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Results for “Cell Aggregation”

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PubMed1976

Characterization of tumour cell aggregation promoting factor from rat ascites hepatoma cells: Separation of two factors with different antigenic property.

The previously described glycoprotein that promotes tumour cell aggregation, derived from rat ascites hepatoma cells and capable of partial purification by chromatography, was found to be a mixture of 2 factors with different antigenic property. One was not absorbed by immunoadsorbent chromatography with anti-rat serum antibody and the other was. The action of the unabsorbed factor was clearly more potent than that of the absorbed factor. Both the factors were found in the serum of tumour bearing rats and the action of the unabsorbed factor was also more potent than that of the absorbed factor; its amount increased with time after i.p. inoculation of the cells. The serum of healthy rats contained the absorbed factor but not the unabsorbed factor. It was thus assumed that the unabsorbed factor was associated with the hepatoma cell surface itself and released into the serum, while the absorbed factor was associated with serum protein coating the cell.

Animals↗

PubMed1987

Temperature-dependence of red cell aggregation.

To investigate the temperature-dependence of red cell aggregation 20 blood samples of normal donors and 20 blood samples of patients with venous ulcers of the leg were examined by photometric aggregometry at 3 degrees C, 10 degrees C, 20 degrees C, 30 degrees C and 37 degrees C. With decreasing temperature red cell aggregates become more resistant to hydrodynamic dispersion and they become more prone to growing under low shear stress. It is concluded that a decrease in temperature causes an increase in adsorptive energy of red cell aggregation, which is most likely due to an increase in molecular adsorption stress. Red cell aggregate formation as an overall process is retarded by a decrease in temperature, which is primarily due to an increase in plasma viscosity causing increased damping of aggregate formation. Accordingly the rate constant of aggregate formation corrected for plasma viscosity increases with decreasing temperature. The temperature-dependence of the kinetic parameters can be explained by a theoretical model that suggests the increase in contact area between aggregating red blood cells as the rate-limiting step of red cell aggregation. As a whole red cell aggregation is favoured by lowering of temperature.

Erythrocyte Aggregation↗

PubMed1983

Calcium-induced compaction and its inhibition in embryonal carcinoma cell aggregates.

H6 embryonal carcinoma cells form aggregates of cells in culture medium which contains 2 mM calcium. These aggregates are described as uncompacted, indicating that the individual cells of the aggregate are spherical and are in limited contact with each other. In contrast, compaction of the aggregate, induced by increasing the calcium concentration, results in a tight mass of cells flattened against one another and connected by intercellular junctions. At least 85-97% of the aggregates undergo compaction in 7 mM calcium and are subsequently decompacted if removed to 2 mM calcium. Since calcium ionophore A23187 does not induce compaction, extracellular rather than intracellular calcium seems to be the limiting factor. We have demonstrated that this calcium-induced morphogenetic change is sensitive to inhibition by agents which also prevent the calcium-dependent compaction of the 8-cell mouse embryo. The cytoskeletal-binding drugs tetracaine HCl, colcemid, vinblastine, colchicine, and cytochalasin B each inhibit compaction of H6 aggregates. Interference at surface molecule sites by exposure to the lectins wheat germ agglutinin or concanavalin A or by interruption of glycosylation with exposure to tunicamycin, or by reaction with anti-H6 Fab or anti-F9, also prevent compaction. Since the mouse embryo and embryonal carcinoma cells share certain processes which are involved in initiating and maintaining compaction, these processes and their subsequent roles in differentiation may be examined using embryonal carcinoma cell aggregates.

Animals↗

PubMed1992

Red cell aggregation and the echogenicity of whole blood.

