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PubMed2004

Localization of plasminogen activator activity within normal and injured lungs by in situ zymography.

During inflammatory lung injury, the fibrinolytic activity that is normally present within bronchoalveolar lavage (BAL) fluid (BALF) is often suppressed due to increased levels of inhibitors, including plasminogen activator inhibitor (PAI)-1. Despite this suppression, BALF frequently contains fibrin degradation products, indicating persistence of fibrinolytic activity within the lung. To address this discrepancy and determine the sites where plasminogen activation is occurring, we developed an in situ zymographic technique for frozen sections of lung tissue that localizes plasminogen activator activity at the cellular level. After validating the method using enzyme inhibitors and mice with genetic manipulations of their plasminogen system genes, we applied the technique to lungs of normal and bleomycin-exposed mice. In normal mice, plasminogen activator activity was localized to bronchial epithelial cells, cells of the alveolar walls, and alveolar macrophages. After bleomycin exposure, in situ zymography showed that, despite loss of fibrinolytic activity within BALF, abundant enzymatic activity was associated with aggregates of inflammatory cells. PAI-1-deficient mice that are protected from bleomycin-induced fibrosis had preserved plasminogen activator activity in BALF and increased tissue activity, as determined by in situ zymography. We conclude that analysis of BALF does not adequately reflect the fibrinolytic activity that persists within microenvironments of the lung during inflammation.

Animals↗
PubMed1995

Hematopoietic stem cells in the hereditarily anemic Belgrade laboratory (b/b) rat.

The Belgrade (b/b) rat has hereditary hypochromic microcytic anemia as the consequence of intracellular iron deficiency. Studies in the b/b rat have also demonstrated alteration in hematopoiesis at the progenitor cell level. In the present study, investigations were extended to the bone marrow hematopoietic stem cells as determined by measurements of marrow repopulating ability (MRA) and day 8 spleen colony-forming units (CFU-S-8). A reduced number of CFU-S-8 per femur was found, together with a low incidence per 10(5) bone marrow cells and a nondetectable proliferation rate. The proliferation rate did not increase after treating b/b rat bone marrow cells in vitro with a stimulator for CFU-S proliferation, indicating a proliferative block. The treatment of b/b rats with iron enhanced the proliferation rate and partially increased the number of CFU-S-8 in bone marrow. Chronic transfusion of b/b rats with washed RBC from non-anemic animals restored both the number and the proliferative response of bone marrow CFU-S-8. The MRA of b/b rats was reduced, but in proportion to the decrease in the bone marrow cellularity of these animals. MRA (pre-CFU-S) of b/b rats recovered completely after both iron treatment and chronic transfusions, suggesting that changes in the pre-CFU-S pool are secondary rather than directly induced by the genetic defect. These results indicate the importance for stem cell proliferation of normal oxygenation--the arterial oxygen content in b/b rats is six times lower than in (+/+, b/+) rats--which recovered after the iron treatment and was completely restored after chronic transfusions. High-dose iron therapy abrogated the proliferative block of CFU-S-8, but number of CFU-S-8 was not completely recovered in spite of normalized oxygenation, indicating a possible suppressive effect of iron overload on the marrow microenvironment.

Anemia↗
PubMedDate not supplied

Relevance of microenvironmental pH for self-organized tumor growth and invasion.

The process of tumor cell growth, invasion and metastasis involves a self-organized cascade of multiple tumor-host and tumor-immune interactions. The prediction of cancer development based exclusively on molecular evidence is still impossible because of the complex and heterogeneous control mechanisms actually acting in cellular systems. In contrast, most tumor cell systems display a limited spectrum of macroscopically observable modes of action which emerge as a result of cellular self-organization. The stability of the dynamic modes is controlled by relatively few order parameters. Their number and characteristics are different in normal and neoplastic growth. A systems-oriented analysis utilizing our method of Structured Biological Modelling (SBM) suggests that microenvironmental pH (pHme) can function as an important order parameter for self-organized cancer development. In the scope of an integrated minimal model for the multistep development of invasive tumor growth, this finding will be discussed with respect to its evolution, diagnostic relevance and possible therapeutical implications. The study underlines the necessity of minimal invasive methods for the on-line in vitro and in vivo monitoring of pH, oxygen, signal transducing molecules and essential nutrients in the microenvironment of tumor cells.

