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Biomedical subjects

S C Silverstein

Publications and source records attributed to S C Silverstein.

143 records · Page 8Linked to original sources
PubMed1975

Characterization of the macrophage receptro for complement and demonstration of its functional independence from the receptor for the Fc portion of immunoglobulin G.

The complement receptor of the macrophage membrane recognizes particle-bound C3b but does not recognize particle-bound C3d. C3-b-coated sheep erythrocytes were bound to macrophages via their C3b receptors, and the preparations were then incubated with either latex particles or opsonized pneumococci (test particles). Macrophages ingested the test particles, but erythrocytes were not ingested; they remained bound to C3b receptors of the macrophage plasma membrane. Thus, a signal initiating ingestion via one type of receptor is not transmitted to all receptors which have the potential to mediate phagocytosis.

Animals↗
PubMed1975

Studies of the macrophage complement receptor. Alteration of receptor function upon macrophage activation.

We have examined the roles of Fc receptors and complement receptors in mediating the interaction of sensitized sheep erythrocytes (E) with activated and with nonactivated mouse peritoneal macrophages. Both activated and nonactivated macrophages ingest IgG-coated erythrocytes [E(IgG)]; activated cells intest 1.5-2 times as man E(IgG) as do nonactivated macrophages. Thus, there is a quantitative difference in Fc receptor-mediated ingestion between activated and nonactivated macrophages. There is, however, a qualitative difference in function of complement receptors of activated and nonactivated macrophages. Nonactivated macrophages avidly bind complement-coated E [E(IgM)Ia1, but do not ingest them to a significant degree. Activated macrophages, on the other hand, bind and ingest E(IgM)C. The possibility of Fc receptor participation in mediating ingestion of E(IgM)C by activated macrophages was eliminated by blocking Fc receptors with an antimacrophage IgG fraction. Activated macrophages treated with antimacrophage IgG did not ingest E(igG) but did ingest both E(IgM)C AND E(IgM)C. Nonactivated macrophages treated with antimacrophage IgG did not interact at all with E(IgG). These cells bound, but did not ingest, E(IgM)C and E(IgM)C. Complement receptor-mediated ingestion is a marker for macrophage activation and may be physiologically important in the elimination of complement-coated particles.

Animals↗
PubMed1975

Correlated suppression by 5-bromodeoxyuridine of tumorigenicity and plasminogen activator in mouse melanoma cells.

The decrease of tumorigenicity by mouse melanoma clone B559 after growth in the presence of 5-bromodeoxyuridine (BrdU) has been correlated with a decrease in detectable cellular plasminogen activator. Reduction of both activities occurs after one to two cell divisions in the presence of this thymidine analog and is virtually complete within three to four cell cycles. These changes are fully reversible; four to five cell divisions in the absence of BrdU are sufficient to allow both tumorigenicity and plasminogen activator levels to return to normal. These results support the hypotheses that (a) the expression of a cellular plasminogen activator is closely associated with the transformation of normal to malignant cells and that (b) the suppression of tumorigenicity by BrdU reflects the capacity of this base analog to inhibit the expression of specialized functions which accompany the malignant state.

Animals↗
PubMed1974

Segmental response of the macrophage plasma membrane to a phagocytic stimulus.

A method of attaching mouse RBCs to mouse macrophages is described. Both cell types were coated with rabbit anti-mouse macrophage F(ab')(2), and cross-linkage of cells was effected with sheep F(ab')(2) directed against rabbit F(ab')(2). 98% of macrophages attached an average of 11 RBCs each. Attachment occurred at 37 degrees C and was stable for at least 4 h. Less than 0.1% of macrophages ingested RBCs under these conditions. Latex particles and opsonized pneumococci were ingested as avidly by RBC-coated macrophages as by native macrophages. Ingestion of these particles did not prompt ingestion of attached RBCs. When anti-RBC IgG was added, however, over 90% of macrophages ingested an average of six RBCs each. Thus, ingestion of one particle does not trigger generalized phagocytosis of all particles attached to the cell's plasma membrane, and the phagocytic stimulus is confined to the segment of the cell's plasma membrane immediately adjacent to the particle being ingested.

Animals↗
PubMed1974

Determination of the absolute number of Escherichia coli membrane vesicles that catalyze active transport.

