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Biomedical subjects

A R Berendt

Publications and source records attributed to A R Berendt.

At least 19 recordsLinked to original sources
PubMed2000

Sulfated glycoconjugates enhance CD36-dependent adhesion of Plasmodium falciparum-infected erythrocytes to human microvascular endothelial cells.

A novel adhesive pathway that enhances the adhesion of Plasmodium falciparum-infected erythrocytes (IEs) to endothelial cells has been identified. The sulfated glycoconjugates heparin, fucoidan, dextran sulfate 5000, and dextran sulfate 500 000 caused a dramatic increase in adhesion of IEs to human dermal microvascular endothelial cells. The same sulfated glycoconjugates had little effect on IE adhesion to human umbilical vein endothelial cells, a CD36-negative cell line. The effect was abolished by a monoclonal antibody directed against CD36, suggesting that enhanced adhesion to endothelium is dependent on CD36. No effect was observed on adhesion to purified platelet CD36 cells immobilized on plastic. The same sulfated glycoconjugates enhanced adhesion of infected erythrocytes to COS cells transfected with CD36, and this was inhibited by the CD36 monoclonal antibody. These findings demonstrate a role for sulfated glycoconjugates in endothelial adherence that may be important in determining the location and magnitude of sequestration through endogenous carbohydrates. In addition, they highlight possible difficulties that may be encountered from the proposed use of sulfated glycoconjugates as antiadhesive agents in patients with severe malaria.

Animals↗
PubMed2000

Clinical isolates of Staphylococcus aureus exhibit diversity in fnb genes and adhesion to human fibronectin.

OBJECTIVES: The fibronectin-binding proteins (FnBPs) of Staphylococcus aureus are involved in the pathogenesis of infection, but their characteristics in clinical isolates are incompletely defined. The aim of this study was to evaluate phenotypic and genotypic characteristics of the FnBPs of a large collection of recent isolates. METHODS: The adherence of 163 S. aureus isolates to immobilized fibronectin was compared with that of S. aureus 8325-4 using a microtitre assay. The presence of the genes encoding the fibronectin-binding proteins FnBPA and FnBPB was evaluated by Southern dot blot using probes specific for region A of fnbA or fnbB. RESULTS: The adherence of clinical isolates to fibronectin (expressed as a percentage of the mean adherence of S. aureus 8325-4) was 56%-125% for 155 isolates (95%), and less than 20% for eight isolates (5%). Adherence of the bacterial group associated with orthopaedic implant-associated infection was significantly greater than that for isolates associated with nasal carriage, endocarditis, or septic arthritis/osteomyelitis. Southern dot blot demonstrated that 126/163 isolates had two genes (77%) and 37/163 had one detectable gene (23%). There was no difference in adherence between isolates with one or two fnb, but isolates associated with invasive disease (endocarditis or primary septic arthritis and/or osteomyelitis) were more likely to have two genes. CONCLUSIONS: These data demonstrate diversity in the FnBPs of clinical isolates of S. aureus. The findings suggest that the interplay between pathogenesis and a single virulence determinant is unlikely to be a uniform process across a spectrum of infections. This confirms the need to extend the study of staphylococcal pathogenesis from the laboratory to non-uniform populations of clinically relevant isolates.

Adhesins, Bacterial↗
PubMed1999

Outcome following haemodialysis catheter-related Staphylococcus aureus bacteraemia.

Staphylococcus aureus is a frequent cause of haemodialysis access-related bacteraemia. The propensity for this organism to seed from the bloodstream to distant sites is well recognized, but the rate at which this occurs is poorly defined in patients with removable haemodialysis catheters. This retrospective study identified 47 patients with 50 episodes of S. aureus haemodialysis catheter-related bacteraemia between August 1993 and December 1995. Adverse events were recorded until February 1996. Thirty of 50 episodes (60%) were apparently uncomplicated. Bacterial seeding to heart valves or distant sites was documented in eight episodes (16%), of which six occurred during antibiotic therapy. A further 12 patients had persistent bacteraemia in the absence of a defined focus of infection, the last positive blood culture ranging from 2-19 days (mean 6.6, median 5) after removal of the haemodialysis catheter and commencing appropriate antibiotic treatment. The serious nature of this infection confirms the need for prevention, together with effective strategies for investigation and treatment in this patient population.

Adult↗
PubMed1999

Pyoderma gangrenosum. A diagnosis not to be missed.

We describe a case of pyoderma gangrenosum which presented with severe wound breakdown after elective hip replacement. The patient was treated successfully with minimal wound debridement and steroids. This diagnosis should always be considered when confronted with an enlarging painful skin lesion which does not grow organisms when cultured and fails to respond to antibiotic therapy, especially if there are similar lesions in other sites. In patients who have a past history of pyoderma gangrenosum, prophylactic steroids may be indicated at the time of surgery or may be required early in the postoperative period.

