, skin, and CNS. Although B. burgdorferi infection induces both innate and adaptive immune responses, they are ultimately ineffective in clearing the infection from reservoir hosts, leading to bacterial persistence. Here, we review some mechanisms by which B. burgdorferi evades the immune system of the rodent host, focusing in particular on the effects of innate immune mechanisms and recent findings suggesting that T-dependent B cell responses are subverted during infection. A better understanding of the mechanisms causing persistence in rodents may help to increase our understanding of the pathogenesis of Lyme disease and ultimately aid in the development of therapies that support effective clearance of the bacterial infection by the host’s immune system.

T Cells Exacerbate Lyme Borreliosis in TLR2-Deficient Mice

Infection of humans with the spirochete, Borrelia burgdorferi, causes Lyme borreliosis and can lead to clinical manifestations such as arthritis, carditis, and neurological conditions. Experimental infection of mice recapitulates many of these symptoms and serves as a model system for the investigation of disease pathogenesis and immunity. Innate immunity is known to drive the development of Lyme arthritis and carditis, but the mechanisms driving this response remain unclear. Innate immune cells recognize B. burgdorferi surface lipoproteins primarily via toll-like receptor (TLR)2; however, previous work has demonstrated TLR2^−/− mice had exacerbated disease and increased bacterial burden. We demonstrate increased CD4 and CD8 T cell infiltrates in B. burgdorferi-infected joints and hearts of C3H TLR2^−/− mice. In vivo depletion of either CD4 or CD8 T cells reduced Borrelia-induced joint swelling and lowered tissue spirochete burden, whereas depletion of CD8 T cells alone reduced disease severity scores. Exacerbation of Lyme arthritis correlated with increased production of CXCL9 by synoviocytes, and this was reduced with CD8 T cell depletion. These results demonstrate T cells can exacerbate Lyme disease pathogenesis and prolong disease resolution possibly through dysregulation of inflammatory responses and inhibition of bacterial clearance.

Ikaros mediates the DNA methylation-independent silencing of MCJ/DNAJC15 gene expression in macrophages

MCJ (DNAJC15) is a mitochondrial protein that regulates the mitochondrial metabolic status of macrophages and their response to inflammatory stimuli. CpG island methylation in cancer cells constitutes the only mechanism identified for the regulation of MCJ gene expression. However, whether DNA methylation or transcriptional regulation mechanisms are involved in the physiological control of this gene expression in non-tumor cells remains unknown. We now demonstrate a mechanism of regulation of MCJ expression that is independent of DNA methylation. IFNγ, a protective cytokine against cardiac inflammation during Lyme borreliosis, represses MCJ transcription in macrophages. The transcriptional regulator, Ikaros, binds to the MCJ promoter in a Casein kinase II-dependent manner, and mediates the repression of MCJ expression. These results identify the MCJ gene as a transcriptional target of IFNγ and provide evidence of the dynamic adaptation of normal tissues to changes in the environment as a way to adapt metabolically to new conditions.

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.

BB0238, a presumed tetratricopeptide repeat-containing protein, is required during Borrelia burgdorferi mammalian infection

The Lyme disease spirochete, Borrelia burgdorferi, occupies both a tick vector and mammalian host in nature. Considering the unique enzootic life cycle of B. burgdorferi, it is not surprising that a large proportion of its genome is composed of hypothetical proteins not found in other bacterial pathogens. bb0238 encodes a conserved hypothetical protein of unknown function that is predicted to contain a tetratricopeptide repeat (TPR) domain, a structural motif responsible for mediating protein-protein interactions. To evaluate the role of bb0238 during mammalian infection, a bb0238-deficient mutant was constructed. The bb0238 mutant was attenuated in mice infected via needle inoculation, and complementation of bb0238 expression restored infectivity to wild-type levels. bb0238 expression does not change in response to varying culture conditions, and thus, it appears to be constitutively expressed under in vitro conditions. bb0238 is expressed in murine tissues during infection, though there was no significant change in expression levels among different tissue types. Localization studies indicate that BB0238 is associated with the inner membrane of the spirochete and is therefore unlikely to promote interaction with host ligands during infection. B. burgdorferi clones containing point mutations in conserved residues of the putative TPR motif of BB0238 demonstrated attenuation in mice that was comparable to that in the bb0238 deletion mutant, suggesting that BB0238 may contain a functional TPR domain.

