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排序方式: 共有957条查询结果,搜索用时 15 毫秒
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The in vitro synthesis of interferon (IFN) by human lymphocytes stimulated in mixed-lymphocyte culture (MLC) was examined. The production of IFN in MLC was restricted to T lymphocytes and maximum levels of IFN were detected in supernatants from cells incubated for 5 to 7 days. The IFN produced was identified as IFN-gamma by antibody neutralization. To identify the T cell responsible for IFN production, purified T lymphocytes were separated into subpopulations after incubation in 5 mM theophylline. Theophylline-resistant (T-res) T cells retain the ability to form sheep erythrocyte (SRBC) rosettes and are depleted in IgG Fc receptor-positive T cells (T gamma cells). Theophylline-sensitive (T-sens) T cells fail to form rosettes after theophylline treatment and are enriched in T gamma cells. In addition, analyses using monoclonal antibodies showed that T-sens cells were enriched in OKM1-, HNK-1-, and 7.2-positive cells and T-res cells contained increased numbers of 9.6- and OKT4-positive cells. Following MLC stimulation, equivalent levels of IFN-gamma were produced by T-res and T-sens cells and both subpopulations maintained natural killer (NK)-like cytotoxicity against K562 target cells. Addition of partially purified IFN-gamma to unstimulated T-res and T-sens cells resulted in the maintenance of NK-like cytotoxicity in a manner analogous to that observed after MLC. Additional experiments indicated that peripheral blood lymphocytes depleted of 9.6- or OKM1-positive cells by complement-mediated lysis were devoid of cytotoxicity against K562 cells. Furthermore, MLC stimulation of 9.6- or OKM1-depleted cells failed to restore cytotoxic activity. In summary, these experiments demonstrate that the maintenance of NK-like cytotoxicity by MLC-stimulated T cells is associated with the synthesis of IFN-gamma, that MLC stimulated T-res and T-sens T-cell subsets produce equivalent amounts of IFN, and that 9.6- or OKM1-positive cells are required for the maintenance of NK-like cytotoxicity in MLC. 相似文献
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Robin S. Manasse Maureen L. Stanton 《Evolution; international journal of organic evolution》1991,45(4):883-890
We present evidence that extreme seed size variation in fruits of Crinum erubescens (range: 0.1 to 66.5 g per seed) occurs when mating pairs are inbred, either from selfing or biparental inbreeding. Several relatively uniform seeds of intermediate size are produced when pollen from several pollen donors is applied simultaneously to a flower. Selfed fruits and some fruits pollinated with a single pollen donor produce both large and small seeds, although selfed fruits produce fewer seeds than outcrossed fruit. These results are contrary to the hypothesis that variation in seed size is attributable to either pollen competition or differential allocation of maternal resource to seeds of different genotypes. 相似文献
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The neurotrophic factors brain-derived neurotrophic factor and neurotrophin-3 are ligands for the trkB tyrosine kinase receptor. 总被引:48,自引:0,他引:48
D Soppet E Escandon J Maragos D S Middlemas S W Reid J Blair L E Burton B R Stanton D R Kaplan T Hunter 《Cell》1991,65(5):895-903
Neurotrophic factors are essential for neuronal survival and function. Recent data have demonstrated that the product of the tyrosine kinase trk proto-oncogene binds NGF and is a component of the high affinity NGF receptor. Analysis of the trkB gene product, gp145trkB, in NIH 3T3 cells indicates that this tyrosine kinase receptor is rapidly phosphorylated on tyrosine residues upon exposure to the NGF-related neurotrophic factors BDNF and NT-3. Furthermore, gp145trkB specifically binds BDNF and NT-3 in NIH 3T3 cells and in hippocampal cells, but does not bind NGF. Thus, the trk family of receptors are likely to be important signal transducers of NGF-related trophic signals in the formation and maintenance of neuronal circuits. 相似文献
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In this paper we examine some ecological consequences and phenotypic correlates of flower size variation in wild radish, Raphanus sativus. Mean corolla diameter varied significantly among individuals within natural populations of R. sativus in California. On the average, almost 40% of flower biomass was allocated to corolla tissue. In field experiments, pollinator visitation increased significantly with corolla size. Large flowers also accumulated more nectar when pollinators were excluded from plants. In three populations, corolla size was positively correlated with allocation to pollen per flower (either anther weight or pollen grain number), but there was usually no phenotypic relationship between corolla size and several measures of female allocation (ovule number per flower, proportion fruit set, and total seed mass per fruit). Plants growing in the field produced fewer large flowers per unit of stem, and stem biomass was negatively related to corolla size for plants grown under controlled greenhouse conditions. Male and female fitness may covary differently with allocation to attractive floral features in species such as R. sativus, where seed production is often limited by resources rather than by pollen. 相似文献
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Synergism of v-myc and v-Ha-ras in the in vitro neoplastic progression of murine lymphoid cells. 总被引:19,自引:11,他引:8
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R C Schwartz L W Stanton S C Riley K B Marcu O N Witte 《Molecular and cellular biology》1986,6(9):3221-3231
Murine bone marrow was either singly or doubly infected with retroviral vectors expressing v-myc (OK10) or v-Ha-ras. The infected bone marrow was cultured in a system that supports the long-term growth of B-lineage lymphoid cells. While the v-myc vector by itself had no apparent effect on lymphoid culture establishment and growth, infection with the v-Ha-ras vector or coinfection with both v-myc and v-Ha-ras vectors led to the appearance of growth-stimulated cell populations. Clonal pre-B-cell lines stably expressing v-Ha-ras alone or both v-myc and v-Ha-ras grew out of these cultures. In comparison with cell lines expressing v-Ha-ras alone, cell lines expressing both v-myc and v-Ha-ras grew to higher densities, had reduced dependence on a feeder layer for growth, and had a marked increase in ability to grow in soft-agar medium. The cell lines expressing both oncogenes were highly tumorigenic in syngeneic animals. These experiments show that the v-myc oncogene in synergy with v-Ha-ras can play a direct role in the in vitro transformation of murine B lymphoid cells. 相似文献
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L B Rosenberger M A Griffin H C Stanton 《Canadian journal of physiology and pharmacology》1983,61(7):685-692
Coronary vasoconstrictor responses to ergonovine were examined in helical coronary arterial strips of young swine. Both ergonovine and serotonin (5-hydroxytryptamine) produced dose-dependent contractions of the strips. The distal region (less than 1.00 mm outer diameter) of the circumflex coronary artery was most sensitive to the responses of serotonin and ergonovine. Methysergide and nifedipine significantly depressed the contractions induced by ergonovine and serotonin. Atropine, propranolol, and the alpha 1 blocker, prazosin, did not antagonize ergonovine-induced contractions. The ergonovine response may depend entirely upon extracellular Ca2+ while the effect of serotonin may be mediated in part through the mobilization of intracellular Ca2+ stores. Increases in 45Ca2+ cellular contents occurred after ergonovine or serotonin and these increases were blocked by methysergide or nifedipine at concentrations which blocked mechanical responses to the agonist. It is concluded that the contractions of the porcine coronary artery produced by ergonovine and serotonin are as follows: (i) regionally sensitive; (ii) blocked by Ca2+ antagonists and therefore may utilize Ca2+ channels similar to those described in other excitable tissues; (iii) blocked by methysergide. These studies indicate that the major mechanism of ergonovine's action in the porcine coronary artery is through the activation of serotonin receptors on coronary arteries which are, in turn, linked to Ca2+ channels. However, this mechanism of action may be different in an intact animal. 相似文献