Gene expression profiling reveals unique pathways associated with differential severity of lyme arthritis

Gene expression profiles and pathways in skin inflammation induced by three different sensitizers and an irritant

It is often difficult to discriminate between chemically induced skin irritation and sensitization due to their similar clinical, pathological, and immunological responses. More information than that currently available from local lymph node assays (LLNAs), such as data from gene expression and pathway analysis, can provide more insightful data than the assay itself for distinguishing skin sensitization from skin irritation. This study investigated the gene expression profiles and pathways in ear skins of mice topically exposed daily for three consecutive days to the known strong contact sensitizer 1-chloro-2,4-dinitrobenzene, the skin contact sensitizer 2-phenyl-4-ethoxymethylene-5-oxazolone, the skin or respiratory sensitizer toluene 2,4-diisocyanate, or to the non-sensitizing irritant croton oil. All the sensitizers induced histological changes in ear tissues similar to those induced by the croton oil. In gene expression microarrays, sensitizers up-regulated 193 genes and down-regulated 61 genes in ear skin following chemical exposure. 13 genes whose expression was affected by more than two-fold by all three of the sensitizers, but not by the irritant, were selected by microarray analysis. Microarray and real-time RT-PCR analyses revealed that, of these genes, the allergic inflammation-related genes Oasl2 and Zbp1 were up-regulated in skin inflammation by the sensitizers. In gene expression pathway analysis of all the sensitizers and the croton oil, the top functions of the 48 genes were related to cytokine and cytokine receptors interactions, and only two genes (Cxcl9 and Cxcl10) were specific to skin sensitizer-induced skin inflammation. Thus, although contact sensitizer-induced skin inflammation is similar to irritant-induced responses in terms of histological changes and gene expression profiles, the regulation of allergic inflammation-related gene transcripts, such as those of Oasl2 and Zbp1 or Cxcl9 and Cxcl10, could help to discriminate skin sensitization from chemically induced skin inflammation.

Lipidomic analysis of dynamic eicosanoid responses during the induction and resolution of Lyme arthritis

Eicosanoids and other bioactive lipid mediators are indispensable regulators of biological processes, as demonstrated by the numerous inflammatory diseases resulting from their dysregulation, including cancer, hyperalgesia, atherosclerosis, and arthritis. Despite their importance, a robust strategy comparable with gene or protein array technology for comprehensively analyzing the eicosanoid metabolome has not been forthcoming. We have developed liquid chromatography-tandem mass spectrometry methodology that quantitatively and comprehensively analyzes the eicosanoid metabolome and utilized this approach to characterize eicosanoid production during experimental Lyme arthritis in mice infected with the bacterium Borrelia burgdorferi. Eicosanoids were extracted throughout infection from the joints of Lyme arthritis-resistant and -susceptible mice and subjected to lipidomic profiling. We identified temporal and quantitative differences between these mouse strains in the production of eicosanoids, which correlated with differences in arthritis development. The eicosanoid biosynthetic enzyme cyclooxygenase (COX)-2 has been implicated in the regulation of Lyme arthritis pathology, and subsequent lipidomic profiling of B. burgdorferi-infected COX-2(-/-) mice identified reductions not only in COX-2 products but, surprisingly, also significant off-target reductions in 5-lipoxygenase metabolites. Our results demonstrate the utility of a comprehensive lipidomic approach for identifying potential contributors to disease pathology and may facilitate the development of more precisely targeted treatment strategies.

Activation of human monocytes by live Borrelia burgdorferi generates TLR2-dependent and -independent responses which include induction of IFN-beta

