Lupus nephritis: toll the trigger!
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Autoantigens↗
Biomedical subjects
Kelly D Smith
Publications and source records attributed to Kelly D Smith.
The pathogen-associated iroA gene cluster mediates bacterial evasion of lipocalin 2.
Numerous bacteria cope with the scarcity of iron in their microenvironment by synthesizing small iron-scavenging molecules known as siderophores. Mammals have evolved countermeasures to block siderophore-mediated iron acquisition as part of their innate immune response. Secreted lipocalin 2 (Lcn2) sequesters the Escherichia coli siderophore enterobactin (Ent), preventing E. coli from acquiring iron and protecting mammals from infection by E. coli. Here, we show that the iroA gene cluster, found in many pathogenic strains of Gram-negative enteric bacteria, including E. coli, Salmonella spp., and Klebsiella pneumoniae, allows bacteria to evade sequestration of Ent by Lcn2. We demonstrate that C-glucosylated derivatives of Ent produced by iroA-encoded enzymes do not bind purified Lcn2, and an iroA-harboring strain of E. coli is insensitive to the growth inhibitory effects of Lcn2 in vitro. Furthermore, we show that mice rapidly succumb to infection by an iroA-harboring strain of E. coli but not its wild-type counterpart, and that this increased virulence depends on evasion of host Lcn2. Our findings indicate that the iroA gene cluster allows bacteria to evade this component of the innate immune system, rejuvenating their Ent-mediated iron-acquisition pathway and playing an important role in their virulence.
Acute-Phase Proteins↗
Dual ligand stimulation of RAW 264.7 cells uncovers feedback mechanisms that regulate TLR-mediated gene expression.
To characterize how signaling by TLR ligands can be modulated by non-TLR ligands, murine RAW 264.7 cells were treated with LPS, IFN-gamma, 2-methyl-thio-ATP (2MA), PGE(2), and isoproterenol (ISO). Ligands were applied individually and in combination with LPS, for 1, 2, and 4 h, and transcriptional changes were measured using customized oligo arrays. We used nonadditive transcriptional responses to dual ligands (responses that were reproducibly greater or less than the expected additive responses) as a measure of pathway interaction. Our analysis suggests that cross-talk is limited; <24% of the features with significant responses to the single ligands responded nonadditively to a dual ligand pair. PGE(2) and ISO mainly attenuated, while 2MA enhanced, LPS-induced transcriptional changes. IFN-gamma and LPS cross-regulated the transcriptional response induced by each other: while LPS preferentially enhanced IFN-gamma-induced changes in gene expression at 1 h, IFN-gamma signaling primarily attenuated LPS-induced changes at 4 h. Our data suggest specific cross-talk mechanisms: 1) LPS enhances the expression of IFN-gamma-response genes by augmenting STAT1 activity and by activating NF-kappaB, which synergizes with IFN-gamma-induced transcriptional factors; 2) IFN-gamma attenuates the late LPS transcriptional response by increasing the expression of suppressor of cytokine signaling 1 and cytokine-inducible SH2-containing protein expression; 3) 2MA modulates LPS secondary transcriptional response by increasing IFN-beta and inhibiting IL-10 gene expression; 4) PGE(2) and ISO similarly regulate the LPS transcriptional response. They increase IL-10 transcription, resulting in attenuated expression of known IL-10-suppressed genes.
Adenosine Triphosphate↗
Myeloid differentiation primary response gene (88)- and toll-like receptor 2-deficient mice are susceptible to infection with aerosolized Legionella pneumophila.