Aged↗
PubMed1998

Prospective evaluation of criteria for microbiological diagnosis of prosthetic-joint infection at revision arthroplasty. The OSIRIS Collaborative Study Group.

A prospective study was performed to establish criteria for the microbiological diagnosis of prosthetic joint infection at elective revision arthroplasty. Patients were treated in a multidisciplinary unit dedicated to the management and study of musculoskeletal infection. Standard multiple samples of periprosthetic tissue were obtained at surgery, Gram stained, and cultured by direct and enrichment methods. With reference to histology as the criterion standard, sensitivities, specificities, and likelihood ratios (LRs) were calculated by using different cutoffs for the diagnosis of infection. We performed revisions on 334 patients over a 17-month period, of whom 297 were evaluable. The remaining 37 were excluded because histology results were unavailable or could not be interpreted due to underlying inflammatory joint disease. There were 41 infections, with only 65% of all samples sent from infected patients being culture positive, suggesting low numbers of bacteria in the samples taken. The isolation of an indistinguishable microorganism from three or more independent specimens was highly predictive of infection (sensitivity, 65%; specificity, 99.6%; LR, 168.6), while Gram staining was less useful (sensitivity, 12%; specificity, 98%; LR, 10). A simple mathematical model was developed to predict the performance of the diagnostic test. We recommend that five or six specimens be sent, that the cutoff for a definite diagnosis of infection be three or more operative specimens that yield an indistinguishable organism, and that because of its low level of sensitivity, Gram staining should be abandoned as a diagnostic tool at elective revision arthroplasty.

Arthroplasty, Replacement, Hip↗
PubMed1998

Systemic endothelial activation occurs in both mild and severe malaria. Correlating dermal microvascular endothelial cell phenotype and soluble cell adhesion molecules with disease severity.

Fatal Plasmodium falciparum malaria is accompanied by systemic endothelial activation. To study endothelial activation directly during malaria and sepsis in vivo, the expression of cell adhesion molecules on dermal microvascular endothelium was examined in skin biopsies and correlated with plasma levels of soluble (circulating) ICAM-1, E-selectin, and VCAM-1 and the cytokine tumor necrosis factor (TNF)-alpha. Skin biopsies were obtained from 61 cases of severe malaria, 42 cases of uncomplicated malaria, 10 cases of severe systemic sepsis, and 17 uninfected controls. Systemic endothelial activation, represented by the up-regulation of inducible cell adhesion molecules (CAMs) on endothelium and increased levels of soluble CAMs (sCAMs), were seen in both severe and uncomplicated malaria and sepsis when compared with uninfected controls. Plasma levels of sICAM-1, sVCAM-1, and sE-selectin correlated positively with the severity of malaria whereas TNF-alpha was raised nonspecifically in malaria and sepsis. Immunohistochemical evidence of endothelial activation in skin biopsies did not correlate with sCAM levels or disease severity. This indicates a background of systemic endothelial activation, which occurs in both mild and severe malaria and sepsis. The levels of sCAMs in malaria are thus not an accurate reflection of endothelial cell expression of CAMs in a particular vascular bed, and other factors must influence their levels during disease.

Adolescent↗
PubMed1997

Intercellular adhesion molecule-1 and CD36 synergize to mediate adherence of Plasmodium falciparum-infected erythrocytes to cultured human microvascular endothelial cells.

We have compared the adhesion of Plasmodium falciparum-infected erythrocytes to human dermal microvascular endothelial cells (HDMEC) and human umbilical vein endothelial cells (HUVEC) and have assessed the relative roles of the receptors CD36 and intercellular adhesion molecule-1 (ICAM-1). HUVEC (a cell line that expresses high levels of ICAM-1 but no CD36) mediate low levels of adhesion, whereas HDMEC (which constitutively express CD36) mediate high levels of adhesion even before ICAM-1 induction ICAM-1 expression leads to yet greater levels of adhesion, which are inhibited both by anti-ICAM-1 and CD36 mAbs, despite no increase in the expression of CD36. The results indicate the presence of a substantial population of infected cells that require the presence of both receptors to establish adhesion. Synergy between these receptors could be demonstrated using a number of parasite lines, but it could not be predicted from the binding of these same parasite lines to purified ICAM-1 and CD36. This phenomenon could not be reproduced using either purified receptors presented on plastic, or formalin-fixed HDMEC, suggesting that receptor mobility is important. This is the first study to demonstrate receptor synergy in malaria cytoadherence to human endothelial cells, a phenomenon necessary for parasite survival and associated with disease severity.

