Borrelia burgdorferi activates a T helper type 1-like T cell subset in Lyme arthritis

Effects of Regulatory T Cell Depletion in BALB/c Mice Infected with Low Doses of Borrelia burgdorferi

We previously demonstrated that a depletion of regulatory T (Treg) cells in Lyme arthritis-resistant C57BL/6 mice leads to pathological changes in the tibiotarsal joints following infection with Borrelia burgdorferi. Here, we assessed the effects of Treg cells on the response to B. burgdorferi infection in BALB/c mice, which exhibit infection-dose-dependent disease and a different sequence of immune events than C57BL/6 mice. The depletion of Treg cells prior to infection with 1 × 102, but not 5 × 103, organisms led to increased swelling of the tibiotarsal joints. However, Treg cell depletion did not significantly affect the development of histopathology at these low doses of infection. BALB/c mice depleted of Treg cells before infection with 1 × 103 spirochetes harbored a higher borrelial load in the hearts and exhibited higher levels of serum interleukin-10 five weeks later. These results indicate that Treg cells regulate certain aspects of the response to B. burgdorferi in a mouse strain that may display a range of disease severities. As the presentation of Lyme disease may vary among humans, it is necessary to consider multiple animal models to obtain a complete picture of the various means by which Treg cells affect the host response to B. burgdorferi.

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.

Autism spectrum disorders and natural killer cells: a review on pathogenesis and treatment

Introduction: Autism spectrum disorder (ASD), as a wide spectrum of neurodevelopmental disorders, is characterized by early-onset impairments in social-communication, repetitive behaviors, and restrictive interests.Areas covered: Although still unknown, there are some pieces of evidence suggesting altered immune function in the etiology of ASD. This review aims to summarize studies linking Natural Killer (NK) cells to ASD by searching through databases like MEDLINE and Scopus up to October 2020. NK cells play important roles in the innate immune system and immune regulation. As parts of the immune system, they interact with the neural system as well. Immune dysregulations such as autoimmunity and improper immune responses to both internal and external stimulations, especially in early developmental stages of the brain, may induce neurodevelopmental disorders. NK cells' dysfunction in children with ASD as well as their parents have been highlighted in many studies.Expert opinion: Changes in the frequency, gene expressions, cytotoxicity features, and receptors of NK cells are reported in children with ASD. Immune therapy for children with ASD with immune abnormality has shown promising results. However, further studies are needed to elucidate the exact role of NK cells in the pathogenesis of ASD providing future treatment options for these children.

Human Fcγ-receptor IIb modulates pathogen-specific versus self-reactive antibody responses in lyme arthritis

Pathogen-specific antibody responses need to be tightly regulated to generate protective but limit self-reactive immune responses. While loss of humoral tolerance has been associated with microbial infections, the pathways involved in balancing protective versus autoreactive antibody responses in humans are incompletely understood. Studies in classical mouse model systems have provided evidence that balancing of immune responses through inhibitory receptors is an important quality control checkpoint. Genetic differences between inbred mouse models and the outbred human population and allelic receptor variants not present in mice; however, argue for caution when directly translating these findings to the human system. By studying Borrelia burgdorferi infection in humanized mice reconstituted with human hematopoietic stem cells from donors homozygous for a functional or a non-functional FcγRIIb allele, we show that the human inhibitory FcγRIIb is a critical checkpoint balancing protective and autoreactive immune responses, linking infection with induction of autoimmunity in the human immune system.

Borrelia miyamotoi Activates Human Dendritic Cells and Elicits T Cell Responses

The spirochete Borrelia miyamotoi has recently been shown to cause relapsing fever. Like the Lyme disease agent, Borrelia burgdorferi, B. miyamotoi is transmitted through the bite of infected ticks; however, little is known about the response of the immune system upon infection. Dendritic cells (DCs) play a central role in the early immune response against B. burgdorferi We investigated the response of DCs to two different strains of B. miyamotoi using in vitro and ex vivo models and compared this to the response elicited by B. burgdorferi. Our findings show that B. miyamotoi is phagocytosed by monocyte-derived DCs, causing upregulation of activation markers and production of proinflammatory cytokines in a similar manner to B. burgdorferi. Recognition of B. miyamotoi was demonstrated to be partially mediated by TLR2. DCs migrated out of human skin explants upon inoculation of the skin with B. miyamotoi. Finally, we showed that B. miyamotoi-stimulated DCs induced proliferation of naive CD4⁺ and CD8⁺ T cells to a larger extent than B. burgdorferi. In conclusion, we show in this study that DCs respond to and mount an immune response against B. miyamotoi that is similar to the response to B. burgdorferi and is able to induce T cell proliferation.

Microbiota-mediated mucosal inflammation in arthritis

Mucosal surfaces are a unique symbiotic environment between a host and a vast and diverse ecology of microbes. These microbes have great immunomodulatory potential with respect to the host organism. Indeed, the mucosal immune system strikes a delicate balance between tolerance of commensal organisms and overt inflammation to ward off pathogens. Disruptions of the microbial ecology at mucosal surfaces has been described in a vast number of different human disease processes including many forms of arthritis, and the resulting implications are still being understood to their fullest. Herein, we review the current state of knowledge in microbe-host interactions as it relates to the development of arthritis through bacterial translocation, bacterial metabolite production, education of the immune response, and molecular mimicry.