Cell Division↗
PubMed2004

Trafficking of tumor peptide-specific cytotoxic T lymphocytes into the tumor microcirculation.

The major histocompatibility complex class I-restricted CD8(+) cytotoxic T-lymphocyte (CTL) effector arm of the adaptive immune response can specifically recognize and destroy tumor cells expressing peptide antigens. Although adoptive T-cell therapy has been successfully used for the treatment of viral and malignant diseases, little is known of the trafficking and fate of adoptively transferred antigen-specific T cells. In the present study, splenocytes derived from mice that rejected their tumors (CT26 or CT26-clone 25 tumors) in response to direct intratumor injection of disabled infectious single-cycle herpes simplex virus (DISC-HSV) encoding murine GM-CSF were restimulated with peptide in vitro. CTLs specific for the AH-1 and beta-gal peptides expressed by CT26 and CT26-clone 25 tumor cells, respectively, were generated and used for adoptive cellular therapy and trafficking studies. Intravenous administration of AH-1-specific CTLs 3 days following i.v. injection of CT26 cells resulted in significant tumor growth inhibition, whereas administration of control CTLs generated against a bacterial beta-gal peptide did not inhibit the growth of tumors. Trafficking of AH-1-specific lymphocytes and their interaction with the CT26 tumor microcirculation was analyzed using real-time in vivo microscopy (IVM). AH-1-specific but not beta-gal-specific CTLs adhered and localized in the CT26 tumor microvasculature, but neither population adhered to the endothelium of the normal microcirculation. This study provides direct visual evidence suggesting that AH-1-specific CTLs that mediate a therapeutic response traffic to and localize within the tumor microenvironment.

Animals↗
PubMed1996

Ultrastructural characterization of the acetylcholine innervation in adult rat neostriatum.

The ultrastructural features of acetylcholine axon terminals (varicosities) in adult rat neostriatum were characterized by electron microscopy after immunostaining with a sensitive monoclonal antibody against rat choline acetyltransferase. Several hundred single sections from these varicosities were analysed for shape, size and content, presence of a synaptic membrane specialization, and composition of the microenvironment. An equivalent number of unlabeled varicosities selected at random from the same micrographs were similarly examined. The immunostained varicosity profiles were relatively small and seldom showed a junctional membrane specialization. Stereological extrapolation to the whole volume of these varicosities indicated that less than 10% were synaptic. Far fewer dendritic spines were juxtaposed to these predominantly asynaptic profiles than to their unlabeled counterparts. This difference seemed imputable to the low synaptic incidence of the acetylcholine varicosities and was consistent with the view that these are randomly distributed in relation to surrounding elements. The bulk of the data was suggestive of volume transmission. This raised the possibility that, in such a densely innervated area, a basal level of acetylcholine is permanently maintained around all cellular elements, contributing to the modulatory properties of this transmitter. This basal level of acetylcholine could also serve as a regulatory signal controlling the expression of different receptor subtypes in neurons, glia and blood vessels.

Acetylcholine↗
PubMed2026

Unbiased Spatial Proteomics Uncovers Hepatic in Situ Regulation in Alcohol-Associated Hepatitis.

Alcohol-associated hepatitis (AH) is an acute inflammatory form of alcohol-associated liver disease. Previous studies have explored molecular mechanisms associated with AH pathogenesis through bulk liver tissue analysis; however, the heterogeneity of liver tissue and hence the spatial regulation within the AH liver microenvironment remained unaddressed. Here, an unbiased spatial proteomics analysis on the pathologic regions (PRs) of AH liver tissue is presented, including immune cell infiltration foci, lipid droplets, chicken-wire fibrosis, and fibrotic bands. Through combining a highly efficient nanodroplet processing in one pot for trace samples platform with ultrasensitive liquid chromatography-mass spectrometry, this study identified and quantified a total of 5186 unique proteins from PRs isolated in 200-μm-long × 200-μm-wide × 10-μm-thick areas. This in-depth spatial proteome coverage allowed us to discover mechanistic regulations within individual PRs, including compromised resolution of inflammation with infiltrated neutrophils at infiltration foci, increase of mitochondrial and peroxisomal fatty acid β-oxidation at lipid droplets, and differential cellular and extracellular regulations between chicken-wire fibrosis and fibrotic bands. Overall, this study demonstrated a new capability for AH research, revealed the significance of understanding spatial regulation within AH liver tissue, and further facilitated the development of therapeutic strategies at high resolution.

