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排序方式: 共有107条查询结果,搜索用时 15 毫秒
51.
Mark A. Marsili Michael K. Robinson Gary A. Truitt E. Frederick Wheelock 《Cancer immunology, immunotherapy : CII》1999,16(1):59-64
Summary Previous experiments have demonstrated a temporal relationship between the decline of cytotoxic T lymphocyte (CTL) activity in the peritoneal cavity of DBA/2 mice harboring L5178Y cells in a tumor-dormant state and the appearance of ascitic tumors. Some tumor-dormant mice remain clinically normal for many weeks after the decline of CTL activity, and this activity can be rapidly restimulated by an IP inoculation of irradiated L5178Y cells. We report here that the peritoneal cells from many tumor-dormant mice can be stimulated to cytolytic activity in vitro when cultured for 4 days either with or without the addition of irradiated L5178Y cells. Peritoneal cell populations which cannot be stimulated in vitro can suppress the generation of CTL in those populations which can be stimulated. The tumor-dormant state may terminate when suppressor cells in the peritoneal cavity of tumor-dormant mice inhibit the generation of CTL activity and permit tumor cells to produce an ascitic tumor.
Abbreviations used in this paper: C, complement; CTL, cytotoxic thymus-derived lymphocyte; PC, peritoneal cells; DPC, days post challange; NAD, nonadherent; SC, subcutaneous; IP, intraperitoneal 相似文献
52.
53.
Seasonal and interannual variability in the taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake,Oregon 总被引:2,自引:2,他引:0
Taxonomic composition and production dynamics of phytoplankton assemblages in Crater Lake, Oregon, were examined during time
periods between 1984 and 2000. The objectives of the study were (1) to investigate spatial and temporal patterns in species
composition, chlorophyll concentration, and primary productivity relative to seasonal patterns of water circulation; (2) to
explore relationships between water column chemistry and the taxonomic composition of the phytoplankton; and (3) to determine
effects of primary and secondary consumers on the phytoplankton assemblage. An analysis of 690 samples obtained on 50 sampling
dates from 14 depths in the water column found a total of 163 phytoplankton taxa, 134 of which were identified to genus and
101 were identified to the species or variety level of classification. Dominant species by density or biovolume included Nitzschia gracilis, Stephanodiscus hantzschii, Ankistrodesmus spiralis, Mougeotia parvula, Dinobryon sertularia, Tribonema
affine, Aphanocapsa delicatissima, Synechocystis sp., Gymnodinium inversum, and Peridinium inconspicuum. When the lake was thermally stratified in late summer, some of these species exhibited a stratified vertical distribution
in the water column. A cluster analysis of these data also revealed a vertical stratification of the flora from the middle
of the summer through the early fall. Multivariate test statistics indicated that there was a significant relationship between
the species composition of the phytoplankton and a corresponding set of chemical variables measured for samples from the water
column. In this case, concentrations of total phosphorus, ammonia, total Kjeldahl nitrogen, and alkalinity were associated
with interannual changes in the flora; whereas pH and concentrations of dissolved oxygen, orthophosphate, nitrate, and silicon
were more closely related to spatial variation and thermal stratification. The maximum chlorophyll concentration when the
lake was thermally stratified in August and September was usually between depths of 100 m and 120 m. In comparison, the depth
of maximum primary production ranged from 60 m to 80 m at this time of year. Regression analysis detected a weak negative
relationship between chlorophyll concentration and Secchi disk depth, a measure of lake transparency. However, interannual
changes in chlorophyll concentration and the species composition of the phytoplankton could not be explained by the removal
of the septic field near Rim Village or by patterns of upwelling from the deep lake. An alternative trophic hypothesis proposes
that the productivity of Crater Lake is controlled primarily by long-term patterns of climatic change that regulate the supply
of allochthonous nutrients. 相似文献
54.