Arthritis is inhibited in Borrelia-primed and infected interleukin-17A-deficient mice after administration of anti-gamma-interferon, anti-tumor necrosis factor alpha and anti-interleukin-6 antibodies

The role that cytokines play in the induction of Lyme arthritis is gradually being delineated. We showed previously that severe arthritis developed in a T-cell-driven murine model, even in mice lacking interleukin-17A (IL-17A) and administered anti-gamma-interferon (IFN-γ) antibody. Increased levels of tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6), two pro-inflammatory cytokines, were detected in cultures of popliteal lymph node cells obtained from these mice. We hypothesized that concomitantly administered anti-IL-6, anti-TNF-α and anti-IFN-γ antibodies would inhibit the development of arthritis in IL-17A-deficient mice. Our results showed that swelling of the hind paws and histopathological changes consistent with arthritis were significantly reduced in IL-17A-deficient mice that administered the three anti-cytokine antibodies. These results suggest that treatment with multiple anti-cytokine antibodies can abrogate the induction of Lyme arthritis in mice.

An Enzyme-Linked Immunosorbent Spot Assay Measuring Borrelia burgdorferi B31-Specific Interferon Gamma-Secreting T Cells Cannot Discriminate Active Lyme Neuroborreliosis from Past Lyme Borreliosis: a Prospective Study in the Netherlands

Two-tier serology testing is most frequently used for the diagnosis of Lyme borreliosis (LB); however, a positive result is no proof of active disease. To establish a diagnosis of active LB, better diagnostics are needed. Tests investigating the cellular immune system are available, but studies evaluating the utility of these tests on well-defined patient populations are lacking. Therefore, we investigated the utility of an enzyme-linked immunosorbent spot (ELISpot) assay to diagnose active Lyme neuroborreliosis. Peripheral blood mononuclear cells (PBMCs) of various study groups were stimulated by using Borrelia burgdorferi strain B31 and various recombinant antigens, and subsequently, the number of Borrelia-specific interferon gamma (IFN-γ)-secreting T cells was measured. We included 33 active and 37 treated Lyme neuroborreliosis patients, 28 healthy individuals treated for an early manifestation of LB in the past, and 145 untreated healthy individuals. The median numbers of B. burgdorferi B31-specific IFN-γ-secreting T cells/2.5 × 10⁵ PBMCs did not differ between active Lyme neuroborreliosis patients (6.0; interquartile range [IQR], 0.5 to 14.0), treated Lyme neuroborreliosis patients (4.5; IQR, 2.0 to 18.6), and treated healthy individuals (7.4; IQR, 2.3 to 14.9) (P = 1.000); however, the median number of B. burgdorferi B31-specific IFN-γ-secreting T cells/2.5 × 10⁵ PBMCs among untreated healthy individuals was lower (2.0; IQR, 0.5 to 3.9) (P ≤ 0.016). We conclude that the Borrelia ELISpot assay, measuring the number of B. burgdorferi B31-specific IFN-γ-secreting T cells/2.5 × 10⁵ PBMCs, correlates with exposure to the Borrelia bacterium but cannot be used for the diagnosis of active Lyme neuroborreliosis.

Borrelia-primed and -infected mice deficient of interleukin-17 develop arthritis after neutralization of gamma-interferon

The immune mechanisms responsible for development of Lyme arthritis are partially understood with interleukin-17 (IL-17) and gamma-interferon (IFN-γ) playing a generally accepted role. Elevated levels of IL-17 and/or IFN-γ have been reported in samples from human Lyme arthritis patients and experimental mice. In addition, IL-17 and IFN-γ have been implicated in the onset of arthritis in Borrelia-primed and -infected C57BL/6 mice. Recently, we showed that IL-17-deficient mice developed swelling and histopathological changes consistent with arthritis in the presence of high levels of IFN-γ. We hypothesized that neutralization of IFN-γ in IL-17-deficient mice would inhibit Borrelia-induced arthritis. Our results, however, showed that swelling of the hind paws and histopathological changes of arthritis did not differ between Borrelia-primed and -infected IL-17-deficient and wild-type mice with or without neutralization of IFN-γ. We also found higher levels of tumor necrosis factor alpha (TNF-α) and IL-6 in the popliteal lymph node cells of Borrelia-primed and -infected IL-17-deficient mice after neutralization of IFN-γ. These results suggest that multiple cytokines interact in the development of Borrelia-induced arthritis.

CD4+ cell-derived interleukin-17 in a model of dysregulated, Borrelia-induced arthritis

Lyme borreliosis, which is caused in the United States by the spirochete Borrelia burgdorferi, may manifest as different arrays of signs, symptoms and severities between infected individuals. Recent studies have indicated that particularly severe forms of Lyme borreliosis in humans are associated with an increased Th17 response. Here, we hypothesized that a murine model combining the dysregulated immune response of an environment lacking interleukin-10 (IL-10) with a robust T-cell-driven inflammatory response would reflect arthritis associated with the production of IL-17 by CD4+ cells. We demonstrate that IL-10 regulates the production of IL-17 by Borrelia-primed CD4+ cells early after interaction with Lyme spirochetes in vitro and that infection of Borrelia-primed mice with B. burgdorferi leads to significant production of IL-17 that contributes to the development of severe arthritis. These results extend our previous findings by demonstrating that a dysregulated adaptive immune response to Lyme spirochetes can contribute to severe, Th17-associated arthritis. These findings may lead to therapeutic measures for individuals with particularly severe symptoms of Lyme borreliosis.

Arthritis is developed in Borrelia-primed and -infected mice deficient of interleukin-17

Interleukin-17 (IL-17) has been shown to participate in the development of Lyme arthritis in experimental mice. For example, neutralization of IL-17 with antibodies inhibits induction of arthritis in Borrelia-primed and -infected C57BL/6 wild-type mice. We hypothesized that mice lacking IL-17 would fail to develop Borrelia-induced arthritis. IL-17-deficient and wild-type C57BL/6 mice were primed with heat-inactivated Borrelia and then infected with viable spirochetes 3 weeks later. No swelling or major histopathological changes of the hind paws were detected in IL-17-deficient or wild-type mice that were primed with Borrelia or infected with viable spirochetes. By contrast, IL-17-deficient and wild-type mice that were primed and subsequently infected with heterologous Borrelia developed severe swelling and histopathological changes of the hind paws. In addition, Borrelia-primed and -infected IL-17-deficient mice exhibited elevated gamma-interferon (IFN-γ) levels in sera and increased frequencies of IFN-γ-expressing lymphocytes in popliteal lymph nodes compared to Borrelia-primed and -infected wild-type mice. These results demonstrate that IL-17 is not required for development of severe pathology in response to infection with Borrelia burgdorferi, but may contribute to disease through an interaction with IFN-γ.

