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At least 487 records · Page 27Linked to original sources
PubMed1983

Studies on in vitro chrysotile-pleural mesothelial cell interaction: morphological aspects and metabolism of benzo-3,4-pyrene.

Cultures of rat pleural mesothelial cells (PMC) were exposed to nonlethal doses of UICC chrysotile A. The morphology was studied by optical and electron microscopy. The consequences of chrysotile ingestion on the rate of pinocytosis of horseradish peroxidase (HPR) metabolism and benzo-3-4-pyrene (BP) were studied. Nonlethal doses of chrysotile (5 micrograms/mL) induced a time-dependent vacuolation of PMC; a dose-dependent inhibition of the vacuolation was observed when PMC were pretreated with DMSO. The origin of the vacuoles is not clear, but some features of autophagy and lysosomal storage were observed. Chrysotile fibers did not modify the rate of pinocytosis of HRP. Similarly, the metabolism of BP was unchanged when BP and chrysotile were both added to the culture medium or when PMC were preincubated with the fibers 24 hr prior to the addition of BP.

Animals↗
PubMed1988

The role of renal macrophages in the aglomerular kidney of the sea-horse (teleost) in the removal of exogenous macromolecules from circulating blood.

Mechanisms involved in the removal of exogenous macromolecules from circulating blood were investigated in the aglomerular nephrons of the kidney of the sea-horse, Hippocumpus kuda Bleeker, using either native anionic or cationized probes. After intraperitoneal injection of native anionic horse-spleen ferritin (HS-AF) or cationized one (HS-CF) into the sea-horse, kidneys and gills were examined morphologically at intervals of 1 h to 14 days. Histochemical and immunohistochemical studies and transmission electron microscopy of the kidneys revealed that most of the injected HS-AF or HS-CF were taken up by macrophages in the sinusoids of hemopoietic tissue through pinocytosis, being gradually accumulated into their phagolysosomes. By the 14th day, the injected ferritin particles were degraded and the ferric agglomerates were concentrated within the phagolysosomes. Then the macrophages heavily laden with densely packed ferric catabolites migrated into the hemopoietic area forming macrophage agglomerates or macrophage centers. Some HS-AF and HS-CF particles infiltrated into the tubular basement membrane, where they were taken up by the tubular epithelial cells through pinocytosis, translocated into the phagolysosomes, fragmented into small ferric catabolites and then excreted into the urinary space. In contrast, examination of the gills revealed neither HS-AF, HS-CF particles nor their histochemically detectable ferric catabolites in either the interstitial space including basal lamina or the alveolar epithelia. It seems that no appreciable egress of exogenous substances occurs from the gill into the environmental water.

Animals↗
PubMed2000

Macrophages present pinocytosed exogenous antigen via MHC class I whereas antigen ingested by receptor-mediated endocytosis is presented via MHC class II.

Macrophages present exogenous Ag either via MHC class I or MHC class II molecules. We investigated whether the mode of hemagglutinin (HA) uptake influences the class of MHC molecule by which this Ag is presented. Normally, HA is ingested by receptor-mediated endocytosis, but this may be switched to macropinocytosis and pinocytosis by adding phorbol esters to the cells. This switch resulted in altered intracellular routing of ingested Ag and a transition from Ag presentation via MHC class II molecules to presentation via MHC class I molecules. Similarly, inhibition of receptor-mediated HA endocytosis, by treating the cells with the HA receptor destroying enzyme neuraminidase, abrogated Ag presentation via MHC class II molecules and induced presentation via MHC class I molecules. If, however, under these conditions, receptor-mediated uptake of HA was restored, by virtue of HA/anti-HA Ab interaction and subsequent uptake of HA via the Fc receptor, presentation via MHC class II was restored as well, whereas presentation of HA via MHC class I molecules was no longer detectable. We conclude that in macrophages the mode of Ag uptake is decisive in determining via which class of MHC molecules Ag is presented: pinocytosis and macropinocytosis produce exclusive presentation of exogenous Ag via MHC class I molecules whereas receptor-mediated endocytosis leads exclusively to presentation via class II molecules.

