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Biomedical subjects

J Coburn

Publications and source records attributed to J Coburn.

At least 19 recordsLinked to original sources
PubMed2001

Platelet activation by a relapsing fever spirochaete results in enhanced bacterium-platelet interaction via integrin alphaIIbbeta3 activation.

Borrelia hermsii, a spirochaete responsible for relapsing fever in humans, grows to high density in the bloodstream and causes thrombocytopenia. We show here that B. hermsii binds to human platelets. Extended culture in bacteriological medium resulted in both diminished infectivity in vivo and diminished platelet binding in vitro. Platelet binding was promoted by the platelet integrin alphaIIbbeta3: the bacterium bound to purified integrin alphaIIbbeta3, and bacterial binding to platelets was diminished by alphaIIbbeta3 antagonists or by a genetic defect in this integrin. Integrin alphaIIbbeta3 undergoes a conformational change upon platelet activation, and bacteria bound more efficiently to activated rather than resting platelets. Nevertheless, B. hermsii bound at detectable levels to preparations of resting platelets. The bacterium did not recognize a point mutant of alphaIIbbeta3 that cannot acquire an active conformation. Rather, B. hermsii was capable of triggering platelet and integrin alphaIIbbeta3 activation, as indicated by the expression of the platelet activation marker P-selectin and integrin alphaIIbbeta3 in its active conformation. The degree of platelet activation varied depending upon bacterial strain and growth conditions. Prostacyclin I2, an inhibitor of platelet activation, diminished bacterial attachment, indicating that activation enhanced bacterial binding. Thus, B. hermsii signals the host cell to activate a critical receptor for the bacterium, thereby promoting high-level bacterial attachment.

Animals↗
PubMed2001

Recognition of multiple antibody epitopes throughout Borrelia burgdorferi p66, a candidate adhesin, in patients with early or late manifestations of Lyme disease.

Antibody responses to p66, a candidate integrin ligand of Borrelia burgdorferi, were studied in 79 patients with early or late manifestations of Lyme disease. The central portion of p66 was previously shown to contain all of the information required for specific recognition of beta3-chain integrins, but work by others had suggested that the C-terminal portion of the protein contains a single surface-exposed, immunodominant loop. In examining antibody responses to full-length p66 and to three overlapping fragments of the protein, we found that the majority of Lyme disease patients had immunoglobulin M (IgM) and/or IgG responses to p66 and that, particularly early in the disease, epitopes throughout p66 were recognized. Among patients with later manifestations of the illness, antibody responses to the C-terminal portion of the protein were more prominent. These results demonstrate that Lyme disease patient sera recognize epitopes throughout p66.

Antibodies, Bacterial↗
PubMed2000

Mechanism of binding of surfactant protein D to influenza A viruses: importance of binding to haemagglutinin to antiviral activity.

Collectins are important in the initial containment of a variety of pathogens, including influenza A virus (IAV). We provide the first systematic evaluation of the oligosaccharide-binding sites for pulmonary surfactant protein D (SP-D) on specific IAV coat glycoproteins and define the relationship between this binding and antiviral activity. With the use of several techniques, SP-D was found to bind via its carbohydrate-recognition domain (CRD) to mannosylated, N-linked carbohydrates on the HA(1) domain of the haemagglutinin (HA) and on the neuraminidase of IAV. Using a set of IAV strains that differed in the level and site of glycosylation, and a panel of recombinant collectins, we found that binding of SP-D to the globular domain of the HA was critical in mediating the inhibition of viral haemagglutination activity and infectivity. We also demonstrated that the pattern of binding of a collectin to IAV glycoproteins can be modified by altering the monosaccharide-binding affinity of its CRD or by linking the CRD to a different N-terminal/collagen domain. These studies clarify the mechanisms of viral neutralization by collectins and might be useful in engineering collectins for enhanced antiviral activity.

Amidohydrolases↗
PubMed2000

Microbiology. Arresting features of bacterial toxins.

Bacteria produce an arsenal of sophisticated toxins that disrupt the normal processes of the host cell, usually by modifying or inactivating host cell proteins. Now, as Coburn and Leong discuss in their Perspective, members of the cytolethal distending toxin (CDT) family have been identified as enzymes that attack DNA (and not protein) within the host cell (Lara-Tejero and Galán). By attacking DNA, perhaps during chromosomal replication, CDTs cause the host cell to halt in G2 phase of the cell cycle.

Animals↗
PubMed2000

Prominent expression of mRNA for proinflammatory cytokines in synovium in patients with juvenile rheumatoid arthritis or chronic Lyme arthritis.