It is widely believed that innate immune responses to Borrelia burgdorferi (Bb) are primarily triggered by the spirochete's outer membrane lipoproteins signaling through cell surface TLR1/2. We recently challenged this notion by demonstrating that phagocytosis of live Bb by peripheral blood mononuclear cells (PBMCs) elicited greater production of proinflammatory cytokines than did equivalent bacterial lysates. Using whole genome microarrays, we show herein that, compared to lysates, live spirochetes elicited a more intense and much broader transcriptional response involving genes associated with diverse cellular processes; among these were IFN-β and a number of interferon-stimulated genes (ISGs), which are not known to result from TLR2 signaling. Using isolated monocytes, we demonstrated that cell activation signals elicited by live Bb result from cell surface interactions and uptake and degradation of organisms within phagosomes. As with PBCMs, live Bb induced markedly greater transcription and secretion of TNF-α, IL-6, IL-10 and IL-1β in monocytes than did lysates. Secreted IL-18, which, like IL-1β, also requires cleavage by activated caspase-1, was generated only in response to live Bb. Pro-inflammatory cytokine production by TLR2-deficient murine macrophages was only moderately diminished in response to live Bb but was drastically impaired against lysates; TLR2 deficiency had no significant effect on uptake and degradation of spirochetes. As with PBMCs, live Bb was a much more potent inducer of IFN-β and ISGs in isolated monocytes than were lysates or a synthetic TLR2 agonist. Collectively, our results indicate that the enhanced innate immune responses of monocytes following phagocytosis of live Bb have both TLR2-dependent and -independent components and that the latter induce transcription of type I IFNs and ISGs.

Lyme disease is a tick-borne infectious disorder caused by the spirochetal pathogen Borrelia burgdorferi (Bb). Innate immune responses to Bb are thought to be triggered by the spirochete's outer membrane lipoproteins signaling through cell surface toll-like receptors (TLR1/2). Using a whole genome microarray technique, we showed that live spirochetes elicited a more intense and broader immune response in human peripheral blood mononuclear cells (PBMCs) than could be explained simply by TLR1/2 cell surface stimulation. Of particular interest, live Bb also uniquely induced transcription of type I interferons. In similarly stimulated isolated human monocytes, live Bb generated a greater production of pro- and anti-inflammatory cytokines (TNF-α, IL-6, IL-10 and IL-1β), as well as interferon-β (IFN-β). Secreted IL-18, which like IL-1β requires cytosolic cleavage of its inactive form by activated caspase-1, was generated only in response to live Bb. The cytosolic responses occurred despite evidence that phagocytosed spirochetes were rapidly degraded in phagosomal vacuoles, and unable to escape unscathed into the cell cytosol. We conclude that the innate immune signals generated in human monocytes by phagocytosed spirochetes allow the host to control the bacterium through a number of non-exclusive pathways, that are both TLR2-dependent and -independent, and include a type I interferon response.

Matrix metalloproteinase 9 plays a key role in lyme arthritis but not in dissemination of Borrelia burgdorferi

Borrelia burgdorferi, the causative agent of Lyme arthritis, does not produce any exported proteases capable of degrading extracellular matrix despite the fact that it is able to disseminate from a skin insertion site to infect multiple organs. Prior studies have shown that B. burgdorferi induces the host protease, matrix metalloproteinase 9 (MMP-9), and suggested that the induction of MMP-9 may allow the organism to disseminate and produce local tissue destruction. We examined the role of MMP-9 in dissemination of B. burgdorferi and pathogenesis of Lyme arthritis. In a MMP-9(-/-) mouse model, MMP-9 was not required for the dissemination of the spirochete to distant sites. However, MMP-9(-/-) exhibited significantly decreased arthritis compared to wild-type mice. The decrease in arthritis was not due to an inability to control infection since the spirochete numbers in the joints were identical. Levels of inflammatory chemokines and cytokines were also similar in MMP-9(-/-) and wild-type mice. We examined whether decreased inflammation in MMP-9(-/-) mice may be the result of decreased production of neoattractants by MMP-9-dependent cleavage of collagen. MMP-9 cleavage of type I collagen results in increased monocyte chemoattraction. MMP-9 plays an important role in regulating inflammation in Lyme arthritis, potentially through the cleavage of type I collagen.

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.

