Whole genome sequencing of human Borrelia burgdorferi isolates reveals linked blocks of accessory genome elements located on plasmids and associated with human dissemination.

Lyme disease is the most common vector-borne disease in North America and Europe. The clinical manifestations of Lyme disease vary based on the genospecies of the infecting Borrelia burgdorferi spirochete, but the microbial genetic elements underlying these associations are not known. Here, we report the whole genome sequence (WGS) and analysis of 299 B. burgdorferi (Bb) isolates derived from patients in the Eastern and Midwestern US and Central Europe. We develop a WGS-based classification of Bb isolates, confirm and extend the findings of previous single- and multi-locus typing systems, define the plasmid profiles of human-infectious Bb isolates, annotate the core and strain-variable surface lipoproteome, and identify loci associated with disseminated infection. A core genome consisting of ~900 open reading frames and a core set of plasmids consisting of lp17, lp25, lp36, lp28-3, lp28-4, lp54, and cp26 are found in nearly all isolates. Strain-variable (accessory) plasmids and genes correlate strongly with phylogeny. Using genetic association study methods, we identify an accessory genome signature associated with dissemination in humans and define the individual plasmids and genes that make up this signature. Strains within the RST1/WGS A subgroup, particularly a subset marked by the OspC type A genotype, have increased rates of dissemination in humans. OspC type A strains possess a unique set of strongly linked genetic elements including the presence of lp56 and lp28-1 plasmids and a cluster of genes that may contribute to their enhanced virulence compared to other genotypes. These features of OspC type A strains reflect a broader paradigm across Bb isolates, in which near-clonal genotypes are defined by strain-specific clusters of linked genetic elements, particularly those encoding surface-exposed lipoproteins. These clusters of genes are maintained by strain-specific patterns of plasmid occupancy and are associated with the probability of invasive infection.

Lyme Arthritis: A 50-Year Journey.

Lyme arthritis (LA) was recognized as a separate entity in 1975 because of geographic clustering of children often diagnosed with juvenile rheumatoid arthritis in Lyme, Connecticut. After identification of erythema migrans as a common early feature of the illness, a prospective study of such patients implicated Ixodes scapularis ticks in disease transmission. In 1982, the causative agent, now called Borrelia burgdorferi, was cultured from these ticks and from Lyme disease patients. Subsequently, it was shown that LA could usually be treated successfully with oral antibiotics but sometimes required intravenous antibiotics. Yet, a small percentage of patients developed a dysregulated, proinflammatory immune response leading to persistent postinfectious synovitis with vascular damage, cytotoxic and autoimmune responses, and fibroblast proliferation, a lesion similar to that of rheumatoid arthritis. The message from postinfectious LA for other autoimmune arthritides is that a complex immune response with autoimmune features can begin with a microbial infection.

Variants in the Late Cornified Envelope Gene Locus Are Associated With Elevated T-helper 17 Responses in Patients With Postinfectious Lyme Arthritis.

BACKGROUND: Postinfectious Lyme arthritis (LA) is associated with dysregulated immunity and autoreactive T- and B-cell responses in joints. Here we explored the role of host genetic variation in this outcome. METHODS: The frequency of 253 702 single-nucleotide polymorphisms (SNPs) was determined in 147 patients with LA (87 with postinfectious LA and 60 with antibiotic-responsive LA), and for comparison in 90 patients with erythema migrans or the general population (n = 2504). Functional outcome of candidate SNPs was assessed by evaluating their impact on clinical outcome and on immune responses in blood and synovial fluid in patients with LA. RESULTS: Six SNPs associated with late cornified envelope (LCE3) genes were present at greater frequency in patients with postinfectious LA compared to those with antibiotic-responsive LA (70% vs 30%; odds ratio, 2; P < .01). These SNPs were associated with heightened levels of inflammatory Th17 cytokines in serum but lower levels of interleukin 27, a regulatory cytokine, implying that they may contribute to dysregulated Th17 immunity in blood. Moreover, in patients with postinfectious LA, the levels of these Th17 mediators correlated directly with autoantibody responses in synovial fluid, providing a possible link between LCE3 SNPs, maladaptive systemic Th17 immunity, and autoreactive responses in joints. CONCLUSIONS: Variation in the LCE3 locus, a known genetic risk factor in psoriasis and psoriatic arthritis, is associated with dysregulated systemic Th17 immunity and heightened autoantibody responses in joints. These findings underscore the importance of host genetic predisposition and systemic Th17 immunity in the pathogenesis of postinfectious (antibiotic-refractory) Lyme arthritis.