Animals↗
PubMed1997

Characterization of two vaccinia CD36 recombinant-virus-generated monoclonal antibodies (10/5, 13/10): effects on malarial cytoadherence and platelet functions.

Extensive evidence is now available to show that the human CD36 antigen is a cellular receptor for thrombospondin, collagen, modified low-density lipoproteins, and long-chain fatty acids. Moreover, CD36 functions as one of the receptors that mediates the adhesion of Plasmodium-falciparum-infected erythrocytes to microvascular endothelium. In an attempt to identify new functional sites of this surface glycoprotein, anti-CD36 monoclonal antibodies were prepared using a vaccinia CD36 recombinant virus as a highly efficient immunization vector. In functional studies, one of these antibodies (clone 10/5) strongly inhibited the adhesion of P. falciparum-infected erythrocytes to purified CD36. This antibody also potentiated ADP-induced platelet activation. In contrast, a second antibody (clone 13/10) did not affect the cytoadherence of infected erythrocytes or platelet functions. Previous structural work performed on these antibodies has shown that clone 10/5 is directed against an epitope within the CD36 domain 155-183, whereas clone 13/10 interacts with another antigenic determinant defined by amino acids 30-76 [Daviet, L., Buckland, R., Puente Navazo, M. D. & McGregor, J. L. (1995) Biochem. J. 305, 221-224]. Taken together, these current studies show that: (a) the methodology of immunization using recombinant vaccinia virus is a powerful tool in the generation of monoclonal antibodies directed against polyimmunogenic membrane glycoproteins such as CD36; (b) the CD36 domain, recognized by clone 10/5 but not by 13/10, is functionnally important regarding the adhesion of P. falciparum-infected erythrocyte and CD36-dependent platelet activation.

Animals↗
PubMed1997

Molecular identification of a novel fibrinogen binding site on the first domain of ICAM-1 regulating leukocyte-endothelium bridging.

Binding of fibrinogen to intercellular adhesion molecule 1 (ICAM-1) enhances leukocyte adhesion to endothelium by acting as a bridging molecule between the two cell types. Here, a panel of four monoclonal antibodies (mAbs) to ICAM-1 was used to dissect the structure-function requirements of this recognition. All four mAbs bound to ICAM-1 transfectants and immunoprecipitated and immunoblotted ICAM-1 from detergent-solubilized JY lymphocyte extracts. Functionally, mAbs 1G12 and 2D5 inhibited binding of 125I-fibrinogen to ICAM-1-transfectants and abrogated the enhancing effect of fibrinogen on mononuclear cell adhesion to endothelium and transendothelial migration. In contrast, mAbs 3D6 and 6E6 did not affect ICAM-1 recognition of fibrinogen. With respect to other ligands, mAbs 1G12 and 2D5 completely inhibited attachment of Plasmodium falciparum-infected erythrocytes to immobilized recombinant ICAM-1-Fc, whereas they had no effect on LFA-1-dependent T cell binding to ICAM-1-Fc. Conversely, mAbs 3D6 and 6E6 completely abolished LFA-1 binding to ICAM-1-Fc. Epitope assignment using ICAM-1 chimeras and receptor mutants revealed that the fibrinogen-blocking mAbs 1G12 and 2D5 reacted with domain 1 of ICAM-1, and their binding was disrupted by 97 and 70% by mutations of D26 and P70, respectively, whereas mAbs 3D6 and 6E6 bound to domain 2 of ICAM-1. By recognizing a site distinct from that of beta2 integrins Mac-1 or LFA-1, fibrinogen binding to ICAM-1 may provide an alternative pathway of intercellular adhesion and/or modulate integrin-dependent adherence during inflammation and vascular injury.

Antibodies, Monoclonal↗
PubMed1997

PfEMP1, polymorphism and pathogenesis.

The virulence of Plasmodium falciparum relative to the other species of malarial parasite which infect humans is thought to be due to this parasite's ability to adhere to endothelial cells lining small blood vessels and, in some cases, to its ability to form rosettes with uninfected erythrocytes. The latter phenotype has been found more frequently in cases of severe disease. The former property means that only the younger, asexual, intra-erythrocytic forms circulate whereas the more mature developmental stages are sequestered in the vasculature of a variety of organs. When large numbers of parasites accumulate in a vulnerable target organ such as the brain, the the life-threatening condition of cerebral malaria may result. While the factors that control whether or not cerebral malaria develops are not clearly defined, one crucial determinant my be the endothelial receptors utilised by the infecting isolate. Many such receptors have been identified, including CD36, thrombospondin, ICAM-1, VCAM, E-selectin and chondroitin-4-sulphate. The results of laboratory, field, post-mortem and direct receptor-binding studies indicate that, of the receptors currently identified, ICAM-1 binding is more likely to be associated with the development of cerebral malaria. The molecule expressed on the surface of the infected erythrocyte which mediates adherence to endothelium belongs to a large family of clonally variable antigens encoded by the var genes. The evidence for this conclusion and progress in defining the regions of var-gene products responsible to receptor-specific binding are discussed. Finally, the organization of the var genes within and between parasites is discussed in relation to the evolution of the var-gene family and its functions of antigenic variation and endothelial adhesion.

