Autocrine and exocrine regulation of interleukin-10 production in THP-1 cells stimulated with Borrelia burgdorferi lipoproteins.
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We have recently demonstrated that interleukin-10 (IL-10), produced by THP-1 monocytes in response to Borrelia burgdorferi lipoproteins, dampens the production of concomitantly elicited inflammatory cytokines. Thus, IL-10 could potentially down-regulate inflammatory and microbicidal effector mechanisms of the innate immune response to a B. burgdorferi infection, facilitating the establishment of the spirochete. To understand the mechanism(s) implicated in the regulation of the synthesis and release of IL-10 during early infection, we investigated the autocrine effects of IL-6, IL-12, tumor necrosis factor alpha (TNF-alpha), and IL-10 itself, as well as the exocrine effect of IFN-gamma on the production of macrophage-derived IL-10 with lipoprotein as a stimulant. In addition, in view of the differences in the receptor and signal transduction pathways of lipopolysaccharide (LPS) and bacterial lipoproteins, we also investigated the effects described above with LPS as a stimulant. The THP-1 human monocytic cell line and purified recombinant lipidated OspA (L-OspA) were used as the model target cell and stimulant, respectively. TNF-alpha increased the production of IL-10, as elicited by lipoproteins. The production of IL-10 by THP-1 cells stimulated with L-OspA was autoregulated by a negative feedback mechanism involving the IL-10 receptor (IL-10R). Exogenous IFN-gamma significantly inhibited the production of IL-10. Both autocrine (IL-10) and exocrine (IFN-gamma) inhibition of IL-10 production resulted in an increase in the production of the proinflammatory cytokines IL-6 and IL-12. The same results were obtained when the stimulant was LPS. The results further illustrate that IL-10 may play a pivotal role in Lyme disease pathogenesis. Moreover, the regulation of its production with lipoprotein as a stimulant is indistinguishable from that observed when LPS acts as a stimulant. (+info)
Clonal polymorphism of Borrelia burgdorferi strain B31 MI: implications for mutagenesis in an infectious strain background.
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A major obstacle to studying the functions of particular gene products in the mouse-tick infectious cycle of Borrelia burgdorferi has been an inability to knock out genes in pathogenic strains. Here, we investigated conditions for site-directed mutagenesis in B31 MI, the low-passage-number, infectious B. burgdorferi strain whose genome was sequenced. We inactivated several plasmid and chromosomal genes in B31 MI and determined that clones carrying these mutations were not infectious for mice. However, we found extensive heterogeneity among clones and mutants derived from B31 MI based on colony phenotype, growth rate, plasmid content, protein profile, and transformability. Significantly, several B31 MI clones that were not subjected to mutagenesis but that lacked particular plasmids also exhibited defects at various stages in the infectious cycle. Therefore, the high degree of clonal polymorphism within B31 MI complicates the assessment of the contributions of individual genes to the observed phenotypes of the mutants. Our results indicate that B31 MI is not an appropriate strain background for genetic studies in infectious B. burgdorferi, and a well-defined isogenic clone is a prerequisite for targeted mutagenesis. To this end, we derived several wild-type clones from B31 MI that were infectious for mice, and gene inactivation was successful in one of these clones. Due to the instability of the genome with in vitro propagation, careful monitoring of plasmid content of derived mutants and complementation of inactivated genes will be crucial components of genetic studies with this pathogen. (+info)
Vector interactions and molecular adaptations of lyme disease and relapsing fever spirochetes associated with transmission by ticks.
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Pathogenic spirochetes in the genus Borrelia are transmitted primarily by two families of ticks. The Lyme disease spirochete, Borrelia burgdorferi, is transmitted by the slow-feeding ixodid tick Ixodes scapularis, whereas the relapsing fever spirochete, B. hermsii, is transmitted by Ornithodoros hermsi, a fast-feeding argasid tick. Lyme disease spirochetes are generally restricted to the midgut in unfed I. scapularis. When nymphal ticks feed, the bacteria pass through the hemocoel to the salivary glands and are transmitted to a new host in the saliva after 2 days. Relapsing fever spirochetes infect the midgut in unfed O. hermsi but persist in other sites including the salivary glands. Thus, relapsing fever spirochetes are efficiently transmitted in saliva by these fast-feeding ticks within minutes of their attachment to a mammalian host. We describe how B. burgdorferi and B. hermsii change their outer surface during their alternating infections in ticks and mammals, which in turn suggests biological functions for a few surface-exposed lipoproteins. (+info)
Geographic uniformity of the Lyme disease spirochete (Borrelia burgdorferi) and its shared history with tick vector (Ixodes scapularis) in the Northeastern United States.
