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Biomedical subjects

S Chen

Publications and source records attributed to S Chen.

At least 1,495 records · Page 83Linked to original sources
PubMed1983

Maturation of cytotoxic T cells within sponge matrix allografts.

Two parallel events may provide cytotoxic effector cells at the site of allograft challenge: 1) the migration of effector cells to the graft, and 2) the local maturation of effector cells. Various experimental conditions were manipulated to ascertain the relative role of local maturation of precytotoxic cells at the site of alloantigen challenge. A C57BL/6 allogeneic-coated sponge matrix allograft was placed in a BALB/c animal. The entire animal with the sponge was subjected to sublethal irradiation, or alternatively, just the animal was subjected to the same dose of irradiation, and the sponge was shielded. The data demonstrate that by day 5, precytotoxic cells directed against donor alloantigen appears within the sponge matrix allograft. These precytotoxic cells are in themselves x-ray sensitive, but in the absence of irradiation and in the absence of further contributions from the host can develop into mature cytotoxic cells with specificity limited to that of donor alloantigen. The relative role of local maturation vs continued influx of mature cytotoxic cells cannot be determined from these sets of experiments. These data, however, show that there is potential for local development of mature cytotoxic cells in the absence of other host influences.

Animals↗
PubMed1983

Total synthesis of yeast alanine transfer ribonucleic acid.

By a combination of chemical and enzymatic methods, small oligonucleotides with lengths varying from 2 to 8 nucleotides were synthesized from mononucleotides. The small oligonucleotides were then ligated with T4 RNA ligase into six large oligonucleotides (9 to 19 nucleotides long) which were further ligated to form two half molecules with 35 and 41 nucleotides respectively. Finally, the two synthetic half molecules were annealed and ligated to obtain the whole molecule of yeast alanine tRNA (tRNAAlay). Prior to this, two semi-syntheses were performed, i.e. ligation of the synthetic 5'-half molecule with the natural 3'-half molecule and that of the natural 5'-half molecule with the synthetic 3'-half molecule. Both the semi-synthetic tRNAAlay and the synthetic tRNAAlay occupy the same position as the natural tRNAAlay after electrophoresis on a 20% polyacrylamide gel. They have the same chemical composition (containing 9 modified nucleotides of 7 different species) and structure as the natural tRNAAlay and are biologically active, i.e. accepting and transferring alanine into proteins in a cell-free protein synthesizing system, the accepting activity of the synthetic product is 52-66% of that of the natural tRNAAlay and 91-106% of that of the reconstituted product of the two natural half molecules. The incorporation activity of alanine into proteins of the synthetic 3H-alanine tRNAAlay is 63%, corresponding to 91% of that of the natural tRNAAlay and 115% of that of the reconstituted product of the two natural half molecules. To the best of our knowledge, this is the first time that a natural RNA with biological activity is synthesized.

Base Sequence↗
PubMed1983

Synthesis of the 5'-half molecule of yeast alanine tRNA.

In this paper, we report the synthesis of the 5'-half molecule of yeast alanine tRNA (tRNAAlay) by ligating three oligonucleotide fragments corresponding to the nucleotide sequences 1-13, 14-22 and 23-35 respectively under the catalysis of T4 RNA ligase (Fig. 1). Because of the high purity of the oligonucleotide fragments and the excellent quality of T4RNA ligase and polynucleotide kinase we prepared, the isolation steps were simplified and the overall yields were much higher. The ligating yield of the docosamer (IV) was 75%, that of the pentatriacontamer (V), 90%, and the isolated yield of the final product was 21% calculated on the basis of the tridecamer (III) used in the first reaction. Under the action of T4 RNA ligase the synthetic 5'-half molecule was joined with the natural 3'-half molecule forming a semi-synthetic tRNAAlay, which possessed the biological activities of both accepting (3H)-alanine and incorporating it into proteins. The correctness of the structure of the synthetic 5'-half molecule was verified by both chemical analysis and biological activity assay.

Base Sequence↗
PubMed1982

Plasticity of the parallel fiber-Purkinje cell synapse by spine takeover and new synapse formation in the adult rat.

Alteration in synaptic connectivity between Purkinje cell spines and parallel fibers of the cerebellum were studied following partial deafferentation of Purkinje cells in the the adult rat. Transection of parallel fibers by two lesions placed at a 1 mm interval on the folial crest were used to produce degeneration of these afferents. Ultrastructural analysis of synapses on Purkinje cell spines revealed degeneration with vacating of postsynaptic sites within 6 h. Reactive synaptogenesis as takeover of Purkinje cell spines by formation of new synapses from remaining parallel fibers occurred even before degenerating parallel fibers had vacated postsynaptic sites. This was accompanied by a marked increase in the number of dual innervations by reactive parallel fibers within one day. Some vacated postsynaptic sites were lost as indicated by a reduction in the number of synapses and others may have been taken over by newly formed synapses on spines. In addition, new synapses formed between the shafts of Purkinje cell branchlets and parallel fibers. Sprouting of parallel fibers occurred as small extensions without tubules while Purkinje cell spines reacted by forming elongated and multiple heads which contacted different parallel fibers. After 5 days degenerating boutons were rarely found. Enlarged spine heads were each capped by a proportionally enlarged parallel fiber bouton and joined by an elongated synaptic junction to parallel fibers. Some parallel fiber boutons were greatly enlarged and capped numerous profiles of spines. This study shows that formation of new pre- and postsynaptic sites takes precedence over reoccupation of original contacts and that multiple synapses on individual spines are being eliminated to give rise to single contacts with boutons. This elimination resulted in enlargement of synaptic contact areas between Purkinje cell spines and parallel fibers by taking over postsynaptic sites from some vacated and eliminated boutons.