Transport of vinylglycolate (2-hydroxy-3-butenoic acid) via the lactate transport system is the limiting step for covalent labeling of membrane vesicles prepared from E. coli ML 308-225. Thus, the rate and extent of vinylglycolate labeling is stimulated about 10-fold by ascorbate-phenazine methosulfate, and stimulation is abolished by 2,4-dinitrophenol and by phospholipase treatment, neither of which affect the rate of vinylglycolate oxidation. [(3)H]Vinylglycolate of high specific activity has been prepared, and vesicles have been labeled with this compound in the presence of ascorbate-phenazine methosulfate. Examination of these preparations by high resolution radioautography in the electron microscope demonstrates that virtually all of the vesicles are labeled. The experiments provide a strong indication that most, if not all, of the membrane vesicles in these preparations catalyze active transport.

Ascorbic Acid↗
PubMed1974

Shythesis of reovirus oligo adenylic acid in vivo and in vitro.

The formation of reovirus double-stranded (ds) RNA and of oligo adenylic acid (oligo A) is inhibited by 5 mug of actinomycin D per ml added at the time of viral infection. Viral proteins are synthesized and assembled into dsRNA-deficient particles under these conditions. The addition of cycloheximide to infected cells during the mid-logarithmic phase of viral replication terminates protein and dsRNA synthesis, but allows continued oligo A synthesis for about 1 h. The (3)H-labeled oligo A formed in the presence of cycloheximide is incorporated into particles whose density in CsCl is identical to that of reovirions. Using the large particulate or virus factory-containing cytoplasmic fraction of infected L-cells, we have established an in vitro system for the synthesis of oligo A. The in vitro product migrates slightly faster in sodium dodecyl sulfate acrylamide gels than marker oligo A. Oligo A synthesis in vitro continues for about 1 h, requires, the presence of only one ribonucleoside triphosphate (ATP), is not inhibited by DNase or RNase, but is abruptly terminated by the addition of chymotrypsin to the reaction mixture. Oligo A formed both in vivo and in vitro is released from the factory fraction by chymotrypsin digestion. The enzymes which catalyze the synthesis of oligo A, dsRNA, and single-stranded RNA all exhibit a similar temperature dependence with an optimum of approximately 45 C. These results indicate that oligo A is formed within the core of the nascent virion after the completion of dsRNA synthesis; they suggest that the oligo A polymerase is an alternative activity of the virion-bound transcriptase and that it is regulated by outer capsomere proteins.

Adenosine Monophosphate↗
PubMed1973

The effect of poly-L-lysine on the uptake of reovirus double-stranded RNA in macrophages in vitro.

The effect of polycations on cultured mouse peitoneal macrophages has been examined. Polycations, at concentrations greater than 5 microg/ml, are toxic for macrophages) as measured by failure of the cells to exclude vital dyes. At toxic concentrations polycations bind in large amounts to nuclei and endoplasmic reticulum, while at nontoxic levels polycations bind selectively to the cell surface. Nontoxic concentrations of polycations stimulate binding of reovirus double-stranded (ds) RNA to the macrophages by forming polycation-dsRNA complexes either in the medium or at the cell surface. These complexes enter the cell in endocytic vacuoles and are concentrated in secondary lysosomes. Despite exposure to the acid hydrolases within this cell compartment, the dsRNA and the polycation (poly-L-lysine) are conserved in a macromolecular form within the vacuolar system. The mechanism(s) by which the uptake of infectious nucleic acids and the induction of interferon by dsRNA are stimulated by polycations are discussed.

Animals↗
PubMed1971

Asynchronous synthesis of the complementary strands of the reovirus genome.

The mechanism of replication of the double-stranded RNA genome of reovirus has been analyzed by tracing the fate of the parental double-stranded RNA genome and by determining whether the complementary strands, which comprise the progeny double-stranded RNA, are synthesized simultaneously or sequentially. The results indicate that the parental double-stranded RNA is conserved as the original duplex molecule within a subviral particle throughout the viral replicative cycle. The complementary strands, which form the progeny double-stranded RNA, are produced asynchronously. Minus strands are synthesized on preformed plus-strand templates, whereas plus strands appear to be synthesized on double-stranded RNA templates.

Centrifugation↗
PubMed1971

Mechanism of reovirus double-stranded ribonucleic acid synthesis in vivo and in vitro.