BACKGROUND: Toll-like receptors (TLRs) are a family of proteins that orchestrate innate immune responses to microbes. Although pathogens are typically recognized by multiple TLRs, the specific roles of individual TLRs in mediating host protection during in vivo infection are not well understood. METHODS: We compared the roles of myeloid differentiation primary response gene (88) (MyD88), which regulates signaling through multiple TLRs, and TLR2 in mediating resistance to aerosolized Legionella pneumophila infection in vivo. RESULTS: In comparison with wild-type mice, MyD88-deficient (MyD88(-/-)) mice had dramatically higher bacterial counts in the lungs, with decreased neutrophil counts in the bronchoalveolar lavage fluid as well as absent cytokine and chemokine production at early time points. By day 6 of infection, the MyD88(-/-) mice developed organizing pneumonia with dissemination of L. pneumophila to the lymph nodes and spleen. TLR2(-/-) mice were also more susceptible to L. pneumophila, with higher bacterial counts in the lung. However, TLR2(-/-) mice produced proinflammatory cytokines, recruited neutrophils to the lung alveoli, and cleared the infection without progression to organizing pneumonia and disseminated disease. CONCLUSIONS: These results suggest that a MyD88-dependent pathway is required for eradication of L. pneumophila and prevention of organizing pneumonia. TLR2 mediates partial resistance to L. pneumophila, which indicates that additional MyD88-dependent, TLR2-independent pathways are essential for full protection.
Adaptor Proteins, Signal Transducing↗
Membranous glomerulopathy with spherules: an uncommon variant with obscure pathogenesis.
BACKGROUND: Occasional case reports of membranous glomerulopathy described unique subepithelial accumulations of an unusual type of immune deposit composed of spherular structures. The identity of such structures as nuclear pores has been suggested, but not established. METHODS: We identified a cohort of patients (n = 14, including 1 patient with disease recurrence in an allograft) who presented with nephrotic syndrome and had renal biopsy specimens with light and immunofluorescence microscopic findings characteristic of membranous glomerulopathy. These patients were distinguished by ultrastructural studies that showed glomerular capillary wall accumulations of subepithelial immune deposits composed of uniform spherular structures, while lacking the typical granular electron-dense deposits seen in membranous glomerulopathy. The molecular identity of these spherular structures as nuclear pores was tested by using immunofluorescence microscopy and immunohistochemistry with mouse monoclonal antinuclear pore antibodies (Covance, Princeton, NJ) and anti-Nuclear Pore-O-Linked Glycoprotein (Affinity BioReagents Inc, Golden, CO) antibodies. RESULTS: Measurement of spherular structures by using high-magnification electron microscopy showed an average diameter of 84.5 nm, which correlated well with accepted diameters of nuclear pores (80 to 120 nm). Immunofluorescence microscopy and immunoperoxidase staining with both antibodies showed characteristic beaded staining of nuclear membranes of multiple cell types within normal control kidney, but no staining of immune-type deposits within glomerular basement membranes. CONCLUSION: These cases form a rare, but distinctive, morphological subclass of membranous glomerulopathy. The antigenic specificity of immune deposits in these cases remains elusive.
Adult↗
Nodular glomerulopathy in a 50-year-old diabetic man.
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Capillaries↗
The evolution of vertebrate Toll-like receptors.
The complete sequences of Takifugu Toll-like receptor (TLR) loci and gene predictions from many draft genomes enable comprehensive molecular phylogenetic analysis. Strong selective pressure for recognition of and response to pathogen-associated molecular patterns has maintained a largely unchanging TLR recognition in all vertebrates. There are six major families of vertebrate TLRs. This repertoire is distinct from that of invertebrates. TLRs within a family recognize a general class of pathogen-associated molecular patterns. Most vertebrates have exactly one gene ortholog for each TLR family. The family including TLR1 has more species-specific adaptations than other families. A major family including TLR11 is represented in humans only by a pseudogene. Coincidental evolution plays a minor role in TLR evolution. The sequencing phase of this study produced finished genomic sequences for the 12 Takifugu rubripes TLRs. In addition, we have produced >70 gene models, including sequences from the opossum, chicken, frog, dog, sea urchin, and sea squirt.
Animals↗
Evasion of Toll-like receptor 5 by flagellated bacteria.