Laboratory Diagnosis of Lyme Borreliosis.

Lyme borreliosis is caused by a growing list of related, yet distinct, spirochetes with complex biology and sophisticated immune evasion mechanisms. It may result in a range of clinical manifestations involving different organ systems, and can lead to persistent sequelae in a subset of cases. The pathogenesis of Lyme borreliosis is incompletely understood, and laboratory diagnosis, the focus of this review, requires considerable understanding to interpret the results correctly. Direct detection of the infectious agent is usually not possible or practical, necessitating a continued reliance on serologic testing. Still, some important advances have been made in the area of diagnostics, and there are many promising ideas for future assay development. This review summarizes the state of the art in laboratory diagnostics for Lyme borreliosis, provides guidance in test selection and interpretation, and highlights future directions.

Multicenter Clinical Evaluation of Modified Two-Tiered Testing Algorithms for Lyme Disease Using Zeus Scientific Commercial Assays.

Modified two-tiered testing (MTTT) algorithms for Lyme disease (LD), which involve the sequential use of orthogonal enzyme immunoassays (EIAs) without immunoblotting, are acceptable alternatives to standard two-tiered testing (STTT; EIA followed by immunoblots) provided the EIAs have been FDA-cleared for this intended use. We evaluated four Zeus Scientific LD EIAs used in two distinct MTTT algorithms for FDA review. MTTT 1 used a VlsE1/pepC10 polyvalent EIA followed by a whole-cell sonicate (WCS) polyvalent EIA. MTTT 2 used the same first-tier EIA followed by separate IgM and IgG WCS EIAs. In a retrospective phase, we compared each MTTT algorithm to STTT using archived samples from LD patients or control subjects. In a prospective phase, we used the same algorithms to analyze consecutive excess samples submitted for routine LD serology to three clinical laboratories. For the retrospective phase, MTTTs 1 and 2 were more sensitive (56% and 74%) than STTT (41%; P ≤ 0.03) among 61 patients with acute erythema migrans (EM). In LD patients with neuroborreliosis, carditis, or arthritis (n = 75), sensitivity was comparable between algorithms (96 to 100%; P = 1.0). Among 190 control subjects without past LD, all algorithms were highly and comparably specific (≥99%, P = 0.48). For the prospective phase, (n = 2,932), positive percent-agreement (PPA), negative percent-agreement (NPA), and overall agreement of MTTT 1 with STTT were 93%, 97.7% and 97.4% (kappa 0.80). MTTT 2 yielded higher PPA (98%) but lower NPA (96.1%) and overall agreement (96.2%, kappa 0.74; all P < 0.05). Compared with STTT, both MTTT algorithms provided increased sensitivity in EM patients, comparable sensitivity in later disease and non-inferior specificity.

Borrelia burgdorferi peptidoglycan is a persistent antigen in patients with Lyme arthritis.