CD83 Modulates B Cell Activation and Germinal Center Responses

CD83 is a maturation marker for dendritic cells. In the B cell lineage, CD83 is expressed especially on activated B cells and on light zone B cells during the germinal center (GC) reaction. The function of CD83 during GC responses is unclear. CD83(-/-) mice have a strong reduction of CD4(+) T cells, which makes it difficult to analyze a functional role of CD83 on B cells during GC responses. Therefore, in the present study we generated a B cell-specific CD83 conditional knockout (CD83 B-cKO) model. CD83 B-cKO B cells show defective upregulation of MHC class II and CD86 expression and impaired proliferation after different stimuli. Analyses of GC responses after immunization with various Ags revealed a characteristic shift in dark zone and light zone B cell numbers, with an increase of B cells in the dark zone of CD83 B-cKO mice. This effect was not accompanied by alterations in the level of IgG immune responses or by major differences in affinity maturation. However, an enhanced IgE response was observed in CD83 B-cKO mice. Additionally, we observed a strong competitive disadvantage of CD83-cKO B cells in GC responses in mixed bone marrow chimeras. Furthermore, infection of mice with Borrelia burgdorferi revealed a defect in bacterial clearance of CD83 B-cKO mice with a shift toward a Th2 response, indicated by a strong increase in IgE titers. Taken together, our results show that CD83 is important for B cell activation and modulates GC composition and IgE Ab responses in vivo.

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.

Interleukin-10 (IL-10) inhibits Borrelia burgdorferi-induced IL-17 production and attenuates IL-17-mediated Lyme arthritis

Previous studies have shown that cells and cytokines associated with interleukin-17 (IL-17)-driven inflammation are involved in the arthritic response to Borrelia burgdorferi infection. Here, we report that IL-17 is a contributing factor in the development of Lyme arthritis and show that its production and histopathological effects are regulated by interleukin-10 (IL-10). Spleen cells obtained from B. burgdorferi-infected, "arthritis-resistant" wild-type C57BL/6 mice produced low levels of IL-17 following stimulation with the spirochete. In contrast, spleen cells obtained from infected, IL-10-deficient C57BL/6 mice produced a significant amount of IL-17 following stimulation with B. burgdorferi. These mice developed significant arthritis, including erosion of the bones in the ankle joints. We further show that treatment with antibody to IL-17 partially inhibited the significant hind paw swelling and histopathological changes observed in B. burgdorferi-infected, IL-10-deficient mice. Taken together, these findings provide additional evidence of a role for IL-17 in Lyme arthritis and reveal an additional regulatory target of IL-10 following borrelial infection.

Hamster and murine models of severe destructive Lyme arthritis

Arthritis is a frequent complication of infection in humans with Borrelia burgdorferi. Weeks to months following the onset of Lyme borreliosis, a histopathological reaction characteristic of synovitis including bone, joint, muscle, or tendon pain may occur. A subpopulation of patients may progress to a chronic, debilitating arthritis months to years after infection which has been classified as severe destructive Lyme arthritis. This arthritis involves focal bone erosion and destruction of articular cartilage. Hamsters and mice are animal models that have been utilized to study articular manifestations of Lyme borreliosis. Infection of immunocompetent LSH hamsters or C3H mice results in a transient synovitis. However, severe destructive Lyme arthritis can be induced by infecting irradiated hamsters or mice and immunocompetent Borrelia-vaccinated hamsters, mice, and interferon-gamma- (IFN-γ-) deficient mice with viable B. burgdorferi. The hamster model of severe destructive Lyme arthritis facilitates easy assessment of Lyme borreliosis vaccine preparations for deleterious effects while murine models of severe destructive Lyme arthritis allow for investigation of mechanisms of immunopathology.

Role of interleukin-23 (IL-23) receptor signaling for IL-17 responses in human Lyme disease

Interleukin-23 (IL-23) is known to play a crucial role in the development and maintenance of T helper 17 cells. It has been previously demonstrated that IL-17 is involved in experimental Lyme arthritis, caused by Borrelia burgdorferi bacteria. However, the precise role of the IL-23 receptor (IL-23R) for the B. burgdorferi-induced IL-17 responses or human Lyme disease has not yet been elucidated. IL-23R single nucleotide polymorphism (SNP) rs11209026 was genotyped using the TaqMan assay. Functional studies were performed using peripheral blood mononuclear cells, and cytokines were measured using enzyme-linked immunosorbent assay (ELISA). Dose-dependent production of IL-23 and IL-17 by B. burgdorferi could be observed. Interestingly, when IL-23 bioactivity was inhibited by a specific antibody against IL-23p19, IL-17 production was significantly downregulated. In contrast, production of gamma interferon (IFN-γ) was not affected after the blockade of IL-23 activity. Moreover, individuals bearing a single nucleotide polymorphism in the IL-23R gene (Arg381Gln) produced significantly less IL-17 after B. burgdorferi stimulation compared with that of the individuals bearing the wild type. Despite lower IL-17 production, the IL-23R gene polymorphism did not influence the development of chronic Lyme disease in a cohort of patients with Lyme disease. This study demonstrates that IL-23R signaling is needed for B. burgdorferi-induced IL-17 production in vitro and that an IL-23R gene SNP leads to impaired IL-17 production. However, the IL-23R gene polymorphism is not crucial for the pathogenesis of chronic Lyme.

