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At least 1,153 records · Page 64Linked to original sources
PubMed1982

Microenvironments controlling the transdifferentiation of vertebrate pigmented epithelial cells in in vitro culture.

The transdifferentiation of pigmented epithelial cells in vitro is briefly introduced. Several environmental conditions regulating the process have been demonstrated experimentally. On the basis of these data we have suggested regulatory factors in relation to the mechanisms for the initiation of the transdifferentiation of pigmented epithelial cells, focussing particularly on cell surface functions. Finally, we have presented data which contributes to the establishment of a useful and powerful cell culture system which makes it possible for us to analyse the molecular basis of transdifferentiation.

Animals↗
PubMed1983

Studies on the in vitro microenvironment in man.

In a preliminary manner, the data presented here characterize some features of MSC and their progenitors. The progenitors, at least in chronic myelogenous leukemia, are derived from the neoplastic pluripotent stem cell that also differentiates along lymphoid and myeloid pathways. In addition, we have demonstrated that the precursor for MSC is lacking both the Ia and CALLA determinants. Several antigenic and functional characteristics of the mature stromal cell population have also been identified. Stromal cells express CALLA, synthesize types I, III, and IV collagen, and may express factor VIII associated antigen. It is of interest that fibroblasts do not express factor VIII associated antigen, do not synthesize type IV collagen in measurable quantities, but do express CALLA [9]. Endothelial cells express factor VIII associated antigen, synthesize type IV collagen, but are not CALLA positive. Thus, MSC have some features in common with fibroblasts and others with endothelial cells. The unique characteristics of MSC are that they are transplantable and are derived from a common progenitor with other hematopoietic cells. These features clearly distinguish this cell population from fibroblasts, which are neither transplantable nor derived from the neoplastic clone in CML.

Anemia, Aplastic↗
PubMed1983

Morphology of cerebral endothelium and astrocytes as determinants of the neuronal microenvironment.

The morphological features of the blood-brain barrier to macro-molecules under normal and perturbed conditions are reviewed in the context of some recent investigations. The electric charge on molecules of horseradish peroxidase (HRP) affect its pinocytosis and intracellular fate which pertains to problems of distinguishing endocytosis from vesicular transport across endothelium. When the barrier is opened, the number of pits, vesicles and tubules increases. Such cerebral endothelium resembles normal endothelium of certain fish where numerous membrane invaginations do not signify vesicular or tubular transport. However, such transport has not been entirely ruled out in reactive endothelium. Another route of exudation during barrier opening may be via patent endothelial junctions, especially during intravascular infusion of hyperosmotic solutions. The permeability of the tight junctions, however, is not reflected unequivocally by its intramembranous structure. Although astrocytes do not provide a barrier to the extracellular flow of solutes, their ubiquity may enable them to modify the composition of perineuronal fluid. Their orthogonal arrays of intramembranous particles may be involved. The number of assemblies increases in astrocytes reacting to trauma and to the extracellular accumulation of lactate and CO2. The assemblies might thus participate in the transport of catabolites to and from extracellular fluid.

Animals↗
PubMed1995

Conditioned media of carcinoma cells cultured in hypoxic microenvironment stimulate angiogenesis in vitro; relationship to basic fibroblast growth factor.

Conditioned media (CM) harvested from human pulmonary squamous cell carcinoma (QG56), pulmonary small cell carcinoma (QG90) and gastric adenocarcinoma (MKN28) cultivated under hypoxic conditions (3% oxygen), enhanced the angiogenic activity in vitro more than those obtained under normoxic cultivation (20% oxygen). The total length of the tube structures formed by bovine capillary endothelial cells (BCEs) in the CM cultured at 3% oxygen was about 1.5 (QG56 and MKN28) or 1.9 (QG90) times longer than that at 20% oxygen. Tube formation was diminished by the preincubation of CM with anti-basic fibroblast growth factor (bFGF) IgG. After performing the fractionations of the CM and the crude extracts of cell lysates cultured using a heparin-Sepharose column, the mitogenic activity in the CM from all cancer cells at 3% oxygen was about twice that of CM at 20% oxygen, while it decreased in the cell lysates at 3% oxygen to about 40% of those at 20% oxygen. This mitogenic activity of BCEs in the CM from all cancer cells was almost totally suppressed by anti-bFGF IgG, but not with anti-vascular endothelial growth factor IgG. Hypoxia is an important factor in tumor angiogenesis by bFGF or bFGF-like molecule(s) derived from tumour cells.

Animals↗
PubMed1981

Thymic microenvironment and cultures derived from mouse thymic explants. A morphological study.

Cultures derived from thymus fragments of embryonic (18-19 day old), newborn or one month old C57BL mice have been characterized functionally l(phagocytic and nonspecific esterase activities) and morphologically by means of light, scanning (SEM) and transmission (TEM) electron microscopy. The observations show the heterogeneity of the cell populations composing the monolayers. After a few days incubation macrophages appear as the predominating cell type, while epithelial cells usually constitute no more than 30% of the cells. Experiments designed to determine the fate of lymphocytes adhering to the monolayers lead us to believe (on the basis of SEM morphometric analysis) that the survival of lymphocytes attached either to thymic macrophages or to epithelial cells is improved during the first days of coculture. This survival enhancement does not, however, appear to be a specific inductive effect since a similar survival increase is found when lymphocytes adhere to non-thymic cells. In contrast with the monolayer, the explant provides a three-dimensional culture system able to preserve intact thymic microenvironmental conditions since numerous lymphocytes are found even in five week old cultures which were not overlaid with thymocytes or spleen cells.

