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J Blok

Publications and source records attributed to J Blok.

At least 55 records · Page 3Linked to original sources
PubMed1984

Comparison of dengue viruses and some other flaviviruses by cDNA-RNA hybridization analysis and detection of a close relationship between dengue virus serotype 2 and Edge Hill virus.

Variable amounts of cDNA were synthesized in vitro from RNA extracted from several flaviviruses, including the four prototype dengue (DEN) virus serotypes. The synthesis was carried out using an oligo(dT) primer, suggesting the presence of a short poly(A) region at or near the 3' end of some flavivirus genomes. The DEN-1 and DEN-2 prototype strains produced the largest amount of cDNA and were therefore used to investigate further the relatedness of flavivirus genomes by cDNA-RNA hybridization. The flaviviruses studied are related to each other to some extent since the hybrids formed exhibited about 30% S1 nuclease resistance, but a closer relationship was detected between dengue viruses of serotype 1 and 4 and between dengue virus serotype 2 and Edge Hill virus. A monoclonal antibody to the envelope protein (V3) of dengue viruses reacted with Edge Hill virus, confirming the genetic relationship between the viruses.

Antigens, Viral↗
PubMed1983

Heterogeneity in 5'-nucleotidase activity of mouse peritoneal macrophages. An EM-cytochemical and biochemical study.

After stimulation of the mouse peritoneal cavity with newborn calf serum (NBCS), four types of monocyte and macrophage were distinguished on the basis of peroxidase (PO) patterns. Cytochemically, these cells showed strong heterogeneity in 5'-nucleotidase (5'N) activity. Monocytes and monocyte-derived macrophages with PO activity in granules lacked 5'N activity. Resident macrophages (with PO activity in RER and nuclear envelope) generally had significant 5'N activity on the plasma membrane, the pattern showing close correlation with the biochemical findings. The group of PO-negative macrophages comprised both 5'N-negative and 5'N-positive cells. These findings suggest two possibilities, i.e., that monocytes (5'N-)transform via PO-negative cells (5'N -/+) into resident macrophages (5'N +), or that the monocytes and monocyte-derived macrophages and the resident macrophages represent separate lineages. The fourth type of macrophage, the exudate-resident cell (with PO activity both in granules and in the RER and nuclear envelope), occurred only in low numbers and very late after NBCS stimulation, and is therefore considered not to be a transitional cell between monocytes and resident macrophages.

5'-Nucleotidase↗
PubMed1982

Endocytosis in absorptive cells of cultured human small-intestinal tissue: effect of cytochalasin B and D.

The effect of cytochalasin B (CB) and cytochalasin D (CD) on the endocytotic uptake of horseradish peroxidase (HRP) by intestinal absorptive cells was investigated by morphometric methods. The results showed that CD inhibited endocytosis considerably, and without any detrimental side-effects. CB had hardly any effect on the endocytosis of HRP, but caused a significant decrease in the number of apical vesicles and tubules involved in the transport of cell-coat glycoproteins from the Golgi apparatus to the brush border. Electron-microscopic autoradiographic analysis of the effect of CD showed that although endocytosis is inhibited significantly by the drug, the amount of radiolabelled cell-coat material entering the lysosome-like bodies was unaltered compared with control cultures. These observations support our hypothesis that the cell-coat glycoproteins of the absorptive cells enter the lysosome-like bodies by a crinophagic rather than by an exocytotic-endocytotic mechanism.

Cells, Cultured↗
PubMed1982

A cytochemical method for the demonstration of 5'-nucleotidase in mouse peritoneal macrophages, with cerium ions used as trapping agent.

A method was developed for the demonstration of 5'-nucleotidase in murine peritoneal resident macrophages. The cells are incubated cytochemically without agitation and cerium chloride is used as a trapping agent. Under these conditions, the great majority of the macrophages in the unstimulated peritoneal cavity show enzyme activity in the plasma membrane. In the presence of AMP-S (an AMP analogue inhibiting 5'-nucleotidase, as shown biochemically) there was a decrease in both the number of positive macrophages and the amount of reaction product on the plasma membranes. This indicates that the enzyme activity detected by our cytochemical procedure is attributable to 5'-nucleotidase.

5'-Nucleotidase↗
PubMed1981

The effect of chloroquine on lysosomal function and cell-coat glycoprotein transport in the absorptive cells of cultured human small-intestinal tissue.

The effect of chloroquine, an inhibitor of intralysosomal catabolism, on the synthesis, transport, and degradation of cell-coat glycoproteins in absorptive cells of cultured human small-intestine tissue was investigated by morphometrical, autoradiographical, and biochemical methods. Neither synthesis nor transport of cell-coat material was affected by the drug, but culturing of the absorptive cells in the presence of chloroquine led to a dose- and time-dependent enlargement of the dense bodies; other cell structures showed no alterations. 3H-fucose-labelled material accumulated in the dense bodies of the absorptive cells of these cultures. Since no increase of beta-glucuronidase and acid phosphatase activity (both lysosomal enzymes of glycoprotein nature) was found, this accumulation of radiolabeled material can be explained as a chloroquine-mediated inhibition of the degradation of cell-coat glycoproteins. These macromolecules probably enter the lysosome-like bodies by a crino-phagic mechanism, i.e., fusion of these organelles with the apical vesicles and tubules involved in intracellular transport. These findings suggest that the lysosome-like bodies have a function in the regulating of cell-coat glycoprotein transport in human intestinal absorptive cell, i.e., the degradation of excess cell-coat material.

