Search PubMed⌕ Search

Biomedical subjects

D Burger

Publications and source records attributed to D Burger.

At least 109 records · Page 6Linked to original sources
PubMed1984

Molecular homogeneity of heat-stable enterotoxins produced by bovine enterotoxigenic Escherichia coli.

Heat-stable enterotoxins (STs) from four strains of bovine enterotoxigenic Escherichia coli representing four serogroups were purified to homogeneity by utilizing previously published purification schemata. Biochemical characterization of the purified STs showed that they met the basic criteria for the heat-stable enterotoxins of E. coli. Amino acid analysis of the purified STs revealed that they were peptides of identical amino acid composition. This composition consisted of 18 residues of 10 different amino acids, 6 of which were cysteine. The amino acid composition of the four ST peptides was identical to that reported for the STs of human and porcine E. coli. In addition, complete sequence analysis of two of the ST peptides and partial sequencing of several others revealed strong homology to the sequences of STs from human and porcine E. coli and to the sequence predicted from the last 18 codons of the transposon Tn1681. There was also substantial homology to the sequence predicted from the ST-coding genetic element of human E. coli, which may indicate the existence of identical bioactive configuration among ST peptides of E. coli strains of various host origins. These data support the hypothesis that STs produced by human, bovine, and porcine E. coli are coded by a closely related genetic element which may have originated from a single, widely disseminated transposon.

Amino Acid Sequence↗
PubMed1983

Free energy coupling in the interactions between Ca2+, calmodulin, and phosphorylase kinase.

Interactions between Ca2+, exogenous calmodulin, and white skeletal muscle phosphorylase kinase have been quantitatively studied by equilibrium gel filtrations and analyzed by means of the so-called "linked functions" theory (Weber, G. (1975) Adv. Protein Chem. 29, 1-83). Four moles of calmodulin, each saturated with at least 3 Ca2+ ions, bind to 1 mol of phosphorylase kinase with a Kdiss of 2.3 nM. The activation of the enzyme as a function of free [Ca2+] shows that the intrinsic Ca-binding properties of phosphorylase kinase do not change upon binding of exogenous calmodulin, and confirms that alpha beta gamma delta X Ca3 is the functional catalytic unit through which activation occurs. Direct binding studies reveal that the intrinsic Ca-binding properties of the enzyme remain the same in the presence of either 0.5 or 8 mM Mg2+, indicating that phosphorylase kinase is endowed with Ca-specific sites. Upon interaction with the enzyme, calmodulin acquires strong positive cooperativity in Ca2+-binding: whereas its first two stoichiometric Ca-binding constants are not significantly different from those of free calmodulin, the third Ca2+ ion binds with an affinity at least 10(5)-fold higher than the corresponding one in free calmodulin. Calmodulin liganded with 1 or 2 Ca2+ displays the same low affinity for the enzyme as calmodulin depleted of Ca2+ (approximate Kdiss = 10(-4)-10(-3) M). The alpha beta gamma delta X calmodulin X Ca3 complex is strengthened by a free energy coupling of -8 kcal/mol upon complexation. The quantitative analysis of our results predicts that in spite of this high free energy barrier the dissociation of the complex (i.e. the inactivation of phosphorylase kinase) occurs rapidly upon lowering free [Ca2+].

Animals↗
PubMed1983

Precursor frequency of antigen-specific T cells: effects of sensitization in vivo and in vitro.

Limiting dilution analysis (LDA) of primary lymphocyte cultures was used to determine the frequency of keyhole limpet hemocyanin (KLH)-specific precursors in the peripheral blood of unimmunized individuals. The KLH-specific precursor frequencies ranged from 1:150,000 to 1:340,000. In contrast, frequencies of KLH-specific cells in the blood from immune donors ranged from 1:25,000 to 1:42,000. LDA of KLH-stimulated primary cultures indicated that the frequency of KLH-specific cells increased with time in culture reaching a four- to fivefold expansion relative to the frequency obtained prior to culture. The data presented suggest that the enhanced kinetics of secondary T-cell responses observed after in vitro sensitization are due to a decrease in the proportion of lymphocytes which exhibit a suppressor phenotype.

Adult↗
PubMed1983

Enhanced expression of H-2K and H-2D antigens on reticulocytes infected with Plasmodium yoelii.