Lyme disease is a multisystem disorder caused by the spirochete Borrelia burgdorferi A common late-stage complication of this disease is oligoarticular arthritis, often involving the knee. In ∼10% of cases, arthritis persists after appropriate antibiotic treatment, leading to a proliferative synovitis typical of chronic inflammatory arthritides. Here, we provide evidence that peptidoglycan (PG), a major component of the B. burgdorferi cell envelope, may contribute to the development and persistence of Lyme arthritis (LA). We show that B. burgdorferi has a chemically atypical PG (PGBb) that is not recycled during cell-wall turnover. Instead, this pathogen sheds PGBb fragments into its environment during growth. Patients with LA mount a specific immunoglobulin G response against PGBb, which is significantly higher in the synovial fluid than in the serum of the same patient. We also detect PGBb in 94% of synovial fluid samples (32 of 34) from patients with LA, many of whom had undergone oral and intravenous antibiotic treatment. These same synovial fluid samples contain proinflammatory cytokines, similar to those produced by human peripheral blood mononuclear cells stimulated with PGBb In addition, systemic administration of PGBb in BALB/c mice elicits acute arthritis. Altogether, our study identifies PGBb as a likely contributor to inflammatory responses in LA. Persistence of this antigen in the joint may contribute to synovitis after antibiotics eradicate the pathogen. Furthermore, our finding that B. burgdorferi sheds immunogenic PGBb fragments during growth suggests a potential role for PGBb in the immunopathogenesis of other Lyme disease manifestations.

Clinical Practice Guidelines by the Infectious Diseases Society of America (IDSA), American Academy of Neurology (AAN), and American College of Rheumatology (ACR): 2020 Guidelines for the Prevention, Diagnosis and Treatment of Lyme Disease.

This evidence-based clinical practice guideline for the prevention, diagnosis, and treatment of Lyme disease was developed by a multidisciplinary panel representing the Infectious Diseases Society of America (IDSA), the American Academy of Neurology (AAN), and the American College of Rheumatology (ACR). The scope of this guideline includes prevention of Lyme disease, and the diagnosis and treatment of Lyme disease presenting as erythema migrans, Lyme disease complicated by neurologic, cardiac, and rheumatologic manifestations, Eurasian manifestations of Lyme disease, and Lyme disease complicated by coinfection with other tick-borne pathogens. This guideline does not include comprehensive recommendations for babesiosis and tick-borne rickettsial infections, which are published in separate guidelines. The target audience for this guideline includes primary care physicians and specialists caring for this condition such as infectious diseases specialists, emergency physicians, internists, pediatricians, family physicians, neurologists, rheumatologists, cardiologists and dermatologists in North America.

Clinical Practice Guidelines by the Infectious Diseases Society of America (IDSA), American Academy of Neurology (AAN), and American College of Rheumatology (ACR): 2020 Guidelines for the Prevention, Diagnosis and Treatment of Lyme Disease.

This evidence-based clinical practice guideline for the prevention, diagnosis, and treatment of Lyme disease was developed by a multidisciplinary panel representing the Infectious Diseases Society of America (IDSA), the American Academy of Neurology (AAN), and the American College of Rheumatology (ACR). The scope of this guideline includes prevention of Lyme disease, and the diagnosis and treatment of Lyme disease presenting as erythema migrans, Lyme disease complicated by neurologic, cardiac, and rheumatologic manifestations, Eurasian manifestations of Lyme disease, and Lyme disease complicated by coinfection with other tick-borne pathogens. This guideline does not include comprehensive recommendations for babesiosis and tick-borne rickettsial infections, which are published in separate guidelines. The target audience for this guideline includes primary care physicians and specialists caring for this condition such as infectious diseases specialists, emergency physicians, internists, pediatricians, family physicians, neurologists, rheumatologists, cardiologists and dermatologists in North America.

CD1b presents self and Borrelia burgdorferi diacylglycerols to human T cells.

Lyme disease is a common multisystem disease caused by infection with a tick-transmitted spirochete, Borrelia burgdorferi and related Borrelia species. The monoglycosylated diacylglycerol known as B. burgdorferi glycolipid II (BbGL-II) is a major target of antibodies in sera from infected individuals. Here, we show that CD1b presents BbGL-II to human T cells and that the TCR mediates the recognition. However, we did not detect increased frequency of CD1b-BbGL-II binding T cells in the peripheral blood of Lyme disease patients compared to controls. Unexpectedly, mapping the T cell specificity for BbGL-II-like molecules using tetramers and activation assays revealed a concomitant response to CD1b-expressing APCs in absence of BbGL-II. Further, among all major classes of self-lipid tested, BbGL-II responsive TCRs show strong cross-reactivity to diacylglycerol, a self-lipid antigen with structural similarities to BbGL-II. Extending prior work on MHC and CD1b, CD1c, and CD1d proteins, this study provides evidence for cross-reactive CD1b-restricted T cell responses to bacterial and self-antigens, and identifies chemically defined targets for future discovery of self and foreign antigen cross-reactive T cells.