Biological Transport↗
PubMed1981

Endocytosis in absorptive cells of cultured human small-intestinal tissue: horseradish peroxidase, lactoperoxidase, and ferritin as markers.

The occurrence of endocytotic mechanisms in human small-intestinal absorptive cells was investigated by culturing biopsy specimens in the presence of horseradish peroxidase (HRP), lactoperoxidase (LPO), and ferritin. The results indicate that both HRP and LPO entered the cells by apical endocytosis, after which they were transported via apical vesicles and tubules to the lysosome-like bodies. Ferritin, which showed a distinct affinity for the cell-coat glycoproteins, was not interiorized by the absorptive cells. These findings suggest that although human absorptive cells have an endocytotic mechanism, possibly fluid-phase endocytosis, cell-coat glycoproteins are not taken up by the cells, as indicated by the absence of ferritin in the apical vesicles and tubules, as well as the lysosome-like bodies. These findings provide indirect support for our hypothesis that the lysosome-like bodies have a function in the regulation of cell-coat glycoprotein transport via a crinophagic mechanism (fusion of apical vesicles and tubules with lysosome-like bodies) rather than via an exocytotic-endocytotic mechanism.

Cells, Cultured↗
PubMed1981

The effect of colchicine on the intracellular transport of 3H-fucose-labelled glycoproteins in the absorptive cells of cultured human small-intestinal tissue. An autoradiographical and biochemical study.

The effect of colchicine on the intracellular transport of 3H-fucose-labelled glycoproteins in the absorptive cells of cultured biopsy specimens of the human intestine was investigated by light- and electron-microscopical autoradiography and by biochemical methods. The results showed a decrease in the radioactivity of the cell coat on the microvilli and an increase in the Golgi apparatus and in the apical vesicles and tubules. This divergence is attributed to a colchicine-induced impairment of the normal transport of cell-coat glycoproteins from the Golgi apparatus, via the apical vesicles and tubules, to the apex of the cell. The radioactivity of the lysosome-like bodies in the absorptive cells cultured with colchicine also increased. This finding supports a crinophagic function of these organelles in the degradation of excess cell-coat material.

Biological Transport↗
PubMed1981

The effect of chloroquine on the intralysosomal degradation of cell-coat glycoproteins in the absorptive cells of cultured human small-intestinal tissue as shown by silver proteinate staining.

The effect of chloroquine on the intralysosomal degradation of cell-coat glycoproteins in cultured intestinal absorptive cell was investigated by silver proteinate staining. The results of this staining method, which is specific for carbohydrate containing macromolecules such as glycoproteins and mucopolysaccharides, showed that in the presence of the drug considerable amounts of silver proteinate-positive material accumulated in one type of lysosome-like body: the dense bodies. The staining pattern of other cell organelles was not affected by chloroquine. The presence of the drug in the culture medium also resulted in the occurrence of numerous small vesicular structures in the matrix of the dense bodies. These showed a similar size and structure to those present in the other type of lysosome-like body: the multivesicular bodies. This observation, together with earlier autoradiographical data, suggests that cell-coat material is transferred from multivesicular to dense bodies by fusion between these organelles. This study thus provides further evidence for a regulatory mechanism of cell-coat glycoprotein transport by the lysosome-like bodies in human intestinal absorptive cells.

Chloroquine↗
PubMed1980

Binding of cationized ferritin to the cell-coat glycoproteins of human and rat small-intestinal absorptive cells.

The binding of cationized ferritin (CF) to the cell-coat (glycocalyx) glycoproteins of human and rat intestinal absorptive cells was investigated in relation to the amount of sialic acid in these macromolecules. The cell coat of human absorptive cells exhibited poor binding of CF and contained a small amount of sialic acid. The cell coat of rat absorptive cells had about ten times more sialic acid than that of human cells and showed a strong affinity for the marker. The removal of sialic acid from the cell-coat glycoproteins of rat intestinal cells by neuraminidase treatment abolished CF binding. These results suggest that sialic acid is necessary for CF binding and that human and rat intestinal absorptive cells show a species-specific difference in the sugar composition of the cell coat.

Animals↗
PubMed1979

Effect of calcium ions on the infection of Bacillus subtilis by bacteriophage SF 6.

Infection of Bacillus subtilis 168Wt by SF 6 resulted in a rapid reduction in the number of phages. This could be counteracted by the addition of calcium, barium or strontium ions. At the optimum concentration of 7.5 x 10(-2) M, the number of p.f.u. remained constant until lysis began. Although cultures of another host. B. subtilis 31 try- his-, at the end of the logarithmic growth phase produced a substance which inactivated free phages, this was not the major cause of the reduction in the numbers of p.f.u. during infection experiments at low Ca2+ concentrations. The diminution of the number of p.f.u. was therefore attributed to the fact that at least one of the steps of the lytic cycle was calcium dependent. Adsorption of SF 6 was equally effective in media containing high or low concentrations of calcium ions. Infection experiments with phages whose DNA had been labelled radioactively revealed that, at high concentrations of calcium ions, the label remained associated with the host cells until lysis commenced. At low concentrations, however, a dissociation between phage DNA and the host was found, although adsorption took place at a normal rate. From these experiments we concluded that a high concentration of calcium ions was required for the penetration of phage DNA. Similar experiments with phages whose protein coat had been labelled showed the same results, indicating that desorption of the inactivated phages occurred. Both electron microscopy and column chromatogarphy with hydroxyapatite showed that a considerable fraction of the inactivated phages had ejected their DNA into the medium. A hypothesis explaining these results is presented.

Adsorption↗