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Biomedical subjects

D Burger

Publications and source records attributed to D Burger.

At least 91 records · Page 5Linked to original sources
PubMed1990

Organ-specific modification of the dose-response relationship of scrapie infectivity.

The dose-response relationships of scrapie strain 263K-infected hamster brain and spleen homogenates were compared to determine if intracerebral end-point titrations of infectivity in these homogenates were measures of the same pathogenic phenomenon. Analysis of the dose-response curves indicated that the average increase in incubation period per 10-fold dilution (i.e., the dilution kinetics) of brain infectivity was significantly different from that of spleen infectivity. This difference contradicted the assumption that the same pathogen or pathogenic mechanisms were responsible for producing disease in each titration. Therefore, the end-point titrations and infectivity titers of the brain and spleen homogenates were measures of two different phenomena. Subsequent passage of a scrapie-infected spleen homogenate demonstrated that the dose-response relationship of scrapie infectivity in this agent-host system was dependent on the organ titrated, not the tissue source or inoculation route of previous passage.

Animals↗
PubMed1990

The epitope(s) recognized by HNK-1 antibody and IgM paraprotein in neuropathy is present on several N-linked oligosaccharide structures on human P0 and myelin-associated glycoprotein.

The mouse monoclonal antibody HNK-1 and the human monoclonal IgM antibody present in patients with polyneuropathy both recognize carbohydrate epitope(s) on human myelin-associated glycoprotein and P0. In the present study, the oligosaccharide structures that bear the antibody epitope(s) were investigated. The extracellular derivative of myelin-associated glycoprotein (dMAG) was purified by immunoaffinity chromatography. P0 was electroeluted from gel slices. Western blot analysis of whole glycoproteins demonstrated that the epitopes for HNK-1 and the human monoclonal IgM antibody were different. The glycopeptides obtained by proteolysis of purified dMAG and P0 were separated and characterized by affinity chromatography on concanavalin A-Sepharose. Both dMAG and P0 displayed heterogeneity in their oligosaccharide structures, i.e., they both contained mainly tri- and tetraantennary oligosaccharides (approximately 80%), although biantennary (10%) and high-mannose and/or hybrid (10%) oligosaccharides were present. The human monoclonal IgM antibody epitope was present on all types of isolated oligosaccharide structures from either dMAG and P0. The HNK-1 epitope was present on all types of oligosaccharide structures of dMAG, whereas it was present only on tri- and tetraantennary structures of P0.

Antibodies, Monoclonal↗
PubMed1989

Human alpha 2-macroglobulin as an inhibitor of insoluble trypsin.

alpha 2-Macroglobulin binds to insoluble trypsin bound on agarose beads inducing a reduction of proteolytic activity of the enzyme towards large substrates such as azocasein. When trypsin was bound on other matrices like sheep red blood cells or latex beads, the inhibition of proteolytic activity by alpha 2-macroglobulin was complete. These results show that alpha 2-macroglobulin inhibits similarly both soluble and insoluble proteinases.

Enzymes, Immobilized↗
PubMed1989

Studies on the human plasma kallikrein-kinin system: alpha-kallikrein does not directly activate blood neutrophils.

alpha-Kallikrein was prepared using an improved purification protocol (Burger, D., Schleuning, W.-D. and Schapira, M. (1986) J. Biol. Chem. 261, 324-327) and was employed to reevaluate our previous observations indicating that kallikrein activates blood neutrophils by a mechanism requiring an uncleaved Mr 52,000 NH2-terminal heavy chain. Cellular activation was evaluated by measuring neutrophil aggregation, release of both vitamin B12 binding capacity and myeloperoxidase, and generation of superoxide anion. Whereas all these indicators were evoked by exposing neutrophils to f-Met-Leu-Phe, phorbol myristate acetate, zymosan activated serum, or the calcium ionophore A 23187, we show here that neutrophils incubated with alpha-kallikrein remained unactivated. Moreover, we demonstrate that this lack of activation is accompanied by an inability of neutrophils to specifically bind alpha-kallikrein.

Binding, Competitive↗
PubMed1989

Rapid epithelial restitution of human and rabbit colonic mucosa.