Animals↗
PubMed1991

Neutrophil activation through high-affinity Fc gamma receptor using a monomeric antibody with unique properties.

The high-affinity, type I Ig Fc receptor (Fc gamma RI) for human IgG1, human IgG3, murine IgG2a, and murine IgG3 is highly expressed on monocytes, neutrophils (PMN) in certain disease states, and phagocytes treated with interferon-gamma (IFN-gamma). We studied the activation of the human PMN oxidative burst and stimulated fluid pinocytosis induced by three monoclonal antibodies (MoAbs) directed against Fc gamma RI (CD64) to study the role of this receptor in Fc-mediated cellular activation. All three MoAbs were capable of triggering PMN activation from IFN-gamma-treated PMN when cross-linked with goat antimurine Ig reagents. However, MoAb 197 alone demonstrated a concentration-dependent activation of the oxidative burst without the use of a second cross-linking antibody. The oxidative burst and stimulated fluid pinocytosis responses induced by monomeric MoAb 197 could be elicited only after the IFN-gamma induction of approximately 8,000 Fc gamma RI receptor equivalents and did not occur in freshly isolated or control-cultured PMN. Competitive blocking of Fc binding of MoAb 197 by human IgG or purified Fc fragments inhibited cellular activation. We believe the ability of MoAb 197 to activate these oxidative burst and fluid pinocytic responses was because of its murine IgG2a subclass, which allowed it to function as a trivalent anti-Fc gamma RI antibody binding through the combination of its two FAB regions and the Fc domain. This study demonstrates that the cross-linking of CD64 can activate PMN oxidative and endocytic responses and supports a role for Fc gamma RI in the human neutrophil inflammatory response.

Antibodies, Monoclonal↗
PubMed1979

Evidence of active transport (filtration?) of plasma proteins across the capillary walls in muscle and subcutis.

Under slight lymphatic stasis (tilting the body 15 degrees) we measured the arrival of locally injected 131I-albumin in the plasma pool. From 30 min to 90 min after the injection the return rate was zero, i.e. local back transport in the two tissues studied, muscle and subcutaneous fat, is very small. Compared with a suggested steady state total 131I-albumin clearance of 1.7%/hour in the horizontal body position, we conclude that a maximum of 1% of the interstitial albumin can have a local transendothelial escape, i.e. can be handled by passive forces, such as diffusion and pinocytosis. Since passive flux is proportional to the concentration, and since the interstitial albumin concentration is about half the plasma concentration, then also diffusion and/or pinocytosis of albumin from the plasma is negligible in the resting normal human. We suggest that filtration through large leaks is the main mechanism for transendothelial protein transport.

Adipose Tissue↗
PubMed1988

Cationization of protein antigens. IV. Increased antigen uptake by antigen-presenting cells.

Cationization of BSA generates a molecule that mounts antibody responses of increased magnitude and duration and induces T cell proliferation at concentrations 500 times less than native BSA (nBSA). To explain the alteration in immunogenic properties of this Ag, the uptake of nBSA and cationized BSA (cBSA) by splenic APC has been investigated. T cell proliferation assays were conducted with nBSA and cBSA preparations with varying degrees of substitution. An inverse correlation between the degree of cationization and the amounts of Ag needed for optimal T cell reactivity was observed. To determine whether affinity for APC resulted in an increased uptake of cBSA, splenic APC were incubated with nBSA or cBSA for varying amounts of time. Comparisons were made at each time point between untreated Ag-pulsed APC (Ag uptake) and paraformaldehyde-fixed Ag-pulsed APC (processed Ag). Proliferation of T cells primed with nBSA or cBSA increased in proportion to the amount of time of APC exposure to high concentrations of nBSA, first appearing after a 2-h pulse and peaking at 8 h. Conversely, untreated APC needed only a 30-min cBSA exposure to induce either nBSA- or cBSA-primed T cell proliferation, indicating a rapid uptake of cBSA. Comparisons with proliferation induced by paraformaldehyde-fixed cBSA APC indicate that nBSA T cells recognize a lag phase-processed form of cBSA, whereas a majority of cBSA T cells recognize either a rapidly processed form of cBSA, or a membrane-processed cBSA molecule without a classical lag phase processing event. When monensin was used as an inhibitor of fluid phase pinocytosis in splenic APC, the presentation of nBSA was inhibited by 85%, but the presentation of cBSA was inhibited by only 20%. These results imply that nBSA enters the cell by fluid phase pinocytosis, whereas cBSA enters by a nonspecific adsorptive mechanism. The different modes of cellular entry for the two molecules, nBSA and cBSA, resulting in a rapid uptake of cBSA, may have important ramifications on T cell activation and immunoregulation.