To study the relationship between red cell aggregation and whole blood echogenicity, red cell aggregation was quantitated by a photometric method, whole blood echogenicity was quantitated by videodensitometry and sedimentation rate was quantitated by a modified Westergren method. Changes in red cell aggregation were produced by alterations in the hematocrit. The results showed that red cell aggregation increased in a linear fashion with increases in hematocrit. The sedimentation rate decreased in a linear manner with increases in hematocrit. Whole blood echogenicity showed a biphasic response, with an initial increase in echogenicity, peaking at hematocrits varying from 14-24% and decreasing thereafter. Over the physiologic range of hematocrits, an increase in the formation of red cell aggregates is associated with a decrease in the echogenicity of whole blood. Thus, red cell aggregates were not visible using our ultrasound equipment at physiologic hematocrits, and the echo contrast in blood under our experimental conditions at these hematocrits must represent either plasma spaces, platelet aggregates or possibly white cell aggregates. The association between spontaneous contrast and a propensity for thromboembolism imply that platelet aggregates are the most likely origin of in vivo echo contrast in flowing blood.

Animals↗

PubMed1968

On the shear rate dependence of red cell aggregation in vitro.

Non-Newtonian viscosity of blood, i.e., the rise in apparent viscosity at low flow, was believed to be a result of reversible aggregation of red cells at low velocity gradients (shear rate). By making a cone-plate viscometer transparent, direct observation was made possible of the blood flowing under defined shear rates. Red cell aggregates, occurring in all cases at low flow, were reversibly dispersed by increasing the shear rate. This behavior was independent of the addition of anticoagulants, but it could be altered by changing the plasma protein composition. Red cells in serum did not form aggregates; such nonaggregating samples did show an increase in viscosity at low shear rates. Since the sedimentation rate can be influenced by many parameters, it is not reliable in describing red cell aggregation. Aggregation of red cells is linked with a marked separation of plasma and cells. Such a separation is of considerable influence on cone-plate viscometry.

Journal Article↗

PubMed1979

Role of hydrogen bonding in red cell aggregation.

The role of hydrogen bonding in red cell aggregation induced by dextran was studied with the use of urea, an inhibitor for hydrogen bonding. In order to avoid hemolysis of red cells by the high concentration of urea, the studies were performed on human red cells hardened in glutaraldehyde. The degree of red cell aggregation at Hct = 45% was estimated by the use of a coaxial cylinder viscometer. The viscometric aggregation index (VAI) was calculated from viscosity values at shear rates of 52 sec-1 (eta H) and 0.05 sec-1 (eta L); VAI = (eta L - eta H)/eta H. Red cells with surface charge intact and with charge removal by neuraminidase treatment were studied. Urea at high concentrations, e.g., 6 M, significantly inhibited red cell aggregation induced by dextran. These findings indicate that hydrogen bonding plays an important role in dextran-induced red cell aggregation. An understanding of the nature of the forces involved in red cell aggregation serves to establish the physicochemical principles of cell-to-cell interactions induced by macromolecules.

Blood Viscosity↗

PubMed1991

Importance of cell-aggregation during induction of neural differentiation in PCC-7 embryonal carcinoma cells.

The importance of cell-aggregation during retinoic acid-induced neural differentiation of embryonal carcinoma cells was studied on the PCC-7 cell line. These cells were chosen as they display low tendency for spontaneous aggregation, and they develop preferentially to neurons upon induced in vitro differentiation. Forced aggregation of these cells, in the absence of retinoic acid, did not result in development of neuron- or glial-like cells. Application of retinoic acid prior to or after the cell-aggregation did not result in neural tissue-like differentiation, either. Irreversible induction of neural development was achieved if cell-aggregation and retinonic acid acted simultaneously, and for a period longer than 48 h. Retinoic acid, on the other hand, was found to be toxic on non-aggregated PCC-7 cells. Our data suggest that cell to cell contacts alter the response of these cells to retinoic acid, and their close apposition is a prerequisite for the retinoic acid-induced neural differentiation.

Animals↗

PubMed1975

Purification and characterization of the retina-specific cell-aggregating factor.

The tissue-specific, cell-aggregating component of embryonic neural retina cells was purified from the retina cell-aggregating factor and characterized as a glycoprotein. Its molecular weight in solution is in the range of 50,000, and it contains 10-15% carbohydrate. The amino-acid and carbohydrate compositions have been determined. The glycoprotein is produced by embryonic neural retina cells in primary monolayered cultures and is released into the medium. Its tissue-specific, cell-aggregating effect requires integrity of the polypeptide portion, but not of the carbohydrate portion. We suggest that the isolated molecule is a specific determinant of the embryonic retina cell-surface and that it is involved in mediating self-recognition and selective adhesiveness of these cells.