Robust interferon signature and suppressed tissue repair gene expression in synovial tissue from patients with postinfectious, Borrelia burgdorferi-induced Lyme arthritis.

In most patients with Lyme arthritis (LA), antibiotic therapy results in Borrelia burgdorferi pathogen elimination, tissue repair, and return to homeostasis. However, despite spirochetal killing, some patients develop proliferative synovitis, characterised by synovial hyperplasia, inflammation, vascular damage, and fibrosis that persists for months to several years after antibiotic treatment, called postinfectious LA. In this study, we characterised the transcriptomes of postinfectious LA patients' synovial tissue, the target tissue of the immune response. High-throughput RNA sequencing to a depth of ~30 million reads per sample was used to profile gene expression in synovial tissue from 14 patients with postinfectious LA, compared with eight patients with other types of chronic inflammatory arthritis and five with minimally inflammatory osteoarthritis (OA). Synovium from postinfectious LA and other inflammatory arthritides shared gene signatures associated with antigen presentation, innate immune responses, and cell-mediated immune activation, whereas these responses were diminished in OA synovium. Unique to postinfectious LA was a particularly robust interferon-gamma (IFNγ) signature. Moreover, this heightened IFNγ signature inversely correlated with expression of genes involved in repair of damaged tissue, including genes associated with stromal cell proliferation and differentiation, neovascularisation, and extracellular matrix synthesis, which were markedly suppressed in postinfectious LA. Transcriptional observations were confirmed by cytokine profiling, histologic analyses, and clinical correlations. We propose that in patients with postinfectious LA, overexpression of IFNγ in synovium prevents appropriate repair of tissue damaged by B. burgdorferi infection, blocking return to tissue homeostasis long after completion of antibiotic therapy and resolution of active infection.

Interferon-gamma production in Lyme arthritis synovial tissue promotes differentiation of fibroblast-like synoviocytes into immune effector cells.

Lyme arthritis (LA), a late disease manifestation of Borrelia burgdorferi infection, usually resolves with antibiotic therapy. However, some patients develop proliferative synovitis lasting months to several years after spirochetal killing, called postinfectious LA. In this study, we phenotyped haematopoietic and stromal cell populations in the synovial lesion ex vivo and used these findings to generate an in vitro model of LA using patient-derived fibroblast-like synoviocytes (FLS). Ex vivo analysis of synovial tissue revealed high abundance of IFNγ-producing T cells and NK cells. Similar to marked IFNγ responses in tissue, postinfectious LA synovial fluid also had high levels of IFNγ. HLA-DR-positive FLS were present throughout the synovial lesion, particularly in areas of inflammation. FLS stimulated in vitro with B. burgdorferi, which were similar to conditions during infection, expressed 68 genes associated primarily with innate immune activation and neutrophil recruitment. In contrast, FLS stimulated with IFNγ, which were similar to conditions in the postinfectious phase, expressed >2,000 genes associated with pathogen sensing, inflammation, and MHC Class II antigen presentation, similar to the expression profile in postinfectious synovial tissue. Furthermore, costimulation of FLS with B. burgdorferi and IFNγ induced greater expression of IL-6 and other innate immune response proteins and genes than with IFNγ stimulation alone. These results suggest that B. burgdorferi infection, in combination with IFNγ, initiates the differentiation of FLS into a highly inflammatory phenotype. We hypothesise that overexpression of IFNγ by lymphocytes within synovia perpetuates these responses in the postinfectious period, causing proliferative synovitis and stalling appropriate repair of damaged tissue.

Direct Diagnostic Tests for Lyme Disease.