Animals↗
PubMed1987

Shape, movement and function of neutrophil granulocytes.

Evidence that distinct types of shapes and movement can be induced by different neutrophil-activating agents like the chemotactic peptides and PMA is reviewed. Front-tail polarity seems to be preferentially associated with locomotion, whereas non-polar cells with surface projections show preferentially pinocytosis. The following partially hypothetical concept on neutrophil shape changes has been derived from these experiments: Neutrophils are capable to perform distinct types of movements depending on the stimulus or stimuli. Distinct movements are preferentially associated with distinct functions such as locomotion, pinocytosis or others. The underlying cytoskeletal changes may differ accordingly.

Animals↗
PubMed1974

Normal peritoneal lymphocytes: A population with increased capacity for endocytosis.

The existence of lymphocyte to macrophage transformation among normal peritoneal lymphocytes (NPLs) was considered. We described the conditions under which pinocytosis of the enzyme tracer horseradish peroxidase (HRP) and phagocytosis of latex particles by NPLs occurred and compared these data with results obtained with splenic lymphocytes (SpLs), a better characterized source of lymphocytes. In the presence of relatively large concentrations (200 mug/ml to 1 mg/ml) of HRP, at least three times as many NPLs took up the protein by pinocytosis as did corresponding SpLs. Also, on the average, NPLs took up about twice as much HRP per cell than did SpLs. The uptake was rapid, and pinocytotic vesicles containing HRP were seen as early as 15 minutes after exposure to the tracer in NPLs but not in SpLs. In contrast to peritoneal macrophages, NPLs retained HRP in a variety of cytoplasmic vesicles and vacuoles in relatively undegraded form for at least 24 hours. Finally, if NPLs, which were nonphagocytic when freshly isolated, were cultured for 24 hours, both erythrophagocytosis and phagocytosis of latex spheres were observed. The cells which had taken up the latex were nonadherent to plastic, resembled lymphocytes ultrastructurally and were peroxidase negative. We concluded that under these culture conditions, NPLs had not transformed into morphologic macrophages, but phagocytic lymphocytes.

Animals↗
PubMed1982

Membrane activity and topography of F-Met-Leu-Phe-Treated polymorphonuclear leukocytes. Acute and sustained responses to chemotactic peptide.

The chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (f-Met-Leu-Phe) causes a dramatic stimulation of membrane ruffling and a fluid pinocytosis in polymorphonuclear leukocytes (PMNs). These responses are maximal by 1 minute and subside within 5-10 minutes. The same immediate responses characterize cells exposed to several peptide hormones and may thus represent an essential component of target cell activation by peptides. The stimulation of the whole membrane following f-Met-Leu-Phe binding is succeeded by the development of a polarized cell shape with a posterior uropod and a broad anterior lamellipodium, both subtended by microfilaments. Membrane components and functions segregate into distinct domains on polarized PMNs. Thus, succinyl concanavalin A-receptor complexes are capped and internalized by receptor-mediated endocytosis at the uropod; the uptake by fluid pinocytosis of fluorescein-dextran is restricted to the uropod; and coated pits and coated vesicles are concentrated at the uropod. The lamellipodium excludes coated pits and lacks pinocytic activity but shows preferential binding of immunoglobulin aggregates, presumably to Fc receptors. The origin and physiologic implications of these asymmetries of membrane molecular and functional topography on polarized cells are discussed.