Rapid epithelial restitution is now considered one of the primary defense mechanisms of the stomach and duodenum. Because there is currently no evidence as to whether restitution occurs in human tissue, this study examined human and rabbit colonic mucosa after superficial injury and monitored the potential difference, alkaline flux, and speed and mechanisms of mucosal restitution as observed with light and electron microscopy. Luminal exposure of the in vivo rabbit colon to 100 mM HCl for 5 min or the in vitro human colon to 10 mM HCl for 10 min caused superficial mucosal injury to 76% of the epithelial surface in the rabbit and 95% in the human. The necrotic epithelial cells detached in sheets from the intact basal lamina and formed a protective mucoid layer. Morphologic evidence of restitution occurred within 15 min after injury in the rabbit and 30 min in the human, as viable nongoblet cells projected lamellipodia and migrated over the denuded basal lamina at a speed of approximately 2 microns/min. One hour after damage 61% of the mucosal surface was still damaged in the rabbit, and 86% of the human mucosal surface was damaged after 2 h. In the following 60 min restitution progressed rapidly, so that only 10% of the surface remained unrepaired in the rabbit after 2 h and 19% in the human after 3 h. Small areas with deeper injury did not repair until 5 h after damage. The potential difference dropped after mucosal injury and did not recover despite morphologic repair. Rapid epithelial restitution is considered to be a basic defense mechanism of the gastrointestinal mucosa that is obviously not necessarily related to the presence of an acidic environment in the stomach or duodenum.

Animals↗
PubMed1989

Molecular interactions of Leishmania promastigote surface protease with human alpha 2-macroglobulin.

The interaction of Leishmania promastigote surface protease (PSP) with the plasmatic protease inhibitor alpha 2-macroglobulin (alpha 2M) was investigated. In plasma, solubilized PSP forms covalent complexes only with alpha 2M, at the exclusion of other protease inhibitors. The formation of complexes is accompanied by the proteolytic cleavage of the alpha 2M subunit and by the transition from the 'slow' to the 'fast' form of alpha 2M. The proteolytic activity of solubilized PSP on azocasein is inhibited by alpha 2M. In contrast, we found no evidence for a specific interaction of alpha 2M with the surface of promastigotes and PSP proteolytic activity on intact cells was not inhibited by alpha 2M.

Animals↗
PubMed1989

In vivo and in vitro characteristics of contagious ecthyma virus isolates: host response mechanism.

Three Vero cell culture-adapted contagious ecthyma virus (CEV) isolates were compared by plaque morphology, ability to induce vesicles in skin and in vivo growth curve characteristics by sampling sequentially experimental skin lesions produced in four sheep and one goat. Two of the isolates (CEV-29A and CEV-378) were from outbreaks of ecthyma in sheep and one (CEV-102) from a human case of orf. When replicating in Vero cells, the viruses exhibited similar growth parameters, but were distinguishable from each other on the basis of plaque morphology. In vivo latent periods for these isolates were 48 h (CEV-29A), 96 h (CEV-102), and 120 h (CEV-378). When isolates CEV-102 and CEV-29A were passaged into another sheep, they produced similar patterns of growth. Isolate CEV-102 produced the highest infectivity titer [1.4 X 10(9) plaque forming units (PFU) g-1], followed by CEV-29A (6.8 X 10(7) PFU g-1) and CEV-378 (2.5 X 10(7) PFU g-1). In addition, these viruses varied in their ability to induce vesicle formation. Virus was no longer detectable at the inoculation sites at 288 h post-infection (PI). We conclude that plaque morphology, ability to induce vesicle formation in the skin and growth curves in the skin can be considered as important criteria to differentiate CEV isolates. A comparison of the growth curves of CEV-378 in the skin of sheep and goats suggested differences in virus-host interaction between the two animal species. Since intravenous injection of 1 X 10(9) PFU of CEV failed to produce lesions in the sham-scarified skin of sheep, virus spread via the hematogenous route from one site to another appears unlikely. No virus-neutralizing antibody or interferons were found in serum samples or in skin homogenates collected between 0 and 24 days PI. Virus-neutralizing antibody was present in the circulation as late as 24 days PI. Lymphocytes collected from CEV-exposed sheep as early as 12 days PI responded specifically to stimulation with CEV antigen. As this was about the time when infectious virus disappeared from the sites, we assume that cell-associated immune mechanisms may play a larger role in virus clearance from skin lesions than virus-neutralizing antibody.

Animals↗
PubMed1989

A syngeneic monoclonal anti-idiotype antibody against HNK-1: characterization and cytotoxic activity in vitro.

