Experimental immunization against Lyme borreliosis with recombinant Osp proteins: an overview

Structure of a human monoclonal antibody in complex with Outer surface protein C (OspC) of the Lyme disease spirochete, Borreliella burgdorferi

Lyme disease is a tick-borne, multisystem infection caused by the spirochete, Borreliella burgdorferi . Although antibodies have been implicated in the resolution of Lyme disease, the specific B cell epitopes targeted during human infections remain largely unknown. In this study, we characterized and defined the structural epitope of a patient-derived bactericidal monoclonal IgG ("B11") against Outer surface protein C (OspC), a homodimeric lipoprotein necessary for B. burgdorferi tick-mediated transmission and early-stage colonization of vertebrate hosts. High-resolution epitope mapping was accomplished through hydrogen deuterium exchange-mass spectrometry (HDX-MS) and X-ray crystallography. Structural analysis of B11 Fab-OspC A complexes revealed the B11 Fabs associated in a 1:1 stoichiometry with the lateral faces of OspC A homodimers such that the antibodies are essentially positioned perpendicular to the spirochete's outer surface. B11's primary contacts reside within the membrane proximal regions of α-helices 1 and 6 and adjacent loops 5 and 6 in one OspC A monomer. In addition, B11 spans the OspC A dimer interface, engaging opposing α-helix 1', α-helix 2', and loop 2-3' in the second OspC A monomer. The B11-OspC A structure is reminiscent of the recently solved mouse transmission blocking monoclonal IgG B5 in complex with OspC A , indicating a mode of engagement with OspC that is conserved across species. In conclusion, we provide the first detailed insight into the interaction between a functional human antibody and an immunodominant Lyme disease antigen long considered an important vaccine target.

Agglutination of Borreliella burgdorferi by Transmission-Blocking OspA Monoclonal Antibodies and Monovalent Fab Fragments

Lyme disease vaccines based on recombinant Outer surface protein A (OspA) elicit protective antibodies that interfere with tick-to-host transmission of the disease-causing spirochete Borreliella burgdorferi. Another hallmark of OspA antisera and certain OspA monoclonal antibodies (MAbs) is their capacity to induce B. burgdorferi agglutination in vitro, a phenomenon first reported more than 30 years ago but never studied in molecular detail. In this report, we demonstrate that transmission-blocking OspA MAbs, individually and in combination, promote dose-dependent and epitope-specific agglutination of B. burgdorferi. Agglutination occurred within minutes and persisted for hours. Spirochetes in the core of the aggregates exhibited evidence of outer membrane (OM) stress, revealed by propidium iodide uptake. The most potent agglutinator was the mouse MAb LA-2, which targets the OspA C terminus (β-strands 18 to 20). Human MAb 319-44, which also targets the OspA C terminus (β-strand 20), and 857-2, which targets the OspA central β-sheet (strands 8 to 10), were less potent agglutinators, while MAb 221-7, which targets β-strands 10 to 11, had little to no measurable agglutinating activity, even though its affinity for OspA exceeded that of LA-2. Remarkably, monovalent Fab fragments derived from LA-2, and to a lesser degree 319-44, retained the capacity to induce B. burgdorferi aggregation and OM stress, a particularly intriguing observation considering that "LA-2-like" Fabs have been shown to experimentally entrap B. burgdorferi within infected ticks and prevent transmission during feeding to a mammalian host. It is therefore tempting to speculate that B. burgdorferi aggregation triggered by OspA-specific antibodies in vitro may in fact reflect an important biological activity in vivo.

DipA, a pore-forming protein in the outer membrane of Lyme disease spirochetes exhibits specificity for the permeation of dicarboxylates

Lyme disease Borreliae are highly dependent on the uptake of nutrients provided by their hosts. Our study describes the identification of a 36 kDa protein that functions as putative dicarboxylate-specific porin in the outer membrane of Lyme disease Borrelia. The protein was purified by hydroxyapatite chromatography from Borrelia burgdorferi B31 and designated as DipA, for dicarboxylate-specific porin A. DipA was partially sequenced, and corresponding genes were identified in the genomes of B. burgdorferi B31, Borrelia garinii PBi and Borrelia afzelii PKo. DipA exhibits high homology to the Oms38 porins of relapsing fever Borreliae. B. burgdorferi DipA was characterized using the black lipid bilayer assay. The protein has a single-channel conductance of 50 pS in 1 M KCl, is slightly selective for anions with a permeability ratio for cations over anions of 0.57 in KCl and is not voltage-dependent. The channel could be partly blocked by different di- and tricarboxylic anions. Particular high stability constants up to about 28,000 l/mol (in 0.1 M KCl) were obtained among the 11 tested anions for oxaloacetate, 2-oxoglutarate and citrate. The results imply that DipA forms a porin specific for dicarboxylates which may play an important role for the uptake of specific nutrients in different Borrelia species.