Musculoskeletal features of Lyme disease: understanding the pathogenesis of clinical findings helps make appropriate therapeutic choices

Patients with Lyme disease, that is, active infection with Borrelia burgdorferi, experience many types of musculoskeletal complaints, with different explanatory mechanisms. Appropriate therapy depends on understanding the underlying cause of the complaint and addressing that specific root cause. In the case of active infection the dosage, duration, drug, and method of administration of antibiotics should be determined by the state of the infection and history of prior therapy, according to the established and validated recommendations of the Infectious Disease Society of America. Many patients have musculoskeletal complaints not attributable to active infection; some patients have residual complaints following a documented infection that has been adequately treated with antibiotics previously, and others never had true B. burgdorferi infection in the first place. For such patients, antibiotics are not warranted and in fact may be physically and emotionally harmful. Complaints following an episode of Lyme disease are not necessarily due to ongoing infection, especially adequately treated. Consideration of other diagnoses may suggest use of other effective modalities, including physical therapy and emotional support. Appropriate ordering and interpretation of the various validated seroconfirmatory tests available to study B. burgdorferi infection are critical, as these tests are often misapplied and misconstrued in pursuit of strategies aimed at eliminating patients' suffering. Although seronegative Lyme disease has been reported, seronegativity in a reputable laboratory makes the likelihood of Lyme arthritis very low. On the other hand, a positive result from certain unvalidated laboratories or novel assays proves nothing and should not be viewed as substantiating the diagnosis.

Interleukin-35 enhances Lyme arthritis in Borrelia-vaccinated and -infected mice

Interleukin-35 (IL-35) has been reported to inhibit the production of interleukin-17 (IL-17) as a means of preventing arthritis and other inflammatory diseases. We previously showed that treatment of Borrelia-vaccinated and -infected mice with anti-IL-17 antibody at the time of infection prevented the development of arthritis. The anti-IL-17 antibody-treated mice lacked the extensive tissue damage, such as bone and cartilage erosion, that occurred in the tibiotarsal joints of untreated Borrelia-vaccinated and -infected control mice. We hypothesized that IL-35 would reduce the severity of arthritis by suppressing the production of IL-17 in Borrelia-vaccinated and -infected mice. Here, we show that administration of recombinant IL-35 (rIL-35) to Borrelia-vaccinated and -infected mice augments the development of severe arthritis compared to the results seen with untreated control mice. Borrelia-vaccinated and -infected mice treated with rIL-35 had significantly (P < 0.05) greater hind paw swelling and histopathological changes from day 4 through day 10 than non-rIL-35-treated Borrelia-vaccinated and -infected mice. In addition, the treatment with IL-35 only slightly decreased the production of IL-17 in Borrelia-primed immune cells and did not prevent the development of borreliacidal antibody. Our data do not support a role for IL-35 as a potential therapeutic agent to reduce inflammation in Lyme arthritis.

Significant differences between the Borrelia-infection and Borrelia-vaccination and -infection models of Lyme arthritis in C3H/HeN mice

The immunological events leading to the development of Lyme arthritis in humans are partially understood. Much of this information has been gained by studying the course of infection of naïve or vaccinated mice with Borrelia burgdorferi. However, the Borrelia-vaccination and -infection model has not been described using the organismal parameters commonly used in the widely accepted Borrelia-infection model. This is the first comparison between the Borrelia-infection and the Borrelia-vaccination and -infection models of arthritis. Borrelia-vaccinated and -infected C3H/HeN mice develop acute inflammation comparable to that of nonvaccinated, Borrelia-infected C3H/HeN mice. The duration and severity of arthritis in Borrelia-vaccinated and -infected mice was slightly increased compared with Borrelia-infected mice. Significantly, Borrelia-vaccinated and -infected C3H/HeN mice produce interleukin-17 (IL-17), while Borrelia-infected mice that had not been previously vaccinated do not. Neutralization of IL-17 in Borrelia-vaccinated and -infected C3H/HeN mice decreased the severity of arthritis, although not to the degree we observed previously in C57BL/6 mice. Collectively, these findings show that the Borrelia-vaccination and -infection model of Lyme arthritis incorporates elements of adaptive immunity that likely have relevance to human disease, but may not be observed in Borrelia-infected C3H/HeN mice.

Borrelia species induce inflammasome activation and IL-17 production through a caspase-1-dependent mechanism

Borrelia burgdorferi spirochetes cause Lyme disease, which can result in severe clinical symptoms such as multiple joint inflammation and neurological disorders. IFN-γ and IL-17 have been suggested to play an important role in the host defense against Borrelia, and in the immunopathology of Lyme disease. The caspase-1-dependent cytokine IL-1β has been linked to the generation of IL-17-producing T cells, whereas caspase-1-mediated IL-18 is crucial for IFN-γ production. In this study, we show by using knockout mice the role of inflammasome-activated caspase-1 in the regulation of cytokine responses by B. burgdorferi. Caspase-1-deficient cells showed significantly less IFN-γ and IL-17 production after Borrelia stimulation. A lack of IL-1β was responsible for the defective IL-17 production, whereas IL-18 was crucial for the IFN-γ production. Caspase-1-dependent IL-33 played no role in the Borrelia-induced production of IL-1β, IFN-γ or IL-17. In conclusion, we describe for the first time the role of the inflammasome-dependent caspase-1 activation of cytokines in the regulation of IL-17 production induced by Borrelia spp. As IL-17 has been implicated in the pathogenesis of chronic Lyme disease, these data suggest that caspase-1 targeting may represent a new immunomodulatory strategy for the treatment of complications of late stage Lyme disease.

Treg cell numbers and function in patients with antibiotic-refractory or antibiotic-responsive Lyme arthritis

OBJECTIVE

In a murine model of antibiotic-refractory Lyme arthritis, the numbers of Treg cells are dramatically reduced. The aim of this study was to examine Treg cell numbers and function in patients with antibiotic-refractory Lyme arthritis.

