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S C Silverstein

Publications and source records attributed to S C Silverstein.

At least 19 recordsLinked to original sources
PubMed1992

The role of protected extracellular compartments in interactions between leukocytes, and platelets, and fibrin/fibrinogen matrices.

Polymorphonuclear leukocytes express multiple surface receptors that mediate their adhesion to extracellular matrices and to other cells. These receptors also play roles in cell migration and phagocytosis. We have studied the role of one class of polymorphonuclear leukocytes surface receptors, the beta 2 integrins, in the interactions of these cells with fibrinogen. We have found that the beta 2 integrins, CD11b/CD18 (complement receptor three) and CD11c/CD18 mediate attachment of polymorphonuclear leukocytes to fibrinogen-coated surfaces. Polymorphonuclear leukocytes must be stimulated with chemoattractants, such as fMLP, or with cytokines, such as tumor necrosis factor to bind to fibrinogen via these integrins. Moreover, each of these integrins interacts with a different segment of the fibrinogen molecule. PMN adherence to fibrinogen via CD11b/CD18 depends on the carboxy terminus of fibrinogen, whereas adherence via CD11c/CD18 depends on the amino terminus of fibrinogen's alpha-chain. One of the physiological consequences of these interactions is that polymorphonuclear leukocytes stimulated with either chemoattractants or TNF form protected compartments at their interface with fibrinogen-coated surfaces and that elastase released into these compartments is inaccessible to protease inhibitors present in the plasma. These protected compartments exclude plasma proteins of > 40,000 daltons such as alpha 1 anti-proteinase, thereby allowing polymorphonuclear leukocyte proteases to degrade matrix proteins within this compartment without interference by plasma anti-proteinases.

Animals↗
PubMed1992

Gemfibrozil enhances the listeriacidal effects of fluoroquinolone antibiotics in J774 macrophages.

J774 macrophage-like cells express organic anion transporters that promote the efflux of fluoroquinolone antibiotics such as norfloxacin (NFX) from these cells. Gemfibrozil (GFZ) blocks organic anion transport in J774 cells, thereby facilitating the intracellular accumulation of NFX (Cao, C., H.C. Neu, and S.C. Silverstein. 1991. J. Cell Biol. 115:467a [Abstr.]). To determine whether GFZ enhances the efficacy of fluoroquinolone antibiotics against intracellular bacterial pathogens, J774 cells were infected with Listeria monocytogenes and incubated in medium containing a fluoroquinolone antibiotic in the presence or absence of GFZ. Intracellular growth of L. monocytogenes was evaluated by lysing J774 cells and assaying for colony-forming units of Listeria. GFZ intensified the bacteriostatic effect of 4 micrograms/ml NFX and rendered 8 micrograms/ml bactericidal for L. monocytogenes. GFZ had a similar potentiating effect when used in combination with 2 micrograms/ml ciprofloxacin (CFX). CFX plus GFZ was bactericidal for intracellular L. monocytogenes. Treatment of J774 cells with NFX plus GFZ markedly reduced the cytotoxic effect of the bacteria on these cells. Over 55% of cells treated with 8 micrograms/ml NFX alone were dead 16 h after infection, whereas only 5% of cells treated with 8 micrograms/ml NFX plus GFZ were dead at 16 h. Similarly, GFZ potentiated the ability of 2 micrograms/ml to protect J774 cells against the cytocidal effect of Listeria. NFX in combination with GFZ limited cell-to-cell spread of L. monocytogenes. In antibiotic-free medium, > 99% of J774 cells contained intracellular L. monocytogenes at 14 h after infection. NFX alone in the medium did not change this outcome. However, 4 micrograms/ml NFX plus GFZ decreased bacterial spread by approximately 40% at 24 h postinfection, and 8 micrograms/ml NFX plus GFZ prevented all spread beyond the initially infected cell population. These results suggest that GFZ could be used clinically to enhance the efficacy of fluoroquinolone and of other anionic antibiotics against bacteria that grow and/or reside within macrophages and/or other cells.