Population Dynamics of Borrelia burgdorferi in Lyme Disease

Many chronic inflammatory diseases are known to be caused by persistent bacterial or viral infections. A well-studied example is the tick-borne infection by the gram-negative spirochaetes of the genus Borrelia in humans and other mammals, causing severe symptoms of chronic inflammation and subsequent tissue damage (Lyme Disease), particularly in large joints and the central nervous system, but also in the heart and other tissues of untreated patients. Although killed efficiently by human phagocytic cells in vitro, Borrelia exhibits a remarkably high infectivity in mice and men. In experimentally infected mice, the first immune response almost clears the infection. However, approximately 1 week post infection, the bacterial population recovers and reaches an even larger size before entering the chronic phase. We developed a mathematical model describing the bacterial growth and the immune response against Borrelia burgdorferi in the C3H mouse strain that has been established as an experimental model for Lyme disease. The peculiar dynamics of the infection exclude two possible mechanistic explanations for the regrowth of the almost cleared bacteria. Neither the hypothesis of bacterial dissemination to different tissues nor a limitation of phagocytic capacity were compatible with experiment. The mathematical model predicts that Borrelia recovers from the strong initial immune response by the regrowth of an immune-resistant sub-population of the bacteria. The chronic phase appears as an equilibration of bacterial growth and adaptive immunity. This result has major implications for the development of the chronic phase of Borrelia infections as well as on potential protective clinical interventions.

The pathogenesis of lyme neuroborreliosis: from infection to inflammation

This review describes the current knowledge of the pathogenesis of acute Lyme neuroborreliosis (LNB), from invasion to inflammation of the central nervous system. Borrelia burgdorferi (B.b.) enters the host through a tick bite on the skin and may disseminate from there to secondary organs, including the central nervous system. To achieve this, B.b. first has to evade the hostile immune system. In a second step, the borrelia have to reach the central nervous system and cross the blood-brain barrier. Once in the cerebrospinal fluid (CSF), the spirochetes elicit an inflammatory response. We describe current knowledge about the infiltration of leukocytes into the CSF in LNB. In the final section, we discuss the mechanisms by which the spirochetal infection leads to the observed neural dysfunction. To conclude, we construct a stringent concept of the pathogenesis of LNB.

Molecular analysis of decorin-binding protein A (DbpA) reveals five major groups among European Borrelia burgdorferi sensu lato strains with impact for the development of serological assays and indicates lateral gene transfer of the dbpA gene

The Borrelia (B.) burgdorferi adhesin DbpA (decorin-binding protein A) is a valuable antigen for serodiagnosis of Lyme borreliosis and a promising candidate for a vaccine. To investigate the heterogeneity of DbpA, we aligned DNA sequences of 83 different dbpA genes (37 from the database, where the majority of sequences belong to B. burgdorferi sensu stricto and 46 were newly sequenced). Analysis of 25 sequences from the species B. burgdorferi s.s., 16 from B. afzelii, 40 from B. garinii, and two from the recently described human pathogenic genospecies A14S revealed five distinct DbpA groups. Group I comprises B. burgdorferi s.s. and group II B. afzelii. B. garinii is divided into groups III and IV, whereas A14S strains form group V. Formation of groups is mainly due to insertions of whole sequence sections. Comparison of dbpA sequences with ospC sequences from a subset of 59 strains revealed all kinds of cross-connections indicating processes of lateral gene transfer among strains. The extent of sequence identity within the dbpA genes decreases from the DNA (67%) to the amino acid (AA) level (44%) by about 23%, in contrast ospC sequence identities differed only by about 10%. This might be an indication that DbpA plays an important role in immune escape. Immunoblots using four recombinant DbpAs representing groups I-IV show that DbpA proteins are sensitive and specific antigens and complement one another in their reactivity. Part of the sera showed group-specific reactivity which could also be demonstrated with monoclonal antibodies.

Whole-genome DNA array analysis of the response of Borrelia burgdorferi to a bactericidal monoclonal antibody

Identification and characterization of genes that contribute to infection with Borrelia burgdorferi and, of those, genes that are targets of host responses is important for understanding the pathogenesis of Lyme disease. The complement-independent bactericidal monoclonal antibody (MAb) CB2 recognizes a carboxy-terminal, hydrophilic epitope of the outer surface protein B (OspB). CB2 kills B. burgdorferi by an unknown bactericidal mechanism. Upon binding of CB2 to OspB, differentially expressed gene products may be responsible for, or associated with, the death of the organism. A time course of the response of B. burgdorferi to CB2 was completed to analyze the differential gene expression in the bacteria over a period of visual morphological changes. Bacteria were treated with a sublethal concentration in which spirochetes were visibly distressed by the antibody but not lysed. Preliminary whole-genome DNA arrays at various time points within 1 h of incubation of B. burgdorferi with the antibody showed that most significant changes occurred at 25 min. Circular plasmid 32 (cp32)-encoded genes were active in this period of time, including the blyA homologs, phage holin system genes. DNA array data show that three blyA homologs were upregulated significantly, >/==" BORDER="0">2 standard deviations from the mean of the log ratios, and a P value of </=0.01. Quantitative real-time PCR analysis verified blyA and blyB upregulation over an 18- to 35-min time course. The hypothesis to test is whether the killing mechanism of CB2 is through uncontrolled expression of the blyA and blyB phage holin system.