METHODS

CD4+ T cell subsets were enumerated in the peripheral blood (PB) and synovial fluid (SF) of 12 patients with antibiotic-refractory arthritis and 6 patients with antibiotic-responsive arthritis. Treg cell function was examined using Borrelia-specific and nonspecific Treg cell proliferation assays.

RESULTS

In both patient groups, interferon-gamma-positive Th1 cells in SF were abundant and enriched (approximately 50% of CD4+ T cells). In patients with antibiotic-refractory arthritis, the median percentages of FoxP3-positive Treg cells were significantly higher in SF than in PB (12% versus 6%; P = 0.03) or in SF from patients with antibiotic-responsive arthritis (12% versus 5%; P = 0.04). Moreover, in the antibiotic-refractory group, a higher percentage of Treg cells in SF correlated with a shorter duration until resolution of arthritis (r = -0.74, P = 0.006). In contrast, patients with fewer Treg cells had suboptimal responses to disease-modifying antirheumatic drugs and a longer duration of arthritis after antibiotic treatment, and they often required synovectomies for arthritis resolution. In each group, Treg cells in SF dampened Borrelia burgdorferi-specific proliferative responses, and in 2 patients with antibiotic-refractory arthritis, Treg cells were functional in nonspecific suppression assays.

CONCLUSION

Treg cells were functional in patients with antibiotic-refractory arthritis, and in some patients, higher numbers of these cells in SF appeared to participate in arthritis resolution. However, as in the murine model, patients with antibiotic-refractory arthritis and lower numbers of Treg cells seemed unable to achieve resolution of synovial inflammation.

HLA-DR alleles determine responsiveness to Borrelia burgdorferi antigens in a mouse model of self-perpetuating arthritis

OBJECTIVE

Arthritis is a prominent manifestation of Lyme disease, which is caused by infection with Borrelia burgdorferi (Bb). Chronic Lyme arthritis persisting even after antibiotic treatment is linked to HLA-DRB1*0401 (DR4) and related alleles. In contrast, patients whose Lyme arthritis resolves within 3 months postinfection show an increased frequency of HLA-DRB1*1101 (DR11). The aim of this study was to analyze the underlying mechanism by which HLA-DR alleles confer genetic susceptibility or resistance to antibiotic-refractory Lyme arthritis.

METHODS

We generated DR11-transgenic (DR11-Tg) mice on a murine MHCII-/- background and compared their immune response to Bb antigens with the response of DR4-Tg mice after immunization with Bb outer surface protein A (OspA) or infection with live Bb.

RESULTS

T cells from OspA-immunized and Bb-infected DR11-Tg mice had defective production of interferon-gamma as compared with those from DR4-Tg mice. In contrast, DR11-Tg mice developed higher titers of anti-OspA and anti-Bb antibodies, respectively, than did DR4-Tg mice. Consistent with this observation, we found that the Bb-infected DR11-Tg mice had a decreased spirochetal burden as compared with the DR4-Tg mice, as measured by quantitative polymerase chain reaction.

CONCLUSION

This study provides direct evidence that in the presence of HLA-DR11, the immune response against Bb antigens is directed toward a protective antibody response. In contrast, an inflammatory Th1 response is induced in the presence of DR4. These observations offer an explanation for the differential genetic susceptibility of DR4+ and DR11+ individuals to the development of chronic Lyme arthritis and, eventually, the progression to antibiotic-refractory Lyme arthritis.

CXCL13 expression in Chlamydia trachomatis infection of the female reproductive tract

Chlamydia trachomatis is the most common cause of acute salpingitis worldwide. The socioeconomic impact of sexually transmitted infections (STI) caused by C. trachomatis is considerable. The purpose of this study was to investigate secretion of a unique chemokine, CXCL13, during the inflammatory process in human fallopian tube tissue in response to infection with C. trachomatis. We employed two models for our experiments: archived fallopian tube paraffin sections from known cases of salpingitis of unknown etiology and human fallopian tube organ culture established from fresh fallopian tube biopsies subsequently infected in vitro with C. trachomatis serovar E. We used immunohistochemistry, microarray analysis and cytometric bead array to study these specimens. In both models, we found that the fallopian tissue infected with C. trachomatis expressed CXCL13 and other characteristics of tertiary lymphoid tissue. In addition, we found that CXCL13 was expressed in multiple cell types, including endothelial cells, demonstrating a mechanism for the lymphoid aggregation seen in fallopian tube tissue during salpingitis and infection with C. trachomatis.

CD57+ T lymphocytes and functional immune deficiency

CD57(+) expression in T lymphocytes has been recognized for decades as a marker of in vitro replicative senescence. In recent years, accumulating evidences have pointed on the utility of this marker to measure functional immune deficiency in patients with autoimmune disease, infectious diseases, and cancers. We review here the relevant literature and implications in clinical settings.

Persistent arthritis in Borrelia burgdorferi-infected HLA-DR4-positive CD28-negative mice post-antibiotic treatment

OBJECTIVE

The immunologic events that lead to persistent joint inflammation in certain patients with Lyme arthritis post-antibiotic treatment have been elusive so far. The prevalence of this condition is highest in individuals with rheumatoid arthritis-associated HLA-DR alleles. This study was undertaken to generate a murine model with persistent arthritis post-antibiotic treatment.

METHODS

We have previously shown that CD28(-/-) mice develop intermittent monarticular Lyme arthritis that is responsive to antibiotics. Since there seems to be a link in humans between persistent arthritic manifestations post-antibiotic treatment and the HLA-DR4 allele, we generated DR4+/+CD28(-/-)MHCII(-/-) mice, infected them with Borrelia burgdorferi, and subsequently treated them with antibiotics.