Adsorption↗
PubMed1982

[Morphofunctional study of human pericardial macrophages].

Human pericardial macrophages have been studied with the light and electron microscope. The cells showed high activities of acid phosphatase and of non-specific and acid esterases. The macrophages are able to pinocytosis the extracellular space marker--horseradish peroxidase. The network of intracytoplasmic cavities, continuous with the extracellular space, has been documented by applying two different methods of visualization of the cellular surface. A possible role of these cavities in pinocytosis is discussed.

Adult↗
PubMed1981

Endocytosis of simple proteins by rat yolk sacs and by rat peritoneal macrophages incubated in vitro.

The specificity of endocytosis of the 125I-labelled forms of LDH H4 and M4 and BSA was investigated in rat yolk sac and resident rat peritoneal macrophages incubated in vitro. The rate of uptake of the more basic LDH M4 by yolk sac is only slightly higher than that of LDH H4, but in macrophages the isoenzyme M4 is taken up three times more rapidly than the H4 form. Both cell types possess little affinity for BSA, but an increase in the hydrophobicity of this protein by formaldehyde-denaturation resulted in a several-fold increase in uptake by yolk sac cells as well as by macrophages. Apparently, yolk sacs and macrophages both contain binding sites for positively charged and hydrophobic proteins, but, in yolk sac hydrophobicity is relatively more important, whereas in macrophages positive charge is the main characteristic for adsorptive pinocytosis of simple proteins. In this respect, the binding characteristics of peritoneal macrophages resemble those of sinusoidal liver cells. The study also compares the serum-dependence of fluid-phase pinocytosis in both cell types; a decrease in serum concentration gives rise to an increase in the rate of pinosome formation in yolk sac, but has the opposite effect in macrophages.

Animals↗
PubMed1978

Evidence of active transport (filtration?) of plasma proteins across the capillary walls in muscle and subcutis.

Under slight lymphatic stasis (tilting the body 15 degrees) we measured the arrival of locally injected I-albumin to the plasma pool. From 30 min. to 90 min. after the injection the return rate was zero i.e. local back transport in the two tissues studied viz.muscle and subcutaneous fat is very small. Compared to a suggested steady state total 131 I-albumin clearance of 1.7%/hour in the horizontal body position we conclude that maximally one percent of the interstitial albumin can have a local transendothetial escape i.e. can be handled by passive forces as is diffusion and pinocytosis. As passive flux is proportional to the concentration and the interstitial albumin comcentration is about half the plasma concentration then also diffusion and or pinocytosis from the plasma of albumin is negligble in the resting normal man. We suggest filtration through big leaks as the main mechanism for transendothelial protein transport.

Biological Transport, Active↗
PubMed1976

Reversible blood-brain barrier dysfunction to peroxidase after a small stab wound in the rat cerebral cortex.

Small stab wounds were made in the rat frontal lobe. The animals were injected with horseradish peroxidase intravenously at different times after the injury in order to study the extravasation of this tracer. There was a leakage of peroxidase into the brain during the first 3 days after the injury. The route of passage from the vessel lumen into the brain was through disrupted blood vessels in the injured region. Endothelial pinocytosis and formation of thin, trans-endothelial channel-like structures with or without a content of peroxidase were two other possible routes of passage across the blood vessels. Occasionally, badly damaged endothelial cells displayed a diffuse cytoplasmic distribution of peroxidase, indication a diffusion into and possibly across these injured cells. No widened tight junctions were seen. Thus, this study indicated four possible routes of passage of horseradish peroxidase across the endothelial cells: cellular gross damage with disrupture of the cells, diffusion across badly injured endothelial cells, possibly pinocytosis and formation of trans-endothelial channel-like structures. The cellular uptake of the tracer was vesicular in most neurons, astrocytes, oligodendrocytes and hematogeneous phagocytes. However, a diffuse distribution of the tracer was seen in some "dark" neurons near leaking vessels in the vicinity of the stab wound.

