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Biomedical subjects

M Tavassoli

Publications and source records attributed to M Tavassoli.

At least 217 records · Page 12Linked to original sources
PubMed1981

Morphological studies on 'adherent cells' in bone marrow cultures from humans, dogs, and mice.

Comparative morphological studies were conducted on adherent cells in bone marrow cultures obtained from humans, dogs, and mice. Scanning electron micrographs demonstrated that the adherent colonies are much more homogeneous in humans and dogs and appear larger and more flattened than in mice. In mice, many more rounded cells (macrophages) were seen intermixed with the flattened cells. Transmission electron microscopy demonstrated that the flattened type of cells are characterized by a large primitive nucleus and abundant cytoplasm exhibiting an extensive network of microtubules and submembranous microfilaments and the formation of endoplasmic reticulum-associated secretory bodies. Our results would favor a fibroblastic rather than epithelial nature of the flattened cell type.

Animals↗
PubMed1981

Red cell egress from bone marrow in state of transfusion plethora.

Marrow sinuses have been shown to undergo rhythmic dilatations and this has been suggested as a mechanism controlling cell egress from the marrow. Within the rigid frame of bone where the volume of the marrow is fixed, dilatation of sinuses can only lead to the displacement of cells into the lumen. The absence of tight junction between sinus endothelial cells is thought to permit the overlapping segments of these cells to slide over one another. To test this hypothesis, the length of overlapping segments between endothelial cells was measured before and after the induction of transfusion plethora and this was correlated with the magnitude of reticulocyte traffic across the sinus wall. Within one hour after the induction of plethora, marrow sinuses were dilated, packed with red cells, and the mean length of overlapping segments was reduced significantly from 0,75 micrometer to 0.41 micrometer. This was associated with a decline in the magnitude of reticulocyte transit across the wall (0.73 vs 0.13/mm). These observations are consistent with the theory that the overlapping segments of sinus endothelial cells can slide over each other to change the luminal caliber. Transfusion plethora results in a sustained maximal dilatation of sinuses, thus preventing their rhythmic changes necessary for cell delivery into the circulation.

Animals↗
PubMed1981

Structure and function of sinusoidal endothelium of bone marrow.

The endothelium of marrow sinuses is the site of cellular and molecular exchange between the circulation and the hemopoietic compartment. Here, mature cells are delivered into circulation by passing through the cytoplasm of a single endothelial cell. Similarly, stem cells are probably trapped here. The endothelium which is structurally polarized, and shows segmental surface differentiations, can maintain a gradient for a variety of substances between blood and marrow (the marrow-blood barrier). Transendothelial cell migration involves channel formation through fusion-fission reorganization of the membrane. The endothelium is involved in other interactions particularly with perisinal macrophages. Little is known of the surface characteristics of the endothelium, an area that may help the understanding of how the cell can selectively exchange cells and molecules between the marrow and blood.

Animals↗
PubMed1980

Receptor binding and internalization of immobilized transcobalamin II by mouse leukaemia cells.

Membrane transport of vitamin B12 (cyanocobalamin; Cbl) into mammalian cells is mediated by the serum protein transcobalamin II (TCII). In mouse leukaemia L1210 cells, TCII-Cbl binds to membrane receptors in a rapid, temperature-independent step and is internalized by a slow, temperature-dependent process. To delineate the location of receptors on these cells, we have constructed a visual probe by covalently coupling purified TCII-Cbl to submicrometre latex particles (minibeads). We report here that when L1210 cells are incubated with minibeads containing TCII-Cbl at 4 degrees C and examined by scanning electron microscopy (SEM), the particles are found attached predominantly to microvilli. Incubation of the cells at 37 degrees C results in the internalization of the minibeads. As visualized by transmission electron microscopy (TEM), this endocytotic process seems to occur in clathrin-coated pits and vesicles at the cell surface.

Animals↗
PubMed1980

Membrane fusion induced by the membrane mobility agent, A2C. Differentiation between fusible and non-fusible cells. Transfer of fusibility.