An effective second-generation outer surface protein A-derived Lyme vaccine that eliminates a potentially autoreactive T cell epitope

The antigenic component of a common Lyme disease vaccine is recombinant outer surface protein A (rOspA) of Borrelia burgdorferi (Bb), the causative agent of Lyme disease. Coincidentally, patients with chronic, treatment-resistant Lyme arthritis develop an immune response against OspA, whereas those with acute Lyme disease usually do not. Treatment-resistant Lyme arthritis occurs in a subset of Lyme arthritis patients and is linked to HLA.DRB1*0401 (DR4) and related alleles. Recent work from our laboratory identified T cell crossreactivity between epitopes of OspA and lymphocyte function-associated antigen 1alpha(L) chain (LFA-1alpha(L)) in these patients. We generated a form of rOspA, FTK-OspA, in which the LFA-1alpha(L)/rOspA crossreactive T cell epitope was mutated to reduce the possible risk of autoimmunity in genetically susceptible individuals. FTK-OspA did not stimulate human or mouse DR4-restricted, WT-OspA-specific T cells, whereas it did stimulate antibody responses specific for WT-OspA that were similar to mice vaccinated WT-OspA. We show here that the protective efficacy of FTK-OspA is indistinguishable from that of WT-OspA in vaccination trials, as both C3H/HeJ and BALB/c FTK-OspA-vaccinated mice were protected from Bb infection. These data demonstrate that this rOspA-derived vaccine lacking the predicted cross-reactive T cell epitope, but retaining the capacity to elicit antibodies against infection, is effective in generating protective immunity.

Update on Lyme Disease Vaccine: Focus on Dosing and Adverse Events

With the rapid pace of immunologic research, it is more important than ever for readers to understand rational immunodiagnosis, immuno-prophylaxis, and immunotherapy. This column is intended to help you ensure proper immunologic drug use in your practice.

Interactions between mycoplasma lipoproteins and the host immune system

Mycoplasmas typically have a number of distinct lipoproteins anchored on the outer face of the plasma membrane. These surface antigens have a potent modulin activity and are preferential targets of the host immune response. However, the variation of some of these lipoproteins provides mycoplasmas with an effective means of evading the host immune defence system.

Lyme disease

Lyme disease (LD) is the most common tick-borne disease in the United States. The overall trend has been an average annual increase in reported cases since surveillance was initiated by the Centers for Disease Control and Prevention in 1982. Ixodes ticks often carry more than one potential pathogen, and co-infection with Borrelia burgdorferi and other organisms has been reported. The impact of dual infection upon the clinical course of LD is not known. Further studies of erythema migrans-like rashes in the Southern United States have indicated that it is likely caused by a related spirochetal organism. Case reports of unusual presentations have broadened our understanding of the clinical spectrum of LD. Studies in patients with chronic Lyme arthritis have indicated that an autoimmune process may be responsible for such cases. Results of two large, placebo-controlled trials of a recombinant Lyme vaccine have been reported and results indicate that the vaccine is safe and effective in preventing LD in adults.

Spiralin, a mycoplasmal membrane lipoprotein, induces T-cell-independent B-cell blastogenesis and secretion of proinflammatory cytokines

Mycoplasmas are bacteria which can cause respiratory, arthritic, and urogenital diseases. During the early phase of infection, mycoplasmas usually induce an inflammatory response and a humoral response preferentially directed against their membrane-bound, surface-exposed lipoproteins. In this report, we describe the effects on immune cells of spiralin, a well-characterized mycoplasmal lipoprotein. Purified spiralin stimulated the in vitro proliferation of human peripheral blood mononuclear cells and murine splenocytes. The stimulation pathway was probably different from that followed by Escherichia coli lipopolysaccharide because the effect of spiralin was not abolished by polymyxin B. Comparison of the effects of whole, native spiralin with those induced by proteinase K-digested spiralin or by the C-terminal half of spiralin (peptide p[13.5]T) revealed that the first half of the protein, which contains the lipoylated N terminus, is responsible for the mitogenic activity. In contrast to whole spiralin, proteinase K-digested spiralin did not trigger murine B-cell differentiation and immunoglobulin G and M secretion. Stimulation of human or murine immune cells led to early secretion of proinflammatory cytokines (human tumor necrosis factor alpha and murine interleukin 1 or 6). Spiralin induced the T-cell-independent blastogenesis of murine B cells but did not stimulate T cells. Altogether, our data demonstrate that spiralin possesses potent immunostimulating activity, similar to that reported for lipoproteins of pathogenic gracilicutes (gram-negative eubacteria; e.g., Borrelia burgdorferi OspA and E. coli Braun lipoprotein), and are consistent with the fact that lipoproteins are major antigens during mycoplasma infections.