MicroRNA-146a provides feedback regulation of lyme arthritis but not carditis during infection with Borrelia burgdorferi

MicroRNAs have been shown to be important regulators of inflammatory and immune responses and are implicated in several immune disorders including systemic lupus erythematosus and rheumatoid arthritis, but their role in Lyme borreliosis remains unknown. We performed a microarray screen for expression of miRNAs in joint tissue from three mouse strains infected with Borrelia burgdorferi. This screen identified upregulation of miR-146a, a key negative regulator of NF-κB signaling, in all three strains, suggesting it plays an important role in the in vivo response to B. burgdorferi. Infection of B6 miR-146a-/- mice with B. burgdorferi revealed a critical nonredundant role of miR-146a in modulating Lyme arthritis without compromising host immune response or heart inflammation. The impact of miR-146a was specifically localized to the joint, and did not impact lesion development or inflammation in the heart. Furthermore, B6 miR-146a-/- mice had elevated levels of NF-κB-regulated products in joint tissue and serum late in infection. Flow cytometry analysis of various lineages isolated from infected joint tissue of mice showed that myeloid cell infiltration was significantly greater in B6 miR-146a-/- mice, compared to B6, during B. burgdorferi infection. Using bone marrow-derived macrophages, we found that TRAF6, a known target of miR-146a involved in NF-κB activation, was dysregulated in resting and B. burgdorferi-stimulated B6 miR-146a-/- macrophages, and corresponded to elevated IL-1β, IL-6 and CXCL1 production. This dysregulated protein production was also observed in macrophages treated with IL-10 prior to B. burgdorferi stimulation. Peritoneal macrophages from B6 miR-146a-/- mice also showed enhanced phagocytosis of B. burgdorferi. Together, these data show that miR-146a-mediated regulation of TRAF6 and NF-κB, and downstream targets such as IL-1β, IL-6 and CXCL1, are critical for modulation of Lyme arthritis during chronic infection with B. burgdorferi.

Dual role for Fcγ receptors in host defense and disease in Borrelia burgdorferi-infected mice

Arthritis in mice infected with the Lyme disease spirochete, Borrelia burgdorferi, results from the influx of innate immune cells responding to the pathogen in the joint and is influenced in part by mouse genetics. Production of inflammatory cytokines by innate immune cells in vitro is largely mediated by Toll-like receptor (TLR) interaction with Borrelia lipoproteins, yet surprisingly mice deficient in TLR2 or the TLR signaling molecule MyD88 still develop arthritis comparable to that seen in wild type mice after B. burgdorferi infection. These findings suggest that other, MyD88-independent inflammatory pathways can contribute to arthritis expression. Clearance of B. burgdorferi is dependent on the production of specific antibody and phagocytosis of the organism. As Fc receptors (FcγR) are important for IgG-mediated clearance of immune complexes and opsonized particles by phagocytes, we examined the role that FcγR play in host defense and disease in B. burgdorferi-infected mice. B. burgdorferi-infected mice deficient in the Fc receptor common gamma chain (FcεR_γ^−/− mice) harbored ~10 fold more spirochetes than similarly infected wild type mice, and this was associated with a transient increase in arthritis severity. While the elevated pathogen burdens seen in B. burgdorferi-infected MyD88^−/− mice were not affected by concomitant deficiency in FcγR, arthritis was reduced in FcεR_γ^−/−MyD88^−/− mice in comparison to wild type or single knockout mice. Gene expression analysis from infected joints demonstrated that absence of both MyD88 and FcγR lowers mRNA levels of proteins involved in inflammation, including Cxcl1 (KC), Xcr1 (Gpr5), IL-1beta, and C reactive protein. Taken together, our results demonstrate a role for FcγR-mediated immunity in limiting pathogen burden and arthritis in mice during the acute phase of B. burgdorferi infection, and further suggest that this pathway contributes to the arthritis that develops in B. burgdorferi-infected MyD88^−/− mice.

Ménage à trois: Borrelia, dendritic cells, and tick saliva interactions

Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, is inoculated into the skin during an Ixodes tick bite where it is recognised and captured by dendritic cells (DCs). However, considering the propensity of Borrelia to disseminate, it would appear that DCs fall short in mounting a robust immune response against it. Many aspects of the DC-driven immune response to Borrelia have been examined. Recently, components of tick saliva have been identified that sabotage DC responses and aid Borrelia infection. In this review, we summarise what is currently known about the immune response of DCs to Borrelia and explore the mechanisms by which Borrelia manages to circumvent this immune response, with or without the help of tick salivary proteins.