The 17XNL strain of Plasmodium yoelii induces a highly effective and permanent T-cell dependent immunity in mice of the CBA strain; the lethal variant P. yoelii 17XL and P. berghei (ANKA) fail to activate an effective immune response in the same host. These differences in immunogenicity are unexplained. We recently observed that in CBA/CaJ mice the intracellular blood stages of P. yoelii 17XNL were almost exclusively within reticulocytes whereas lethal P. yoelii 17XL and P. berghei (ANKA), at comparable stages of infection, were predominantly erythrocytic. Induction of a reticulocytosis converted the normally lethal P. yoelii 17XL infection into a nonlethal one, and reticulocytic P. yoelii was shown to be more immunogenic than the erythrocytic form. Since one of the differences between reticulocytes and erythrocytes that might have influenced the development of immunity was greater expression of MHC antigens of the former cell type we examined the expression of H-2K, H-2D and Ia on reticulocytes infected with P. yoelii 17XNL. These cells showed a very marked increase in H-2K and D antigen expression compared to normal reticulocytes or erythrocytes. No Ia was detected. Red blood cells (RBC) infected with lethal P. yoelii 17XL or P. berghei showed no increase in H-2K or H-2D antigen expression. Finally, the level of expression of H-2K on P. yoelii 17XNL parasitized red blood cells from different strains of mice correlated closely with the ability of these strains to control the infection.

Animals↗
PubMed1983

Purification and characterization of heat-stable enterotoxin from bovine enterotoxigenic Escherichia coli.

Heat-stable enterotoxin (ST) from Escherichia coli pathogenic for cattle was mass produced in a chemically defined medium. The toxin was concentrated and purified by sequentially applying batch adsorption chromatography on Amberlite XAD-2 resin, acetone fractionation, and preparative isoelectric focusing in a flatbed granulated gel. Reverse-phase high-performance liquid chromatography was used to purify the toxin further and to eliminate contaminating ampholytes. The toxin was purified more than 2,000-fold and had a minimal effective dose of less than 0.5 ng. It was biologically active after heating to 100 degrees C for 30 min and was not hydrolyzed by trypsin, pronase, and subtilisin, but it was inactivated by treatment with 0.1 M 2-mercaptoethanol or 4 X 10(-5) M dithiothreitol, suggesting that disulfide bonds are essential for retaining its biological activity. The amino acid analysis revealed 18 amino acid residues per molecule, which is in agreement with the composition of ST from a human strain of enterotoxigenic E. coli. The amino acid composition of our ST matched the published coding sequence of the last 18 codons of Tn1618, a transposon isolated from the bovine enterotoxigenic E. coli strain B41 and shown to be present also in some strains of porcine enterotoxigenic E. coli. These findings further support the existence of a form of ST common to bovine, porcine, and human strains of enterotoxigenic E. coli.

Amino Acids↗
PubMed1983

Isolation of virus and antibody containing immune complexes from mink with Aleutian disease by affinity chromatography of equine complement clq.

Affinity chromatography on immobilized equine complement Clq was used for the isolation of complement-binding immune complexes in sera of mink infected with Aleutian disease virus. Immune complexes were isolated and quantitated from 4 of 5 infected mink, as early as 2 weeks after infection and before hypergammaglobulinemia had appeared. The quantity of immunoglobulin G in these immune complexes ranged from 180 to 370 micrograms/ml serum. There were no Clq-binding immune complexes found in mink which were negative for Aleutian disease antibody. Using 125I-labeled BSA-anti-BSA complexes, we demonstrated that the affinity columns bound selectively immune complexes which had formed in antibody excess, whereas immune complexes in antigen excess were not bound. By neutralization of sensitized virus with anti-mink IgG serum, non Clq-binding immune complexes were also detected, which indicates that circulating immune complexes in persistently infected mink are heterogeneous as far as their reactivity with equine Clq is concerned.

Aleutian Mink Disease↗
PubMed1983

A monokine regulates colony-stimulating activity production by vascular endothelial cells.

Human umbilical vein endothelial cells were cultured in supernatants of peripheral blood monocytes that had been cultured for 3 days with and without lactoferrin. Colony-stimulating activity (CSA) was measured in supernatants of the endothelial cell cultures and appropriate control cultures using normal, T-lymphocyte-depleted, phagocyte-depleted, low-density bone marrow cells in colony growth (CFU-GM) assays. Monocyte-conditioned medium contained a nondialyzable, heat labile factor that enhanced 4-15--fold the production of CSA by endothelial cells. The addition of lactoferrin to monocyte cultures reduced the activity of this monokine by 69%. Lactoferrin did not inhibit CSA production by monokine-stimulated endothelial cells. Therefore, vascular endothelial cells are potent sources of CSA, the production of CSA by these cells is regulated by a stimulatory monokine, and the production and/or release of the monokine is inhibited by lactoferrin, a neutrophil-derived putative feedback inhibitor of granulopoiesis. Inasmuch as a similar monokine is known to stimulate CSA production by fibroblasts and T lymphocytes, we suggest that mononuclear phagocytes play a pivotal role in the regulation of granulopoiesis by recruiting a variety of cell types to produce CSA.

Cells, Cultured↗
PubMed1982

Sensitization of human lymphocytes in vitro. Kinetics and specificity of the response to hemocyanins.