OBJECTIVE: To examine the cytokine profiles in synovium of patients with juvenile rheumatoid arthritis (JRA) or Lyme arthritis, 2 chronic inflammatory arthritides that affect children. METHODS: We used in situ hybridization with specific riboprobes to determine the expression of mRNA for proinflammatory or antiinflammatory cytokines in synovial samples from 5 patients with early, untreated JRA, 15 patients with late, treated JRA, and 9 patients with chronic Lyme arthritis. For comparison, synovia were examined from 6 patients with rheumatoid or psoriatic arthritis, and from 9 patients with various orthopedic conditions. RESULTS: Among the children with early, untreated JRA, a median of 3 to 8% of inflammatory cells in synovial samples expressed mRNA for the proinflammatory cytokines interleukin 1beta (IL-1beta), tumor necrosis factor-alpha(TNF-alpha), or interferon-gamma (IFN-gamma). Although a median of 3.9% of the cells expressed mRNA for the antiinflammatory cytokine IL-10, none had IL-4 mRNA. Most of the patients with late, treated JRA, chronic Lyme arthritis, rheumatoid, or psoriatic arthritis had mRNA for each of these proinflammatory cytokines in about 1% of the cells, whereas mRNA for the antiinflammatory cytokines was less frequent. The inflammatory cell density was much less in the synovium of patients with various orthopedic conditions, but about 1% of the infiltrating cells expressed mRNA for at least one of the proinflammatory cytokines. CONCLUSION: Patients with early or late JRA or chronic Lyme arthritis have expression of mRNA in synovial tissue primarily for proinflammatory cytokines, with less expression of antiinflammatory cytokines.

Adult↗
PubMed1999

A natural variant of the cysteine protease virulence factor of group A Streptococcus with an arginine-glycine-aspartic acid (RGD) motif preferentially binds human integrins alphavbeta3 and alphaIIbbeta3.

The human pathogenic bacterium group A Streptococcus produces an extracellular cysteine protease [streptococcal pyrogenic exotoxin B (SpeB)] that is a critical virulence factor for invasive disease episodes. Sequence analysis of the speB gene from 200 group A Streptococcus isolates collected worldwide identified three main mature SpeB (mSpeB) variants. One of these variants (mSpeB2) contains an Arg-Gly-Asp (RGD) sequence, a tripeptide motif that is commonly recognized by integrin receptors. mSpeB2 is made by all isolates of the unusually virulent serotype M1 and several other geographically widespread clones that frequently cause invasive infections. Only the mSpeB2 variant bound to transfected cells expressing integrin alphavbeta3 (also known as the vitronectin receptor) or alphaIIbbeta3 (platelet glycoprotein IIb-IIIa), and binding was blocked by a mAb that recognizes the streptococcal protease RGD motif region. In addition, mSpeB2 bound purified platelet integrin alphaIIbbeta3. Defined beta3 mutants that are altered for fibrinogen binding were defective for SpeB binding. Synthetic peptides with the mSpeB2 RGD motif, but not the RSD sequence present in other mSpeB variants, blocked binding of mSpeB2 to transfected cells expressing alphavbeta3 and caused detachment of cultured human umbilical vein endothelial cells. The results (i) identify a Gram-positive virulence factor that directly binds integrins, (ii) identify naturally occurring variants of a documented Gram-positive virulence factor with biomedically relevant differences in their interactions with host cells, and (iii) add to the theme that subtle natural variation in microbial virulence factor structure alters the character of host-pathogen interactions.

Alleles↗
PubMed1999

Lack of Borrelia burgdorferi DNA in synovial samples from patients with antibiotic treatment-resistant Lyme arthritis.

OBJECTIVE: To determine whether Borrelia burgdorferi DNA may be detected in synovial tissue from patients with Lyme arthritis who have persistent synovial inflammation after antibiotic treatment. METHODS: Synovial specimens obtained at synovectomy from 26 patients with antibiotic treatment-resistant Lyme arthritis and from 10 control subjects were tested for B burgdorferi DNA using 3 primer-probe sets that target genes encoding outer surface proteins A or B or a flagellar protein (P41) of the spirochete. RESULTS: The 26 patients with Lyme arthritis, who had received antibiotic therapy for a mean total duration of 8 weeks prior to synovectomy, and the 10 control subjects each had negative polymerase chain reaction (PCR) results in synovial samples. When the samples were spiked with approximately 1-10 B burgdorferi, all but 1 had positive PCR results, suggesting that spirochetal DNA could have been detected in most of the unspiked samples if it had been present. CONCLUSION: These results indicate that synovial inflammation may persist in some patients with Lyme arthritis after the apparent eradication of the spirochete from the joint with antibiotic therapy.