A syngeneic, monoclonal, anti-idiotype antibody, G6D9, was raised against the mouse monoclonal IgM HNK-1. G6D9, characterized as an IgG1-kappa, inhibits the binding of HNK-1 to the myelin-associated glycoprotein (MAG). G6D9 does not interfere with the binding of various human monoclonal anti-MAG IgM to their specific antigen. G6D9 binds HNK-1 hybridoma cells on their surface and within their cytoplasm, as demonstrated using indirect immunofluorescence. In the presence of complement, G6D9 is cytotoxic for HNK-1-secreting cells. A cell lysis of 32% was observed and compared to lysis obtained with other antibodies directed against mouse lymphocyte antigens. The use of G6D9 as a tool to study specific cytotoxicity and immunotherapy in vivo is discussed.

Animals↗
PubMed1988

Acousto-optic laser-scanning cytometer.

An instrument has been developed that uses a computer-controlled rapidly scanning laser beam to make cytometric measurements on cells or particles and which can measure low levels of fluorescence when using low-power lasers (Gershman, Hoffman, and O'Connell, "Methods and Apparatus for Analysis of Particles and Cells.") The method used is based upon acousto-optic principles of light diffraction. A vertically polarized 5-mW He-Ne laser is directed into an acousto-optic Bragg cell in which a portion of the incident light undergoes a small angular variation or deflection. Suitable optics focus the beam to a 25 microns diameter spot, at the 1/e2 point, in a sample cuvette while translating the angular variation into a linear scan. The cuvette enclosing the sample is slowly moved (approximately 1 micron/ms) via a stepper drive into the scanning beam while the forward angle light scatter sensor is monitored for the presence of valid signal events. When an event occurs, appropriate software optimizes the position of the focused laser beam onto the cell. Subsequently, scanning is stopped to allow for cell interrogation times that last for milliseconds or longer.

Acoustics↗
PubMed1988

Epidemiological features of Wilms' tumor: results of studies by the International Society of Paediatric Oncology (SIOP).

This descriptive epidemiology study of 1,040 children with Wilms' tumor (WT) registered in the International Society of Paediatric Oncology (SIOP) clinical trials confirms the findings reported by the National Wilms' Tumor Study. The male:female rate was 0.89:1. The mean age at diagnosis of the 43 bilateral cases was significantly younger than children with unilateral renal involvement (32.4 vs 45 months). However, the mean ages of diagnosis for unilateral multicentric and for unicentric WT were very similar. On the other hand, the mean age at diagnosis of children with sporadic aniridia and hypospadias was younger than the mean age of patients with or without other congenital malformations. Thus aniridia as well as hypospadias could be indices of the first mutation, according to the Knudson and Stron hypothesis. WT was reported in two members of each of five families. However, these familial cases were comparable in terms of demographic and clinical features to the nonfamilial ones. These data suggest that the heritable fraction of WT is relatively small and that genetic and environmental factors interact in the development of WT.

Congenital Abnormalities↗
PubMed1987

Biochemical studies on a cell surface determinant involved in T-cell proliferation.

Previous studies have shown that a monoclonal antibody (TH5.2) recognizes a cell-surface determinant which is involved in the proliferative capability of T cells. The work reported here demonstrates that the T-cell-surface antigen recognized by TH5.2 is a glycoprotein of 55,000 to 60,000 molecular weight. The molecule shows a single molecular weight species upon reduction and denaturation, and it contains only a few percent of tunicamycin-sensitive carbohydrate structures. As shown in sequential immunoprecipitation studies, the TH5.2 antigen is on a molecule distinct from the interleukin-2 (Tac) receptor and the T4 molecule. Cell-surface antigenic modulation experiments indicate that the TH5.2 antigen does not comodulate with, and therefore is distinct from, the T3, T4, T8, and Leu-5 T-cell antigens.

Antibodies, Monoclonal↗
PubMed1987

Heat-stable (STa) enterotoxin of enterotoxigenic Escherichia coli: binding of the enterotoxin to coagulated milk and casein.

Oral or intragastric inoculation of the STa enterotoxin of Escherichia coli has been the standard laboratory test for that toxin. We demonstrated that the severity of the secretory response of 2-4-day-old mice to a single dose of the toxin was influenced by weaning of these mice. After oral application of 50-250 fmol of purified, radioiodinated STa toxin (12-13 Ci mmol-1) approximately 55-65% of the administered toxin bound to the stomach contents. Binding of the toxin did not destroy its biological activity. The binding was pH dependent; stomach contents bound 75% of the toxin at pH 2.3 and only 7.4% at pH 10.1. The principle in the stomach contents which bound the toxin was also demonstrated in murine and bovine milk. Further studies with renin-coagulated milk and commercial casein indicated that milk casein bound the toxin. Based on these findings, we speculate that in cases of food-poisoning involving casein-containing foods STa toxin may be present in the absence of cultivable enterotoxigenic E. coli.