Different patterns of expression and of IL-10 modulation of inflammatory mediators from macrophages of Lyme disease-resistant and -susceptible mice

C57BL/6J (C57) mice develop mild arthritis (Lyme disease-resistant) whereas C3H/HeN (C3H) mice develop severe arthritis (Lyme disease-susceptible) after infection with the spirochete Borrelia burgdorferi. We hypothesized that susceptibility and resistance to Lyme disease, as modeled in mice, is associated with early induction and regulation of inflammatory mediators by innate immune cells after their exposure to live B. burgdorferi spirochetes. Here, we employed multiplex ELISA and qRT-PCR to investigate quantitative differences in the levels of cytokines and chemokines produced by bone marrow-derived macrophages from C57 and C3H mice after these cells were exposed ex vivo to live spirochetes or spirochetal lipoprotein. Upon stimulation, the production of both cytokines and chemokines was up-regulated in macrophages from both mouse strains. Interestingly, however, our results uncovered two distinct patterns of spirochete- and lipoprotein-inducible inflammatory mediators displayed by mouse macrophages, such that the magnitude of the chemokine up-regulation was larger in C57 cells than it was in C3H cells, for most chemokines. Conversely, cytokine up-regulation was more intense in C3H cells. Gene transcript analyses showed that the displayed patterns of inflammatory mediators were associated with a TLR2/TLR1 transcript imbalance: C3H macrophages expressed higher TLR2 transcript levels as compared to those expressed by C57 macrophages. Exogenous IL-10 dampened production of inflammatory mediators, especially those elicited by lipoprotein stimulation. Neutralization of endogenously produced IL-10 increased production of inflammatory mediators, notably by macrophages of C57 mice, which also displayed more IL-10 than C3H macrophages. The distinct patterns of pro-inflammatory mediator production, along with TLR2/TLR1 expression, and regulation in macrophages from Lyme disease-resistant and -susceptible mice suggests itself as a blueprint to further investigate differential pathogenesis of Lyme disease.

Macrophage p38 mitogen-activated protein kinase activity regulates invariant natural killer T-cell responses during Borrelia burgdorferi infection

The interaction of macrophages with infectious agents leads to the activation of several signaling cascades, including mitogen-activated protein (MAP) kinases, such as p38. We now demonstrate that p38 MAP kinase-mediated responses are critical components to the immune response to Borrelia burgdorferi. The pharmacological and genetic inhibition of p38 MAP kinase activity during infection with the spirochete results in increased carditis. In transgenic mice that express a dominant negative form of p38 MAP kinase specifically in macrophages, production of the invariant natural killer T (iNKT) cell-attracting chemokine MCP-1 and of the antigen-presenting molecule CD1d are significantly reduced. The expression of the transgene therefore results in the deficient infiltration of iNKT cells, their decreased activation, and a diminished production of interferon γ (IFN-γ), leading to increased bacterial burdens and inflammation. These results show that p38 MAP kinase provides critical checkpoints for the protective immune response to the spirochete during infection of the heart.

Detection of established virulence genes and plasmids to differentiate Borrelia burgdorferi strains

Borrelia burgdorferi sensu stricto is the major causative agent of Lyme disease in the United States, while B. garinii and B. afzelii are more prevalent in Europe. The highly complex genome of B. burgdorferi is comprised of a linear chromosome and a large number of variably sized linear and circular plasmids. Many plasmids of this spirochete are unstable during its culture in vitro. Given that many of the B. burgdorferi virulence factors identified to date are plasmid encoded, spirochetal plasmid content determination is essential for genetic analysis of Lyme pathogenesis. Although PCR-based assays facilitate plasmid profiling of sequenced B. burgdorferi strains, a rapid genetic content determination strategy for nonsequenced strains has not yet been described. In this study, we combined pulsed-field gel electrophoresis (PFGE) and Southern hybridization for detection of genes encoding known virulence factors, ribosomal RNA gene spacer restriction fragment length polymorphism types (RSTs), ospC group determination, and sequencing of the variable dbpA and ospC genes. We show that two strains isolated from the same tick and both originally named N40 are in fact very distinct. Furthermore, we failed to detect bbk32, which encodes a fibronectin-binding adhesin, in one "N40" strain. Thus, two distinct strains that show different plasmid profiles, as determined by PFGE and PCR, were isolated from the same tick and vary in their ospC and dbpA sequences. However, both belong to group RST3B.

CD14 cooperates with complement receptor 3 to mediate MyD88-independent phagocytosis of Borrelia burgdorferi

Phagocytosis of Borrelia burgdorferi, the causative agent of Lyme disease, is a poorly understood process, despite its importance during the host immune response to infection. B. burgdorferi has been shown to bind to different receptors on the surface of phagocytic cells, including the β(2) integrin, complement receptor 3 (CR3). However, whether these receptors mediate the phagocytosis of the spirochete remains unknown. We now demonstrate that CR3 mediates the phagocytosis of the spirochete by murine macrophages and human monocytes. Interaction of B. burgdorferi with the integrin is not sufficient, however, to internalize the spirochete; phagocytosis requires the interaction of CR3 with the GPI-anchored protein, CD14, independently of TLR/MyD88-induced or inside-out signals. Interestingly, the absence of CR3 leads to marked increases in the production of TNF in vitro and in vivo, despite reduced spirochetal uptake. Furthermore, the absence of CR3 during infection with B. burgdorferi results in the inefficient control of bacterial burdens in the heart and increased Lyme carditis. Overall, our data identify CR3 as a MyD88-independent phagocytic receptor for B. burgdorferi that also participates in the modulation of the proinflammatory output of macrophages. These data also establish a unique mechanism of CR3-mediated phagocytosis that requires the direct cooperation of GPI-anchored proteins.