Toll-like receptor 5 (TLR5) recognizes an evolutionarily conserved site on bacterial flagellin that is required for flagellar filament assembly and motility. The alpha and epsilon Proteobacteria, including the important human pathogens Campylobacter jejuni, Helicobacter pylori, and Bartonella bacilliformis, require flagellar motility to efficiently infect mammalian hosts. In this study, we demonstrate that these bacteria make flagellin molecules that are not recognized by TLR5. We map the site responsible for TLR5 evasion to amino acids 89-96 of the N-terminal D1 domain, which is centrally positioned within the previously defined TLR5 recognition site. Salmonella flagellin is strongly recognized by TLR5, but mutating residues 89-96 to the corresponding H. pylori flaA sequence abolishes TLR5 recognition and also destroys bacterial motility. To preserve bacterial motility, alpha and epsilon Proteobacteria possess compensatory amino acid changes in other regions of the flagellin molecule, and we engineer a mutant form of Salmonella flagellin that evades TLR5 but retains motility. These results suggest that TLR5 evasion is critical for the survival of this subset of bacteria at mucosal sites in animals and raise the intriguing possibility that flagellin receptors provided the selective force to drive the evolution of these unique subclasses of bacterial flagellins.
Amino Acid Sequence↗
Dissecting innate immune responses with the tools of systems biology.
Systems biology strives to derive accurate predictive descriptions of complex systems such as innate immunity. The innate immune system is essential for host defense, yet the resulting inflammatory response must be tightly regulated. Current understanding indicates that this system is controlled by complex regulatory networks, which maintain homoeostasis while accurately distinguishing pathogenic infections from harmless exposures. Recent studies have used high throughput technologies and computational techniques that presage predictive models and will be the foundation of a systems level understanding of innate immunity.
Animals↗
Polyomavirus nephropathy in native kidneys of non-renal transplant recipients.
Chronic renal dysfunction is common in non-renal solid organ (SOT) and hematopoietic stem cell transplant (HSCT) recipients and is commonly attributed to calcineurin inhibitor toxicity, often without renal histopathologic evaluation. Polyomavirus nephropathy (PVN) is an important cause of allograft dysfunction in kidney transplant recipients but has rarely been reported in native kidneys of non-renal transplant recipients. We report the clinical, pathologic and virologic features of PVN in native kidneys of two allograft recipients. In both, severe renal dysfunction was accompanied by histopathologic evidence of PVN, including characteristic viral inclusions by routine stains, immunohistochemistry and electron microscopy. High levels of BK virus (BKV) DNA were detected in kidney tissue of patients using BKV-specific polymerase chain reaction (PCR). In 1 patient, high levels of BKV DNA were detected in plasma and urine, and administration of low-dose cidofovir was associated with clearance of BK viremia. These results extend the populations in which PVN has been documented in native kidneys to include heart and stem cell transplant recipients, and suggest that cidofovir has activity against BKV in vivo. Studies to define the incidence and potential contribution of PVN to chronic renal dysfunction commonly attributed to calcineurin inhibitor toxicity in non-renal transplant recipients are warranted.
Adult↗
IgA nephropathy with crescents in kidney transplant recipients.
BACKGROUND: Crescentic glomerulonephritis is an uncommon finding in renal allografts. Recurrence or de novo mesangial deposition of immunoglobulin A (IgA) in renal allografts most often is clinically benign, but some case reports have shown that IgA nephropathy in renal allografts can present as crescentic glomerulonephritis and may lead to rapid deterioration of graft function and/or graft loss. METHODS: We reviewed diagnoses of all allograft biopsies at University of Washington Medical Center (Seattle, WA) from 1989 to 2003 and found 33 cases of glomerulonephritis with crescents. Eight of these cases were the result of recurrent or de novo IgA nephropathy. Clinical and pathological features of these patients were reviewed. RESULTS: Six of 8 cases with crescents were the result of recurrent IgA nephropathy, and 2 cases were presumptive de novo IgA nephropathy. Of the 8 patients with IgA nephropathy with crescents, 6 patients presented clinically with increasing serum creatinine levels; 4 patients, with proteinuria; and 4 patients, with hematuria. In 6 patients, there was 10% to 30% involvement of glomeruli, with crescents partially or completely filling urinary spaces. The other patients showed lesser (approximately 7% of sampled glomeruli) involvement. Four patients with IgA nephropathy with crescents developed renal failure and returned to hemodialysis therapy. Three patients had a benign clinical course, with stabilization of renal function. One patient was lost to follow-up. CONCLUSION: We identified a cohort of patients with glomerulonephritis with crescents in renal allografts with IgA nephropathy as the cause. In half the affected patients, this led to early progressive renal insufficiency and return to hemodialysis therapy.
