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排序方式: 共有3106条查询结果,搜索用时 46 毫秒
41.
草鱼免疫应答的初步研究 总被引:11,自引:0,他引:11
研究了草鱼在不同水温条件下受抗原刺激后其中和抗体的变化。15℃培养条件下中和抗体上升缓慢,9周内滴度低于1:8;20℃时,3周后抗体可上升到1:256,最高达1:5270,而在25℃时,1周中和抗体即达到1:570,最高可达1:20000以上。并探索了从草鱼血清中提纯抗体的条件,研究其抗体的特性。草鱼血清中的抗体为大分子蛋白,容易解离为抗原性相同,分子量近似于人IgG的较小分子,含有较多的二硫键,具有类似IgM的某些特性。 相似文献
42.
Edward T. Harrison Jr. Frank P. Luyten A. H. Reddi 《In vitro cellular & developmental biology. Animal》1992,28(6):445-448
Summary The single and combined actions of transforming growth factor (TGF)-beta and osteogenin were evaluated with regard to induction
of colony formation and reexpression of the differentiated phenotype by dedifferentiated rabbit articular chondrocytes in
soft agarose under serum-free conditions. TGF-beta alone did not promote colony formation and induced accumulation of proteoglycans
and type II collagen at significantly lower levels than those induced by osteogenin. Although synergism between these two
growth factors occurred with respect to the induction of colony formation, their joint action on reexpression of the differentiated
phenotype was additive. Complex interactions between the two growth factors may explain the latter phenomenon. 相似文献
43.
Cloning of the ColE3-CA38 colicin and immunity genes and identification of a plasmid region which enhances colicin production 总被引:8,自引:0,他引:8
The colicin and immunity genes of plasmid ColE3-CA38 have been localized by characterization of bacteria carrying its cloned restriction fragments. They are within a 3.14-kb EcoRI segment, such that the immunity gene contains the KpnI site, and the colicin gene is adjacent to it within a 2.1-kb KpnI-HincII segment. The immunity gene and one end of the colicin gene are in the region of ColE3-CA38 which is not homologous to the closely related plasmid ColE2-P9. A 0.64-kb PvuI-EcoRI segment of the plasmid adjacent to that containing the colicin and immunity genes was found to augment colicin production on solid media, and also affected the morphology of clearing zones produced by the cells when used as indicators in overlays of stabs of colicin E2 or E7 producers. The 0.64-kb segment was required in its native orientation relative to the 3.14-kb EcoRI segment to cause its effects. 相似文献
44.
The courses of infection in inbred mouse strains were compared following infection with three Stabilates of high, intermediate, and low virulence of Trypanosoma vivax stock Zaria Y486. Mouse strains could only be shown to differ in their resistance to T. vivax infections as judged by the height of the initial parasitemia and survival times when a trypanosome population of low or intermediate virulence was used. A T. vivax population of high virulence was uniformly lethal. Comparison of lytic antibody titers between groups of resistant () and susceptible () mice did not show any significant differences in titers of the surviving mice but the mice in either group which did not control the initial parasitemia had lower lytic antibody titers than those which did. A significantly larger number of mice failed to control the initial infection as compared to the . Treatment with cyclophosphamide did not ablate differences in susceptibility between the two strains. The use of congenic mice showed that these differences in susceptibility were not related to differences in the major histocompatibility complex between these strains. 相似文献
45.
Comparative electrophoretic phenotypes of 18 of the 32 species of the lizard genus Varanus have been determined for four proteins. The animals studied were representative of species from Africa, Israel, Southeast Asia and Australia. Malate dehydrogenase (A2) exhibited a single phenotype throughout. Lactate dehydrogenase (B4) showed four distinctive electrophoretic forms which grouped the various subgenera as follows: (1) Polydaedalus, Empagusia (African); (2) Psammosaurus (Israel); (3) three species of Varanus, V. gouldii, V. spenceri, V. mertensi (Australian); (4) Dendrovaranus, Indovaranus (Southeast Asian), other Varanus species, Odatria (Australian). Electrophoretic and previously reported karyotypic data were used to interpret the phylogenetic relationships as well as the mode and direction of evolution of these animals. In particular, the results questioned the reality of the subgenus Varanus as a taxonomic unit, since four distinct karyotypic forms and two LDH-B4 phenotypes were observed for these animals, of which one belongs to another subgenus. Serum albumin and carbonic anhydrase phenotypes were of little use in deciding phenotypic groupings. 相似文献
46.
《Cell》2022,185(23):4409-4427.e18
47.
