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H Leung

Publications and source records attributed to H Leung.

53 records · Page 3Linked to original sources
PubMed1991

Paired cytoskeletal patterns in an epithelium of siamese twin cells.

The epidermis of some insects is a sheet of siamese twin cells which are formed by conserving the midbody between siblings after cell division. We have found that for about 36 h after ecdysis to the 5th stage, the cells of Calpodes caterpillars contain one to five or more actin bundles. The variation in number of bundles occurs in an epithelium that is presumed to be otherwise genetically and developmentally homogeneous. The number of bundles is paired in adjacent cells (P less than 0.005, n = 617). Confocal microscopy shows midbodies between paired but not between unpaired cells. The pairing is reminiscent of the paired nucleolar patterns in these siamese twin cells (Locke, M., H. Leung, Tissue and Cell 17, 573-588 (1985)) or the mirrored patterns of stress fibers in newly divided 3T3 cells (Albrecht-Buehler, G., J. Cell Biol. 72, 595-603 (1977)). The pairing provides further evidence for the operation of transiently heritable factors as determinants for cell pattern.

Actins↗
PubMed1989

Presence of the inflammatory cytokines IL-1, TNF, and IL-6 in preparations of monoclonal antibodies.

We have detected significant levels of IL-1, TNF and IL-6 in ascitic fluid from mice injected with different hybridomas. Each of these murine cytokines is active on a wide range of both human and murine target cells, and all are involved in inflammatory responses in vivo. We could not detect TNF or IL-1 in culture supernatant from the hybridoma line, used to generate the ascites; however, one out of ten did produce high levels of IL-6. These cytokines can interfere in many in vitro systems where monoclonal antibodies are used as diluted ascitic fluid to inhibit their ligands. A potentially more serious problem could arise with monoclonal antibodies used for therapy, in vivo diagnosis, or as ex vivo reagents. The use of monoclonal antibodies derived from culture supernatants is, therefore, obviously preferable to use of ascitic fluid for clinical applications, however, even with supernatant it cannot be assumed that cytokines are not present. Cytokine levels should, therefore, be monitored in all starting solutions and if present, their clearance during purification should be determined.

Animals↗
PubMed1987

A two-site sandwich immunoradiometric assay of human lymphotoxin with monoclonal antibodies and its applications.

Three monoclonal antibodies (MoAbs L49-15, L81-11 and L238-14) were raised against recombinant human lymphotoxin (rLT) derived from E. coli containing the cDNA sequence specifying LT. MoAb L81-11 strongly neutralised the cytotoxicity of LT derived either from E. coli or the RPMI 1788 lymphoblastoid cell line, whilst the other two MoAbs were only weakly neutralising in this respect. L81-11 and L238-14 MoAbs bound to different antigenic determinants on the rLT molecule, but neither bound to other lymphokines such as the structurally related tumour necrosis factor (TNF). As such, these MoAbs were ideal reagents for immunoassay of LT and a very sensitive, highly specific immunoradiometric assay (IRMA) was developed. This assay was rapid to perform and was capable of detecting as little as 10 pg/ml of LT. Application of the LT IRMA in combination with previously developed human gamma-interferon (IFN-gamma) and human TNF-specific IRMA (Crane et al., 1985; Meager et al., 1987) permitted independent estimations of these three substances to be carried out in parallel. By these means, it was found that RPMI 1788 produced both LT and TNF, but not IFN-gamma. Extensive analyses on cytokine (monokine and lymphokine) preparations derived from a variety of activated lymphocytes are also reported. Co-production of LT, TNF and IFN-gamma was a common finding, even occurring in alloantigen-specific T helper cell clones.

Antibodies, Monoclonal↗
PubMed1987

Preparation and characterization of monoclonal antibodies directed against antigenic determinants of recombinant human tumour necrosis factor (rTNF).

