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71.
Cytotoxic T lymphocyte (CTL) activation requires specific T cell receptor (TCR)-class I major histocompatibility complex (MHC) antigen complex interactions as well as the participation of coreceptor or accessory molecules on the surface of CTL. CD8 can serve as a coreceptor in that it binds to the same MHC class I molecules as the TCR to facilitate efficient TCR signaling. In addition, CD8 can be "activated" by TCR stimulation to bind to class I molecules with high avidity, including class I not recognized by the TCR as antigenic complexes (non-antigen [Ag] class I), to augment CTL responses and thus serve an accessory molecule function. A Glu/Asp227-->Lys substitution in the class I alpha 3 domain acidic loop abrogates lysis of target cells expressing these mutant molecules by alloreactive CD8-dependent CTL. Lack of response is attributed to the destruction of the CD8 binding site in the alpha 3 domain which is likely to disrupt CD8 coreceptor function. The relative importance of the class I alpha 3 domain acidic loop Glu227 in coreceptor as opposed to accessory functions of CD8 is unclear. To address this issue, we examined CTL adhesion and degranulation in response to immobilized class I-peptide complexes formed in vitro from antigenic peptides and purified class I molecules containing wild-type or Glu227-->Lys substituted alpha 3 domains. The alpha 3 domain mutant class I-peptide complexes were bound by CTL and triggered degranulation, however to much lower levels than wild-type class I-peptide complexes. In further experiments, it is directly demonstrated that the alpha 3 domain mutant class I molecules, which lack the Glu227 CD8 binding site, still serve as TCR-activated, avidity-enhanced CD8 accessory ligands. However, mutant class I peptide Ag complexes failed to effectively serve as CD8 coreceptor ligands to initiate TCR-dependent signals required to induce avidity-enhanced CD8 binding to coimmobilized non-Ag class I molecules. Thus the Glu227-->Lys mutation effectively distinguishes CD8 coreceptor and avidity-enhanced CD8 accessory functions. 相似文献
72.
R Ottman JH Lee WA Hauser S Hong D Hesdorffer N Schupf TA Pedley ML Scheuer 《Canadian Metallurgical Quarterly》1993,43(12):2526-2530
Methods for standardized classification of epileptic seizures are important for both clinical practice and epidemiologic research. In this study, we developed a strategy for standardized classification using a semistructured telephone interview and operational diagnostic criteria. We interviewed 1,957 adults with epilepsy ascertained from voluntary organizations. To confirm and expand the seizure history, we also interviewed a first-degree relative for 67% of subjects and obtained medical records for 59%. Three lay reviewers used all available information to classify seizures. To assess reliability, each reviewer classified a sample of subjects assigned to the others. In addition, an expert physician classified a sample of subjects assigned to two of the reviewers. Agreement was "moderate-substantial" for generalized-onset seizures, both for the comparisons between pairs of lay reviewers and for the neurologist versus lay reviewers. Agreement was "substantial-almost perfect" for partial-onset seizures, both for pairs of lay reviewers and for the neurologist versus lay reviewers. These results suggest that seizures can be reliably classified by lay reviewers, using operational criteria applied to symptoms ascertained in a semistructured telephone interview. 相似文献
73.
The relative effect of protozoan and bacterial predators on the survival of Escherichia coli in estuarine water samples was examined. Predacious protozoa exerted their major influence on E. coli destruction during the first 2 days of a 10-day-decline period. Inhibition of protozoa after day 2 had little effect on E. coli survival. Bacterial predators also contributed to E. coli destruction but in natural estuarine water samples were maintained at lower levels due to "grazing" by predacious protozoa. 相似文献
74.
TA Reader 《Canadian Metallurgical Quarterly》1976,50(1):11-30
The structure and function of the digestive gland of the gastropod mollusc, Bithynia tentaculata, was investigated using ultrastructural, histochemical, and cytochemical techniques. The digestive gland was shown to be composed of two main cell types, the "digestive" cells and "secretory" cells. The digestive cells appeared to be concerned with the absorption and digestion of nutrients, while secretory cells produced digestive enzymes and calcareous concretions. Undifferentiated cells were scattered between these two main cell types. The pathological effects of larval digeneans on the digestive gland were also investigated, at the ultrastructural level. In such infected snails the digestive gland appeared to be degenerating. The significance of this tissue destruction was briefly discussed. 相似文献
75.
PDF417二维条码肖像图片压缩编码的优化算法研究 总被引:1,自引:0,他引:1
针对PDF417二维条码存储空间有限的问题,提出了一种基于小波变换的有损图像压缩算法,通过这个算法,可以将静态图片信息加入PDF417条码中,并能够满足在指定字节数情况下保证高质量地压缩图像,该文在分析小波变换等算法理论的基础上,详细介绍了PDF417二维条码肖像图片压缩编码的优化算法及该算法的实验结果与美国Symbol公司的PC2VQ算法结果对比。 相似文献
76.
M Harmsen TA Oosterlaken C Tangerman H Snippe CA Kraaijeveld 《Canadian Metallurgical Quarterly》1993,43(2):137-146
3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (EC 1.1.1.34) is the rate limiting step in the mevalonate pathway that produces isoprenoids and cholesterol. Inhibitors of HMG-CoA reductase are teratogenic in vivo and induce neural tube defects in rat embryo culture, effects which appear unrelated to cholesterol deficiency. This study is the first to localize HMG-CoA reductase mRNA by in situ hybridization (ISH). Expression of reductase mRNA was examined in post-implantation rat embryos, and for control purposes in rat liver and UT-1 cells, using a digoxigenin-11 (dig-11) labelled cRNA probe. Eighteen-day fetal liver showed heavy but patchy hybridization, and adult rat liver showed strong hybridization only on some periportal hepatocytes, which was absent in livers of fasted animals. UT-1 cells stimulated to overexpress HMG-CoA reductase mRNA were strongly positive with the same probe. Control hybridizations with sense strand RNA probe, or with cRNA probe on pre-RNased tissue were negative. Strong hybridization signal for HMG-CoA reductase mRNA was observed in all tissues of the post-implantation rat embryo, from egg cylinder to 30 somite stages (7 to 12 days). Heavy signal was noted in primitive ectoderm and neural tube. The wide embryonic and extraembryonic distribution and abundance of HMG-CoA reductase mRNA may reflect developmental requirements for products of the mevalonate pathway, e.g., isoprenoids for post-translational farnesylation of p21ras. 相似文献
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在准备金评估中,由于多数随机准备金模型基本假设的限制是不能直接处理含有零值和负值增量赔款三角形,本文利用一个变换和广义线性模型的混合模型去解决这种情况. 相似文献
80.