Hormonally regulated programmed cell death in barley aleurone cells 总被引:13,自引:0,他引:13
Cell death was studied in barley (cv Himalaya) aleurone cells treated with abscisic acid and gibberellin. Aleurone protoplasts incubated in abscisic acid remained viable in culture for at least 3 weeks, but exposure to gibberellin initiated a series of events that resulted in death. Between 4 and 8 days after incubation in gibberellin, >70% of all protoplasts died. Death, which occurred after cells became highly vacuolated, was manifest by an abrupt loss of plasma membrane integrity followed by rapid shrinkage of the cell corpse. Hydrolysis of DNA began before death and occurred as protoplasts ceased production of alpha-amylase. DNA degradation did not result in the accumulation of discrete low molecular weight fragments. DNA degradation and cell death were prevented by LY83583, an inhibitor of gibberellin signaling in barley aleurone. We conclude that cell death in aleurone cells is hormonally regulated and is the final step of a developmental program that promotes successful seedling establishment. 相似文献
55.
56.
alpha 1-Proteinase inhibitors (alpha 1-PIs) are members of the serpin
superfamily of proteinase inhibitors, and are important in the maintenance
of homeostasis in a wide variety of animal taxa. Previous studies have
shown that in mice (genus Mus), evolution of alpha 1-PIs is characterized
by gene amplification, region-specific concerted evolution, and rapid
accumulation of amino acid substitutions. The latter occurs primarily in
the reactive center, which is the region of the alpha 1-PI molecule that
determines the inhibitor's specificity for target proteinases. The P1
residue within the reactive center, which is methionine in so-called
orthodox alpha 1-PIs and an amino acid other than methionine in unorthodox
alpha 1-PIs, is a primary determinant of inhibitor specificity. In the
present study, we find that the expression of mRNAs encoding unorthodox
alpha 1-PIs is polymorphic within Mus species, i.e., among individuals or
inbred strains. This is in striking contrast to mRNAs that encode orthodox
alpha 1-PIs, whose concentrations are relatively invariant. The
intraspecies variations in mRNA expression represent polymorphisms in the
structure of the alpha 1- PI gene family. The results, taken together with
previously described aspects of alpha 1-PI evolution, indicate that the
dissimilar levels of polymorphism exhibited by orthodox and unorthodox
alpha 1-PIs, which likely have distinct physiological functions, may
reflect different levels of selective constraint. The significance of this
finding to the evolution of gene families is discussed.
相似文献
57.
R L Truitt B D Johnson C Hanke S Talib J E Hearst 《Journal of immunology (Baltimore, Md. : 1950)》1999,163(9):5145-5156
Donor leukocyte infusions after allogeneic bone marrow transplantation can provide a curative graft-vs-leukemia (GVL) effect, but there is a significant risk of graft-vs-host (GVH) disease. A simple and effective method for controlling the fate of naive or primed T-lymphocytes in vivo without eliminating their beneficial properties is needed. In this report, photochemical treatment (PCT) ex vivo with a synthetic psoralen (S-59) and UVA light was evaluated as a pharmacological approach to limiting the proliferation and GVH potential of naive and primed donor T cells in vivo. S-59 rapidly intercalates into and cross-links DNA on UVA illumination. The effects of PCT on T cells were found to be both S-59 and UVA dose dependent. With selected PCT regimens, treated T cells still expressed activation markers (CD25 and CD69) and secreted IL-2 on activation, but they showed limited proliferative capacity in vitro and in vivo. Clonal expansion of CTL in MLR was reduced after PCT, but short term lytic activity of primed CTL was not affected. In a murine model of MHC-mismatched bone marrow transplantation, the addition of PCT-treated T cells to T-depleted bone marrow facilitated donor engraftment and complete chimerism without causing acute or chronic graft-vs-host disease. Allospecific GVL reactivity was reduced but not eliminated after PCT treatment. In an MHC-matched model using host-presensitized donor T cells, PCT significantly reduced GVH-associated mortality without eliminating GVL reactivity. Thus, PCT ex vivo offers a simple, rapid, and inexpensive method by which to control the fate of naive and primed T cells in vivo. 相似文献
58.