Localized production of IL-10 suppresses early inflammatory cell infiltration and subsequent development of IFN-γ-mediated Lyme arthritis

IL-10 is a nonredundant inflammatory modulator that suppresses arthritis development in Borrelia burgdorferi-infected mice. Infected C57BL/6 (B6) IL-10(-/-) mice were previously found to have a prolonged IFN-inducible response in joint tissue. Infection of B6 IL-10 reporter mice identified macrophages and CD4(+) T cells as the primary sources of IL-10 in the infected joint tissue, suggesting that early local production of IL-10 dampened the proarthritic IFN response. Treatment of B6 IL-10(-/-) mice with anti-IFN-γ reduced the increase in arthritis severity and suppressed IFN-inducible transcripts to wild-type levels, thereby linking dysregulation of IFN-γ to disease in the B6 IL-10(-/-) mouse. Arthritis in B6 IL-10(-/-) mice was associated with elevated numbers of NK cell, NKT cell, α/β T cell, and macrophage infiltration of the infected joint. FACS lineage sorting revealed NK cells and CD4(+) T cells as sources of IFN-γ in the joint tissue of B6 IL-10(-/-) mice. These findings suggest the presence of a positive-feedback loop in the joint tissue of infected B6 IL-10(-/-) mice, in which production of inflammatory chemokines, infiltration of IFN-γ-producing cells, and additional production of inflammatory cytokines result in arthritis. This mechanism of arthritis is in contrast to that seen in C3H/He mice, in which arthritis development is linked to transient production of type I IFN and develops independently of IFN-γ. Due to the sustained IFN response driven by NK cells and T cells, we propose the B6 IL-10(-/-) mouse as a potential model to study the persistent arthritis observed in some human Lyme disease patients.

Severe course of Lyme neuroborreliosis in an HIV-1 positive patient; case report and review of the literature

Background

Lyme Neuroborreliosis (LNB) in a human immunodeficiency virus (HIV) positive patient is a rare co-infection and has only been reported four times in literature. No case of an HIV patient with a meningoencephalitis due to LNB in combination with HIV has been described to date.

Case presentation

A 51 year old woman previously diagnosed with HIV presented with an atypical and severe LNB. Diagnosis was made evident by several microbiological techniques. Biochemical and microbiological recovery during treatment was rapid, however after treatment the patient suffered from severe and persistent sequelae.

Conclusions

A clinician should consider LNB when being confronted with an HIV patient with focal encephalitis, without any history of Lyme disease or tick bites, in an endemic area. Rapid diagnosis and treatment is necessary in order to minimize severe sequelae.

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.

The caspase 1 inflammasome is not required for control of murine Lyme borreliosis

The contribution of the inflammasome to the development of immune responses and disease during infection with the Lyme disease spirochete, Borrelia burgdorferi, is not well defined. Host defense against the spirochete is severely impaired in mice deficient in the adaptor molecule myeloid differentiation antigen 88 (MyD88), which is required not only for Toll-like receptor-mediated responses but also for the production of the proforms of interleukin 1beta (IL-1beta) and IL-18. These cytokines are released in active forms after cleavage by the inflammasome-associated enzyme caspase 1. To investigate the contribution of the inflammasome to host defense against B. burgdorferi, we examined Lyme borreliosis in mice deficient in either caspase 1 or apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC), a molecule upstream of caspase 1 in the inflammasome signaling cascade. We found that caspase 1-deficient mice had a mild transient elevation in pathogen burden and a trend toward an increase in the prevalence of arthritis early in infection, but these differences resolved by day 14 postinfection. Caspase 1 deficiency had no effect on B. burgdorferi-induced humoral immunity, T-cell responses, or the abilities of macrophages to ingest and degrade spirochetes. The absence of the ASC protein had no effect on the control of the spirochete or the development of immune responses and disease. These findings reveal that the caspase 1 inflammasome is not critical to host defense against the extracellular pathogen Borrelia burgdorferi.