Animals↗
PubMed1996

Stimulation of cis-diamminedichloroplatinum(II) accumulation by modulation of passive permeability with genistein: an altered response in accumulation-defective resistant cells.

The effect of the tyrosine kinase inhibitor genistein on the accumulation of cisplatin (DDP) was investigated in DDP-sensitive and -resistant human 2008 ovarian carcinoma cell lines. DDP accumulation after a 1-h exposure was maximally increased by concurrent 40 micrometer genistein. The maximal stimulation of accumulation was observed after 2 h of total genistein exposure and was 83 +/- 13% (n = 5) higher than controls. With resistant C13(*) cells, however, the stimulation of accumulation was delayed until 4 h and was increased only 46 +/- 18% compared to controls. Revertant RH4 cells that retained the accumulation defect behaved like the C13(*) cells. Genistein stimulated [3H]mannitol accumulation (a marker of passive permeability) by 43 +/- 9% (n = 3) in 2008 cells, and the effect was maximal after 2 h of total genistein exposure. Changes in [3H]mannitol accumulation in 2008 parent cells were highly correlated with DDP accumulation (r = 0.9010). These experiments also revealed that [3H]mannitol accumulation after 2 h in C13(*) cells was reduced 38% compared to 2008 cells, a decrease that reflected the DDP accumulation defect. Fluid-phase pinocytosis determined with lucifer yellow CH as a marker showed no difference between 2008 and C13(*) cells and no effect of genistein. Genistein was demonstrated to clearly inhibit protein-tyrosine phosphorylation initiated by the epidermal growth factor receptor kinase. Differences were noted in the phosphotyrosine pattern between the 2008 and C13(*) cells. Under the conditions that had the maximal effect on DDP accumulation in 2008 cells, genistein decreased the IC50 of DDP 8.2-fold in 2008 cells and 4.7-fold in C13(*) cells. We conclude that: (a) genistein stimulates DDP accumulation by modulating the passive permeability of the plasma membrane; (b) C13(*) cells are less permeable to passively diffusing small molecules, which offers a mechanism for the DDP accumulation defect without invoking carrier proteins; (c) the effect of tyrosine kinase inhibition on passive permeability is altered in C13(*) cells; and (d) pinocytosis contributes insignificantly to DDP accumulation. Genistein, a dietary isoflavone, thus seems to be a promising clinical candidate for combination with DDP.

Antineoplastic Agents↗
PubMed1996

Granulocytes from chronic myeloid leukemia (CML) patients show differential response to different chemoattractants.

Binding of chemoattractant to polymorphonuclear leukocytes (PMNL) triggers a series of events like polymerization of actin and tubulin, orientation of cells, chemotaxis, increase in fluid pinocytosis and phagocytosis, and stimulation of microbicidal pathways which includes lysosomal degranulation and generation of reactive oxygen species. Earlier studies from our laboratory have shown that stimulation of chemotaxis, fluid pinocytosis, and actin polymerization of CML PMNL in response to a synthetic chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP) is significantly lower than that in normal PMNL. It is not known whether this lower response of CML PMNL to fMLP is a global phenomenon involving different chemoattractant receptors or is restricted to the fMLP pathway. We have evaluated chemoattractant induced degranulation process in normal and CML PMNL to fMLP, platelet activating factor (PAF), leukotriene B4 (LTB4), and an analogue of fMLP viz formyl-methionine-1 aminocyclooctane 1 carboxylic acid-phenylalanine-O-methionine (FACC8) using release of lysozyme as a parameter. We find that after stimulation with fMLP and FACC8, the mean percent release of lysozyme was significantly lower in CML PMNL as compared to that in normal cells (P < 0.001). There was no significant difference between the two after stimulation with PAF and LTB4. The results indicate that the fMLP pathway is suppressed in CML granulocytes whereas PAF and LTB4 pathways appear unaltered in these cells. We therefore also studied the kinetics of peptide-receptor interaction with a labelled hexapeptide fNLPNTL which binds to the fMLP receptor. Our results show that the number of fMLP receptors/cell is significantly lower in CML PMNL (P < 0.05) than in normal PMNL, while their affinity constants and dissociation constants were comparable.