Animals↗
PubMed1992

J774 macrophages secrete antibiotics via organic anion transporters.

Mouse macrophages and J774 macrophage-like cells express probenecid-inhibitable organic anion transporters that remove anionic dyes from the cells' cytoplasmic matrix and secrete these dyes into the extracellular medium. The present studies show that these transporters also secrete antibiotics from J774 macrophages. Penicillin G permeates J774 cells poorly, but after it was introduced into the cell cytoplasm, it was secreted in a probenecid-inhibitable fashion. The quinolone norfloxacin enters macrophages readily. Probenecid retarded the secretion of intracellular norfloxacin by J774 cells and enhanced norfloxacin accumulation three- to fourfold. Thus the intracellular accumulation of norfloxacin is regulated in part by organic anion transporters that secrete norfloxacin (and penicillin G) from J774 cells. This transport process may have clinical significance, as fluoroquinolones inhibit growth of intracellular pathogens such as mycobacteria and Brucella organisms in vitro but fail to arrest infections with these organisms in vivo.

Adenosine Triphosphate↗
PubMed1992

Hypoxia-induced increased permeability of endothelial monolayers occurs through lowering of cellular cAMP levels.

Prolonged exposure to hypoxia, as at high altitude, results in increased vascular permeability that may be ameliorated by administration of glucocorticoids. To understand mechanisms underlying these observations, cultured bovine aortic and pulmonary artery endothelial cells (ECs) were subjected to hypoxia, and changes in monolayer permeability and adenosine 3',5'-cyclic monophosphate (cAMP) levels were assessed. Exposure of both types of cultured ECs to hypoxia (PO2 approximately 14 Torr) led to a time- and dose-dependent increase in monolayer permeability, as measured by diffusion of radiolabeled solutes, which was associated with a progressive decrease in EC cAMP levels from 60 to 15 pmol/mg protein, and a decrease in EC adenylate cyclase activity. The change in endothelial barrier function was prevented by addition of cAMP analogues. Pertussis toxin protected EC monolayers from hypoxia-mediated increase in permeability while maintaining cAMP levels and adenylate cyclase activity. Addition of dexamethasone to EC monolayers before or simultaneously with their incubation under hypoxic conditions blocked the hypoxia-mediated increase in monolayer permeability. Dexamethasone pretreatment also prevented the decline in cAMP and adenylate cyclase levels in oxygen-deprived cultures. These data indicate that hypoxia decreases EC barrier function by lowering adenylate cyclase activity and cellular cAMP levels. They suggest that dexamethasone may exert its protective effect, in part, by preventing the hypoxia-induced decline in adenylate cyclase activity, leading to an increase in cellular cAMP and maintenance of EC barrier function.

Animals↗
PubMed1992

Hypoxia induces glucose transporter expression in endothelial cells.

Endothelial cells in various tissues of the body are often exposed to hypoxic conditions. To examine the effects of sustained hypoxia on energy metabolism in endothelial cells, we have maintained bovine aortic and human umbilical vein endothelial cells in an atmosphere containing low oxygen concentrations (14 mmHg) for up to 96 h. We report here that endothelial cells maintained under these conditions upregulate their glucose transport activity, consume more glucose, and produce greater amounts of lactic acid than normoxic cells. Upregulation of glucose transport activity by hypoxic endothelial cells required several hours to occur, was associated with increased expression of mRNA and protein for the erythroid/brain form of the facilitative glucose transporter, and was not due to depletion of glucose from the medium. Prolonged treatment of endothelial cells with inhibitors or uncouplers of oxidative phosphorylation (antimycin, azide, dinitrophenol) under normoxic conditions also upregulated glucose transporter expression. These results suggest that reduced rates of oxidative metabolism may represent an important signal for cells to adapt metabolically to hypoxia. Furthermore, in our examination of endothelial cell energy metabolism, we discovered that endothelial cells contain phosphocreatine and express both the brain and muscle isozymes of creatine kinase.