Local production of IFN-gamma by invariant NKT cells modulates acute Lyme carditis

The Lyme disease spirochete Borrelia burgdorferi is the only known human pathogen that directly activates invariant NKT (iNKT) cells. The number and activation kinetics of iNKT cells vary greatly among different strains of mice. We now report the role of the iNKT cell response in the pathogenesis of Lyme disease using C57BL/6 mice, a strain with optimal iNKT cell activation that is resistant to the development of spirochetal-induced inflammation. During experimental infection of B6 mice with B. burgdorferi, iNKT cells localize to the inflamed heart where they are activated by CD1d-expressing macrophages. Activation of iNKT cells in vivo results in the production of IFN-gamma, which we demonstrate ameliorates the severity of murine Lyme carditis by at least two mechanisms. First, IFN-gamma enhances the recognition of B. burgdorferi by macrophages, leading to increased phagocytosis of the spirochete. Second, IFN-gamma activation of macrophages increases the surface expression of CD1d, thereby facilitating further iNKT activation. Collectively, our data demonstrate that in the resistant background, B6, iNKT cells modulate the severity of murine Lyme carditis through the action of IFN-gamma, which appears to self-renew through a positive feedback loop during infection.

A chromosomally encoded virulence factor protects the Lyme disease pathogen against host-adaptive immunity

Borrelia burgdorferi, the bacterial pathogen of Lyme borreliosis, differentially expresses select genes in vivo, likely contributing to microbial persistence and disease. Expression analysis of spirochete genes encoding potential membrane proteins showed that surface-located membrane protein 1 (lmp1) transcripts were expressed at high levels in the infected murine heart, especially during early stages of infection. Mice and humans with diagnosed Lyme borreliosis also developed antibodies against Lmp1. Deletion of lmp1 severely impaired the pathogen's ability to persist in diverse murine tissues including the heart, and to induce disease, which was restored upon chromosomal complementation of the mutant with the lmp1 gene. Lmp1 performs an immune-related rather than a metabolic function, as its deletion did not affect microbial persistence in immunodeficient mice, but significantly decreased spirochete resistance to the borreliacidal effects of anti-B. burgdorferi sera in a complement-independent manner. These data demonstrate the existence of a virulence factor that helps the pathogen evade host-acquired immune defense and establish persistent infection in mammals.

The pathogen of Lyme borreliosis, Borrelia burgdorferi, causes disease in many parts of the world, resulting in multi-system complications in infected humans and animals. The microbe produces certain antigens in response to host environments that potentially allow it to persist and cause disease. Here, we analyzed the expression of B. burgdorferi genes encoding potential membrane proteins in infected hosts and show that one of them, termed Lmp1, is dramatically expressed in infected mice, most prominently in cardiac tissue during early infection. Mice and humans diagnosed with Lyme borreliosis also develop antibodies against Lmp1. Deletion of lmp1 in an infectious isolate of B. burgdorferi impairs the pathogen's ability to persist in murine tissues, especially the heart, and to induce disease, which was reversed when the gene was inserted back into the chromosome of the mutant. Lmp1 performs an immune-related, rather than a metabolic, function as its deletion does not affect microbial persistence in immunodeficient mice, but decreases the spirochete's ability to resist the borreliacidal effects of anti-B. burgdorferi sera. These data identify the existence of a surface-located antigen of B. burgdorferi that helps the pathogen evade host-acquired immune defense and establish persistent infection and disease in mammals.

NKT cells prevent chronic joint inflammation after infection with Borrelia burgdorferi

Borrelia burgdorferi is the etiologic agent of Lyme disease, a multisystem inflammatory disorder that principally targets the skin, joints, heart, and nervous system. The role of T lymphocytes in the development of chronic inflammation resulting from B. burgdorferi infection has been controversial. We previously showed that natural killer T (NKT) cells with an invariant (i) TCR alpha chain (iNKT cells) recognize glycolipids from B. burgdorferi, but did not establish an in vivo role for iNKT cells in Lyme disease pathogenesis. Here, we evaluate the importance of iNKT cells for host defense against these pathogenic spirochetes by using Valpha14i NKT cell-deficient (Jalpha18(-/-)) BALB/c mice. On tick inoculation with B. burgdorferi, Jalpha18(-/-) mice exhibited more severe and prolonged arthritis as well as a reduced ability to clear spirochetes from infected tissues. Valpha14i NKT cell deficiency also resulted in increased production of antibodies directed against both B. burgdorferi protein antigens and borrelial diacylglycerols; the latter finding demonstrates that anti-glycolipid antibody production does not require cognate help from Valpha14i NKT cells. Valpha14i NKT cells in infected wild-type mice expressed surface activation markers and produced IFNgamma in vivo after infection, suggesting a participatory role for this unique population in cellular immunity. Our data are consistent with the hypothesis that the antigen-specific activation of Valpha14i NKT cells is important for the prevention of persistent joint inflammation and spirochete clearance, and they counter the long-standing notion that humoral rather than cellular immunity is sufficient to facilitate Lyme disease resolution.

Lyme carditis

Cardiovascular manifestations of Lyme disease were first reported nearly 30 years ago. This article describes Lyme carditis, its epidemiology, pathophysiology, methods of diagnosis, and treatment options.