Adolescent↗
PubMed1999

Characterization of a candidate Borrelia burgdorferi beta3-chain integrin ligand identified using a phage display library.

The spirochaetal agents of Lyme disease, Borrelia burgdorferi (sensu lato) bind to integrins alphaIIbbeta3, alphavbeta3 and alpha5beta1 in purified form and on the surfaces of human cells. Using a phage display library of B. burgdorferi (sensu stricto) DNA, a candidate ligand for beta3-chain integrins was identified. The native B. burgdorferi protein, termed p66, is known to be recognized by human Lyme disease patient sera and to be expressed on the surface of the spirochaete. We show here that recombinant p66 binds specifically to beta3-chain integrins and inhibits attachment of intact B. burgdorferi to the same integrins. When expressed on the surface of Escherichia coli, this protein increases the attachment of E. coli to a transfected cell line that expresses alphavbeta3, but not to the parental cell line, which expresses no beta3-chain integrins. Localization of p66 on the surface of B. burgdorferi, the ability of recombinant forms of the protein to bind to beta3-chain integrins and the fact that p66 and B. burgdorferi bind to beta3-chain integrins in a mutually exclusive manner make p66 an attractive candidate bacterial ligand for integrins alphaIIbbeta3 and alphavbeta3.

ATP-Binding Cassette Transporters↗
PubMed1999

Macrophages and epithelial cells respond differently to the Pseudomonas aeruginosa type III secretion system.

The multiple effects of Pseudomonas aeruginosa type III secretion have largely been attributed to variations in cytotoxin expression between strains. Here we show that the target cell type is also important. While lung epithelial cells showed significant changes in morphology but not viability when infected with P. aeruginosa, macrophages were efficiently killed by P. aeruginosa. Both responses were dependent on the type III secretion system.

3T3 Cells↗
PubMed1998

Different classes of proteoglycans contribute to the attachment of Borrelia burgdorferi to cultured endothelial and brain cells.

The Lyme disease spirochete, Borrelia burgdorferi, infects multiple tissues, such as the heart, joint, skin, and nervous system and has been shown to recognize heparan sulfate and dermatan sulfate proteoglycans. In this study, we examined the contribution of different classes of proteoglycans to the attachment of the infectious B. burgdorferi strain N40 to several immortalized cell lines and primary cultured cells, including endothelial cells and brain cells. Bacterial attachment was inhibited by exogenous proteoglycans or by treatment of host cells with inhibitors of proteoglycan synthesis or sulfation, indicating that proteoglycans play a critical role in bacterial binding to diverse cell types. Binding to primary bovine capillary endothelial cells or a human endothelial cell line was also inhibited by digestion with heparinase or heparitinase but not with chondroitinase ABC. In contrast, binding to glial cell-enriched brain cell cultures or to a neuronal cell line was inhibited by all three lyases. Binding of strain N40 to immobilized heparin could be completely inhibited by dermatan sulfate, and conversely, binding to dermatan sulfate could be completely blocked by heparin. As measured by 50% inhibitory dose, heparin was a better inhibitor of binding than dermatan sulfate, regardless of whether the substrate was heparin or dermatan sulfate. These results are consistent with the hypotheses that the species of proteoglycans recognized by B. burgdorferi vary with cell type and that bacterial recognition of different proteoglycans is mediated by the same bacterial molecule(s).

Animals↗
PubMed1998

Integrins alpha(v)beta3 and alpha5beta1 mediate attachment of lyme disease spirochetes to human cells.

Borrelia burgdorferi (sensu lato), the agent of Lyme disease, is able to cause chronic, multisystemic infections in human and animal hosts. Attachment of the spirochete to host cells is likely to be important for the colonization of diverse tissues. The platelet-specific integrin alpha(IIb)beta3 was previously identified as a receptor for all three species of Lyme disease spirochetes (B. burgdorferi sensu stricto, B. garinii, and B. afzelii). Here we show that B. burgdorferi also recognizes the widely expressed integrins alpha(v)beta3 and alpha5beta1, known as the vitronectin and fibronectin receptors, respectively. Three representatives of each species of Lyme disease spirochete were tested for the ability to bind to purified alpha(v)beta3 and alpha5beta1. All of the strains tested bound to at least one integrin. Binding to one integrin was not always predictive of binding to other integrins, and several different integrin preference profiles were identified. Attachment of the infectious B. burgdorferi strain N40 to purified alpha(v)beta3 and alpha5beta1 was inhibited by RGD peptides and the appropriate receptor-specific antibodies. Binding to alpha(v)beta3 was also shown by using a transfected cell line that expresses this receptor but not alpha(IIb)beta3. Attachment of B. burgdorferi N40 to human erythroleukemia cells and to human saphenous vein endothelial cells was mediated by both alpha5beta1 and alpha(v)beta3. Our results show that multiple integrins mediate attachment of Lyme disease spirochetes to host cells.