Borrelia burgdorferi was discovered to be the cause of Lyme disease in 1983, leading to seroassays. The 1994 serodiagnostic testing guidelines predated a full understanding of key B. burgdorferi antigens and have a number of shortcomings. These serologic tests cannot distinguish active infection, past infection, or reinfection. Reliable direct-detection methods for active B. burgdorferi infection have been lacking in the past but are needed and appear achievable. New approaches have effectively been applied to other emerging infections and show promise in direct detection of B. burgdorferi infections.

Advances in Serodiagnostic Testing for Lyme Disease Are at Hand.

The cause of Lyme disease, Borrelia burgdorferi, was discovered in 1983. A 2-tiered testing protocol was established for serodiagnosis in 1994, involving an enzyme immunoassay (EIA) or indirect fluorescence antibody, followed (if reactive) by immunoglobulin M and immunoglobulin G Western immunoblots. These assays were prepared from whole-cell cultured B. burgdorferi, lacking key in vivo expressed antigens and expressing antigens that can bind non-Borrelia antibodies. Additional drawbacks, particular to the Western immunoblot component, include low sensitivity in early infection, technical complexity, and subjective interpretation when scored by visual examination. Nevertheless, 2-tiered testing with immunoblotting remains the benchmark for evaluation of new methods or approaches. Next-generation serologic assays, prepared with recombinant proteins or synthetic peptides, and alternative testing protocols, can now overcome or circumvent many of these past drawbacks. This article describes next-generation serodiagnostic testing for Lyme disease, focusing on methods that are currently available or near-at-hand.

Immunogenic HLA-DR-Presented Self-Peptides Identified Directly from Clinical Samples of Synovial Tissue, Synovial Fluid, or Peripheral Blood in Patients with Rheumatoid Arthritis or Lyme Arthritis.

Human leukocyte antigen-antigen D related (HLA-DR) molecules are highly expressed in synovial tissue (ST), the target of the immune response in chronic inflammatory forms of arthritis. Here, we used LC-MS/MS to identify HLA-DR-presented self-peptides in cells taken directly from clinical samples: ST, synovial fluid mononuclear cells (SFMC), or peripheral blood mononuclear cells (PBMC) from five patients with rheumatoid arthritis (RA) and eight with Lyme arthritis (LA). We identified 1593 non-redundant HLA-DR-presented peptides, derived from 870 source proteins. A total of 67% of the peptides identified in SFMC and 55% of those found in PBMC were found in ST, but analysis of SFMC/PBMC also revealed new antigen-presented peptides. Peptides were synthesized and examined for reactivity with the patients' PBMC. To date, three autoantigens in RA and four novel autoantigens in LA, presented in ST and/or PBMC, were shown to be targets of T- and B-cell responses in these diseases; ongoing analyses may add to this list. Thus, immunoprecipitation and LC-MS/MS can now identify hundreds of HLA-DR-presented self-peptides from individual patients' tissues or fluids with mixed cell populations. Importantly, identification of HLA-DR-presented peptides from SFMC or PBMC allows testing of more patients, including those early in the disease. Direct analysis of clinical samples facilitates identification of novel immunogenic T-cell epitopes.

T-Helper 17 Cell Cytokine Responses in Lyme Disease Correlate With Borrelia burgdorferi Antibodies During Early Infection and With Autoantibodies Late in the Illness in Patients With Antibiotic-Refractory Lyme Arthritis.