Feeding by the tick, Ixodes scapularis, causes CD4+T cells responding to cognate antigen to develop the capacity to express IL-4

Effects of tick feeding on an early antigen-specific T cell response were studied by monitoring a clonotypic population of adoptively transferred T cell receptor (TCR) transgenic CD4 cells responding to a tick-associated antigen. When recipient mice were infested with pathogen-free Ixodes scapularis nymphs several days prior to T cell transfer and intradermal injection of soluble cognate antigen at the feeding site, the clonotypic CD4 cells gained the ability to express the Th2 effector cytokine IL-4. Notably, this effect was not only observed in BALB/c mice predisposed towards developing Th2 responses but also in B10.D2 mice predisposed towards Th1 responsiveness. Furthermore, tick feeding was able to superimpose IL-4 expression potential onto a strong Th1 response (indicated by robust IFN-gamma expression potential) elicited by immunization with a vaccinia virus expressing the cognate antigen. The magnitude to which tick feeding was able to programme IL-4 expression potential in CD4 cells was partially reduced in mice that had been previously exposed to pathogen-free tick nymphs 6 weeks earlier, as well as when the nymphs were infected with Borrelia burgdorferi. Intradermal injection of salivary gland extract programmed IL-4 expression potential similar to that of tick infestation, suggesting that IL-4 programming activity is contained within tick saliva.

Marginal zone B-cell depletion impairs murine host defense against Borrelia burgdorferi infection

Marginal zone B (MZB) cells are a B-cell subset that produces T-cell-independent antibodies to blood-borne antigens. In this study, we examined the effects of MZB cell depletion on the immune response to the Lyme disease spirochete Borrelia burgdorferi, an extracellular pathogen for which T-cell-independent antibody is an important host defense. MZB cell depletion of C3H/HeJ mice using monoclonal antibody to LFA-1 and alpha(4)beta(1) integrins reduced B. burgdorferi-specific immunoglobulin M (IgM) titers, enhanced pathogen burden, and led to more severe arthritis assessed within the first 2 weeks of infection. In addition, MZB cell-depleted mice had reduced levels of B. burgdorferi-specific IgG, which correlated with diminished splenic CD4+ T-cell-activation, proliferation, and cytokine production. Passive transfer of immune mouse serum from infected control mice into infected MZB cell-depleted mice reduced pathogen burden but did not alter the expression of T-cell activation markers on splenic CD4+ T cells. These findings demonstrate that MZB cells not only are a source of pathogen-specific IgM important for limiting spirochete burden and pathology but also play a prominent role in the priming of splenic T-cell responses to a blood-borne pathogen.

Cerebrospinal fluid-infiltrating CD4+ T cells recognize Borrelia burgdorferi lysine-enriched protein domains and central nervous system autoantigens in early lyme encephalitis

Neurological manifestations of Lyme disease are usually accompanied by inflammatory changes in the cerebrospinal fluid (CSF) and the recruitment of activated T cells into the CSF compartment. In order to characterize the phenotype and identify target antigens of CSF-infiltrating T cells in early neuroborreliosis with central nervous system (CNS) involvement, we combined T-cell cloning, functional testing of T-cell responses with positional scanning synthetic combinatorial peptide libraries, and biometric data analysis. We demonstrate that CD4+ gamma interferon-producing T cells specifically responding to Borrelia burgdorferi lysate were present in the CSF of a patient with acute Lyme encephalitis. Some T-cell clones recognized previously uncharacterized B. burgdorferi epitopes which show a specific enrichment for lysine, such as the heat shock-induced chaperone HSP90. Degenerate T-cell recognition that included T-cell responses to borrelia-specific and CNS-specific autoantigens derived from the myelin protein 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) could be demonstrated for one representative clone. Our results show that spirochetal antigen-specific and Th1-polarized CD4+ lymphocytes infiltrate the CSF during monophasic CNS symptoms of Lyme disease and demonstrate that cross-recognition of CNS antigens by B. burgdorferi-specific T cells is not restricted to chronic and treatment-resistant manifestations.

Stat1 deficiency exacerbates carditis but not arthritis during experimental lyme borreliosis

Activation of the transcription factor Stat1 by interferon-gamma (IFN-gamma) is an important step in the development of antimicrobial effector mechanisms against many bacterial pathogens. Susceptibility to murine Lyme arthritis has been correlated with the production of several proinflammatory cytokines, especially IFN-gamma. To determine the role of IFN-mediated effector mechanisms in the development of Lyme borreliosis, we infected Stat1-deficient mice on both resistant (DBA), and susceptible (C3H) genetic backgrounds. Arthritis in Stat1(/) mice was similar to that of wild-type controls in both mouse strains. Spirochete loads in tissues were also unchanged in Stat1(/) mice. C3H Stat1(/) mice exhibited increased inflammation in the heart, whereas carditis was unchanged in DBA Stat1(/) mice. These results demonstrate that inhibition of macrophage activation and responses to IFN-gamma-mediated signaling do not alter the arthritis resistance or susceptibility phenotype; however, they do affect the severity of carditis in susceptible mouse strains.

