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Biomedical subjects

M C Raff

Publications and source records attributed to M C Raff.

At least 127 records · Page 7Linked to original sources
PubMed1978

Localized mast cell degranulation induced by concanavalin A-sepharose beads. Implications for the Ca2+ hypothesis of stimulus-secretion coupling.

Concanavalin A (Con A) covalently linked to Sepharose 4B beads induced localized degranulation of sensitized rat peritoneal mast cells in regions of contact between beads and cells. This degranulation was Ca2+ dependent and was not seen when sensitized mast cells bound to beads conjugated with a nonstimulating lectin, wheat germ agglutinin, or when unsensitized mast cells bound to Con A-Sepharose. The finding that sensitized mast cells which had adhered to Con A-Sepharose beads degranulated in regions of the cell away from the area of bead contact if exposed to soluble Con A excluded the possibility that the localized release was due to a redistribution of the IgE receptors or putative Ca2+ channels to the region of bead contact. The results suggest that, if an influx of Ca2+ is the mechanism for initiating mast cell degranulation, then the opening of Ca2+ channels in the plasma membrane of activated mast cells is a localized event and that Ca2+ acts locally within the cell to initiate exocytosis.

Animals↗
PubMed1977

Accessory cell dependence of lectin-induced proliferation of mouse T lymphocytes.

Mouse lymph node cells were exposed to carbonyl iron and a magnet to remove phagocytic cells, and passed over Sephadex G-10 and nylon wool and incubated for 12 h on plastic to remove adherent cells and their precursors. More than 99% of the cells in this macrophage-depleted population (which constituted 3-5% of the starting population) were Thy-1+ and Ly-1+, while less than 2% were Ly-2+. These cells usually did not synthesize detectable amounts of DNA when cultured with concanavalin A and responded poorly to phytohemagglutinin. These proliferative responses were completely reconstituted by small numbers of syngeneic or allogeneic peritoneal cells, purified peritoneal macrophages or cells from tertiary cultures of mouse embryo 'fibroblasts', but not by 3T3 cells, P815 mastocytoma cells or Nulli SCC-1 embryonal carcinoma cells, or by 2-mercaptoethanol. The reconstituting peritoneal cells were Thy-1--, Ia+ and present in nu/nu mice; although they had to be alive to reconstitute, they did not have to divide. These results are consistent with the hypothesis that T cell proliferation induced by lectins, like that induced by antigens, may involve the dual recognition of stimulating ligand in association with major histocompatibility complex (Ia) determinants.

Animals↗
PubMed1977

Organ culture studies of nude mouse thymus.

There is evidence that peripheral lymphoid organs of nude mice, born from homozygous matings, contain a small proportion of theta-positive lymphocytes indicating that nude mice may not be totally devoid of T cell function. It has been suggested that such lymphocytes may develop within the dysplastic nude thymus itself. While this suggestion receives no support from morphological studies, it has been claimed that on explanation to organ culture the developing nude thymus becomes lymphoid. In this present study we confirm the presence of theta-positive lymphocytes in peripheral lymphoid tissues of homozygous nude mice born of nude parents. However, when we have organ-cultured nude thymus, explained from homozygous nude embryos at days 13, 14, 16 and 18 of gestation, we have found no histological sign of lymphopoiesis nor have we detected any theta-positive cells in such cultured material. On the contrary, the nude thymus in vitro develops into the polycystic structure characteristic of the adult nude thymus. We conclude that the small number of theta-positive cells present in the periphery result from extrathymic differentiation.

Animals↗
PubMed1977

Molecular events during membrane fusion. A study of exocytosis in rat peritoneal mast cells.

We have used thin section and freeze-fracture electron microscopy to study membrane changes occurring during exocytosis in rat peritoneal mast cells. By labeling degranulating mast cells with ferritin-conjugated lectins and anti-immunoglobulin antibodies, we demonstrate that these ligands do not bind to areas of plasma membrane or granule membrane which have fused with, or are interacting with, granule membrane. Moreover, intramembrane particles are also largely absent from both protoplasmic and external fracture faces of plasma and granule membranes in regions where these membranes appear to be interacting. Both the externally applied ligands and intramembrane particles are sometimes concentrated at the edges of fusion sites. The results indicate that membrane proteins are displaced laterally into adjacent membrane regions before the fusion process and that fusion occurs between protein-depleted lipid bilayers. The finding of protein-depleted blebs in regions of plasma and granule membrane interaction raises the interesting possibility that blebbing may be a process for exposing the granule contents to the extracellular space and for the elimination of excess lipid while conserving membrane proteins.