BACKGROUND: Control of Lyme disease is attributed predominantly to innate and adaptive T-helper 1 cell (TH1) immune responses, whereas the role of T-helper 17 cell (TH17) responses is less clear. Here we characterized these inflammatory responses in patients with erythema migrans (EM) or Lyme arthritis (LA) to elucidate their role early and late in the infection. METHODS: Levels of 21 cytokines and chemokines, representative of innate, TH1, and TH17 immune responses, were assessed by Luminex in acute and convalescent sera from 91 EM patients, in serum and synovial fluid from 141 LA patients, and in serum from 57 healthy subjects. Antibodies to Borrelia burgdorferi or autoantigens were measured by enzyme-linked immunosorbent assay. RESULTS: Compared with healthy subjects, EM patients had significantly higher levels of innate, TH1, and TH17-associated mediators (P ≤ .05) in serum. In these patients, the levels of inflammatory mediators, particularly TH17-associated cytokines, correlated directly with B. burgdorferi immunoglobulin G antibodies (P ≤ .02), suggesting a beneficial role for these responses in control of early infection. Late in the disease, in patients with LA, innate and TH1-associated mediators were often >10-fold higher in synovial fluid than serum. In contrast, the levels of TH17-associated mediators were more variable, but correlated strongly with autoantibodies to endothelial cell growth factor, matrix metalloproteinase 10, and apolipoprotein B-100 in joints of patients with antibiotic-refractory LA, implying a shift in TH17 responses toward an autoimmune phenotype. CONCLUSIONS: Patients with Lyme disease often develop pronounced TH17 immune responses that may help control early infection. However, late in the disease, excessive TH17 responses may be disadvantageous by contributing to autoimmune responses associated with antibiotic-refractory LA.

Evaluation of Modified 2-Tiered Serodiagnostic Testing Algorithms for Early Lyme Disease.

Background: The conventional 2-tiered serologic testing protocol for Lyme disease (LD), an enzyme immunoassay (EIA) followed by immunoglobulin M and immunoglobulin G Western blots, performs well in late-stage LD but is insensitive in patients with erythema migrans (EM), the most common manifestation of the illness. Western blots are also complex, difficult to interpret, and relatively expensive. In an effort to improve test performance and simplify testing in early LD, we evaluated several modified 2-tiered testing (MTTT) protocols, which use 2 assays designed as first-tier tests sequentially, without the need of Western blots. Methods: The MTTT protocols included (1) a whole-cell sonicate (WCS) EIA followed by a C6 EIA; (2) a WCS EIA followed by a VlsE chemiluminescence immunoassay (CLIA); and (3) a variable major protein-like sequence, expressed (VlsE) CLIA followed by a C6 EIA. Sensitivity was determined using serum from 55 patients with erythema migrans; specificity was determined using serum from 50 patients with other illnesses and 1227 healthy subjects. Results: Sensitivity of the various MTTT protocols in patients with acute erythema migrans ranged from 36% (95% confidence interval [CI], 25%-50%) to 54% (95% CI, 42%-67%), compared with 25% (95% CI, 16%-38%) using the conventional protocol (P = .003-0.3). Among control subjects, the 3 MTTT protocols were similarly specific (99.3%-99.5%) compared with conventional 2-tiered testing (99.5% specificity; P = .6-1.0). Conclusions: Although there were minor differences in sensitivity and specificity among MTTT protocols, each provides comparable or greater sensitivity in acute EM, and similar specificity compared with conventional 2-tiered testing, obviating the need for Western blots.

Characterization of the early local immune response to Ixodes ricinus tick bites in human skin.

Little is known about the immunomodulation by tick saliva during a natural tick bite in human skin, the site of the tick-host interaction. We examined the expression of chemokines, cytokines and leucocyte markers on the mRNA levels and histopathologic changes in human skin biopsies of tick bites (n=37) compared to unaffected skin (n=9). Early tick-bite skin lesions (<24 hours of tick attachment) were characterized by a predominance of macrophages and dendritic cells, elevated mRNA levels of macrophage chemoattractants (CCL2, CCL3, CCL4) and neutrophil chemoattractants (CXCL1, CXCL8), of the pro-inflammatory cytokine, IL-1ß, and the anti-inflammatory cytokine, IL-5. In contrast, the numbers of lymphocytes and mRNA levels of lymphocyte cell markers (CD4, CD8, CD19), lymphocyte chemoattractants (CXCL9, CXCL10, CXCL11, CXCL13, CCL1, CCL22), dendritic cell chemoattractants (CCL20), and other pro- (IL-6, IL-12p40, IFN-γ, TNF-α) and anti-inflammatory cytokines (IL-4, IL-10, TGF-ß) did not differ from normal skin. With longer tick attachment (>24 hours), the numbers of innate immune cells and mediators (not significantly) declined, whereas the numbers of lymphocytes (not significantly) increased. Natural tick bites by Ixodes ricinus ticks initially elicit a strong local innate immune response in human skin. Beyond 24 hours of tick attachment, this response usually becomes less, perhaps because of immunomodulation by tick saliva.