Proteomics↗
PubMed2003

HIF-1 in cell cycle regulation, apoptosis, and tumor progression.

Cells in a low oxygen, or hypoxic, microenvironment must have the ability to sense oxygen levels in the nucleus in order to maintain oxygen homeostasis by gene regulation. Hypoxia inducible factor-1 (HIF-1) serves as a molecular bridge between the sensation and utilization of oxygen, and thus functions as a key player in oxygen homeostasis. HIF-1 is a heterodimeric transcription factor and is composed of two subunits, the oxygen-sensitive HIF-1alpha and constitutively expressed HIF-1beta. HIF-1 regulates the expression of a broad range of genes that facilitate acclimation to low oxygen conditions by changes in protein levels in circulation, metabolism, and proliferation. Appropriate temporal and spatial activation of HIF-1 is crucial not only in developmental and physiological processes, characterized by programmed cellular proliferation, but also in pathophysiological conditions such as tumorigenesis, which exhibit unregulated cellular proliferation. However, many contradictory reports as to the role of HIF-1 in the regulation of cellular proliferation have been put forward in recent years. In this review, our first aim is to summarize the current knowledge of oxygen-dependent HIF-1 activation mechanisms based on its structure. Then we will describe the proposed mechanisms through which HIF-1 regulates cellular proliferation of different cell types, including tumor cells as well as non-transformed, nonimmortalized cells under normoxic and hypoxic conditions.

Animals↗
PubMed1998

Osteoblasts promote engraftment of allogeneic hematopoietic stem cells.

Hematopoietic progenitor cells (low density, lineage negative [Lin-], depleted of CD4+, CD8+, B220+, Gr-1+, Mac-1+, CD71+, and Thy1.2+ cells) can engraft lethally irradiated mice when transplanted within, but not across the major histocompatibility (MHC) antigen barrier. We hypothesized that our progenitor cell preparation required "supportive" cells/factors for successful engraftment. Our initial candidate supportive cells, dendritic cells, failed to facilitate engraftment of stem cells across fully allogeneic MHC barriers. Because interaction of stem cells with bone marrow (BM) stromal microenvironment is required for development, maturation, and differentiation of hematopoietic stem cells, and because bone transplants have been found to facilitate BM transplantation (BMT) in some strain combinations, we tested bone progenitor cells, osteoblasts, as facilitators of allogeneic stem cell engraftment. Osteoblasts, purified from donor murine long bones, were cotransplanted with marrow stem cells into fully allogeneic mouse strains. The transplanted mice demonstrated excellent long-term survival, were free of disease, and were entirely engrafted with cells of donor origin. Histologic sections of thymuses and spleens showed full reconstitution of lymphohematopoietic elements. Surprisingly, in contrast to fully allogeneic chimeras reconstituted by allogeneic T lymphocyte-depleted BM, our stem cell chimeras were found to produce an impressive primary antibody response to the cellular antigen, sheep red blood cells. Thus, bone progenitor cells or osteoblasts may represent an essential component of the stromal cell population and facilitate engraftment of marrow stem cells in an allogeneic environment.

Alkaline Phosphatase↗
PubMed2002

Expression pattern of MUM1/IRF4 in the spectrum of pathology of Hodgkin's disease.

Biological and clinical studies have shown that Hodgkin's disease (HD) can be divided into two major categories, termed nodular lymphocyte predominance HD (NLP HD) and classic HD (CHD). Within CHD four subtypes have been distinguished: nodular sclerosis, mixed cellularity, lymphocyte rich and lymphocyte depletion. To refine the histogenesis of the pathological spectrum of HD, 75 CHD and 13 NLP HD were analysed for the expression pattern of MUM1/IRF4 (Multiple Myeloma-1/Interferon Regulatory Factor-4), a lymphocyte-specific member of the IRF family, that is expressed by late centrocytes and post-germinal centre (GC) B cells. MUM1 reacted with Hodgkin's and Reed-Sternberg (HRS) cells of all CHD cases (75/75 cases), with a moderate to strong staining intensity. Conversely, lymphocyte and histiocyte (L & H) cells, the putative tumour cells of NLP HD, were negative for MUM-1 expression (9/13 cases) or displayed a weak reactivity for the antigen in < 10% neoplastic cells (4/13 cases). With respect to HD microenvironment, NLP HD displayed numerous MUM1-positive T lymphocytes located in close proximity to L & H cells whereas, in CHD, MUM1-positive T lymphocytes appeared to be distributed randomly with no specific relationship with HRS cells. Overall, this study shows that MUM1 expression differs in L & H cells versus HRS cells, corroborating the notion that NLP HD and CHD represent different stages of B-cell differentiation. As MUM1-positive T lymphocytes form rosettes around tumour cells of NLP HD, but not of CHD, these data point also to differences in the microenvironment of NLP HD and CHD, and postulate an interactive role of MUM1-positive T lymphocytes with L & H cells.