Physiochemical changes in the state of chromatin shortly following glucocorticoid stimulation of target cells are predicted by the proposed mechanism of steroid action. These changes had not been previously demonstrated in situ. The present experiments demonstrate that in the intact rat, or in one which has been adrenalectomized but given a moderate dose of dexamethasone, the thermal stability of liver cell chromatin is significantly reduced over the level observed in the adrenalectomized untreated animal. This alteration was rated by measuring nuclear acridine orange metachromasia following chromatin denaturation. These data also show an enhanced binding of the dye by the liver cell nuclei under the same conditions. Feulgen dye binding was also found to be enhanced by dexamethasone stimulation but to a level indicative of configurational changes in the chromatin rather than an increase in the amount of DNA in the cells. 相似文献
59.
Bryan D. Watts Fletcher M. Smith Chance Hines Laura Duval Diana J. Hamilton Tim Keyes Julie Paquet Lisa Pirie‐Dominix Jennie Rausch Barry Truitt Brad Winn Paul Woodard 《Journal of avian biology》2021,52(1)
Migrant shorebirds operate within a series of landscapes and must adjust their daily activities to achieve seasonal time and energy objectives. Night roosts are essential landscape elements that provide safety from predators for many shorebird species. What costs migrants incur to use night roosts and how these costs vary across staging sites are poorly understood. We tracked 42 adult whimbrels Numenius phaeopus with satellite transmitters and used night locations to delineate 39 night roosts during spring and fall migration. We used daytime locations to measure round‐trip commuting distances between night roosts and foraging areas and estimated daily commuting costs including distance, time and metabolic energy expenditure. We identified night roosts on offshore islands (n = 20) and onshore locations including along habitat edges (n = 13) and on topographic highs within extensive marshes (n = 6). Mean daily commuting costs varied between roosts. Whimbrels took 3.9–52.1 min (median = 15.2) to fly 3.1–42.2 km (median = 12.3) which costs 6.1–82.4 kj (median = 22.3) in lean mass energy expenditure and 8.1–109.2 kj (median = 31.5) in leaving mass energy. Birds using offshore roosts had twice the commuting distance and associated costs compared to those using onshore roosts. The contribution of commuting costs to the premigratory energy budget ranged from 1.5 to 18.8% with costs for nearly 30% of roosts exceeding 10%. Commuting costs to and from night roosts appear to be biologically relevant within some staging sites and should be considered among other constraints faced by migrants during stopover periods when food or time is limiting. 相似文献
60.
Antigen/antibody complexes can efficiently target antigen presenting cells to allow stimulation of the cellular immune response. Due to the difficulty of manufacture and their inherent instability complexes have proved inefficient cancer vaccines. However, anti-idiotypic antibodies mimicking antigens have been shown to stimulate both antibody and T cell responses. The latter are due to T cell mimotopes expressed within the complementarity-determining regions (CDRs) of antibodies that are efficiently presented to dendritic cells in vivo. Based on this observation we have designed a DNA vaccine platform called ImmunoBody™, where cytotoxic T lymphocyte (CTL) and helper T cell epitopes replace CDR regions within the framework of a human IgG1 antibody. The ImmunoBody™ expression system has a number of design features which allow for rapid production of a wide range of vaccines. The CDR regions of the heavy and light chain have been engineered to contain unique restriction endonuclease sites, which can be easily opened, and oligonucleotides encoding the T cell epitopes inserted. The variable and constant regions of the ImmunoBody™ are also flanked by restriction sites, which permit easy exchange of other IgG subtypes. Here we show a range of T cell epitopes can be inserted into the ImmunoBody™ vector and upon immunization these T cell epitopes are efficiently processed and presented to stimulate high frequency helper and CTL responses capable of anti-tumor activity.Key words: DNA vaccines, cancer vaccines, melanoma, CTL, helper T cells 相似文献