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Biomedical subjects

G Weissmann

Publications and source records attributed to G Weissmann.

At least 217 records · Page 12Linked to original sources
PubMed1978

Mg2+-ATPase as a membrane ecto-enzyme of human granulocytes. Inhibitors, activators and response to phagocytosis.

(1) The Mg2+-ATPase of purified human granulocytes is located at the plasma membrane. Thus, no additional enzyme activity was detected when the cells were disrupted. Moreover, the Mg2+-ATPase activity of intact cells was inhibited by such poorly permeant reagents as diazotized sulfanilic acid and suramin. Finally, the enzyme activity of cell homogenates was recovered in particulate fractions. (2)The surface Mg2+-ATPase of human granulocytes had an apparent Km of 50 microns for ATP and displayed substrate inhibition. (3) The enzyme was not affected by ouabain, but was inhibited by N-ethyl malemide, sodium meta-periodate, suramin and diazotized sulfanilic acid. The enzyme was activated by cytochalasins B and D and by UDP. Activation by UDP was characterized by changes in the enzyme's apparent Km and V and by belief of substrate inhibition. (4)Internalization of surface membranes subsequent to phagocytosis of suitable particles did not result in depletion of Mg2+-ATPase from the cell surface. The enzyme activity did not decrease after exposure to several varieties of paraffin oil emulsion particles, even if the challenged cells had been pretreated with colchicine of cytochalasin B. (5) Since suramin, which inhibited Mg2+-ATPase, had no effect upon other granulocyte functions such as chemotaxis, superoxide anion generation, or phagocytosis, it is unlikely that the enzyme plays a major role in these functions.

Adenosine Triphosphatases↗
PubMed1978

Thromboxane generation by human peripheral blood polymorphonuclear leukocytes.

Human peripheral blood polymorphonuclear leukocytes were stimulated to generate thromboxane B2 in a time- and concentration-dependent fashion upon exposure to serum-treated zymosan particles. Conversion by stimulated PMN of [14C] arachidonic acid to [14C]thromboxane B2 was confirmed by thin-layer radiochromatography, radio-gas chromatography, and mass spectrometry. Generation of thromboxane B2 was independent of platelet contamination and could be inhibited by the cyclooxygenase inhibitor, indomethacin. Cells rendered incapable of ingesting particles by treatment with cytochalasin B generated comparable amounts of thromboxane B2. These results suggest that human peripheral blood polymorphonuclear leukocytes synthesize thromboxanes in response to surface stimulation independently of phagocytosis.

Humans↗
PubMed1978

Comparison of large unilamellar vesicles prepared by a petroleum ether vaporization method with multilamellar vesicles: ESR, diffusion and entrapment analyses.

Large unilamellar vesicles, prepared by a petroleum ether vaporization method, were compared to multilamellar vesicles with respect to a number of physical and functional properties. Rotational correlation time approximations, derived from ESR spectra of both hydrophilic (3-doxyl cholestane) and hydrophobic (3-doxyl androstanol) steroid spin probes, indicated similar molecular packing of lipids in bilayers of multilamellar and large unilamellar liposomes. Light scattering measurements demonstrated a reduction in apparent absorbance of large unilamellar vesicles, suggesting loss of multilamellar structure which was confirmed by electron microscopy. Furthermore, large unilamellar vesicles exhibited enhanced passive diffusion rates of small solutes, releasing a greater percentage of their contents within 90 min than multilamellar vesicles, and reflecting the less restricted diffusion of a unilamellar system. The volume trapping capacity of large unilamellar vesicles far exceeded that of multilamellar liposomes, except in the presence of a trapped protein, soy bean trypsin inhibitor, which reduced the volume of the aqueous compartments of large unilamellar vesicles. Finally, measurement of vesicle diameters from electron micrographs of large unilamellar vesicles showed a vesicle size distribution predominantly in the range of 0.1--0.4 micron with a mean diameter of 0.21 micron.

Chromates↗
PubMed1978

Attack of sea urchin eggs by dogfish phagocytes: model of phagocyte-mediated cellular cytotoxicity.