Amino Acids↗

PubMed1986

A monoclonal antibody that induces T cell aggregation reacts with vascular endothelial cells and placental trophoblasts.

We have found that a mouse monoclonal antibody (alpha Leu-13) to a 16 kilodalton human lymphocyte surface antigen reacts with vascular endothelial cells as determined by immunoperoxidase staining of frozen tissue sections. In earlier studies, alpha Leu-13 was found to induce purified T cells to aggregate when added to cultures in nanogram concentrations. In the studies reported here, alpha Leu-13 stained vascular endothelial cells of arteries, capillaries, and veins in all organs examined from adults. It also reacted weakly with epithelial cells of proximal tubules of the kidney and with nonkeratinized basal epithelial cells of the cervix and esophagus. When a panel of tissues from a 14-wk-old fetus was examined, alpha Leu-13 was not found to react with endothelial cells of any specimen. However, it did stain medullary thymocytes and placental trophoblasts of this fetus. The implications of these findings to the possible function of the Leu-13 antigen in immune ontogeny are discussed.

Antibodies, Monoclonal↗

PubMed1994

Hydra cell aggregate development is blocked by selective fragments of fibronectin and type IV collagen.

The Cnidarian, Hydra, is a simplified metazoan whose body wall is composed of an epithelial bilayer with an intervening extracellular matrix termed the mesoglea. Hydra mesoglea has been shown to have a number of components seen in higher invertebrate and vertebrate matrices, including fibronectin, type IV collagen, laminin, and heparan sulfate proteoglycan. Based on previous studies which indicated that extracellular matrix components are critical to hydra development, the current study was designed to determine the role of intact fibronectin and its various functional domains during development of hydra cell aggregates. Hydra cell aggregation involves the complete morphogenesis of adult hydra from pellets of dissociated hydra cells. During this development process, cells segregate into an epithelial bilayer and then deposit a new extracellular matrix prior to continuation of morphogenesis. Results from this study demonstrate that intact fibronectin and its 30-kDa gelatin binding domain are effective blockers of hydra cell aggregate development. The gelatin binding capacity of the 30-kDa fragment is lost upon reduction and in the present studies reduction and alkylation of this fragment resulted in a loss in its ability to block hydra cell aggregate development. Because of these findings and the potential for collagen interaction with the 30-kDa gelatin binding domain, studies were also performed with various type IV collagen domains. These studies indicated that both the NC1 and 7 S domains of type IV collagen were also effective blockers of hydra cell aggregate development. These results were mimicked when antibodies to fibronectin or type IV collagen were used. Structural changes in mesoglea, inhibition of cell proliferation, and changes in cell differentiation patterns accompanied the blockage of hydra cell aggregates. These results indicate that blockage may be due to alterations in mesoglea structure with accompanying effects on cell behavior. It is concluded that (i) fibronectin and type IV collagen are critical to the early stages of hydra cell aggregate development when the mesoglea is initially formed and that (ii) perturbation of aggregate development by fragments of these extracellular matrix components results in alterations in hydra cell division, cell differentiation, and morphogenesis.

Amino Acid Sequence↗

PubMed2003

A study of whole blood platelet and white cell aggregation using a laser flow aggregometer.

Both platelet aggregation and white blood cell aggregation are involved in pathological processes such as thrombosis, atherosclerosis and chronic inflammation. People in older age groups are likely to suffer from cardiovascular diseases and may have increased white cell and platelet aggregation which could contribute to this increased risk. This study aimed to compare white cell and platelet aggregation between different age and gender groups. Whole blood white cell aggregation and platelet aggregation were carried out on healthy volunteers using cytometric techniques. It was found that both white cell and platelet aggregation in the elderly group (white cell aggregation median value, 0.08; range, 0.02-0.14; platelet aggregation median value, 0.32; range, 0.1-0.39) were significantly higher (P = 0.017 for white cell aggregation, P = 0.007 for platelet aggregation) than in the younger group (white cell aggregation median value, 0.05; range, 0.01-0.14; platelet aggregation median value, 0.18; range, 0.07-0.36). No significant differences were found between the gender groups.