Animals↗
PubMed1982

Species comparisons of bronchoalveolar lavages from guinea pigs and rats exposed in vivo to diesel exhaust for one year.

Male Hartly guinea pigs and Fischer rats 344 were exposed to diesel exhaust (DE) concentrations at 0, 250, and 1500 micrograms/m3 in short terms, as well as long term experiments up to one year. The effects of inhaled DE on these rodents were evaluated using bronchoalveolar lavage technique. Both the morphological and functional studies of free lung cells and the biochemical and immunologic studies of the supernatant lavage fluid provided the basis for a quantitative species comparison of the pulmonary responses of exposed guinea pigs and rats versus age matched controls. Following inhalation of 250 micrograms DE/m3, there were little or no significant changes in either species. In contrast, at higher DE concentration, leukocytic infiltration and elevation of specific proteins in lavage fluids were observed in both species. The findings occurred and persisted in both species. Some of the responses were species specific (e.g., the specific type of exudative leukocytes, appearance of reactive monocytes, and different amounts of free DE particles and debris in the lavage fluid). Other responses were similar in both species. Among them, the emergence and increase of lymphocytes was evidence of immunologic responses. Biochemical data from the supernatant fluid correlates with the changes in cellular population in the lavage. The responses appear to be dose and duration dependent. These data indicate that species differences occur. However, it is clear that the alveolar macrophage and granulocytic leukocytes continue to exert effective defense at the DE dose-durations studied. In general, rats appeared more resistant to DE exposure than guinea pigs.

Animals↗
PubMed1982

Constructions of gene libraries of Rana nigromaculata and Mus musculus with cosmid pHC79.

Gene libraries of Rana nigromaculata and Mus musculus (C57J6) have been constructed by the cosmid system developed by Collins using BamHl and Pstl as cloning restriction enzymes. A simplified formula, which is a modification of Clarke and Carbon derived from approximation, was used for calculating the number of colonies or recombinants necessary for the construction of a gene library. Pro+ and leu+ complementary to the recipient cells (HB101) with the genetic constitution of pro- and leu- have been selected from the BamH1 gene libraries of both Rana nigromaculata and the mouse in the present work.

Animals↗
PubMed1982

A study of free lung cells from young rats chronically exposed to carbon monoxide from birth.

Carbon monoxide (CO) is a well know constituent of cigarette smoke and automobile exhaust. The purpose of this study was to determine the effect of CO on the first line of lung defense, the alveolar macrophage (AM). Free lung cells were obtained by bronchoalveolar lavage with Dulbecco's phosphate buffered saline from rats exposed to 500 ppm CO from birth until 33 days of age and from littermate controls. Morphological and functional parameters of the exposed cells showed minor changes. Hemoglobin concentration and hematocrit were significantly elevated in the CO-exposed group. Recovery yield of lavage fluid, wet lung weight, and lung displaced volume were identical to controls. Neither number of AM, viability, maximal diameter, surface area nor acid phosphatase activity of exposed AM appeared to be different from controls. However, in a test with fluorescent latex spheres, the phagocytic ability of AM was found to be enhanced in CO-exposed rats and was correlated with an increased percentage of spread forms of AM adhering to glass coverslips. The surface features of the AM were somewhat modified. Number and percentage of granular leukocytes were statistically increased in lavages following chronic exposure to CO. These alterations contrast with the effects of diesel exhaust and cigarette smoke.

Aging↗
PubMed1981

Studies on the interaction of arylazido-beta-alanyl NAD+ with the mitochondrial NADH dehydrogenase.

Arylazido-beta-alanyl NAD+ (A3'-O-(3-[N-(4-azido-2-nitrophenyl)amino]propionyl) NAD+) is a potent competitive inhibitor with respect to NADH (apparent Ki, 1.7-2.7 microM) for the purified mitochondrial NADH dehydrogenase (EC 1.6.99.3). Upon photoirradiation of the dehydrogenase in the presence of arylazido-beta-[3-3H]-alanyl NAD+, radioactivity was found to be associated with the Mr = 57,000 subunit without significant labeling of what are considered to be the enzyme's two smaller subunits. This labeling could be prevented by the presence of NADH during photoirradiation. In contrast to arylazido-beta-alanyl NAD+, arylazido-beta-alanyl NADP+ (N3'-O-(3-[N-(4-azido-2-nitrophenyl)amino]-propionyl) NADP+) did not inhibit dehydrogenase activity nor did photoirradiation of the enzyme in the presence of the radiolabeled analogue (arylazido-beta-[3-3H]alanyl NADP+) result in radioactivity being incorporated into the enzyme. It is concluded that the Mr -- 57,000 subunit contains the pyridine nucleotide-binding site of the mitochondrial NADH electron transport system.

Affinity Labels↗