CD4-Positive T-Lymphocytes↗
PubMed2004

Commentary: the role of cell migration in the ontogeny of the lymphoid system.

The foundations of experimental hematology were laid by histologists, and while their contributions were enormous, they were limited in their interpretation of very dynamic processes by the static nature of the methodology. The middle of the twentieth century saw the introduction of techniques for hematopoietic cell marking and development of in vitro and in vivo assays for primitive hematopoietic cells, allowing dynamic studies of hematopoiesis. Paralleling this was an understanding of cellular immunology with the discovery of the role of the thymus and the identification of T and B lymphocyte lineages. In the 1960s a series of ontogenetic studies in birds and subsequently in mice revealed that hematopoietic and lymphoid development involved migration streams of primitive cells that colonized developing primary lymphoid organs as well as spleen, marrow, and liver. The yolk sac was proposed as the ultimate origin of these lympho-hematopoietic precursors. Subsequent studies identified a region associated with the dorsal aorta as the primary site of "definitive" stem cells. These opposing views are currently achieving a compromise that recognizes that both sites contribute stem cells involved in seeding the developing tissues. The clear distinction between the local origin of the inducing microenvironment provided by the endoderm or by stroma derived from mesenchymal stem cells of mesodermal origin, and the immigrant origin of the hematopoietic stem cells and progenitors, raises intriguing questions in the current climate of stem cell plasticity, cell fusion, and discovery of stem cells in adult marrow with the capacity to generate hematopoiesis as well as other mesodermal, ectodermal, and endodermal lineages.

Animals↗
PubMed1992

Chemotactic properties, cellular binding and uptake of peptides and peptide derivatives: studies with Tetrahymena thermophila.

Receptor-mediated binding of leukocyte chemotactic peptide, N-formylMet-Leu-Phe (fMLP), occurs in the ciliated protozoon Tetrahymena thermophila. In vivo labelling of the cells with N-formylMet-Leu-[3H]Phe ([3H]fMLP) shows that the cells bind the ligand with high affinity (KD = 4 x 10(-9) M to 1 x 10(-8) M). Moreover, Scatchard transformations of the binding data show that there are about 5 x 10(5) binding sites per cell on the cell surface. Two fluorescent derivatives of leukocyte chemotactic peptide, N-dansylMet-Leu-Phe (dansMLP) and N-formylMet-Leu-Phe-(N-dansyl-)Lys (fMLPdanLys) compete for the N-formylMet-Leu-Phe (fMLP) binding sites on the cell surface. Moreover, both derivatives have retained significant chemoattracting potentials. Fluorescence from dansMLP, but not from fMLPdansLys and dansyl-beta-endorphin, is internalized preferentially into small vesicles. The differences may, however, reflect that the fluorescence from the dansyl group is strongly quenched by a hydrophilic microenvironment when using the two latter peptide derivatives. In contrast, the dansyl group from dansMLP must be assumed to be embedded in a hydrophobic microenvironment in the vesicular membrane or membrane protein. Rhodamine-labelled bovine serum albumin, egg albumin and cytochrome c as well as dansylated bovine serum albumin, which are poor chemoattractants, are preferentially seen to be internalized into large vesicles (food vacuoles).

Amino Acid Sequence↗
PubMed2000

Amino acid uptake and regulation in multicellular hepatoma spheroids.