Animals↗
PubMed1991

A fluorescence technique to distinguish attached from ingested erythrocytes and zymosan particles in phagocytosing macrophages.

While investigating the role of [Ca2+]i in Fc receptor-mediated phagocytosis, we found that clamping the [Ca2+]i to low levels by a variety of methods often led to increased plasma membrane permeability, rendering the hypotonic lysis method for calculating the phagocytosis index unreliable. To overcome this difficulty we developed a method for calculating the phagocytosis index of IgG-coated RBC that does not depend on hypotonic lysis. It depends on the ability of ingested RBC to create dark-appearing phagocytic vacuoles when the cytoplasm of murine macrophages is stained with acridine orange. Uningested or partially ingested RBC do not change the appearance of the otherwise uniformly stained cytoplasm of the macrophages. Since this method does not rely on hypotonic lysis to distinguish attached from ingested RBC, it can be used in situations when macrophages are unusually sensitive to hypotonic treatment (e.g. after clamping the macrophage [Ca2+]i to low levels). It can also be applied to the study of phagocytosis of particles that are not susceptible to hypotonic lysis (e.g., zymosan).

Acridine Orange↗
PubMed1991

CD11c/CD18 on neutrophils recognizes a domain at the N terminus of the A alpha chain of fibrinogen.

Fibrinogen and fibrin serve as adhesive substrates for a variety of cells including platelets, endothelial cells, and leukocytes. Previously, we identified the C terminus of the gamma chain of fibrinogen as the region of the fibrinogen molecule that contains a ligand for CD11b/CD18 (complement receptor 3) on phorbol ester-stimulated polymorphonuclear leukocytes. In contrast, we report here that neutrophils stimulated with tumor necrosis factor adhere to fibrinogen-coated surfaces, but not to human serum albumin-coated surfaces, via the integrin CD11c/CD18 (p150/95). Monoclonal antibodies LeuM5 and 3.9, which are directed against the alpha subunit of CD11c/CD18, but not monoclonal antibodies OKM10 and OKM1, which are directed against the alpha subunit of CD11b/CD18, inhibit the adhesion of tumor necrosis factor-stimulated neutrophils to fibrinogen-coated surfaces. To identify the site on fibrinogen recognized by CD11c/CD18, we have examined the adhesion of tumor necrosis factor-stimulated neutrophils to surfaces coated with various fibrinogen fragments. Stimulated neutrophils adhere to surfaces coated with the N-terminal disulfide knot fragment of fibrinogen or fibrinogen fragment E. Moreover, peptides containing the sequence Gly-Pro-Arg (which corresponds to amino acids 17-19 of the N-terminal region of the A alpha chain of fibrinogen), and monoclonal antibody LeuM5, block tumor necrosis factor-stimulated neutrophil adhesion to fibrinogen and to the N-terminal disulfide knot fragment of fibrinogen. Thus, CD11c/CD18 on tumor necrosis factor-stimulated neutrophils functions as a fibrinogen receptor that recognizes the sequence Gly-Pro-Arg in the N-terminal domain of the A alpha chain of fibrinogen.

Amino Acid Sequence↗
PubMed1991

Cryopreserved cytoplasts from human neutrophils migrate across monolayers of human endothelial cells in response to a chemoattractant gradient.