Differences in Genotype, Clinical Features, and Inflammatory Potential of Borrelia burgdorferi sensu stricto Strains from Europe and the United States.

Borrelia burgdorferi sensu stricto isolates from patients with erythema migrans in Europe and the United States were compared by genotype, clinical features of infection, and inflammatory potential. Analysis of outer surface protein C and multilocus sequence typing showed that strains from these 2 regions represent distinct genotypes. Clinical features of infection with B. burgdorferi in Slovenia were similar to infection with B. afzelii or B. garinii, the other 2 Borrelia spp. that cause disease in Europe, whereas B. burgdorferi strains from the United States were associated with more severe disease. Moreover, B. burgdorferi strains from the United States induced peripheral blood mononuclear cells to secrete higher levels of cytokines and chemokines associated with innate and Th1-adaptive immune responses, whereas strains from Europe induced greater Th17-associated responses. Thus, strains of the same B. burgdorferi species from Europe and the United States represent distinct clonal lineages that vary in virulence and inflammatory potential.

Matrix metalloproteinase-10 is a target of T and B cell responses that correlate with synovial pathology in patients with antibiotic-refractory Lyme arthritis.

Infection-induced autoimmunity is thought to be a contributing factor in antibiotic-refractory Lyme arthritis, but studies of autoimmunity have been hindered by difficulty in identifying relevant autoantigens. We developed a novel approach that begins with the identification of T cell epitopes in synovial tissue using tandem mass spectrometry. Herein, we identified an immunogenic HLA-DR-presented peptide (T cell epitope) derived from the source protein matrix metalloproteinase-10 (MMP-10) from the synovium of a patient with antibiotic-refractory arthritis. This finding provided a bridge for the identification of autoantibody responses to MMP-10, the "first autoimmune hit" in a subgroup of patients with erythema migrans, the initial skin lesion of the infection. Months later, after priming of the immune response to MMP-10 in early infection, a subset of patients with antibiotic-responsive or antibiotic-refractory arthritis had MMP-10 autoantibodies, but only patients with antibiotic-refractory arthritis had both T and B cell responses to the protein, providing evidence for a "second autoimmune hit". Further support for a biologically relevant autoimmune event was observed by the positive correlation of anti-MMP-10 autoantibodies with distinct synovial pathology. This experience demonstrates the power of new, discovery-based methods to identify relevant autoimmune responses in chronic inflammatory forms of arthritis.

A Highly Expressed Human Protein, Apolipoprotein B-100, Serves as an Autoantigen in a Subgroup of Patients With Lyme Disease.

To discover novel autoantigens associated with Lyme arthritis (LA), we identified T-cell epitopes presented in vivo by human leukocyte antigen (HLA)-DR molecules in patients' inflamed synovial tissue or joint fluid and tested each epitope for autoreactivity. Using this approach, we identified the highly expressed human protein, apolipoprotein B-100 (apoB-100), as a target of T- and B-cell responses in a subgroup of LA patients. Additionally, the joint fluid of these patients had markedly elevated levels of apoB-100 protein, which may contribute to its autoantigenicity. In patients with antibiotic-refractory LA, the magnitude of apoB-100 antibody responses correlated with increased numbers of plasma cells in synovial tissue, greater numbers and activation of endothelial cells, and more synovial fibroblast proliferation. Thus, a subset of LA patients have high levels of apoB-100 in their joints and autoreactive T- and B-cell responses to the protein, which likely contributes to pathogenic autoimmunity in patients with antibiotic-refractory LA.