A large number of monoclonal antibodies (McAb) binding to antigenic determinants of human tumour necrosis factor (TNF) were prepared from two fusions of mouse myeloma NSO cells with spleen cells from Balb/c mice immunized with highly purified recombinant (r)TNF. Several of these McAbs were highly neutralizing with respect to the biological activity (cytotoxicity) of TNF manifested in L-929 C1.10 cells. Antibody competition experiments suggested the presence of at least two antigenic determinants on the rTNF molecule through which binding of McAb effects neutralization of biological activity. Some of these McAbs were shown to be suitable for the development of immunoassays to quantify rTNF.

Animals↗
PubMed1987

The natural 5' splice site of simian virus 40 large T antigen can be improved by increasing the base complementarity to U1 RNA.

The use of alternative 5' splice sites in the simian virus 40 early-transcription unit controls the ratio of large T to small t antigen during viral infection. To study the regulation of these alternative 5' splice sites, we made two mutants which improve the match of the large-T-antigen 5' splice site to the 5' splice site consensus sequence. Whether these mutants were assayed in vitro or in vivo, we found that the efficiency of large-T splicing is increased by improving the match of the large-T-antigen 5' splice site to the consensus. We conclude that the match of a 5' splice site is an important determinant of 5' splice site utilization and that the simian virus 40 large-T-antigen 5' splice site is almost certainly recognized by the U1 small nuclear RNA component of the U1 small nuclear ribonucleoprotein particle.

Base Sequence↗
PubMed1985

Ricin-resistant human T-cell hybridomas producing interferon gamma.

Ricin-resistant variants of the SH9 T-cell line were selected after growth of this line in medium containing toxic amounts of ricin, a lectin derived from Ricinus communis. The ricin-resistant SH9 lines, SH9.R0 and SH9.R1, were demonstrated to be deficient in cell surface ricin-binding sites, but otherwise had the cellular phenotype of SH9 cells. Ricin-resistant T-cell hybridomas were prepared by fusion of SH9.R0 and SH9.R1 with activated T-lymphocytes. The presence of ricin in the selection medium rapidly killed unfused T-lymphocytes and prevented cell transformation by human T-cell leukaemia virus type 1 (HTLV-1) which is shed by the SH9.R0 and SH9.R1 cells. This ensured that the cells growing out were indeed hybridomas. Ricin-resistant T-cell hybridomas were characterised and also shown to lack cell surface receptors for ricin. Analysis of T-cell surface markers indicated that the T-cell hybridomas could be the result of fusions between SH9.R1 cells and T-helper lymphocytes or T-suppressor lymphocytes. All of the T-cell hybridomas prepared in this study spontaneously produced interferon gamma (IFN gamma).

Cell Line↗
PubMed1985

Different genes code for alkaline phosphatases from human fetal and adult intestine.

Alkaline phosphatases from human adult intestine and fetal intestine (meconium) were purified and compared. Electrophoresis in SDS showed one band of protein in the former. There were three bands of protein in the latter, all with essentially the same peptide map. Thus, two of the bands probably arose by proteolysis of the third, which was largest (Mr 73000). In gradient gels of polyacrylamide the alkaline phosphatase from fetal intestine showed only one band of protein coincident with the band of activity (Mr 151000). Radiolabeled mapping showed that the tryptic peptides of the alkaline phosphatase from fetal intestine were distinctly different from those of adult intestine and human liver, and placenta, indicating a gene distinct from the three that code for the enzyme in liver/kidney/bone, placenta, and adult intestine.

Adult↗
PubMed1985

Interferon gamma produced by mitogen-activated T lymphocytes does not directly mediate lymphoproliferation.