Animals↗
PubMed1997

A high frequency African coding polymorphism in the N-terminal domain of ICAM-1 predisposing to cerebral malaria in Kenya.

The malarial parasite Plasmodium falciparum has acted as a potent selective force on the human genome. The particular virulence of this organism is thought to be due to the adherence of parasitised red blood cells to small vessel endothelium through several receptors, including CD36, thrombospondin and intercellular adhesion molecule 1 (ICAM-1, CD54), and parasite isolates differ in their ability to bind to each. Immunohistochemical studies have implicated ICAM-1 as of potential importance in the pathogenesis of cerebral malaria, leading us to reason that if any single receptor were involved in the development of cerebral malaria, then in view of the high mortality of that complication, natural selection should have produced variants with reduced binding capacity. We therefore sequenced the N-terminal domain of ICAM-1 from a number of Africans and discovered a single mutation present at high frequency. Genotypes at this locus from samples from a case-control study indicated an association of the polymorphism with the severity of clinical malaria such that individuals homozygous for the mutation have increased susceptibility to cerebral malaria with a relative risk of two. These counterintuitive results have implications for the mechanism of malaria pathogenesis, resistance to other infectious agents and transplantation immunology.

Animals↗
PubMed1997

Failure to block adhesion of Plasmodium falciparum-infected erythrocytes to ICAM-1 with soluble ICAM-1.

The adhesion of Plasmodium falciparum-infected erythrocytes is thought to play a central role in the pathogenesis of severe malaria. ICAM-1 has been identified as one of the host receptors for parasitized erythrocytes and has been implicated as being involved in progression to cerebral malaria. Thus, intervention strategies based on the reversal of this interaction could potentially be used to reduce morbidity and mortality. We have investigated the inhibition of the interaction between ICAM-1 and infected erythrocytes by using recombinant soluble ICAM-1 as competitor and find that we are unable to reduce adhesion to ICAM-1 in vitro.

Animals↗
PubMed1996

Safe intravenous antibiotic therapy at home: experience of a UK based programme.

Outpatient i.v. antibiotic therapy is well developed in the United States, largely because of pressures from third-party payers to reduce costs of medical care. We have developed an outpatient i.v. antibiotic programme in Oxford, that has evolved from a desire to provide high quality i.v. therapy to AIDS patients with cytomegalovirus retinitis. We describe the rationale of the service and report on our first two years' experience. We treated 67 consecutive patients (eight with HIV infection) at home with i.v. antibiotics. This resulted in a saving of 2275 hospital days for those patients without HIV infection. HIV positive patients received 69 months of home i.v. therapy. Minor intravascular catheter complications occurred in only five patients (7.5%). The only serious complications were three episodes of catheter-related sepsis (4.5%), all occurring in AIDS patients who had lines in for more than six months. We have shown that home i.v. antibiotic therapy can be delivered safely to patients with a wide variety of infectious problems using the existing network of community nurses in the National Health Service. Essential components to the programme include a multidisciplinary team working between the hospital and community and a written shared care protocol. Such a programme can result in reduced lengths of hospital stay and patient, community nurse and physician satisfaction.

Anti-Bacterial Agents↗
PubMed1994

Plasmodium falciparum: a family of sulphated glycoconjugates disrupts erythrocyte rosettes.

The ability of Plasmodium falciparum-infected erythrocytes to form spontaneous rosettes with uninfected red cells is a parasite adhesion property which has been associated with severe malaria. The mechanism of rosetting remains unknown, but the ability of heparin to disrupt rosettes has been recognised previously. In this paper we show that a group of sulphated glycoconjugates including sulphatide, dextran sulphate, and fucoidan are more effective rosette reversing agents than heparin and are active against both laboratory strains and wild isolates. Other related anionic glycosaminoglycans such as the chondroitin sulphates A, B, and C and hyaluronic acid have no effect on rosette formation. This family of sulphated glycoconjugates which are active against rosettes is also known to inhibit sporozoite invasion of hepatocytes and merozoite reinvasion of erythrocytes, suggesting that sulphated glycoconjugate interaction may be an important process in cell adhesion at different stages in the plasmodial life cycle.

Animals↗