RESULTS

Thirty-eight percent of the B burgdorferi-infected DR4+/+CD28(-/-)MHCII(-/-) mice, but none of the B burgdorferi-infected CD28(-/-)MHCII(-/-) mice, remained arthritic post-antibiotic treatment. A significant fraction (36%) of these mice, but none of the mice in which arthritis resolved, had serum antibodies to outer surface protein A of B burgdorferi. After abrogation of active B burgdorferi infection, the inflammatory reaction in mice with persistent joint inflammation was restricted to the joints, since their draining lymph nodes were no longer enlarged. Increased CD20 and interferon-gamma messenger RNA expression in the inflamed joints of these mice suggested a possible role of B cells and inflammatory cytokines in the pathogenesis of persistent arthritis post-antibiotic treatment.

CONCLUSION

The establishment of this murine model allows, for the first time, the elucidation of the immunologic events that lead to persistent Lyme arthritis post-antibiotic therapy in genetically susceptible individuals.

Interleukin-23 is required for development of arthritis in mice vaccinated and challenged with Borrelia species

We recently hypothesized that T helper 17 (Th17) cells and their associated cytokines are involved in the development of arthritis following infection with Borrelia burgdorferi. Here, we show that interleukin-23 (IL-23), a survival factor for Th17 cells, is required for the induction of arthritis in mice vaccinated with B. burgdorferi strain 297 and challenged with "Borrelia bissettii." When Borrelia-vaccinated and -challenged mice were given antibodies to the p19 subunit of IL-23, they failed to develop the histopathological changes observed in untreated vaccinated and challenged mice. In addition, viable B. bissettii organisms stimulated the secretion of IL-17 from Borrelia-immune lymph node cells during in vitro culture. When anti-IL-23 p19 antibody was included in cultures of B. bissettii organisms and Borrelia-immune lymph node cells, the production of IL-17 was reduced to levels observed in cultures containing immune cells alone. Taken together, these results support the hypothesis that Th17 cell-associated cytokines are involved in the development of Borrelia-mediated arthritis. These findings provide insight into previously overlooked immune mechanisms responsible for the development of Lyme arthritis.

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

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

Evaluating human T cell receptor gene expression by PCR

This unit describes the use of PCR to characterize and quantify rearranged transcripts from specific T cell receptor variable gene families in human tissue and peripheral blood lymphocytes. The strategy outlined in this unit has been extensively used on different sources of human tissue including brain, spinal cord, and skeletal muscle. A protocol is provided to clone and sequence PCR-amplified cDNA transcripts to study the junctional diversity of the expressed genes. A support protocol describes a method for reverse transcribing total RNA to make the cDNA required by the other protocols.

CD28 deficiency exacerbates joint inflammation upon Borrelia burgdorferi infection, resulting in the development of chronic Lyme arthritis

Lyme disease, caused by the tick-borne spirochete Borrelia burgdorferi (Bb), is a multisystem illness, affecting many organs, such as the heart, the nervous system, and the joints. Months after Bb infection, approximately 60% of patients experience intermittent arthritic attacks, a condition that in some individuals progresses to chronic joint inflammation. Although mice develop acute arthritis in response to Bb infection, the joint inflammation clears after 2 wk, despite continuous infection, only very rarely presenting with chronic Lyme arthritis. Thus, the lack of an animal system has so far prevented the elucidation of this persistent inflammatory process that occurs in humans. In this study, we report that the majority of Bb-infected CD28-/- mice develop chronic Lyme arthritis. Consistent with observations in chronic Lyme arthritis patients, the infected mutant, but not wild-type mice present recurring monoarticular arthritis over an extended time period, as well as anti-outer surface protein A of Bb serum titers. Furthermore, we demonstrate that anti-outer surface protein A Abs develop in these mice only after establishment of chronic Lyme arthritis. Thus, the Bb-infected CD28-/- mice provide a murine model for studying chronic Lyme arthritis.

High levels of inflammatory chemokines and cytokines in joint fluid and synovial tissue throughout the course of antibiotic-refractory lyme arthritis

OBJECTIVE

To investigate the possible role of chemokines and cytokines in the pathogenesis of Lyme arthritis.

METHODS

Using cytometric bead array and flow cytometry techniques, chemokine and cytokine levels were determined in 65 synovial fluid (SF) samples and 7 synovial tissue (ST) samples from 17 patients with antibiotic-responsive Lyme arthritis and 35 patients with antibiotic-refractory Lyme arthritis seen during the past 18 years. In the ST samples, expression of chemokine receptors was measured using immunohistochemistry.

RESULTS

Before or during antibiotic therapy, when the majority of patients had positive polymerase chain reaction (PCR) results for Borrelia burgdorferi DNA, SF from patients with antibiotic-refractory arthritis contained exceptionally high levels of Th1 chemoattractants and cytokines, particularly CXCL9 and interferon-gamma (IFNgamma). Compared with the patients whose arthritis was responsive to antibiotic treatment, those with antibiotic-refractory arthritis had significantly higher levels of CXCL9 and CXCL10 (both P<or=0.001) and CCL3, CCL4, CXCL8, IFNgamma, tumor necrosis factor alpha, interleukin-1beta (IL-1beta), and IL-6 (all P<or=0.01). During the post-antibiotic period, when the results of PCR for B burgdorferi DNA in SF and ST were uniformly negative, patients with antibiotic-refractory arthritis continued to exhibit high SF and ST levels of these chemokines and cytokines. In addition, synovial samples showed marked expression of the receptors for T cell or macrophage chemokines, CXCR3 and CCR5.

CONCLUSION

Patients with antibiotic-refractory Lyme arthritis have high synovial fluid levels of proinflammatory chemokines and cytokines, especially CXCL9 and IFNgamma, throughout the illness. Thus, even when antibiotic treatment reduces or completely clears the infection in these patients, the inflammatory response in synovium persists.