Human interferon gamma (IFN-gamma) endogenously produced during mitogenic stimulation of human peripheral blood mononuclear cells or human T lymphocyte-enriched cultures was neutralized in situ by the addition of a polyclonal antiserum (anti-L) raised in a rabbit against partially purified natural IFN-gamma derived from peripheral blood mononuclear cells. Small decreases in mitogen-induced [3H]thymidine incorporation (lymphoproliferation) were demonstrated under these conditions. However, an antiserum (anti-G) raised in a sheep against highly purified recombinant IFN-gamma (E. coli-derived) which strongly neutralized the antiviral effect of IFN-gamma either had little effect on mitogen-induced lymphoproliferation or caused slight enhancement of mitogenesis. The interleukin 2 responsiveness of activated T lymphocytes following mitogenic stimulation was not found to be different in the presence of anti-G to that of control cultures incubated in the presence of normal sheep serum. These results suggest that IFN-gamma is not a direct requirement for lymphoproliferation.

Antibodies↗
PubMed1984

The induction and distribution of an insect ferritin--a new function for the endoplasmic reticulum.

Three insect tissues have particular roles as filters to maintain the fluid composition of the hemolymph. Water and ions enter and leave through the midgut. The pericardial cells filter circulating hemolymph. Malpighian tubules, often with the rectum, allow resorption from a hemolymph filtrate that passes to the hindgut. All three tissues have plasma membrane infolds making a reticulum on their hemolymph surfaces, and all three have RER leading to SER extensions into their reticula. SER is a catch-all description for membranes lacking ribosomes in the pre-Golgi complex set of compartments of the vacuolar system. Some kinds of SER are well known for their role in housing enzymes for steroid metabolism and for detoxification. The SER ramifying within the plasma membrane reticular systems of tissues concerned with hemolymph filtration contains ferritin, suggesting that this SER has another, different function. In contrast to vertebrate cells, where ferritin is confined to the cytosol and lysosomes, we have found that in Calpodes and perhaps in most insects, ferritin occurs in the vacuolar system and not in the cytosol. Ferritin occurs naturally in the RER and SER of cells at the hind end of the midgut, in pericardial cells and in the yellow region of the Malpighian tubules. Additional ferritin is induced by loading the gut or hemolymph with iron. Overloading with iron causes ferritin secretion to the gut lumen. We propose that the SER in these cells functions in iron homeostasis by holding ferritin for loading and unloading as it moves to and from the reticulum at the cell surface where it can be maximally exposed to extracellular fluid flow.

Animals↗
PubMed1984

The preparation of interferon gamma-producing T-cell hybridomas from jacalin-stimulated T lymphocytes and the SH9 T-cell line.

Jacalin, a lectin(s) extracted from the seeds of Artocarpus integrifolia (Jackfruit), was shown to induce the production of gamma interferon (IFN gamma) in human peripheral blood mononuclear cells (PBMC) and human T-lymphocyte cultures. The amount of IFN gamma produced was enhanced in the presence of mezerein, a phorbol ester derivative. Fusion of jacalin stimulated T lymphocytes with the SH9 T-cell line resulted in the formation of T-cell hybridomas which spontaneously secreted IFN gamma. The spontaneous production of IFN gamma by T-cell hybridomas was not influenced by the presence of jacalin, although significant enhancement of production was observed when the cells were cultured in the presence of mezerein.

Animals↗
PubMed1979

Effects of ethanol on turnover and function of striatal dopamine.

Acute oral administration of ethanol increased the rate of depletion of dopamine in the striata of rats injected with alpha-methyl-p-tyrosine. This effect was eliminated by pretreatment with atropine or by lesioning of the striato-nigral tract. Ethanol also attenuated the inhibitory effect of apomorphine on turnover of striatal dopamine. Unilateral injection of ethanol into the neostriatum of rats followed by intraperitoneal injection of either apomorphine or amphetamine elicited marked ipsilateral head-to-tail body turning. This turning was blocked by pretreatment with haloperidol. Chronic intubation of ethanol to rats enhanced contralateral body turning elicited by unilateral intrastriatal injection of dopamine. Injection of 6-hydroxydopamine into the substantia nigra led to denervation supersensitivity of dopaminergic functions in the neostriatum. This effect was not seen in rats that were given ethanol postinjection of 6-hydroxydopamine. These results suggested that ethanol has an inhibitory effect on the nigrostriatal dopaminergic system.

Animals↗