Adult↗
Pathogenic mechanisms in membranoproliferative glomerulonephritis.
PURPOSE OF REVIEW: This review considers new information on the pathogenesis of a long recognized and poorly understood form of glomerular injury, membranoproliferative glomerulonephritis. This disease has received growing attention as it is the principal renal manifestation of hepatitis C virus infection, which has become pandemic worldwide. RECENT FINDINGS: This review briefly describes three murine models of membranoproliferative glomerulonephritis suitable for pathogenesis studies. We consider recent evidence implicating innate immune mechanisms in immune and autoimmune-mediated glomerulonephritis, and recent data pointing to the alternative pathway of complement activation in the amplification of glomerulonephritic injury. SUMMARY: Understanding the contribution of complement activation and innate immunity to the evolution of membranoproliferative glomerulonephritis promises to provide new therapeutic targets for this disease. Inhibitors of the complement cascade are already being tested in clinical trials as therapeutic interventions for some human glomerular diseases. Successful tests of this approach in membranoproliferative glomerulonephritis are still awaited. Our understanding of how the innate immune system modulates glomerulonephritis is still in an early stage, and future studies should be directed at identifying targets and specific interventions that may also benefit patients with this disease.
Animals↗
CD4+ T cells and toll-like receptors recognize Salmonella antigens expressed in bacterial surface organelles.
A better understanding of immunity to infection is revealed from the characteristics of microbial ligands recognized by host immune responses. Murine infection with the intracellular bacterium Salmonella generates CD4+ T cells that specifically recognize Salmonella proteins expressed in bacterial surface organelles such as flagella and membrane vesicles. These natural Salmonella antigens are also ligands for Toll-like receptors (TLRs) or avidly associated with TLR ligands such as lipopolysaccharide (LPS). PhoP/PhoQ, a regulon controlling Salmonella virulence and remodeling of LPS to resist innate immunity, coordinately represses production of surface-exposed antigens recognized by CD4+ T cells and TLRs. These data suggest that genetically coordinated surface modifications may provide a growth advantage for Salmonella in host tissues by limiting both innate and adaptive immune recognition.
Animals↗
Lipocalin 2 mediates an innate immune response to bacterial infection by sequestrating iron.
Although iron is required to sustain life, its free concentration and metabolism have to be tightly regulated. This is achieved through a variety of iron-binding proteins including transferrin and ferritin. During infection, bacteria acquire much of their iron from the host by synthesizing siderophores that scavenge iron and transport it into the pathogen. We recently demonstrated that enterochelin, a bacterial catecholate siderophore, binds to the host protein lipocalin 2 (ref. 5). Here, we show that this event is pivotal in the innate immune response to bacterial infection. Upon encountering invading bacteria the Toll-like receptors on immune cells stimulate the transcription, translation and secretion of lipocalin 2; secreted lipocalin 2 then limits bacterial growth by sequestrating the iron-laden siderophore. Our finding represents a new component of the innate immune system and the acute phase response to infection.
Acute-Phase Proteins↗
Gangliosides act as co-receptors for Salmonella enteritidis FliC and promote FliC induction of human beta-defensin-2 expression in Caco-2 cells.