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.

Aggravated Lyme carditis in CD11a-/- and CD11c-/- mice

CD18 hypomorph mice expressing reduced levels of the common beta2 integrin chain develop aggravated Lyme carditis, compared to that developed by wild-type (WT) mice, upon infection with the spirochete Borrelia burgdorferi. The enhancement of Lyme carditis in these mice is characterized by increased macrophage infiltration, correlating with augmented expression of the monocyte/macrophage chemoattractant protein 1 (MCP-1). The lack of CD18 results in the deficiency of all beta2 integrins, i.e., CD11a/CD18 (LFA-1), CD11b/CD18 (Mac-1/CR3), CD11c/CD18 (p150,95/CR4), and CD11d/CD18. To determine the roles of the various beta2 integrins in controlling the development of aggravated Lyme carditis, disease induction was analyzed in CD11a-/-, CD11b-/-, and CD11c-/- mice. CD11a-/- and CD11c-/- mice, but not CD11b-/- mice, developed aggravated Lyme carditis after exposure to B. burgdorferi. Similarly to CD18 hypomorph mice, CD11c-/- mice expressed higher levels of MCP-1, compared to both WT and CD11a-/- mice, as determined by in vitro analysis of MCP-1 secretion by bone marrow-derived dendritic cells and in vivo analysis of MCP-1 mRNA expression in B. burgdorferi-infected hearts. On the other hand, CD11a deficiency was associated with heightened heart B. burgdorferi burden relative to that of WT mice. Overall, our results suggest that the increased severity of Lyme carditis in CD18 hypomorph mice is caused by deficiency in CD11a or CD11c, possibly via different mechanisms.

Up-regulation of Borrelia-specific IL-4- and IFN-γ-secreting cells in cerebrospinal fluid from children with Lyme neuroborreliosis

The clinical course and outcome of several infectious diseases are dependent on the type of immune response elicited against the pathogen. In adults with neuroborreliosis (NB), a type 1 response with high production of Borrelia-specific IFN-gamma, but no IL-4, has been reported. Since children have a more benign course of NB than adults, we wanted to investigate type 1 and type 2 responses in children with NB. Cerebrospinal fluid (CSF) and blood were collected from children during the acute stage of 'confirmed NB' (n = 34), 'possible NB' (n = 30) and 'non-NB' (n = 10). The number of Borrelia-specific IL-4- and IFN-gamma-secreting cells was measured by enzyme-linked immunospot assay. Borrelia-specific secretion of both IL-4 and IFN-gamma was increased in CSF in confirmed (P < 0.05) and possible (P < 0.01) NB, when compared with non-NB controls. Furthermore, children with NB had significantly higher Borrelia-specific IL-4 secretion in CSF than an adult reference material with NB (P < 0.05). There were no differences in cytokine secretion in relation to onset or recovery of neurological symptoms. Since IL-4 is known to down-regulate the pro-inflammatory and possibly harmful effects of prolonged IFN-gamma responses, the prominent IL-4 response observed in the central nervous system compartment might contribute to the more benign disease course seen in children with Lyme NB.

The nervous system as ectopic germinal center: CXCL13 and IgG in lyme neuroborreliosis

Lyme neuroborreliosis (LNB) is a chronic infection in which B-cell activation, plasma cell infiltration, and enhanced Ig production in infected tissue are prominent feature. However, little is known about how B cells and plasma cells invade and persist in target organs. To assess this issue, we developed real-time PCR measurements of IgG and CXCL13 production. We used these RNA assays and specific enzyme-linked immunosorbent assays for protein and demonstrated that human peripheral blood mononuclear cells (PBMCs), stimulated by Borrelia burgdorferi sonicate, produced CXCL13 and IgG. Magnetic separation of PBMC populations and flow cytometry showed that CXCL13 is produced by dendritic cells. We then measure the expression of CXCL13 and IgG in tissues and correlated the expression of these host genes with spirochetal load. We also measured expression of dbpA and BBK32, two spirochetal genes important in chronic infection. There was a strong correlation between host immune response gene expression (CXCL13 and IgG) and spirochetal load. Immunohistochemistry of infected nonhuman primates tissue confirmed that CXCL13 is expressed in the nervous system. We conclude that persistent production of CXCL13 and IgG within infected tissue, two characteristics of ectopic germinal centers, are definitive features of LNB.