We have measured the capacity of two types of granule-poor anucleate cytoplasmic fragments (cytoplasts) from human polymorphonuclear leukocytes (PMN) to migrate across the barrier imposed by monolayers of human umbilical vein endothelial cells (EC) with and without chemotactic stimulation by fMLP. Cytoplasts were made by brief heating of PMN attached to surfaces (CKP) or by discontinuous gradient centrifugation (U-CYT). In the absence of chemoattractant, both types of cytoplast adhered poorly to endothelial cell monolayers, as did unstimulated intact PMN from which the cytoplasts were derived. In the presence of a transendothelial chemoattractant gradient both types of cytoplast exhibited a marked increase in adherence to, and migration across, endothelial monolayers; CKP did so to the same extent as chemoattractant-stimulated intact PMN. Since these motile cytoplasts are markedly deficient in most cytoplasmic organelles they may serve as useful tools for the dissection of cellular mechanisms that mediate PMN migration across endothelia.

Cell Movement↗
PubMed1991

Ca(2+)-independent F-actin assembly and disassembly during Fc receptor-mediated phagocytosis in mouse macrophages.

Phagocytosis of IgG-coated particles by macrophages is presumed to involve the actin-based cytoskeleton since F-actin accumulates beneath forming phagosomes, and particle engulfment is blocked by cytochalasins, drugs that inhibit actin filament assembly. However, it is unknown whether Fc receptor ligation affects the rate or extent of F-actin assembly during phagocytosis of IgG-coated particles. To examine this question we have used a quantitative spectrofluorometric method to examine F-actin dynamics during a synchronous wave of phagocytosis of IgG-coated red blood cells by inflammatory mouse macrophages. We observed a biphasic rise in macrophage F-actin content during particle engulfment, with maxima at 1 and 5 min after the initiation of phagocytosis. F-actin declined to resting levels by 30 min, by which time particle engulfment was completed. These quantitative increases in macrophage F-actin were reflected in localized changes in F-actin distribution. Previous work showed that the number of IgG-coated particles engulfed by macrophages is unaffected by buffering extracellular calcium or by clamping cytosolic free calcium concentration ([Ca2+]i) to very low levels (Di Virgilio, F., B. C. Meyer, S. Greenberg, and S. C. Silverstein. 1988. J. Cell Biol. 106: 657-666). To determine whether clamping [Ca2+]i in macrophages affects the rate of particle engulfment, or the assembly or disassembly of F-actin during phagocytosis, we examined these parameters in macrophages whose [Ca2+]i had been clamped to approximately less than 3 nM with fura 2/AM and acetoxymethyl ester of EGTA. We found that the initial rate of phagocytosis, and the quantities of F-actin assembled and disassembled were similar in Ca(2+)-replete and Ca(2+)-depleted macrophages. We conclude that Fc receptor-mediated phagocytosis in mouse macrophages is accompanied by an ordered sequence of assembly and disassembly of F-actin that is insensitive to [Ca2+]i.

Actin Cytoskeleton↗
PubMed1990

Colocalization of F-actin and talin during Fc receptor-mediated phagocytosis in mouse macrophages.

We have studied the distribution of talin in J774 cells and mouse peritoneal macrophages undergoing Fc receptor-mediated phagocytosis. At early stages of phagocytosis, talin accumulates in the cells' cortical cytoplasm adjacent to the forming phagosome and extends into pseudopods that are encircling the particle. Talin colocalizes with F-actin at these sites. After particle ingestion is completed, F-actin and talin are no longer concentrated adjacent to phagosomes. Thus, talin and F-actin undergo dynamic and coordinate changes in their cytoplasmic location during Fc receptor-mediated phagocytosis.

Actins↗
PubMed1990

Organic anion transport in macrophage membrane vesicles.