Animals↗
PubMed1988

Observations on exsudation of fibronectin, fibrinogen and albumin in the brain after carotid infusion of hyperosmolar solutions. An immunohistochemical study in the rat indicating longlasting changes in the brain microenvironment and multifocal nerve cell injuries.

An immunohistochemical study was carried out on rat brain to determine if a transient opening of the blood-brain barrier (BBB), leading to extravasation of serum albumin, is also associated with exudation and cellular uptake of fibronectin and fibrinogen. Both of them might exert important biological effects provided that they pass the BBB and come into contact with cells of the brain parenchyma. Hyperosmolar solutions of urea or mannitol were infused in the carotid artery for 30 s to open the BBB and the animals were killed at various time intervals thereafter. Formaldehyde-fixed, paraffin-embedded material was used for immunohistochemical demonstration of extravasated proteins by an avidin-biotin peroxidase technique. Multifocal, often confluent areas of widely different sizes with signs of albumin extravasation were observed both in the grey and the white matter of the cerebral hemispheres exposed to the hyperosmolar solutions. Much less pronounced changes were observed in rats given an intracarotid saline infusion alone. Immunoreactive material indicating extravasation of fibronectin and fibrinogen was present in the infused cerebral hemispheres but albumin immunoreactivity was much more widespread. Reaction product was observed in vascular walls, presumably in extracellular spaces and in nerve cells. Immunoreactivity in the perikaryon of neurons formed different patterns in various cells. A granular type most probably represents accumulation of the proteins in lysosomal organelles after pinocytotic uptake into the neuron. The second so-called diffuse variety is presumably the result of a severe nerve cell injury with an uncontrolled leakage of proteins into the cytoplasm. Our results indicate that vascular walls, extracellular spaces, glial cells and neurons will be exposed to extravasated fibronectin and fibrinogen as well as to albumin and that antigenic sites in such compounds remain for a long period after the BBB opening. In addition, there are indications that carotid infusions of hyperosmolar solutions may cause nerve cell injuries in regions with BBB opening. These findings have obvious clinical and experimental significance.

Animals↗
PubMed1984

Production of glial fibrillary acidic protein (GFAP) by neoplastic cells: adaptation to the microenvironment.

In 80 specimens of human glioma the production of glial fibrillary acidic protein (GFAP) by tumour cells invading meninges or connective tissue was studied immuno-cytochemically by the PAP technique. In 38 of 55 cases of astrocytoma, glioblastoma, gliosarcoma, and oligoastrocytoma, GFAP immunoreactivity was greater in the invading cells as compared with the main part of the neoplasm. Fifty-eight percent of the astroglial tumours invading the leptomeninges, all astroglial tumours invading connective tissue and all gliosarcomas showed enhanced GFAP immuno-reactivity of tumour cells getting in contact with collagenous tissue, whereas meningeal infiltrates of 25 non-astroglial tumours (oligodendroglioma, ependymoma, medulloblastoma) remained GFAP-negative like the main part of the respective tumours. In the majority of astroglial tumours an increase of GFAP immunoreactivity was found also in perivascular cells of the main part of the tumour. It is concluded that glioma cells are capable of adapting their cytoskeleton to their micro-environment. Contact with dense collagenous tissue appears as an important factor able to induce an increased production of GFAP by adjacent glial cells.

Astrocytoma↗
PubMed1995

Impairment of lymphocyte locomotion in the tumor microenvironment and the effect of systemic immunotherapy with liposome-encapsulated muramyl-tripeptide-phosphatidylethanolamine.

The ability of the lymphocytes to move through the interstitium is obligatory to the immune response. We previously showed that tumor-infiltrating lymphocytes (TIL) from human melanoma and renal cell carcinoma demonstrate a dramatic decrease in their spontaneous locomotion through three-dimensional collagen gel when compared with peripheral blood lymphocytes (PBL) and lymph node lymphocytes. To determine if this decrease is caused by contact with tumor cells, or mediated through certain diffusible factors, we examined the effects of autologous tumor cells on the locomotion of PBL in a model system where tumor cells were separated from lymphocytes by a 3-mm layer of gelled collagen. After 21-22 h incubation in chamber slides, locomotion distances were assessed in the presence and absence of tumor and normal cells. In the presence of tumor cells, PBL from 14 of 18 patients displayed substantial (466.5 +/- 2.7 microns compared to control 568.9 +/- 10.9 microns, P < 0.001) loss of motility. Inhibition was more prominent in melanoma patients than in renal cell carcinoma patients. Thus the impaired locomotion previously observed in TIL was at least partially due to the presence of tumor. The locomotion of TIL was restored in four of five melanoma patients treated with liposome-encapsulated muramyl-tripeptide-phosphatidylethanolamine (L-MTP-PE). Furthermore, in six of seven examined L-MTP-PE-treated patients, an increase in intrinsic PBL locomotion during the first month of the therapy was observed. These results suggest that the environment of the tumor is not conducive to locomotion of advancing lymphocytes and the therapeutic intervention may ameliorate the loss of lymphocytic infiltration.

Acetylmuramyl-Alanyl-Isoglutamine↗