Bacterial Adhesion↗
PubMed1997

Destructive spondyloarthropathy of the cervical spine in patients with chronic renal failure.

STUDY DESIGN: Eleven patients with chronic renal failure and destructive spondyloarthropathy of the cervical spine were evaluated with plain radiographs, flexion-extension views, computed tomography myelogram, or magnetic resonance imaging to determine the results of surgical and nonsurgical treatment. OBJECTIVES: To determine if cervical spine fusion is an effective method of treatment for patients with chronic renal failure and destructive spondyloarthropathy. SUMMARY OF BACKGROUND DATA: Several reports have described the pathogenesis and appearance of this condition, but little has been reported about the orthopedic management of destructive spondyloarthropathy of the cervical spine. METHODS: Three patients had no spinal surgery, three patients had laminectomies alone, three patients had laminectomies with anterior fusions, and two patients had laminectomies with posterior fusions. Radiographs, computed tomography myelograms, and magnetic resonance images were evaluated to determine the results of treatment. Histologic examinations were performed in two patients. RESULTS: Patients with laminectomy alone had no improvement in pain or neurologic function (one died in the immediate postoperative period), one of three patients with anterior fusions had some improvement (one died in the immediate postoperative period), and both of those patients with posterior fusions improved, although both died within a year of surgery from unrelated causes. CONCLUSIONS: Even though the osteopenia present in patients with chronic renal failure tends to allow wire pull-out and makes internal fixation of the spine difficult, successful cervical spinal fusion can relieve pain and improve neurologic deficits in selected patients with chronic renal failure and destructive spondyloarthropathy, allowing them to remain more active for longer periods of time.

Aged↗
PubMed1995

Hemagglutination and proteoglycan binding by the Lyme disease spirochete, Borrelia burgdorferi.

The ability of the Lyme disease spirochete to attach to host components may contribute to its ability to infect diverse tissues. We present evidence that the Lyme disease spirochete expresses a lectin activity that promotes agglutination of erythrocytes and bacterial attachment to glycosaminoglycans. Among a diverse collection of 21 strains of Lyme disease spirochete, hemagglutinating activity was easily detected in all but 3 strains, and these three strains were noninfectious. The ability to agglutinate erythrocytes was associated with the ability of the spirochete to bind to the sulfated polysaccharide dextran sulfate and to mammalian cells. Soluble dextran sulfate was a potent inhibitor of both hemagglutination and attachment to mammalian cells, while dextran had no effect on either activity, suggesting that dextran sulfate may inhibit attachment by mimicking host cell glycosaminoglycans. Consistent with this, the spirochete bound to immobilized heparin, and soluble heparin inhibited bacterial adhesion to mammalian cells. The bacterium did not bind efficiently to Vero cells treated with heparinase or heparitinase or to mutant CHO cell lines that are deficient in proteoglycan synthesis. Sulfation of glycosaminoglycans was critical for efficient bacterial recognition, as Vero cells treated with an inhibitor of sulfation, or a mutant CHO cell line that produces undersulfated heparan sulfate, did not mediate maximal spirochetal binding. Binding of the spirochete to extracellular matrix also appeared to be dependent upon this attachment pathway. These findings suggest that a glycosaminoglycan-binding activity which can be detected by hemagglutination contributes to the attachment of the Lyme disease spirochete to host cells and matrix.

Animals↗
PubMed1994

Calreticulin is released from activated neutrophils and binds to C1q and mannan-binding protein.

The Ca2+ storage protein calreticulin is associated with the endoplasmic reticulum and shares a high degree of amino acid homology with the surface receptor C1q-R. In this study, flow cytometric analysis detected calreticulin on the neutrophil surface, which decreased during stimulation probably as a consequence of shedding, as calreticulin was found by ELISA in the cell supernatants of stimulated cells. Antibodies raised against C1q-R and calreticulin demonstrated a high degree of immunological cross-reactivity for purified calreticulin as determined by dot blot analysis. Western blots of neutrophil subcellular fractions located calreticulin in both the cytosol and cell membrane fractions; C1q-R was largely confined to the cell membrane. Calreticulin and C1q-R both bind to C1q and mannan-binding protein. Therefore, calreticulin may be shed on cell activation and may be associated with the cell membrane, where it can potentially interact with C1q and serum lectins. The implications of this are discussed.