Anti-p19 antibody treatment exacerbates lyme arthritis and enhances borreliacidal activity

Considerable effort has been made to elucidate the mechanism of Lyme arthritis. We focused on p19, a cell cycle-regulating molecule, because it is known to inhibit cell cycle division of T lymphocytes which may be responsible for the induction of arthritis. We show that anti-p19 antibody treatment enhances the inflammatory response normally detected at the tibiotarsal joints of Borrelia burgdorferi-vaccinated and Borrelia bissettii-challenged mice. Specifically, anti-p19 antibody treatment augmented the severity of inflammation within the synovial and subsynovial tissue. Moreover, treatment with anti-p19 antibody caused severe erosion of cartilage and bone with ankle joint destruction. In addition, anti-p19 antibody treatment of Borrelia-vaccinated and -challenged mice enhanced the borreliacidal antibody response, especially against the vaccine isolate. The novel activities of anti-p19 antibody show that p19 may be an important therapeutic site for the treatment of Lyme arthritis.

Interleukin-10 anti-inflammatory response to Borrelia burgdorferi, the agent of Lyme disease: a possible role for suppressors of cytokine signaling 1 and 3

It has been established that interleukin-10 (IL-10) inhibits inflammatory cytokines produced by macrophages in response to Borrelia burgdorferi or its lipoproteins. The mechanism by which IL-10 exerts this anti-inflammatory effect is still unknown. Recent findings indicate that suppressors of cytokine signaling (SOCS) proteins are induced by cytokines and Toll-like receptor (TLR)-mediated stimuli, and in turn they can down-regulate cytokine and TLR signaling in macrophages. Because it is known that SOCS are induced by IL-10 and that B. burgdorferi and its lipoproteins most likely interact via TLR2 or the heterodimers TLR2/1 and/or TLR2/6, we hypothesized that SOCS are induced by IL-10 and B. burgdorferi and its lipoproteins in macrophages and that SOCS may mediate the inhibition by IL-10 of concomitantly elicited cytokines. We report here that mouse J774 macrophages incubated with IL-10 and added B. burgdorferi spirochetes (freeze-thawed, live, or sonicated) or lipidated outer surface protein A (L-OspA) augmented their SOCS1/SOCS3 mRNA and protein expression, with SOCS3 being more abundant. Pam(3)Cys, a synthetic lipopeptide, also induced SOCS1/SOCS3 expression under these conditions, but unlipidated OspA was ineffective. Neither endogenous IL-10 nor the translation inhibitor cycloheximide blocked SOCS1/SOCS3 induction by B. burgdorferi and its lipoproteins, indicating that the expression of other genes is not required. This temporally correlated with the IL-10-mediated inhibition of the inflammatory cytokines IL-1beta, IL-6, IL-12p40, IL-18, and tumor necrosis factor alpha. Our data are evidence to suggest that expression of SOCS is part of the mechanism of IL-10-mediated inhibition of inflammatory cytokines elicited by B. burgdorferi and its lipoproteins.

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.

Fas ligand deficiency impairs host inflammatory response against infection with the spirochete Borrelia burgdorferi

Lyme disease represents a complex response to Borrelia burgdorferi that involves both bacterial factors as well as host responses. This results in an inflammatory reaction at several sites, including the synovial lining of joints. Synovial tissues of inflamed joints contain cells expressing high levels of Fas and Fas ligand (FasL). Although Fas stimulation is typically associated with cell death, it can also transmit stimulatory signals to certain cell types. Among these are dendritic cells and macrophages, which are abundant in inflamed synovium. To better assess the role of FasL in the pathogenesis of Lyme arthritis, we evaluated the response to B. burgdorferi infection in C3H/HeJgld mice that bear a nonfunctional mutation in FasL. Compared to wild-type C3H+/+ mice, C3Hgld mice had a similar bacterial burden and antibody response 2 weeks and 4 weeks following infection, but they manifested a significantly reduced Borrelia-specific cytokine response. In addition, C3Hgld mice developed a greatly reduced incidence and severity of arthritis. The findings document a contribution of FasL to the host inflammatory response to B. burgdorferi.

Helicobacter pylori, T cells and cytokines: the "dangerous liaisons"

Helicobacter pylori infection is the major cause of gastroduodenal pathologies, but only a minority of infected patients develop chronic and life threatening diseases, as peptic ulcer, gastric cancer, B-cell lymphoma, or autoimmune gastritis. The type of host immune response against H. pylori is crucial for the outcome of the infection. A predominant H. pylori-specific Th1 response, characterized by high IFN-gamma, TNF-alpha, and IL-12 production associates with peptic ulcer, whereas combined secretion of both Th1 and Th2 cytokines are present in uncomplicated gastritis. Gastric T cells from MALT lymphoma exhibit abnormal help for autologous B-cell proliferation and reduced perforin- and Fas-Fas ligand-mediated killing of B cells. In H. pylori-infected patients with autoimmune gastritis cytolytic T cells infiltrating the gastric mucosa cross-recognize different epitopes of H. pylori proteins and H+K+ ATPase autoantigen. These data suggest that peptic ulcer can be regarded as a Th1-driven immunopathological response to some H. pylori antigens, whereas deregulated and exhaustive H. pylori-induced T cell-dependent B-cell activation can support the onset of low-grade B-cell lymphoma. Alternatively, H. pylori infection may lead in some individuals to gastric autoimmunity via molecular mimicry.