Red cells of different species respond differently to the treatment with the membrane mobility agent, A2C, with respect to both the A2C interaction and the subsequent cell-cell interaction. Depending on whether both, one or neither of the processes are effective, some red cells (e.g., nucleated Leghorn hen red cells, rat red cells) fuse easily, some (human red cells) show morphological changes but do not fuse, and others (nucleated Rock hen red cells) show little or no response. Mixed fusion (i.e., between fusible cells of different species) is readily obtained, indicating that no species-specific recognition sites are required for A2C-induced fusion. the potential for fusion is a transferable characteristic. In the presence of fusible cells, A2C induces both heterologous and homologous fusion of otherwise 'non-fusible' cells. Electron micrographs of fusing cells after treatment with A2C reveal 'onion-ring' structures ('whorls'), free of intramembranous protein particles but different from the smooth appearance of A(2)C particles. Whorls are considered to arise from fusion-potent membrane areas. Fusion is apparent at multiple sites along the contact line between apposed membranes. The postulated appearance of vesicle-like structures along the fusion line (Kosower, E.M., Kosower, N.S. and Wegman, P. (1977) Biochim. Biophys. Acta 471, 311-329) is confirmed by micrographs. The mechanism of this fusion process is duscussed and compared to other types of fusion process.

Animals↗
PubMed1980

The origin of hemopoietic cells in ectopic implants of spleen and marrow.

Spleen and marrow tissues were cross-transplanted between CBA and CBA/HT6 mice. The majority of karyotypes in the regenerated implants were of recipient origin indicating that these implants are chimeric structures with the stroma of donor origin providing a framework for the proliferation of the recipient's hemopoietic stem cell.

Animals↗
PubMed1980

Functional potential of ectopic marrow autotransplants.

Ectopic autotransplants of the marrow tissue, form within 4 weeks, stable nodules which respond to erythropoietic modulation in a manner similar to other parts of the marrow. The findings indicate that these autotransplants are an integral part of the total hemopoietic mass.

Animals↗
PubMed1980

Elevation of serum acid phosphatase in cancers with bone metastasis.

In patients with nonprostatic cancer serum acid phosphatase activity is usually elevated when bone metastasis is present but not when bone metastasis is absent. The fraction responsible for serum enzyme elevation is a normal component of serum; it appears in gel electrophoresis as band 5; and is tartrate-resistant. It is suggested that the origin of acid phosphatase elevation is bone osteoclasts rather than cancer tissue, as is the case with prostatic carcinoma. Determination of serum acid phosphatase activity may be useful in the detection of bone metastasis.

Acid Phosphatase↗
PubMed1980

Evidence for the presence of receptors for C3 and IgG Fc on human synovial cells.

The presence of receptors for IgG Fc and fragments of C3 on primary cultures and cryostat sections of normal and rheumatoid synovial tissues was assessed. Significant proportions of large rounded cells with asteroid projections found in such cultures had receptors for both IgG Fc and fragments of C3. Moreover, Gram negative bacteria that had fixed complement, but not EAC, bound in a linear fashion on the superficial layers of synovial cryostat sections. On the basis of morphologic and histochemical criteria, the cultured cells bearing these receptors were tentatively determined to represent a subset of synovial lining cells. The possible role of such receptors on synovial lining cells in the pathogenesis of rheumatoid arthritis is discussed.

Arthritis, Rheumatoid↗
PubMed1980

The Woronets trait: a new familial erythrocyte anomaly.

A dominantly inherited abnormality of the red blood cells is described. It is characterized by the presence of a small population of markedly distorted red blood cells resembling keratocytes. In addition, many of the red cells show minor deformities resembling the beginning stages of formation of echinocytes. Red cell lifespan is normal, and the severely deformed cells appear to represent the senescent population. Inappropriate increases in activities of some, but not all, age-dependent red cell enzymes were observed. The anomaly appeared to be entirely benign; no abnormal clinical findings were associated with this defect. It has been designated the Woronets trait.

Adolescent↗