The complementary strands of reovirus double-stranded ribonucleic acid (ds RNA) are synthesized sequentially in vivo and in vitro. In both cases, preformed plus strands serve as templates for the synthesis of the complementary minus strands. The in vitro synthesis of dsRNA is catalyzed by a large particulate fraction from reovirus-infected cells. Treatment of this fraction with chymotrypsin or with detergents which solubilize cellular membranes does not alter its capacity to synthesize dsRNA. The enzyme or enzymes responsible for dsRNA synthesis remain sedimentable at 10,000 x g after these enzyme or detergent treatments, indicating their particulate nature. Pretreatment of this fraction with ribonuclease, however, abolishes its ability to catalyze dsRNA synthesis, emphasizing the single-stranded nature of the template and its location in a structure permeable to ribonuclease. In contrast, the newly formed dsRNA is resistant to ribonuclease digestion at low salt concentrations and hence is thought to reside within a ribonuclease-impermeable structure.

Animals↗
PubMed1970

The reovirus replicative cycle: conservation of parental RNA and protein.

The fate of parental reovirions in the viral replicative cycle has been analyzed using CsCl density centrifugation. After penetration of L-cells, reovirus is converted from a particle of density 1.39 g/cm(3) to a subviral particle of density 1.41 g/cm(3). This alteration in density is temporally correlated with the hydrolysis of viral coat proteins and is qualitatively similar when particles are labeled in their RNA or protein. Ten hours after infection, when synthesis of progeny virus is underway, the parental RNA and protein are again found at density 1.39 g/cm(3). These data demonstrate conservation of the parental RNA and protein in the subviral particle throughout the replicative cycle.

Centrifugation, Density Gradient↗
PubMedDate not supplied

Inhibition of Fura-2 sequestration and secretion with organic anion transport blockers.

Fura-2 is widely used to measure the concentration of cytosolic free calcium, but in many cells the dye does not remain localized within the cytoplasmic matrix. In these cells, Fura-2 is sequestered within intracellular organelles, secreted into the extracellular medium, or both. We have found that, in mouse peritoneal macrophages, J774 cells, PC12 cells, and N2A cells, Fura-2 sequestration and secretion are mediated by organic anion transport systems and are blocked by the inhibitors probenecid and sulfinpyrazone. Under appropriate conditions these agents have little affect on calcium transients, and may facilitate the use of Fura-2 in a variety of cell types.

Animals↗
PubMedDate not supplied

Microglia, scavenger receptors, and the pathogenesis of Alzheimer's disease.

The senile plaque is the pathological hallmark of Alzheimer's disease. Senile plaques are composed of beta amyloid fibrils, associated with activated microglia, astrocytes, and dystrophic neurons. We have recently identified class A scavenger receptors as the main receptors mediating the interaction of microglia with beta amyloid fibrils. Adhesion of microglia to beta amyloid fibrils leads to immobilization of these cells on the fibrils, and induces them to produce reactive oxygen species. We propose that interactions of microglial scavenger receptors with fibrillar beta amyloid may stimulate the microglia to secrete apolipoprotein E and complement proteins, which may further contribute to neurotoxicity and neuronal degeneration. Therefore, microglial scavenger receptors may be novel targets for therapeutic interventions in Alzheimer's disease.

Alzheimer Disease↗
PubMedDate not supplied

Phagocytosing macrophages exclude proteins from the zones of contact with opsonized targets.

During receptor-mediated phagocytosis, macrophages release toxic molecules such as hydrogen peroxide which enable them to kill antibody-coated tumour cells and parasites, too large to consume. Previous workers observed that while peroxide was clearly responsible for cytolysis of certain antibody-coated tumour cells, extracellular catalase was unable to inhibit this cytolysis, and they suggested that macrophages secrete peroxide into a protected cleft between the phagocyte and target. We have tested this and report here that the space beneath macrophages spread on glass surfaces is accessible to proteins with a molecular weight (MW) as large as 200,000 but the space beneath macrophages plated on glass surfaces coated with phagocytosis-promoting ligands is impermeable to proteins as small as 50,000 MW. It appears indeed that macrophages form a protein-tight seal at the periphery of their contact with ligand-coated surfaces and thereby create a closed compartment between the cell and the target.

Cell Adhesion↗