BACKGROUND: Cancer cells maintained in monolayer tissue culture are frequently used to study tumor biology and nutrient uptake, but there is a concern that this system may not fully reflect clinical tumor physiology. Because cells grown in a 3-D configuration more closely resemble an in vivo environment, a model was developed and characterized for the growth of SK-Hep human hepatoma cells in suspension as multicellular tumor spheroids (MTS). The measurement of nutrient uptake in such a system has never been established. MATERIALS AND METHODS: SK-Hep cultures were initiated as single cell suspensions and grown as MTS in siliconized spinner flasks. The transport of several individual amino acids (arginine, glutamate, leucine, alpha-(N-methylamino)isobutyric acid (MeAIB), and glutamine (GLN)) was measured in SK-Hep single cell suspensions and MTS (0. 50-0.60 mm diameter) by a radiotracer/rapid filtration technique, as was the regulation of glutamine uptake by phorbol esters. l-[(3)H]GLN uptake was also measured in larger spheroids (0.85-1.5 mm diameter). MTS cellularity was evaluated by histological examination, and single cell integrity after the transport assay was confirmed by scanning electron microscopy (SEM). RESULTS: SK-Hep MTS displayed gradients of cellular morphology and staining, with central necrosis visible at diameters >0.8 mm. Single cell suspensions endured the rapid filtration technique based on functional Na(+)-dependent uptake rates and SEM analysis. Of all amino acids tested, only GLN transport rates were visibly affected by growth format. In small MTS, Na(+)-dependent GLN uptake was diminished by 40%, but was 40-53% higher in MTS >1 mm displaying central necrosis, when compared to single cell suspensions. Likewise, slight parallel changes in glutamine transporter ATB(0) mRNA levels were observed in Northern blot analysis. Finally, phorbol ester-dependent GLN transport down-regulation (by 40-50%), previously established in SK-Hep monolayers, remained operative in all cell formats tested. CONCLUSIONS: The data suggest that the tumor microenvironment differentially impacts the uptake of specific nutrients despite the conservation of key regulatory pathways. This MTS technique may prove useful for further studies on the role of nutrient transport in nascent tumor growth.

Amino Acid Transport System ASC↗
PubMed1995

[Cytokines and hematopoiesis].

In hematopoiesis, regulation and differentiation present a very complex functional network in which multiple factors of the microenvironment are involved. In addition to direct cell-to-cell contacts and the modifying influences of the intercellular matrix, soluble mediators play an important role in intercellular communication. Cytokines exert their effects by binding with specific receptors that transfer their signals to individual cells. A common structure shared by subunits of these receptors leads to competitive inhibition in binding the cytokines with different affinity. By this mechanism specificity is reduced, on the one hand; however, on the other the complexity of interactions in the bone marrow is enhanced. A flood of in vitro and in vivo studies have established the impact of various cytokines on single hematopoietic cell lineages and their application for clinical use. However, there is a lack of knowledge concerning the cellular origin of the cytokines. According to the results of our studies elements of the erythro- and megakaryopoiesis are the source of cytokines like IL-1 alpha, IL-3, IL-6, and GM-CSF.

Animals↗
PubMedDate not supplied

Mitosis of the Hofbauer cell: possible implications for a fetal macrophage.

Human chorionic villi from placentae collected during the first half of pregnancy were examined by light microscopy and transmission electron microscopy. In serial semithin sections mitoses of Hofbauer cells, as well as those of other cellular components of the villous stroma, were generally easily identified. In some cases, when the Hofbauer cells showed very few vacuoles, thin sections were helpful in differentiating this cell type from the fixed stromal cells. Hofbauer cells in mitotic division were not uncommon, but were irregularly distributed. Mitosis of the Hofbauer cells could be a mechanism involved in maintaining the permanent presence in the chorionic villi of cell subpopulations with different origins and functions. Another explanation for the mitotic division of these cells could be that they are a self-renewing population independent of fetal monocytes which appear later in gestation in chorionic villi. In addition, mitosis of the Hofbauer cells could allow a rapid increase in their numbers when required by the local microenvironment.

Chorionic Villi↗
PubMed2001

Phage derived peptides for targeting of doxorubicin conjugates to solid tumours.

Barriers are frequently hampering targeting of drugs and toxins to solid tumours and their microenvironment. Nano-conjugates are low molecular weight conjugates of a small drug or toxin and a targeting ligand coupled through a cleavable linker group. They offer potential advantages for tumour specific delivery in diffusion-limited situations. We have exploited fd phage-derived peptides for the targeting of low molecular weight drug conjugates to solid tumours. As a model we have chosen doxorubicin conjugates targeted to the transferrin receptor (TfR). A library of phage expressing a cyclic nona-peptide was panned against TfR. The apparent affinity of phages determined by surface plasmon resonance (SPR) increased with each cycle of the panning procedure. After five rounds approximately 80% of phages expressed the same peptide, which mediated a 30-50-fold increased receptor specific cellular uptake of the phages. The corresponding peptide was synthesised using solid phase peptide chemistry on a sulfonamide based safety catch resin. Crude mixtures of the peptide, as well as transferrin itself, were able to inhibit the phage uptake significantly. The doxorubicin conjugate of the peptide containing a cleavable linker was prepared and endosomal uptake confirmed by fluorescence microscopy.