Antibodies↗
PubMed1977

Studies on the generation of B lymphocytes in fetal liver and bone marrow.

With the use of immunofluorescence techniques, cells containing cytoplasmic IgM (cIgM+), but lacking detectable surface IgM (sIgM+), have been identified in mouse fetal liver and adult bone marrow as a distinct cell population to sIgM+ B lymphocytes. We have shown that there is a considerable difference in the rate of entry of cIgM+ and sIgM+ cells into DNA synthesis in these locations. Moreover, within the cIgM+ population, the largest cells are the main group entering DNA synthesis. Our results are compatible with the notion that a pool of rapidly proliferating, large cIgM+ cells is present in fetal liver and adult bone marrow and that these cells give rise to populations of smaller cIgM+ cells, which move out of cell cycle, and convert to sIgM+ B lymphocytes. However, we recognize that this interpretation is speculative. Finally, we have shown that fetal bone marrow is a site of generation of sIgM+ B lymphocytes, but the question as to whether these cells are derived from Ig- precursors within marrow itself remains open.

Animals↗
PubMed1976

Studies on the generation of B lymphocytes in the mouse embryo.

Using an organ culture technique, the development of B lymphocytes has been studied in a number of isolated embryonic hemopoietic tissues. Developing B lymphocytes were identified by cytoplasmic and surface immunofluorescence using purified class-specific antibodies and a Fab anti-immunoglobulin reagent. In fetal liver cultures these cells were further characterized for Fc and complement receptors and for the presence of mouse-specific B lymphocyte antigen. The results indicate that B lymphocytes develop independently in fetal liver and in fetal spleen; they do not develop in cultures of yolk sac and thymus. In conclusion, it is likely that B lymphocyte maturation in mammals is multifocal and is not dependent upon gastrointestinal influences as suggested previously.

Animals↗
PubMed1975

Differences in susceptibility of mature and immature mouse B lymphocytes to anti-immunoglobulin-induced immunoglobulin suppression in vitro. Possible implications for B-cell tolerance to self.

Purified goat antibodies against mouse mu-chains and rabbit antibodies against mouse Ig determinants, and their Fab fragments, inhibited the development of IgM-bearing B cells in explant cultures of 14-day mouse fetal liver, and caused the disappearance of cell surface IgM in explant and dissociated cell cultures of more developed lymphoid tissues. While treatment of cultures of fetal or newborn liver, or adult bone marrow, with low concentrations (less than or equal to 10 mug/ml) of anti-Ig for less than or equal to 24 h caused the complete, but reversible, disappearance (modulation) of cell surface IgM, treatment for greater than or less than 48 h produced irreversible IgM suppression. In contrast, anti-Ig-induced suppression of cell surface IgM in cultures of adult spleen or lymph nodes required much higher concentrations of antibody (greater than or equal to 100 mug/ml) and was always reversible. These differences between immature and mature IgM-bearing cells could not be related to differences in the amount of surface IgM on the cells. The remarkable sensitivity of newly formed B cells to IgM modulation and irreversible IgM suppression when ligands bind to their Ig receptors, may have important implications for B-cell tolerance to self antigens.

Animals↗
PubMed1975

Induction of increased calcium uptake in mouse T lymphocytes by concanavalin A and its modulation by cyclic nucleotides.

The binding of concanavqlin A to T but not B mouse spleen lymphocytes increases Ca-2+ uptake in these cells which is measurable by 45 s and complete by 1 min. Dibutyrl cyclic AMP, but not sodium azide inhibits induced Ca-2+ uptake, wheras dibutyryl cyclic GMP enhances it. B cell mitogens do not cause a similar Ca-2+ uptake in mouse B lymphocytes. The induction of increased Ca-2+ uptake by T cells is discussed in terms of gated membrane channels for Ca-2+.

Animals↗
PubMed1975

The development of the thymus in the nude mouse.

The developing thymus of nude mouse embryos (derived from homozygous, nu/nu x nu/nu, matings) has been examined from 13 days' gestation onwards for the presence of large basophilic stem cells or their lymphoid progeny. No trace of either stem cells or lymphocytes has been found at any stage, indicating that from the earliest stages of thymic development lymphopoiesis is defective. However, histological evidence alone is not sufficient to rule out the possibility that small numbers of lymphocytes may be present in the nude thymus. Recent evidence that nude mice born of heterozygous (nu/+) females possess some T lymphocytes and "T lineage" cells is discussed in relation to these findings. A series of morphological changes have been defined within the epithelial component of the developing nude thymus, further analysis of which may help to determine the nature of the thymic defect.

Animals↗