Antimicrobial peptides such as defensins are crucial for host defense at mucosal surfaces. We reported previously that Salmonella enteritidis flagellin (FliC) induced human beta-defensin-2 (hBD-2) mRNA expression in Caco-2 cells via NF-kappaB activation (Ogushi, K., Wada, A., Niidome, T., Mori, N., Oishi, K., Nagatake, T., Takahashi, A., Asakura, H., Makino, S., Hojo, H., Nakahara, Y., Ohsaki, M., Hatakeyama, T., Aoyagi, H., Kurazono, H., Moss, J., and Hirayama, T. (2001) J. Biol. Chem. 276, 30521-30526). In this study, we examined the role of ganglioside as co-receptors with Toll-like receptor 5 (TLR5) on FliC induction of hBD-2 expression in Caco-2 cells. Exogenous gangliosides suppressed FliC induction of hBD-2 promoter activity and binding of FliC to Caco-2 cells. Incorporation of exogenous ganglioside GD1a into Caco-2 cell membranes increased the effect of FliC on hBD-2 promoter activity. In support of a role for endogenous gangliosides, incubation of Caco-2 cells with dl-threo-2-hexadecanoylamino-3-morpholino-1-phenylpropanol, a glucosylceramide synthase inhibitor, reduced FliC induction of hBD-2 promoter activity. GD1a-loaded CHO-K1-expressing TLR5 cells had a higher potential for hBD-2 induction following FliC stimulation than GD1a-loaded CHO-K1 cells not expressing TLR5. FliC increased phosphorylation of mitogen-activated protein kinase, p38, and ERK1/2. Exogenous gangliosides GD1a, GD1b, and GT1b each suppressed FliC induction of p38 and ERK1/2 phosphorylation. Furthermore, FliC did not enhance luciferase activity in Caco-2 cells transfected with a plasmid containing a mutated activator protein 1-binding site. These results suggest that gangliosides act as co-receptors with TLR5 for FliC and promote hBD-2 expression via mitogen-activated protein kinase.
Animals↗
A systems approach to dissecting immunity and inflammation.
The immune and inflammatory responses are extraordinarily complex, involving the dynamic interaction of a wide array of tissues, cells, and molecules. Traditional approaches are by and large reductionist, shying away from complexity, but providing detailed knowledge of circumscribed physiologic, cellular and molecular entities. The sequencing of the human genome, in concert with emerging genomic and proteomic technologies permits the definition of a complete and dynamic parts list of the immune and inflammatory systems. When harnessed with powerful new computational approaches, this will for the first time provide a comprehensive description of these complex biological processes.
Computational Biology↗
A common dominant TLR5 stop codon polymorphism abolishes flagellin signaling and is associated with susceptibility to legionnaires' disease.
Although Toll-like receptors (TLRs) are critical mediators of the immune response to pathogens, the influence of polymorphisms in this gene family on human susceptibility to infection is poorly understood. We demonstrated recently that TLR5 recognizes flagellin, a potent inflammatory stimulus present in the flagellar structure of many bacteria. Here, we show that a common stop codon polymorphism in the ligand-binding domain of TLR5 (TLR5392STOP) is unable to mediate flagellin signaling, acts in a dominant fashion, and is associated with susceptibility to pneumonia caused by Legionella pneumophila, a flagellated bacterium. We also show that flagellin is a principal stimulant of proinflammatory cytokine production in lung epithelial cells. Together, these observations suggest that TLR5392STOP increases human susceptibility to infection through an unusual dominant mechanism that compromises TLR5's essential role as a regulator of the lung epithelial innate immune response.
Codon, Terminator↗
Toll-like receptor 5 recognizes a conserved site on flagellin required for protofilament formation and bacterial motility.
Toll-like receptor 5 (TLR5) recognizes bacterial flagellin and activates host inflammatory responses. In this study, we examine the nature of the TLR5-flagellin interaction. With deletional, insertional and alanine-scanning mutagenesis, we precisely mapped the TLR5 recognition site on flagellin to a cluster of 13 amino acid residues that participate in intermolecular interactions within flagellar protofilaments and that are required for bacterial motility. The recognition site is buried in the flagellar filament, and monomeric flagellin, but not the filamentous molecule, stimulated TLR5. Finally, flagellin coprecipitated with TLR5, indicating close physical interaction between the molecules. These studies demonstrate the exquisite ability of the innate immune system to precisely target a conserved site on flagellin that is essential for bacterial motility.
Alanine↗