A critical role for type I IFN in arthritis development following Borrelia burgdorferi infection of mice

Gene expression analysis previously revealed a robust IFN-responsive gene induction profile that was selectively up-regulated in Borrelia burgdorferi-infected C3H mice at 1 wk postinfection. This profile was correlated with arthritis development, as it was absent from infected, mildly arthritic C57BL/6 mice. In this report we now demonstrate that profile induction in infected C3H scid mice occurs independently of B or T lymphocyte infiltration in the joint tissue. Additionally, type I IFN receptor-blocking Abs, but not anti-IFN-gamma Abs, dramatically reduced arthritis, revealing a critical but previously unappreciated role for type I IFN in Lyme arthritis development. Certain examined IFN-inducible transcripts were also significantly diminished within joint tissue of mice treated with anti-IFNAR1, whereas expression of other IFN-responsive genes was more markedly altered by anti-IFN-gamma treatment. These data indicate that induction of the entire IFN profile is not necessary for arthritis development. These findings further tie early type I IFN induction to Lyme arthritis development, a connection not previously made. Bone marrow-derived macrophages readily induced IFN-responsive genes following B. burgdorferi stimulation, and this expression required a functional type I IFN receptor. Strikingly, induction of these genes was independent of TLRs 2,4, and 9 and of the adapter molecule MyD88. These data demonstrate that the extracellular pathogen B. burgdorferi uses a previously unidentified receptor and a pathway traditionally associated with viruses and intracellular bacteria to initiate transcription of type I IFN and IFN-responsive genes and to initiate arthritis development.

Defining a transcriptional fingerprint of murine splenic B-cell development

B-cell development occurs in a stepwise fashion that can be followed by the expression of B cell-specific surface markers. In this study, we wished to identify proteins that could contribute to the changes in expression of such markers. By using RNA from freshly isolated B220+ cells, we hoped to reduce the effect of artifacts that occur during the isolation and amplification steps necessary to use flow cytometry analysis-sorted subsets in microarray experiments. Analyses comparing expression patterns from B220+ 2-week bone marrow (pro-B, pre-B, immature B cells), 2-week spleen (predominantly transitional cells) and 8-week spleen (mainly mature B cells) yielded hundreds of genes. We also examined the B cell-activating factor (BAFF)-dependent effects on immature splenic B cells by comparing expression patterns in the spleen between 2-week A/J vs 2-week A/WySnJ mice, which lack functional BAFF receptor signaling. Genes that showed the expression differences between spleen and bone marrow samples were then analyzed through quantitative PCR on B-cell subsets isolated using two different sorting protocols. A comparison of the results from our study with the results from other analyses showed not only some overlap of preferentially expressed genes but also an expansion of other genes potentially involved in B-cell development.

Pattern of proinflammatory cytokine induction in RAW264.7 mouse macrophages is identical for virulent and attenuated Borrelia burgdorferi

Lyme disease pathogenesis results from a complex interaction between Borrelia burgdorferi and the host immune system. The intensity and nature of the inflammatory response of host immune cells to B. burgdorferi may be a determining factor in disease progression. Gene array analysis was used to examine the expression of genes encoding cytokines, chemokines, and related factors in the joint tissue of infected C3H/HeJ mice and in a murine macrophage-like cell line in response to a disseminating or attenuated clinical isolate of B. burgdorferi. Both isolates elicited a robust proinflammatory response in RAW264.7 cells characterized by an increase in transcript levels of genes encoding CC and CXC chemokines, proinflammatory cytokines, and TNF superfamily members. Transcription of genes encoding IL-1beta, IL-6, MCP-1, MIP-1alpha, CXCR4, and TLR2 induced in RAW264.7 cells by either live or heat-killed spirochetes did not differ significantly at any time point over a 24-h period, nor was there a difference in the protein levels of IL-10, TNF-alpha, IL-6, and IL-12p70 in culture supernatants. Thus, induction of host macrophage expression of proinflammatory mediators by host macrophages does not contribute to the differential pathogenicity of different B. burgdorferi strains.

Biology of infection with Borrelia burgdorferi

The spirochete Borrelia burgdorferi is a tick-borne obligate parasite whose normal reservoir is a variety of small mammals. Although infection of these natural hosts does not lead to disease, infection of humans can result in Lyme disease as a consequence of the human immunopathologic response to B burgdorferi. Consistent with the pathogenesis of Lyme disease, bacterial products that allow B burgdorferi to replicate and survive seem to be primarily what is required for the bacterium to cause disease in a susceptible host. This article describes the basic biology of B burgdorferi and reviews some of the bacterial components required for infection of and survival in the mammalian and tick hosts.