《Cell》2022,185(18):3375-3389.e21
48.
Andrew D. Higginson John M. McNamara Alasdair I. Houston 《Proceedings. Biological sciences / The Royal Society》2016,283(1822)
To explore the logic of evolutionary explanations of obesity we modelled food consumption in an animal that minimizes mortality (starvation plus predation) by switching between activities that differ in energy gain and predation. We show that if switching does not incur extra predation risk, the animal should have a single threshold level of reserves above which it performs the safe activity and below which it performs the dangerous activity. The value of the threshold is determined by the environmental conditions, implying that animals should have variable ‘set points’. Selection pressure to prevent energy stores exceeding the optimal level is usually weak, suggesting that immediate rewards might easily overcome the controls against becoming overweight. The risk of starvation can have a strong influence on the strategy even when starvation is extremely uncommon, so the incidence of mortality during famine in human history may be unimportant for explanations for obesity. If there is an extra risk of switching between activities, the animal should have two distinct thresholds: one to initiate weight gain and one to initiate weight loss. Contrary to the dual intervention point model, these thresholds will be inter-dependent, such that altering the predation risk alters the location of both thresholds; a result that undermines the evolutionary basis of the drifty genes hypothesis. Our work implies that understanding the causes of obesity can benefit from a better understanding of how evolution shapes the mechanisms that control body weight. 相似文献
49.
The cell-surface expression patterns of major histocompatibility complex (MHC) class I, class II and heat-shock protein 72
(HSP72) molecules were measured on human lung (LX-1) and mammary (MX-1) carcinoma cells. No major differences were found in
the MHC cell-surface expression pattern of both cell lines. However, they differ significantly in their capacity to express
HSP72 on their cell surface. Under physiological conditions LX-1 cells express HSP72 molecules on more than 90% of the cells,
whereas MX-1 cells exhibit no significant HSP72 cell-surface expression (less than 5%). These expression patterns remained
stable in all further cell passages tested. The sensitivity to lysis mediated by an interleukin-2 (IL-2)-stimulated, adherent
natural killer (NK) cell population could be correlated with the amount of cell-surface-expressed HSP72 molecules. By antibody-blocking
studies, using HSP72-specific monoclonal antibody (mAb), a strong inhibition of lysis was only found with LX-1 cells but not
with MX-1 cells. In contrast to the cell-surface expression, the cytoplasmic amount of HSP72 in MX-1 cells was twice as high
compared to LX-1 cells under physiological conditions. After nonlethal heat-shock the rate of induction and the total cytoplasmic
amounts of HSP72 were comparable in both cell lines. The clonogenic cell viability of LX-1 cells after incubation at temperatures
ranging from 41°C to 44°C was significantly elevated compared to that of MX-1 cells. In conclusion we state the following:
(i) HSP72 cell-surface expression on human carcinoma cells is independent of the cytoplasmic amount of HSP72; (ii) the cell-surface
expression of HSP72 is associated with an increased sensitivity of tumour cells to lysis mediated by an IL-2-stimulated, adherent
NK cell population; (iii) thermoresistance is not related to the cytoplasmic HSP72 level but might be related to the amount
of HSP72 expressed on the cell surface.
Received: 20 June 1996 / Accepted: 25 September 1996 相似文献
50.
Abstract Significantly higher Giardia lamblia trophozoites load in the intestine of infected mice accompanied pronounced influx of suppressor/cytotoxic T cells (Lyt 2.2+ ), T cells (Thy 1.2+ ) and significant reduction in IgA-containing cells in the gut during the establishment and peak phases of infection. The induction of helper/inducer T cells (Lyt 1.1+ ) and significant enhancement of IgA-containing cells in gut resulted in the decline of the trophozoite loads. However, the prior treatment of animals with dexamethasone alone resulted in significant reduction in helper/inducer T cells (Lyt 1.1+ ) and the IgA-containing cells in the gut; the percents of suppressor/cytotoxic T cells (Lyt 2.2+ ) and IgM-containing cells remained unaltered. Although the G. lamblia infection in such animals further significantly increased the influx of suppressor/cytotoxic T cells, the late response of helper/inducer T cells and IgA-containing cells was abrogated during the decline phase of infection. The significant reduction in the trophozoite load — despite immuno-suppressive therapy — appeared to be due to unaltered IgM response in such animals which probably took over the function of IgA in defense against G. lamblia . The data of the investigation thus suggested a role of helper/inducer T cells and antibodies producing cells in gut as important effector cells resulting in the termination of primary G. lamblia infection. 相似文献