Lyme borreliosis: from infection to autoimmunity

Lyme borreliosis in humans is an inflammatory disease affecting multiple organ systems, including the nervous system, cardiovascular system, joints and muscles. The causative agent, the spirochaete Borrelia burgdorferi, is transmitted to the host by a tick bite. The pathogenesis of the disease in its early stages is associated largely with the presence of viable bacteria at the site of inflammation, whereas in the later stages of disease, autoimmune features seem to contribute significantly. In addition, it has been suggested that chronic persistence of B. burgdorferi in affected tissues is of pathogenic relevance. Long-term exposure of the host immune system to spirochaetes and/or borrelial compounds may induce chronic autoimmune disease. The study of bacterium-host interactions has revealed a variety of proinflammatory and also immunomodulatory-immunosuppressive features caused by the pathogen. Therapeutic strategies using antibiotics are generally successful, but chronic disease may require immunosuppressive treatment. Effective and safe vaccines using recombinant outer surface protein A have been developed, but have not been propagated because of fears that autoimmunity might be induced. Nevertheless, new insights into the modes of transmission of B. burgdorferi to the warm-blooded host have been generated by studying the action of these vaccines.

Cellular FLIP long form-transgenic mice manifest a Th2 cytokine bias and enhanced allergic airway inflammation

Cellular FLIP long form (c-FLIP(L)) is a caspase-defective homologue of caspase-8 that blocks apoptosis by death receptors. The expression of c-FLIP(L) in T cells can also augment extracellular signal-regulated kinase phosphorylation after TCR ligation via the association of c-FLIP(L) with Raf-1. This contributes to the hyperproliferative capacity of T cells from c-FLIP(L)-transgenic mice. In this study we show that activated CD4(+) T cells from c-FLIP(L)-transgenic mice produce increased amounts of Th2 cytokines and decreased amounts of Th1 cytokines. This correlates with increased serum concentrations of the Th2-dependent IgG1 and IgE. The Th2 bias of c-FLIP(L)-transgenic CD4(+) T cells parallels impaired NF-kappa B activity and increased levels of GATA-3, which contribute, respectively, to decreased IFN-gamma and increased Th2 cytokines. The Th2 bias of c-FLIP(L)-transgenic mice extends to an enhanced sensitivity to OVA-induced asthma. Taken together, these results show that c-FLIP(L) can influence cytokine gene expression to promote Th2-driven allergic reaction, in addition to its traditional role of blocking caspase activation induced by death receptors.

Direct Toll-like receptor 2 mediated co-stimulation of T cells in the mouse system as a basis for chronic inflammatory joint disease

The pathogenesis of chronic inflammatory joint diseases such as adult and juvenile rheumatoid arthritis and Lyme arthritis is still poorly understood. Central to the various hypotheses in this respect is the notable involvement of T and B cells. Here we develop the premise that the nominal antigen-independent, polyclonal activation of preactivated T cells via Toll-like receptor (TLR)-2 has a pivotal role in the initiation and perpetuation of pathogen-induced chronic inflammatory joint disease. We support this with the following evidence. Both naive and effector T cells express TLR-2. A prototypic lipoprotein, Lip-OspA, from the etiological agent of Lyme disease, namely Borrelia burgdorferi, but not its delipidated form or lipopolysaccharide, was able to provide direct antigen-nonspecific co-stimulatory signals to both antigen-sensitized naive T cells and cytotoxic T lymphocyte (CTL) lines via TLR-2. Lip-OspA induced the proliferation and interferon (IFN)-γ secretion of purified, anti-CD3-sensitized, naive T cells from C57BL/6 mice but not from TLR-2-deficient mice. Induction of proliferation and IFN-γ secretion of CTL lines by Lip-OspA was independent of T cell receptor (TCR) engagement but was considerably enhanced after suboptimal TCR activation and was inhibitable by monoclonal antibodies against TLR-2.

Populations of human T lymphocytes that traverse the vascular endothelium stimulated by Borrelia burgdorferi are enriched with cells that secrete gamma interferon

Some diseases are characterized by prevalence in the affected tissues of type 1 T lymphocytes, which secrete gamma interferon (IFN-gamma) and other proinflammatory cytokines. For example, type 1 T cells predominate in the lesions of patients with Lyme disease, which is caused by the bacterium Borrelia burgdorferi. We used an in vitro model of the blood vessel wall to test the premise that the vascular endothelium actively recruits circulating type 1 T cells to such lesions. When T lymphocytes isolated from human peripheral blood were examined, the populations that traversed monolayers of resting human umbilical vein endothelial cells (HUVEC) or HUVEC stimulated by interleukin-1beta or B. burgdorferi were markedly enriched for T cells that produced IFN-gamma compared to the initially added population of T cells. No enrichment was seen for cells that produced interleukin-4, a marker for type 2 T lymphocytes. Very late antigen-4 and CD11/CD18 integrins mediated passage of the T cells across both resting and stimulated HUVEC, and the endothelium-derived chemokine CCL2 (monocyte chemoattractant protein 1) was responsible for the enhanced migration of T cells across stimulated HUVEC. These results suggest that the vascular endothelium may contribute to the selective accumulation of type 1 T cells in certain pathological lesions, including those of Lyme disease.

Phenotypes indicating cytolytic properties of Borrelia-specific interferon-gamma secreting cells in chronic Lyme neuroborreliosis

The immuno-pathogenetic mechanisms underlying chronic Lyme neuroborreliosis are mainly unknown. Human Borrelia burgdorferi (Bb) infection is associated with Bb-specific secretion of interferon-gamma (IFN-gamma), which may be important for the elimination of Bb, but this may also cause tissue injury. In order to increase the understanding of the pathogenic mechanisms in chronic neuroborreliosis, we investigated which cell types that secrete IFN-gamma. Blood mononuclear cells from 13 patients with neuroborreliosis and/or acrodermatitis chronicum atrophicans were stimulated with Bb antigen and the phenotypes of the induced IFN-gamma-secreting cells were analyzed with three different approaches. Cells expressing CD8 or TCRgammadelta, which both have cytolytic properties, were the main phenotypes of IFN-gamma-secreting cells, indicating that tissue injury in chronic neuroborreliosis may be mediated by cytotoxic cells.

Elucidation of Lyme arthritis

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