Cells of the J774 mouse macrophage-like cell line possess organic anion transporter that transport fluorescent dyes such as Lucifer Yellow out of the cytoplasmic matrix of the cells; the dye is both sequestered in endosomes and secreted into the extracellular medium. Lucifer Yellow that is sequestered within endosomes is subsequently delivered to the lysosomal compartment. In the present studies we demonstrated that probenecid inhibited removal of Lucifer Yellow from the soluble cytoplasm and sequestration into membrane bound organelles by quantitating Lucifer Yellow fluorescence in both soluble and membrane-associated fractions of J774 cells. In addition, we examined the uptake of Lucifer Yellow into isolated subcellular organelles derived from J774 cells. Lucifer Yellow transport in the organellar fraction of J774 cell homogenates was temperature- and pH-dependent and did not require ATP. Subcellular organelles from J774 cells were fractionated into endosome- and lysosome-enriched fractions by Percoll density gradient centrifugation. Lucifer Yellow was preferentially taken up by vesicles of the endosome-enriched fraction, and this transport was inhibited by probenecid. These studies provide direct evidence that probenecid inhibits Lucifer Yellow transport out of the cytoplasmic matrix and into cytoplasmic vacuoles in J774 cells and that organic anion transport in isolated organelles derived from J774 cells occurs preferentially in endosome, rather than in lysosome-enriched fractions; they suggest that Lucifer Yellow is carried across membranes via a secondary active transport process that requires proton symptom or hydroxyl anion antiport.

Adenosine Triphosphate↗
PubMed1990

Macrophages form circular zones of very close apposition to IgG-coated surfaces.

When phagocytes spread on surfaces coated with ligands such as IgG, they form a tight seal with the substrate. This seal excludes soluble macromolecules in the medium from the interface between the cell and substrate. In contrast, when cells spread on control surfaces that are not coated with ligands, the underside of the cell remains freely accessible to soluble proteins (Wright and Silverstein: Nature 309:359, 1984). We employed reflection-interference microscopy (RIM) to determine where the seal forms during interaction with ligand (IgG)-coated surfaces. Human monocyte-derived macrophages (MO) were plated at 37 degrees C on dinitrophenylated (DNP)-glass coverslips (control substrate), IgM anti-DNP-DNP-coated glass (control substrate), or on IgG anti-DNP-DNP-coated glass (phagocytosis-promoting substrate). Live or fixed cells were examined by RIM. Spreading on control surfaces at 37 degrees C was complete in 25 minutes, whereas spreading on IgG-coated surfaces was maximal within 15 minutes and resulted in cell-substrate contact area 1.6 X that of control cells. Within 1 h at 37 degrees C, 90% of MO that spread on IgG-coated substrates, but not on control substrates, excluded macromolecules from their underside. A minor population of cells (19%) exhibited a uniform iron gray RIM appearance indicating an even, close approach to the substrate. These cells may represent early stages of frustrated phagocytosis. In contrast to cells on control substrates, 70% of cells on IgG-coated substrates developed continuous peripheral dark rings in RIM indicative of close association with the substrate. Essentially all cells with peripheral dark rings in RIM excluded macromolecules from their underside. Enclosed within this ring was an area of greater separation between the cell membrane and the substrate, as indicated by the lighter grey of this region in RIM and by the accessibility of substrate to anti-substrate antibody when breaks in the dark ring occur. Thus, MO can create a closed compartment between plasma membrane and substrate that excludes proteins in the surrounding medium, thereby protecting substances secreted into this space from potentially inhibitory substances in the medium.

Cell Communication↗
PubMed1990

Glucose transporters serve as water channels.

Water traverses the plasma membranes of some eukaryotic cells faster than can be explained by the water permeability of their lipid bilayers. This has led to a search for a water channel. Our previous work identified glucose transporters as candidates for such a channel. We report here that Xenopus laevis oocytes injected with mRNA encoding the brain/Hep G2, adult skeletal muscle/adipocyte, or liver forms of the glucose transporter exhibit an osmotic water permeability of their plasma membranes larger than that of untreated oocytes. The osmotic water permeability component attributable to glucose transporters increased an average of 4.8-fold in the injected oocytes. These studies provide direct evidence that the facilitative, sodium-independent mammalian glucose transporters serve as membrane water channels.

Animals↗
PubMed1990

Defect in the tissue cellular immune response: experimental visceral leishmaniasis in euthymic C57BL/6 ep/ep mice.