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Over 80% of reported cases of Lyme disease in the United States occur in coastal regions of northeastern and mid-Atlantic states. The genetic structure of the Lyme disease spirochete (Borrelia burgdorferi) and its main tick vector (Ixodes scapularis) was studied concurrently and comparatively by sampling natural populations of I. scapularis ticks along the East Coast from 1996 to 1998. Borrelia is genetically highly diverse at the outer surface protein ospC. Since Borrelia is highly clonal, the ospC alleles can be used to define clones. A newly designed reverse line blotting (RLB) assay shows that up to 10 Borrelia clones can infect a single tick. The clone frequencies in Borrelia populations are the same across the Northeast. On the other hand, I. scapularis populations show strong regional divergence (among northeastern, mid-Atlantic, and southern states) as well as local differentiation. The high genetic diversity within Borrelia populations and the disparity in the genetic structure between Borrelia and its tick vector are likely consequences of strong balancing selection on local Borrelia clones. Demographically, both Borrelia and I. scapularis populations in the Northeast show the characteristics of a species that has recently expanded from a population bottleneck. Major geological and ecological events, such as the last glacial maximum (18,000 years ago) and the modern-day expansion of tick habitats, are likely causes of the observed "founder effects" for the two organisms in the Northeast. We therefore conclude that the genetic structure of B. burgdorferi has been intimately shaped by the natural history of its main vector, the northern lineage of I. scapularis ticks. (+info)
Borrelia burgdorferi are susceptible to killing by a variety of human polymorphonuclear leukocyte components.
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The killing of Borrelia burgdorferi by intact human polymorphonuclear leukocytes (PMNL) and by individual PMNL components was compared. Intact PMNL killed B. burgdorferi 6.5-fold more efficiently and 5-fold more completely when spirochetes were opsonized with specific antibodies. U-cytoplasts, which have activatable oxidase, killed opsonized B. burgdorferi with an efficiency similar to that of intact PMNL in killing unopsonized B. burgdorferi. Although B. burgdorferi were susceptible to H(2)O(2) and nitric oxide, PMNL lysates killed B. burgdorferi nearly as well as intact PMNL killed opsonized B. burgdorferi, suggesting a critical role for granule contents. B. burgdorferi were killed by the PMNL antimicrobial components elastase, LL-37, bactericidal/permeability-increasing protein, and human neutrophil peptide-1. B. burgdorferi had limited susceptibility to killing by lysozyme and were not killed by azurocidin, proteinase 3, or lactoferrin. The efficient killing of B. burgdorferi by a variety of PMNL mechanisms highlights the paradoxical persistence of spirochetes in vivo. (+info)
Crystal structure of Lyme disease variable surface antigen VlsE of Borrelia burgdorferi.
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VlsE is an outer surface lipoprotein of Borrelia burgdorferi that undergoes antigenic variation through an elaborate gene conversion mechanism and is thought to play a major role in the immune response to the Lyme disease borellia. The crystal structure of recombinant variant protein VlsE1 at 2.3-A resolution reveals that the six variable regions form loop structures that constitute most of the membrane distal surface of VlsE, covering the predominantly alpha-helical, invariant regions of the protein. The surface localization of the variable amino acid segments appears to protect the conserved regions from interaction with antibodies and hence may contribute to immune evasion. (+info)
Recombinant BBK32 protein in serodiagnosis of early and late Lyme borreliosis.
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Borrelial protein BBK32 was evaluated as an antigen in the serodiagnosis of early and disseminated Lyme borreliosis (LB). bbk32 was cloned and sequenced from eight isolates of the three pathogenic Borrelia species. The identities between the amino acid sequences of the BBK32 proteins from Borrelia burgdorferi sensu stricto, B. garinii, and B. afzelii isolates were 71 to 100%. By immunoglobulin G (IgG) Western blotting (WB) or enzyme-linked immunosorbent assay (ELISA), up to 74 and 100% of acute- and convalescent-phase samples, respectively, from 23 patients with erythema migrans (EM) were positive for recombinant BBK32 protein from B. afzelii. In the serology of disseminated LB, the three variant BBK32 antigens cross-reacted. In total, 14 of 14 samples from patients with neuroborreliosis and 15 of 15 samples from patients with Lyme arthritis were positive. The specificities of the IgG ELISA with the variant BBK32 antigens for EM and disseminated borreliosis were 81 to 92% and 89 to 95%, respectively. Our findings indicate that the BBK32 proteins are promising serodiagnostic antigens for the detection of early and disseminated LB but that variant BBK32 proteins may be needed either in parallel or in combination with an immunoassay for LB to cover all the relevant borrelial species that cause the disease. (+info)
Quantitative detection of Borrelia burgdorferi in 2-millimeter skin samples of erythema migrans lesions: correlation of results with clinical and laboratory findings.
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Variability of disease manifestations has been noted in patients with Lyme disease. A contributing factor to this variation may be the number of spirochetes present in infected patients. We evaluated clinical and laboratory findings for patients with erythema migrans with regard to the number of Borrelia burgdorferi organisms detected by quantitative PCR (qPCR) in 2-mm skin biopsy specimens. B. burgdorferi was detected in 80% (40 of 50) of the specimens tested; the mean number of spirochetes in these specimens ranged over 3 orders of magnitude (10 to 11,000 spirochetes per 2-mm biopsy specimen). Larger numbers of spirochetes were significantly associated with a shorter duration of the erythema migrans skin lesion (P = 0.020), smaller skin lesions (P = 0.020), and infection with a specific genotype of B. burgdorferi (P = 0.008) but not with the number or severity of symptoms. Skin culture positivity was significantly associated with skin lesions containing larger numbers of spirochetes (P = 0.019). (+info)