Gene expression profiling provides insights into the pathways involved in inflammatory arthritis development: murine model of Lyme disease

The spirochete Borrelia burgdorferi, the etiologic agent of Lyme disease, causes severe subacute arthritis in susceptible inbred mouse strains, such as C3H/HeN, but only mild arthritis in resistant strains such as C57BL/6. The degree of Lyme arthritis severity is controlled in part by host genetics and several quantitative trait loci have been identified which contribute to this regulation. In addition, the anti-inflammatory cytokine IL-10 assumes an important role in the control of arthritis in C57BL/6 mice. However, the identification of genes and signaling pathways that dictate arthritis severity has remained elusive. In an attempt to elucidate such genes and pathways, the power of microarray analysis was combined with information gleaned from gene manipulation models. As a result of this approach, two novel gene profiles were identified: an IFN-inducible profile in arthritis-susceptible C3H and IL-10(-/-) mice, and an epidermal/differentiation profile in C57BL/6 mice. Application of this information to TLR2(-/-) mice, which also develop severe arthritis, indicated that they also upregulated IFN-responsive genes. These results provided new insight into the regulation of Lyme arthritis development and illustrated the utility of combining gene expression analyses with genetically manipulated mouse models in unraveling mechanisms underlying specific disease processes.

T cell infiltration is associated with increased Lyme arthritis in TLR2-/- mice

C57BL/6 mice deficient in TLR2 develop more severe arthritis following infection with Borrelia burgdorferi than do wild-type C57BL/6 mice, and this increase is suppressed by the simultaneous presence of the scid mutation. This suggested a requirement for lymphocytes in the development of subacute Lyme arthritis in TLR2(-/-) mice, a feature not commonly associated with this arthritis. The increased pathology of B. burgdorferi-infected TLR2(-/-) mice was also accompanied by an increase in mononuclear cell infiltration. In this study, T cells were found to be responsible for the increase in mononuclear cells in infected TLR2(-/-) C3H mice. Accordingly, transcripts for the IFN-inducible T cell chemokines, CXCL9 and CXCL10, were greatly enhanced in joint tissue from TLR2(-/-) mice, as were transcripts for a prototypical IFN-inducible gene IFN-gamma-induced GTPase (igtp). Treatment of murine synovial cells with sonicated B. burgdorferi resulted in induction of transcripts for chemokines and other IFN-inducible genes, irrespective of the presence of TLR2. The presence of T lymphocytes greatly enhanced the transcriptional response of synovial cells. These results suggest that the increased inflammatory cell infiltration in TLR2(-/-) C3H mice is the result of localized overproduction of T cell attracting chemokines.

Phagocytosis of Borrelia burgdorferi, the Lyme disease spirochete, potentiates innate immune activation and induces apoptosis in human monocytes

We have previously demonstrated that phagocytosed Borrelia burgdorferi induces activation programs in human peripheral blood mononuclear cells that differ qualitatively and quantitatively from those evoked by equivalent lipoprotein-rich lysates. Here we report that ingested B. burgdorferi induces significantly greater transcription of proinflammatory cytokine genes than do lysates and that live B. burgdorferi, but not B. burgdorferi lysate, is avidly internalized by monocytes, where the bacteria are completely degraded within phagolysosomes. In the course of these experiments, we discovered that live B. burgdorferi also induced a dose-dependent decrease in monocytes but not a decrease in dendritic cells or T cells and that the monocyte population displayed morphological and biochemical hallmarks of apoptosis. Particularly noteworthy was the finding that apoptotic changes occurred predominantly in monocytes that had internalized spirochetes. Abrogation of phagocytosis with cytochalasin D prevented the death response. Heat-killed B. burgdorferi, which was internalized as well as live organisms, induced a similar degree of apoptosis of monocytes but markedly less cytokine production. Surprisingly, opsonophagocytosis of Treponema pallidum did not elicit a discernible cell death response. Our combined results demonstrate that B. burgdorferi confined to phagolysosomes is a potent inducer of cytosolic signals that result in (i) production of NF-kappaB-dependent cytokines, (ii) assembly of the inflammasome and activation of caspase-1, and (iii) induction of programmed cell death. We propose that inflammation and apoptosis represent mutually reinforcing components of the immunologic arsenal that the host mobilizes to defend itself against infection with Lyme disease spirochetes.