Calcium-Binding Proteins↗
PubMed1994

Diverse Lyme disease spirochetes bind integrin alpha IIb beta 3 on human platelets.

Lyme disease is a chronic, multisystemic infection caused by Borrelia burgdorferi sensu lato. An infectious strain of B. burgdorferi was previously shown to bind to human platelets via the integrin alpha IIb beta 3. In this study, a diverse group of Lyme disease spirochetes was tested for platelet- and alpha IIb beta 3-binding activity. This collection included representatives of each of the three species that cause Lyme disease, B. burgdorferi (sensu stricto), B. garinii, and B. afzelii. Strains were characterized for infectivity in mouse models or were low-passage isolates from human patients. Each of the 11 infectious strains bound to platelets immobilized in microtiter wells and in suspension. Binding to platelets in suspension was specifically inhibited by a blocking anti-alpha IIb beta 3 antibody, and representatives of each species bound to purified alpha IIb beta 3. The strains that did not bind alpha IIb beta 3 or platelets were all noninfectious. No obvious relationship was observed between binding to platelets and expression of the bacterial outer surface protein OspA, OspB, or OspC, as assessed by immunoblotting. These results demonstrate that integrin alpha IIb beta 3-binding activity is widespread among the Borrelia species that cause Lyme disease and are consistent with a role for alpha IIb beta 3 binding in the transmission and/or pathogenesis of Lyme disease.

Antigens, Bacterial↗
PubMed1993

Integrin alpha IIb beta 3 mediates binding of the Lyme disease agent Borrelia burgdorferi to human platelets.

Lyme disease is a chronic, multisystemic infection caused by the tick-borne spirochete Borrelia burgdorferi. Attachment of the spirochete to host cells via specific receptors is likely to be important in the establishment of infection. B. burgdorferi have previously been shown to bind to a variety of mammalian cells in vitro. Here we demonstrate that binding of B. burgdorferi to human platelets is mediated by the integrin alpha IIb beta 3 (glycoprotein IIb-IIIa), a critical receptor in thrombosis and hemostasis. Functional expression of this receptor requires platelet activation, and binding of the spirochete was observed only to activated platelets. Binding was inhibited by a synthetic Arg-Gly-Asp peptide that blocks ligand interaction with many integrins and by a synthetic peptide based on the gamma chain of fibrinogen that blocks binding to alpha IIb beta 3. In addition, attachment of the spirochete to platelets was inhibited by monoclonal antibodies directed against alpha IIb beta 3 that are known to block ligand-receptor interaction. No inhibition was seen with control peptides or with antibodies directed against other platelet receptors. B. burgdorferi bound efficiently to purified alpha IIb beta 3 but did not bind to platelets deficient in this integrin. Efficient platelet binding was displayed by a cloned, infectious B. burgdorferi strain, whereas a cloned noninfectious strain did not bind to platelets. Binding to integrins may be important for the ability of B. burgdorferi to establish infection in the diverse tissues affected by Lyme disease.

Amino Acid Sequence↗
PubMed1993

The eukaryotic host factor that activates exoenzyme S of Pseudomonas aeruginosa is a member of the 14-3-3 protein family.

Exoenzyme S (ExoS), which has been implicated as a virulence factor of Pseudomonas aeruginosa, catalyzes transfer of the ADP-ribose moiety of NAD+ to many eukaryotic cellular proteins. Its preferred substrates include Ras and several other 21- to 25-kDa GTP-binding proteins. ExoS absolutely requires a ubiquitous eukaryotic protein factor, termed FAS (factor activating ExoS), for enzymatic activity. Here we describe the cloning and expression of a gene encoding FAS from a bovine brain cDNA library and demonstrate that purified recombinant FAS produced in Escherichia coli activates ExoS in a defined cell-free system. The deduced amino acid sequence of FAS shows that the protein (245 residues, calculated molecular mass 27,743 Da) belongs to a highly conserved, widely distributed eukaryotic protein family, collectively designated as 14-3-3 proteins. Various functions have been reported for members of the 14-3-3 family, including phospholipase A2 activity and regulation of tyrosine hydroxylase, tryptophan hydroxylase, and, possibly, protein kinase C activities. Identification of FAS as a 14-3-3 protein establishes an additional function for this family of proteins--the activation of an exogenous ADP-ribosyltransferase. Elucidation of the precise role of FAS in activating ExoS will contribute to understanding the molecular mechanisms by which P. aeruginosa causes disease.

14-3-3 Proteins↗