Beta2 integrins control the severity of murine Lyme carditis

Infection of C57BL/6 (B6) mice with the Lyme disease spirochete Borrelia burgdorferi can result in development of arthritis and carditis. B. burgdorferi induces expression of beta2/CD18 integrins, adhesion molecules that mediate the firm adhesion of leukocytes to the endothelium necessary for cellular extravasation during inflammation. The important role of beta2/CD18 integrins during extravasation suggests that these molecules play a role in the development of Lyme arthritis and carditis. The dependency of these inflammatory processes on the beta2 integrins was investigated in CD18 hypomorph mice, which express low levels of CD18. The results indicate that CD18 deficiency did not abrogate development of Lyme arthritis or carditis. Moreover, it resulted in increased severity of Lyme carditis. B. burgdorferi-infected CD18 hypomorph mice showed an increased macrophage infiltration of the heart, while they produced lower levels of borreliacidal anti-B. burgdorferi antibodies compared to wild-type mice. In accordance with these results, we demonstrate that dendritic cells from CD18 hypomorph mice secrete higher levels of monocyte/macrophage chemoattractant protein 1 (MCP-1/CCL2) in response to B. burgdorferi. Similarly, we show by real-time PCR that B. burgdorferi-infected hearts from CD18 hypomorph mice express increased levels of MCP-1 RNA compared to wild-type mice. Overall, our results indicate that beta2 integrin deficiency does not abrogate B. burgdorferi-induced inflammation; rather, it results in increased recruitment of macrophages into the B. burgdorferi-infected heart, likely due to the increased expression of MCP-1 in this tissue. Thus, beta2 integrins may play a regulatory role in B. burgdorferi-induced inflammation beyond mediating adhesion of leukocytes to the endothelium.

Myeloid differentiation antigen 88 deficiency impairs pathogen clearance but does not alter inflammation in Borrelia burgdorferi-infected mice

The spirochete Borrelia burgdorferi causes acute inflammation in mice that resolves with the development of pathogen-specific adaptive immunity. B. burgdorferi lipoproteins activate innate immune cells via Toll-like receptor 2 (TLR2), but TLR2-deficient mice are not resistant to B. burgdorferi-induced disease, suggesting the involvement of other TLRs or non-TLR mechanisms in the induction of acute inflammation. For this study, we used mice that were deficient in the intracellular adapter molecule myeloid differentiation antigen 88 (MyD88), which is required for all TLR-induced inflammatory responses, to determine whether the interruption of this pathway would alter B. burgdorferi-induced disease. Infected MyD88(-/-) mice developed carditis and arthritis, similar to the disease in wild-type (WT) mice analyzed at its peak (days 14 and 28) and during regression (day 45). MyD88(-/-) macrophages produced tumor necrosis factor alpha only when spirochetes were opsonized, suggesting a role for B. burgdorferi-specific antibody in disease expression. MyD88(-/-) mice produced stronger pathogen-specific Th2-dependent immunoglobulin G1 (IgG1) responses than did WT mice, and their IgM titers remained significantly elevated through 90 days of infection. Despite specific antibodies, the pathogen burden was 250-fold higher in MyD88(-/-) mice than in WT mice 45 days after infection; by 90 days of infection, the pathogen burden had diminished substantially in MyD88(-/-) mice, but it was still elevated compared to that in WT mice. The elevated pathogen burden may be explained in part by the finding that MyD88(-/-) peritoneal macrophages could ingest spirochetes but degraded them more slowly than WT macrophages. Our results show that MyD88-dependent signaling pathways are not required for B. burgdorferi-induced inflammation but are necessary for the efficient control of the pathogen burden by phagocytes.

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.

Humoral immunity reflects altered T helper cell bias in Borrelia burgdorferi-infected gamma delta T-cell-deficient mice

In murine Lyme borreliosis, the absence of gamma delta T lymphocytes augments the T helper cell 2 type humoral response but does not alter disease susceptibility. Arthropod transmission of Borrelia burgdorferi spirochetes results in similar antibody isotypes when gamma delta T cells are present, suggesting that vector effects can negate gamma delta T-cell functions in vivo.

Leukemic dendritic cells: potential for therapy and insights towards immune escape by leukemic blasts

Dendritic cells (DCs) are a system of potent antigen-presenting cells (APCs) specialized to initiate primary immune responses. DCs are considered important elements in the induction of specific antitumor cytotoxic effectors. At present, because of potential therapeutic implications, the critical role of DCs in cancer patients is under intensive investigation. Interactions between DCs and acute myeloid leukemia cells represent an attractive model for the study of DC physiology. Moreover, DCs can be a valuable therapeutic tool for the adjuvant treatment of leukemic patients. However, DC subsets in vivo may also be affected by leukemogenesis and may contribute to the escape of leukemia from immune control. The aim of this review is to shed further light on this paradoxical picture where the line between immune tolerance and immune defense is narrow.

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.