In BALB/c mice, successful defense against visceral leishmaniasis is T cell dependent, expressed by tissue granuloma formation, and probably mediated by macrophages activated by cytokines, including gamma interferon (IFN-gamma). C57BL/6 ep/ep (pale ear) mice, which reportedly exhibit impaired IFN-gamma production, were challenged with Leishmania donovani to determine the outcome of infection in a euthymic host with an apparent defect in lymphokine secretion. In BALB/c and normal C57BL/6 mice, L. donovani liver burdens peaked at 2 weeks and were largely eliminated by 4 weeks. In contrast, in pale ear mice, infection progressed until after 4 weeks and persisted at high levels at 8 weeks. The failure to resolve hepatic infections was not related to deficiencies in (i) Thy-1+, L3T4+, or Lyt-2+ T cells; (ii) IFN-gamma secretion; (iii) liver tissue Ia expression; (iv) macrophage antimicrobial capacity; or (v) antileishmanial antibody production. However, despite the anticipated influx of mononuclear cells into livers, these cells were not properly focused on the parasitized Kupffer cells, the inflammatory infiltrate receded prematurely, and mature granulomas failed to develop. These results suggest that there is a cellular immune defect at the tissue level and emphasize the critical role of granuloma formation in successful resolution of systemic intracellular infections.

Animals↗
PubMed1986

Creatine uptake, metabolism, and efflux in human monocytes and macrophages.

The uptake of creatine in human monocytes and monocyte-derived macrophages can be divided into two components. One component of uptake is saturable (Km = 30 microM), specific for creatine, requires Na+ in the extracellular medium, and enables cells to take up creatine against a concentration gradient of creatine. The second component of uptake is nonsaturable and accounts for less than 10% of creatine uptake at physiological creatine concentrations (20-60 microM). Both monocytes and macrophages have similar Km values for creatine transport. However, macrophages exhibit a fivefold greater rate of creatine uptake than monocytes (3.6 vs. 0.7 pmol X micrograms protein-1 X h-1), indicating that monocyte differentiation into macrophages is associated with an increase in the number of creatine transporters in the membrane. Monocytes do not contain creatine kinase and do not phosphorylate creatine; monocyte-derived macrophages express creatine kinase and phosphorylate approximately 25% of intracellular creatine. These results and the finding that 2-deoxyglucose inhibits creatine phosphorylation by macrophages without affecting the transport of creatine indicate that phosphorylation of creatine is not required for net creatine accumulation.

Biological Transport, Active↗
PubMed1979

Increased ATP and creatine phosphate turnover in phagocytosing mouse peritoneal macrophages.

Resident and thioglycollate-elicited macrophages maintained in culture for 24 h contain approximately 5 x 10(-16) and 12 x 10(-16) mol of ATP per cell, respectively. During particle ingestion, the levels of ATP in these cells did not change. However, the specific activity of ATP extracted from macrophages labeled with [32P]Pi during phagocytosis was 40% lower than ATP extracted from control cells. These results suggested that macrophages contain a high energy phosphate reservoir, in addition to the ATP pool(s). A search for such a reservoir led to the identification of creatine phosphate in both resident and thioglycollate-elicited macrophages at concentrations that are in 3- to 5-fold-molar excess over ATP. Creatine phosphate levels in phagocytosing resident macrophages decreased by 45%, while creatine phosphate levels in phagocytosing thioglycollate-elicited macrophages did not change. Creatine phosphate turnover was measured in macrophages prelabeled with [14C]creatine. Over 90% of the intracellular label was in the form of creatine phosphate. During phagocytosis, there was a 40% decrease in intracellular [14C]creatine phosphate in both resident and thioglycollate-elicited macrophages. These results indicate that creatine phosphate turns over more rapidly during phagocytosis and replenishes the ATP consumed.

Adenosine Triphosphate↗