In vitro primary sensitization of human peripheral blood T-cells to hemocyanins was detected during a 12-14 day culture period with antigen (KLH or HCH)-pulsed macrophages. Primed T-cells proliferate in secondary culture (2-3 days) when restimulated with antigen presented by macrophages. The kinetics of primary sensitization and secondary responsiveness are interrelated and are dependent on the antigen doses employed. Antigen-induced proliferation of cells sensitized in vitro is identical to proliferation of T-cells from immunized donors in terms of antigen specificity and the clonal nature of the response to antigen. Through the use of thymidine suicide techniques, distinct populations of cells responding to KLH or HCH can be demonstrated using cells from actively immunized donors or cells that have been sensitized in vitro to both hemocyanins.

Dose-Response Relationship, Immunologic↗
PubMed1982

Constitutive expression of platelet glycoproteins by the human leukemia cell line K562.

The human leukemia cell line K562 was derived from a patient with chronic granulocytic leukemia. This cell line has subsequently been shown to possess phenotypic markers typical of erythroid and myeloid cells. Using a rabbit antiserum directed against purified platelet glycoproteins (PGPs), we have obtained evidence for the constitutive expression of PGPs on the surface of K562 cells. PGPs expressed have been tentatively identified as IIa and III based on their apparent migration in a 7% sodium dodecylsulfate polyacrylamide gel. K562 may become an important tool for the study of early events involved in megakaryocytic differentiation.

Animals↗
PubMed1982

Differing responses of globin and glycophorin gene expression to hemin in the human leukemia cell line K562.

The human leukemia cell line, K562, produces embryonic and fetal hemoglobins and glycophorin A, proteins normally associated only with erythroid cells. Hemoglobin accumulation is enhanced by exposure of the cells to 0.05 mM hemin. We have examined K562 cells before and after exposure to hemin to determine whether expression of these erythroid proteins was shared by all cells or confined to specific subpopulations. Globin gene expression was examined by quantitation of globin mRNA sequences, using a 3H-globin cDNA molecular hybridization probe. Constitutive cells produced globin mRNA, the content of which was increased 3-4-fold by hemin. Cell-to-cell distribution of globin mRNA was determined by in situ hybridization of 3H-globin cDNA to constitutive and hemin-treated K562 cells. Virtually all cells in the culture exhibited grain counts above background, indicating globin gene expression by all cells, rather than a confined subpopulation. Virtually all hemin-treated cells had 3-5-fold higher grain counts, indicating uniformly increased globin gene expression. The glycophorin content of K562 cells was estimated by fluorescence-activated cell sorting (FACS) of cells labeled with fluorescein-labeled antiglycophorin antiserum. The vast majority of constitutive cells contained glycophorin, but exhibited to apparent increase in glycophorin accumulation after hemin exposure. Thus, glycophorin and globin genes exhibited differential responses to hemin. These differences could reflect normal differences in the patterns of specialized gene expression in stem cells. Alternatively, different aberrations of gene expression could be occurring in response to the determinants of the neoplastic properties of K562.

Amino Acid Sequence↗
PubMed1981

Contagious ecthyma in Alaskan musk-oxen and Dall sheep.

In 1976 and 1977, a disease resembling contagious ecthyma was seen in captive musk-oxen (Ovibos moschatus) in Alaska. A similar disease occurred in 1977 in captive Dall sheep (Ovis dalli). Paravaccinia viruses were detected by electron microscopy and isolated in cell cultures from both species. Experimental inoculation in susceptible and immune domestic sheep (Ovis aries) plus fluorescent antibody tests with ecthyma-immune conjugate indicated that the isolate was contagious ecthyma virus.

Alaska↗
PubMed1980

System for studying the topography of delta rhythm during sleep: further development.

A hybrid system for treatment of all-night sleep EEG records is described, which leads to the representation of sleep cycles by the continuous variation of the amplitude in a given frequency band. This system constitutes the development of a previous purely analogic one. The addition of a micro-processor and of a small computer renders the system far more flexible and easier to use. The results stored on tape are available for further treatments.

Analog-Digital Conversion↗
PubMed1979

System for studying the delta rhythm during sleep and its topographical amplitude distribution.

An analogue system of processing all-night sleep EEG records which leads to the representation of sleep cycles by the continuous variation of the amplitude parameter in a given frequency band is described. The curves obtained are analogous to those resulting from more sophisticated computerized analyses. The cycles which they outline are in good concordance with those of the classic hypnogram. Moreover, the simplicity and the rapidity of the processing easily allow its application to multiple EEG channels. A topographical discrimination of the amplitude parameter during sleep was observed in normal subjecttion. The results obtained are illustrated in the case of a normal child and a young normal adult.

Adult↗