To test whether lysosomal degranulation of phagocytes is associated with antibody-dependent cytotoxicity, eggs of Arbacia punctulata were used as targets for blood phagocytes of Mustelus canis. Eggs were coated with heat-aggregated dogfish IgM and exposed to phagocytes, and cytolysis of eggs was observed by Nomarski optics. Phagocytes adhered, degranulated, and raised fertilization membranes resembling those induced by sperm or ionophore A23187. Lysis was then observed as damage radiating from the point of phagocyte-egg contact. By 4 hr, coated eggs exposed to phagocytes released 8.9, 12.3, and 7.4% of total catalase (EC 1.11.1.6), beta-glucuronidase (EC 3.2.1.31), and superoxide dismutase (EC 1.15.1.1) into the medium. Cytotoxic enzyme release significantly exceeded that from uncoated eggs incubated with phagocytes or eggs alone (uncoated or coated). Because activated eggs release a neutral protease, it was considered possible that this enzyme might be responsible for autolysis of eggs. This possibility was excluded because (i) lysis of eggs was not inhibited by soybean trypsin inhibitor (SBTI) whereas the egg protease was sensitive to SBTI, and (ii) the major trypsin-like activity of phagocytes was not inhibited by SBTI. These experiments demonstrate that Ig-coated cells are first activated, and then killed, when exposed to degranulating phagocytes and suggest that enzymes from attacking phagocytes, and not target cells, are responsible for cell death.

Animals↗
PubMed1978

Changes in membrane potential of human granulocytes antecede the metabolic responses to surface stimulation.

Human granulocytes (polymorphonuclear leukocytes) exposed to surface stimuli [e.g., immune complexes, concanavalin A (Con A)] generate O(2).(-), undergo a respiratory burst, and secrete lysosomal enzymes. To study the earliest reaction of ligands with surface receptors of granulocytes, purified cells were exposed to bovine serum albumin-anti-albumin complexes (Fc receptors) or Con A (glycoprotein receptors). The membrane potential (DeltaPsi) was measured by distribution of the lipophilic cation [(3)H]triphenylmethyl phosphonium ion. The Nernst equation yielded a resting DeltaPsi of -26.7 mV. Beginning within 10 sec after exposure to the antigen-antibody complex or to Con A, the cells responded with a rapid hyperpolarization --> depolarization --> slow hyperpolarization. Even when phagocytosis was inhibited by cytochalasin B, the triphasic response was obtained: evidence for surface interaction. The hyperpolarization response anteceded O(2).(-) generation (continuous recording) by at least 20-30 sec. O(2).(-) generation in response to immune complexes was stimulated by Ca(2+) whereas DeltaPsi remained unchanged; lack of Ca(2+) in the medium did not inhibit the DeltaPsi response. Dissociation of membrane hyperpolarization from subsequent metabolic responses (O(2).(-) generation) was also found in the presence of steroids (hydrocortisone, methylprednisolone), which inhibited O(2).(-) generation but did not inhibit the DeltaPsi response to antigen-antibody complex. Because O(2).(-) generation could be stimulated (Ca(2+)) or depressed (steroids) without affecting DeltaPsi, the data suggest that DeltaPsi is involved in primary triggering of phagocytic cells and that metabolic stimulation is a secondary consequence of ligand-receptor interactions.

Antigen-Antibody Complex↗
PubMed1978

Leukocytes as secretory organs of inflammation.

Polymorphonuclear leukocytes secrete substances that defend against foreign invaders by mechanisms that bear remarkable resemblances to those of exocrine and endocrine glands. Similarly, leukocyte secretions can also damage the very host they are intended to protect. Like other secretory cells, leukocytes also bear surface receptors to detect signals that initiate secretion. Clinical implications are detailed.

Antigen-Antibody Complex↗
PubMed1978

Microfilaments and microtubules in calcium ionophore-induced secretion of lysosomal enzymes from human polymorphonuclear leukocytes.

Human peripheral blood leukocytes (PMN) are induced to release lysosomal enzymes by the calcium ionophore A23187 in the presence but not the absence of extracellular Ca++. Whereas secretion induced by particulate or immune stimuli is accompanied by an increase in visible microtubules and is inhibitable by colchicine, secretion induced by A23187 and Ca++ was not accompanied by an increase in microtubule numbers and was not inhibited by colchicine. Ca++ did not appear to regulate microtubule assembly in these cells since resting PMN had a mean of 22.3 +/- 2.0 microtubules in the centriolar region as compared to 22.3 +/- 1.1 in ionophore-treated cells and 24.9 +/- 1.5 in cells exposed to ionophore and 1 mM Ca++. Bipolar filaments, 10 nm thick and 300--400 nm long, were numerous in the pericortical cytoplasm of cells exposed to both reagents. Microtubules in these cells were decorated with an electron-opaque fibrillar material. PMN exposed to A23187 and Ca++ were contracted in two directions at right angles to each other: (a) Contractions parallel to the plasma membrane resulted in extensive plication of the cell membrane. The cytoplasm subjacent to the plicae contained dense filamentous webs. Plication was prevented by cytochalasin B or reversed by subsequent exposure to an endocytic stimulus such as zymosan. (b) Contractions perpendicular to the plasma membrane, toward the cytocenter, resulted in the formation of vacuoles in normal PMN and of membrane invaginations in cytochalasin B-treated PMN. Whereas contractions parallel to the plasma membrane could occur in the absence of enzyme release (ionophore alone) and enzyme release could occur in the absence of such contractions (ionophore plus calcium plus cytochalasin B), contraction toward the cytocenter occurred in all experimental conditions in which significant enzyme release was obtained. Thus, lysosomal enzyme secretion in PMN involves contractile movements in the plasma membrane toward the lysosomes rather than the reverse. These calcium-mediated contractile events are mediated by cytochalasin B-insensitive microfilaments but not by microtubule assembly.