Chemotactic Factors↗
PubMed2003

Selective enhancement of B cell antigen receptor-mediated antigen presentation by treatment with transforming growth factor-beta.

TGF-beta1 was examined for the ability to regulate Ag-presentation by B cells, using A20-HL B lymphoma cells bearing TNP-specific IgM receptors. Treatment of A20-HL cells with TGF-beta1 at 1 ng/ml, a concentration that inhibited proliferation, enhanced presentation of Ag internalized via surface IgM (sIgM), but not via fluid-phase pinocytosis. TGF-beta1-treatment slightly enhanced surface expression of sIgM, but not of MHC class II molecules. The treatment accelerated recovery of sIgM expression after its removal by ligation with TNP-OVA, and induced prolonged intracellular residence of TNP-OVA internalized via sIgM, which co-localized with intracellular MHC class II molecules. TGF-beta1-treatment increased accumulation of newly synthesized intracellular MHC class II molecules that were localized in compartments positive for lysosome-associated membrane protein 1, although cellular protein synthesis was decreased by the treatment. The accumulated intracellular MHC class II molecules were triggered to the cell surface by ligation of sIgM. Finally, TGF-beta1-treatment induced Igalpha-phosphorylation in response to lower concentrations of TNP-OVA. On the basis of these findings, we conclude that TGF-beta1-treatment of A20-HL cells selectively enhances the ability to present Ag internalized via sIgM, not via fluid-phase pinocytosis, through accelerating sIgM recovery, increasing accumulation of intracellular MHC class II molecules and enhancing the ability of sIgM ligation to induce Igalpha-phosphorylation.

Antigen Presentation↗
PubMed2003

Functional characterization of mannose receptor expressed by immunocompetent mouse microglia.

The mannose receptor is a pattern-recognition receptor involved in innate and adaptive immunity. The receptor is mainly expressed by macrophages and, within the brain, by astrocytes and microglia. This study reports for the first time the effects of two classical proinflammatory (interferon-gamma, IFNgamma) and anti-inflammatory (interleukin-4, IL-4) cytokines on the levels of expression and activity of the mannose receptor expressed by mouse microglia, the brain resident macrophages. As observed for macrophages, IFNgamma treatment led to a decrease and IL-4 to an increase of mannose receptor expression. Consequently, the rates of pinocytosis were strongly upregulated by IL-4 and inhibited by IFNgamma. This latter, however, resumed with time and reached again the constitutive rate of pinocytosis. This recovery resulted from an increased pinocytic activity of the few mannose receptor molecules still expressed by IFNgamma-treated microglia. This may suggest a brain-specific regulation of the effects of IFNgamma since such a phenomenon has not been observed in macrophages. Together, these observations demonstrate that cytokine-stimulated immunocompetent microglia express a functional mannose receptor.

Animals↗
PubMed1994

Cell surface control of differentiation in Acanthamoeba.

Acanthamoeba castellanii (Neff) is a free-living soil amoeba with close relatives that are opportunistic pathogens. Trophozoites differentiate into cysts when deprived of nutrients; cysts convert into trophozoites, leaving the wall behind, in the presence of nutrients. The data presented here, which includes immunoaffinity purification of the receptor, indicate that cell surface molecular signals also control Acanthamoeba differentiation in both directions. Monoclonal antibodies that bind specifically to a 40 kD trophozoite protein initiate the encystment of trophozoites. When bound to cysts the same monoclonal antibodies prevent excystment. Washing away the antibody allows both trophozoites and cysts to resume normal activity. One of these monoclonal antibodies inhibits pinocytosis, while another has no effect on pinocytosis.

Acanthamoeba↗