Antibiotics, Antineoplastic↗
PubMed1986

Avian immune capacity and bone marrow cellularity after in ovo treatment with cyclophosphamide.

Lymphoid tissue, immunity and erythropoiesis in bone marrow were studied in chickens which had received air cell applications of cyclophosphamide (Cy) between 16 and 18 days of their embryonic development. The bursae from the Cy-treated birds were reduced significantly in size, deficient in bursal follicles, and lacked lymphocytes. The agglutinin level of sheep red blood cells of birds treated with Cy (2 mg) as 16, 17 and 18-day embryos was significantly lower than controls. While these Cy-treated birds lacked IgG antibody to sheep red blood cells, about 50% of the Cy birds produced unspecific IgG. Cy treatment did not suppress the graft-versus-host response. Cy did not change the absolute number of lymphocytes, granulocytes or erythroid series of cells in the bone marrow but did eliminate plasma cells. Since some of the Cy-treated birds did not produce specific agglutinin but made Ig, one would have to conclude that the presence of the bursa was not obligatory for Ig synthesis, but that the bursal microenvironment may be a prerequisite for synthesis of specific antibody.

Age Factors↗
PubMed2006

Effect of neurosphere size on the growth rate of human neural stem/progenitor cells.

Neural stem/progenitor cells (NSPCs) proliferate as aggregates in vitro, but the mechanism of aggregation is not fully understood. Here, we report that aggregation promotes the proliferation of NSPCs. We found that the proliferation rate was linear and depended on the size of the aggregate; that is, the population doubling time of the NSPCs gradually decreased as the diameter approached 250 micro m and flattened to a nearly constant value beyond this diameter. Given this finding, and with the intent of enhancing the efficiency of human NSPC expansion, we induced the NSPCs to form aggregates close to 250 micro m in diameter quickly by culturing them in plates with U-bottomed wells. The NSPCs formed aggregates effectively in the U-bottomed wells, with cell numbers approximately 1.5 times greater than those in the aggregates that formed spontaneously in flat-bottomed wells. In addition, this effect of aggregation involved cell-cell signaling molecules of the Notch1 pathway. In the U-bottomed wells, Hes1 and Hes5, which are target genes of the Notch signal, were expressed at higher levels than in the control, flat-bottomed wells. The amount of cleaved Notch1 was also higher in the cells cultured in the U-bottomed wells. The addition of gamma-secretase inhibitor, which blocks Notch signaling, suppressed cell proliferation in the U-bottomed wells. These results suggest that the three-dimensional architecture of NSPC aggregates would create a microenvironment that promotes the proliferation of human NSPCs.

Amyloid Precursor Protein Secretases↗
PubMed2003

Stroma-mediated granulocyte-macrophage colony-stimulating factor (GM-CSF) control of myelopoiesis: spatial organisation of intercellular interactions.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is one of the major cytokines involved in control of haemopoiesis both in bone marrow and in extramedullar sites. Its biological activity depends upon the composition and physicochemical properties of the microenvironment provided by the supporting stroma. GM-CSF activity is modulated and controlled by the stromal heparan-sulphate proteoglycans, but their optimal interaction occurs only at low pH. We questioned whether the microenvironment organisation of the interface between stroma and haemopoietic cells provides such conditions. We studied myeloid progenitor proliferation in contact with bone marrow-derived and extramedullar stromas using electron microscopy and selective labelling of pericellular components. We present evidence that, upon interaction, the two cell types reorganise their interface both in shape and molecular composition. Haemopoietic cells extend projections that considerably increase the area of intercellular contact, and stromal cells form lamellipodia and carry out a redistribution of membrane-associated sialylated glycoconjugates and proteoglycans. Such rearrangements lead to extensive capping of negatively charged molecules at the interface between the supporting stroma and the haemopoietic cells, leading potentially to a local decrease in pH. Our results indicate that the distribution of negative charges at the cellular interface may be responsible for the selectivity of cell response to GM-CSF.

Animals↗