Anti-Bacterial Agents↗
PubMed1978

Polymorphonuclear leukocytes as secretory organs of inflammation.

Polymorphonuclear (PMN) leukocytes mediate that phase of inflammation at which vascular responses become translated into tissue injury. After phagocytosis, the PMN leukocyte generates derivatives of molecular oxygen (O2-.,OH., and H2O2) that stimulate a metabolic burst and assist in the killing of microorganisms. They also release oxidation products of membrane fatty acids (e.g., arachidonate), which are detected as thromboxanes and protaglandins. After interaction of phagocytic ligands (immune complexes and C3b-opsonized particles), the PMN leukocyte secretes lysosomal enzymes from open phagocytic vacuoles, and, especially when phagocytosis is blocked by cytochalasin B, secretes them directly into the cell's surrounding fluids. Secretion is enhanced by agents that elevate intracellular levels of cyclic GMP, and inhibited by agents that raise cyclic AMP. These reciprocal changes are associated with assembly and disassembly (respectively) of cytoplasmic microtubules. These cytoskeletal structures, together with contractile elements, regulate in part the secretory events of inflammation in which lysosomal constituents (e.g., elastase, collagenase, and cathepsin G) are diverted from their intracellular depots to an inappropriate assault on the tissues of the host.

Blood Bactericidal Activity↗
PubMed1978

The earliest membrane responses to phagocytosis: membrane potential changes and Ca++ loss in human granulocytes.

The two findings reported here clearly indicate that the human granulocyte undergoes stimulus-secretion coupling when appropriate stimuli engage the cell surface. These secretory and metabolic responses seem designed to provide efficient mechanisms for bacterial killing or the elimination of immune complexes. First, ligands bind to surface receptors, in the case of concanavalin A, via surface sugars, in the case of immune complexes, via Fc receptors. Our new findings, described above, show that this is followed within five to ten seconds by membrane hyperpolarization: changes in the membrane potential of the cell: delta psi. Local loss of membrane calcium is noted concurrently: not as part of a generalized "triggering" of all the surface membraneof the cell, but only at the point of ligand-receptor interaction: the initiating point of phagocytosis. The subsequent changes, such as superoxide anion production, the generation of thromboxanes and prostaglandins, and the intracellular events which lead to secretion appear, therefore, to be secondary to these earliest membrane responses of phagocytosis.

Antigen-Antibody Complex↗
PubMed1977

Influence of local anesthetics upon human polymorphonuclear leukocyte function in vitro. Reduction of lysosomal enzyme release and superoxide anion production.

Cationic local anesthetics have been reported to influence cellular responses to surface stimuli by interfering with the function of microtubules and microfilaments. Since unimpaired microtubule and microfilament functions are required by human polymorphonuclear leukocytes in order to respond normally to surface stimulation, we have studied effects of the local anesthetic, tetracaine on the function and morphology of these cells in vitro. Tetracaine (0.25--1.0 mM) significantly reduced extracellular release of the lysosomal enzymes, beta-glucuronidase and lysozyme from polymorphonuclear leukocytes exposed to serum-treated zymosan (a particulate stimulus), zymosan-treated serum (a soluble stimulus), and to the surface-active lectin, concanavalin A. Tetracaine also significantly reduced superoixde anion production (superoxide dismutase-inhibitable cytochrome c reduction) by these cells. Tetrancaine was not cytotoxic and its effects could be reversed completely by washing cells once with buffer. Electron microscope examination of tetracaine-treated cells revealed marked alterations of surface membranes. Microtubules and microfilaments appeared normal in "resting" polymorphonuclear leukocytes, but the increase in microtubules normally observed in stimulated cells was not seen after tetracaine treatment. These results suggest that tetracaine interferes with those interactions between immune reactants and the polymorphonuclear leukocyte cell surface which provoke exocytosis and increased oxidative metabolism.

Anesthetics, Local↗