Adult↗

PubMedDate not supplied

Increased red cell aggregation in diabetes mellitus: association with cardiovascular risk factors.

Red cell aggregation may be higher in diabetic patients and may predispose to cardiovascular disease. Red cell aggregation was measured by a simple photometric method in 122 diabetic patients and 100 matched control subjects, to determine its relationship to cardiovascular risk factors. Red cell aggregation was significantly increased in both Type 1 (4.3 +/- 1.3 vs 3.4 +/- 1.2, p < 0.002) and Type 2 diabetic patients (5.5 +/- 1.5 vs 3.2 +/- 1.3, p < 0.0001). In all diabetic patients aggregation correlated with triglycerides, VLDL, and inversely with HDL and in Type 2 diabetic patients also with body mass index, hypertension, and inversely with duration of diabetes. On multiple regression analysis, triglycerides and body mass index showed an independent association with red cell aggregation and in Type 2 diabetic patients smoking was also associated with increased red cell aggregation. It is concluded that increased red cell aggregation may be one mechanism by which some cardiovascular risk factors could promote cardiovascular disease in diabetes.

Adult↗

PubMed2000

Rheo-acoustical study of the shear disruption of reversible aggregates. Ultrasound scattering from concentrated suspensions of red cell aggregates.

Shear-induced disruption of reversible aggregates or clusters in a concentrated suspension is investigated by ultrasound backscattering in the low shear regime. Fractal aggregates are considered as non-Brownian scatterers much smaller than the wavelength with acoustic properties close to those of the surrounding liquid, so that the attenuation of the coherent field is weak and multiple scattering can be neglected. The concept of variance in local particle volume fraction is used to deduce a first-order expression of the ultrasound scattering cross section per unit volume for Rayleigh scatterers in a dense suspension. On the basis of a scaling law for the shear-induced disruption of aggregates, the shear stress dependence of the ultrasonic scattered intensity from a dense suspension of clusters is derived. In a second part, the shear breakup of hardened red blood cell aggregates is investigated in plane-plane flow geometry by ultrasound scattering. Rheo-acoustical experiments are analyzed within the framework of the self-consistent field approximation and the scaling laws currently used in microrheological models. Finally, the ability of ultrasonic, light reflectometry and viscometry methods to provide quantitative information about red blood cell aggregation and membrane adhesiveness is discussed.

Acoustics↗

PubMed1992

Patterning in hydra cell aggregates without the sorting of cells from different axial origins.

Aggregates of Hydra cells were studied to find out how the primary centers that form new heads are generated in a system of cells in which the original pattern has been destroyed. Since cells that originate near the heads (apical cells) temporarily maintain a high level of head activation potential during aggregate formation and may contribute to pattern formation, their distribution in the aggregates was investigated. The mutual distances between labeled epithelial cells were followed by vitally staining apical cells with DAPI. The distribution was random during early regeneration stages (3, 6, 24 hr). These results show that epithelial cells originating from apical regions do not sort. That is, dynamic cell movement to generate rudiments of new heads is not necessary for head formation in aggregates. A possible explanation of the mechanism is discussed.

Animals↗

PubMed1979

Morphological differentiation of mechanically dissociated fetal rat brain in aggregating cell cultures.

Rotation-mediated aggregating cell cultures of mechanically dissociated fetal rat brains (15-16 days) were morphologically characterized at 4, 19, 26 and 40 days in vitro. The dissociated cells coalesced into spherical aggregates which increased in diameter from 340 micrometer at 4 days to 430 micrometer at 40 days. Cells within the aggregates developed from an undifferentiated state at 4 days to a population of morphologically mature neurons, astrocytes and oligodendrocytes (26 days in vitro) before degenerating. Synaptic contacts and myelinated axons appeared as the cells differentiated. Neurons tended to occur in clusters that were located in central regions of the aggregates, whereas astrocytes were more concentrated in the periphery. Synapses and myelinated axons were more abundant in central portions of the aggregates. The amount of myelin formed within the aggregates was less than in organotypic cultures or in vivo. These results show that the morphological differentiation of mechanically dissociated aggregates resembles the development of rat CNS in vitro. The ease with which large amounts of aggregates can be prepared provides an in vitro system which can be analyzed biochemically without the use of micro-methods. This advantage is particularly useful for multidisciplinary investigations in developmental neurobiology.