Animals↗
PubMed1986

Human plasma prekallikrein. Immunoaffinity purification and activation to alpha- and beta-kallikrein.

Prekallikrein was purified from human plasma with a final yield of 76% using as the principal step adsorption to immobilized chicken antikallikrein IgY. When purified prekallikrein (3.4 microM) was incubated in the presence of beta-Factor XIIa (0.068 microM) for 5 min at 37 degrees C and pH 7.5, alpha-kallikrein was obtained. Upon prolonged incubation (0.5-28 h), the Mr 52,000 heavy chain of alpha-kallikrein was progressively cleaved, resulting in the formation of beta-kallikrein. The formation of beta-kallikrein was characterized as an autolytic process because it was prevented by specific inhibitors of kallikrein, including aprotinin and antikallikrein antibody but not by corn trypsin inhibitor, an inhibitor specific for beta-Factor XIIa.

Animals↗
PubMed1985

Virus-associated deficiencies in the mitogen reactivity in celebes black macaques (Macaca nigra).

Celebes black macaques (Macaca nigra) with a history of diabetes mellitus, recurrent bacterial and protozoal infections, diarrhea, anemia, weight loss, anorexia, and a high mortality were studied to determine their immune status. Two groups of monkeys, healthy and unhealthy, were formed on the basis of a clinical assessment. The proliferative response and the pokeweed-mitogen-induced polyclonal IgG response of peripheral blood mononuclear cells of unhealthy monkeys were significantly less than the responses of healthy monkeys. The percentage of HLA-DR+ cells varied greatly in unhealthy monkeys. The OKT4/OKT8 ratios of unhealthy monkeys were generally greater than the ratios of healthy monkeys. Unhealthy monkeys usually had smaller percentages of OKT8+ cells than did healthy monkeys. The two groups of monkeys were examined for the presence of a syncytial forming retrovirus by a coculture assay involving Raji cells, a human B lymphoblastoid cell line. A type D retrovirus was detected in the unhealthy group but not in the healthy group. Retroperitoneal fibromatosis was detected in several monkeys in the unhealthy group.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Effect of cleavage of the heavy chain of human plasma kallikrein on its functional properties.

Human plasma kallikrein consists of an N-terminal heavy chain of molecular weight (mol wt) 52,000, linked by disulfide bonds to two light chain variants (mol wt 36,000 or 33,000). Although the active catalytic site of kallikrein resides on the C-terminal light chain, the role of the N-terminal heavy chain is less clear. We therefore studied an enzyme designated beta-kallikrein, containing a single cleavage in the heavy chain (mol wt 28,000 + 18,000) and compared it to the enzyme, alpha-kallikrein, with an intact heavy chain. The rates of inactivation by C1 inhibitor of plasma alpha- and beta-kallikreins were kinetically identical, as measured by residual amidolytic activity, after various times of incubation with the inhibitor. Both enzymes reacted completely with C1 inhibitor after 18 hours and formed identical C1 inhibitor-kallikrein complexes of mol wt 195,000. The rate of activation of factor XII by alpha-kallikrein and beta-kallikrein was similar. In contrast, the rate of cleavage of high molecular weight kininogen (HMWK) by alpha-kallikrein was at least fivefold faster and the ratio of coagulant activity to amidolytic activity was fourfold greater than for beta-kallikrein. Plasma alpha-kallikrein, at concentrations potentially achievable in plasma, induced aggregation of neutrophils, but beta-kallikrein failed to elicit this response. In addition, human neutrophils pretreated with cytochalasin B released 2.46 +/- 0.10 microgram/10(7) cells of elastase antigen, but beta-kallikrein released only 0.25 +/- 0.10 micrograms/10(7) cells. These observations suggest that cleavage of the heavy chain influences the rate of cleavage of HMWK and decreases its coagulant activity. Moreover, an intact heavy chain appears to be requisite to support the ability of kallikrein to aggregate neutrophils and release elastase.

Blood Coagulation Tests↗