Animals↗

PubMed1990

Prevention and dispersion of contrast media induced red cell aggregates. An in vitro study.

Red cell aggregation was observed microscopically when human blood and contrast media were mixed on glass slides. Aggregation was more frequent in low-osmolal media: mainly rouleaux were formed in ioxaglate but irregular aggregates in non-ionic media. Aggregation was similar at concentrations of 150 and 300 mg I/ml. Pre-treatment of glass slides with heparinized saline reduced red cell aggregation but saline alone was almost as effective. Most of the irregular aggregates dispersed when saline or heparinized saline was applied to them. Saline and heparinized saline had an identical dispersing effect. After incubation of the aggregates in iopamidol in plastic tubes for one or five minutes, saline was injected into the tubes, and after mixing the solution was poured onto glass slides and examined under the microscope. Only a few small irregular aggregates were detected in 6/60 specimens. It is concluded that ionicity of a flushing medium and shear of the injection are able to disperse red cell aggregates during angiography.

Contrast Media↗

PubMed1990

cDNA structure and expression of calpactin, a peptide involved in Ca2(+)-dependent cell aggregation in sponges.

Aggregation of cells of the marine sponge Geodia cydonium is mediated by an aggregation factor (AF) particle of Mr 1.3 X 10(8). It is now reported that the AF particle is associated with calpactin, which was ascribed a role in the cell-adhesion process. In order to identify the sequence similarity to other members of the lipocortin family, the cDNA of sponge calpactin was cloned and found to display an 80% sequence similarity to vertebrate calpactin II but only a 47% similarity to calpactin I. The calpactin gene, which contains the consensus sequence coding for the amino acids G-T-D-E, was expressed in Escherichia coli and subsequently purified to a 37000-Mr polypeptide. Both the p32 and the p37 are provided with approximately two Ca2+ ions/molecule and the property to bind to phospholipids. The dissociation constant (calpactin-Ca2+) was in the absence of phospholipids in the range 500-700 microM-Ca2+ but in their presence about 20-30 microM-Ca2+. On the basis of (i) inhibition studies with antibodies to calelectrin and (ii) competition experiments with soluble phospholipids (both chemically defined as well as total homologous membrane lipids) we conclude that the AF-associated calpactin and plasma-membrane-bound phospholipid(s) are involved in cell-cell aggregation in sponges.

Amino Acid Sequence↗

PubMed2000

CBP1 associates with the Dictyostelium cytoskeleton and is important for normal cell aggregation under certain developmental conditions.

In cells of the eukaryotic microorganism Dictyostelium discoideum, at least eight small, four-EF-hand Ca(2+)-binding proteins of unknown function are expressed at specific times during development. One of these proteins, calcium-binding protein 1 (CBP1), first appears just prior to cell aggregation and then is present at relatively constant levels throughout development. To determine a role for CBP1 during development, the protein was used as bait in a yeast two-hybrid screen to reveal putative CBP1-interacting proteins. Two proteins identified in this screen were the actin-binding proteins, protovillin and EF-1alpha. Using an in vitro binding assay, both of these proteins were found to interact with CBP1 in the absence of Ca(2+), but the interaction of CBP1 with EF-1alpha was increased substantially by Ca(2+). CBP1 was also shown by fluorescence microscopy and by binding assays to associate with the actin cytoskeleton of Dictyostelium cells during development, and these interactions were partially Ca(2+)-dependent. cbpA-null cells grew normally, but under certain developmental conditions, cell aggregation was prolonged and irregular. This defect in aggregation appeared to be related to a general reduction in cell motility rather than to a decrease in the ability of the cells to respond to the chemoattractant cAMP. Together, these results suggest that CBP1 might function to help regulate the reorganization of the Dictyostelium actin cytoskeleton during cell aggregation.

Animals↗