抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

The reverse transcription polymerase chain reaction (RT-PCR) is the most sensitive method for the detection of low-abundance mRNA, often obtained from limited tissue samples. However, it is a complex technique, there are substantial problems associated with its true sensitivity, reproducibility and specificity and, as a quantitative method, it suffers from the problems inherent in PCR. The recent introduction of fluorescence-based kinetic RT-PCR procedures significantly simplifies the process of producing reproducible quantification of mRNAs and promises to overcome these limitations. Nevertheless, their successful application depends on a clear understanding of the practical problems, and careful experimental design, application and validation remain essential for accurate quantitative measurements of transcription. This review discusses the technical aspects involved, contrasts conventional and kinetic RT-PCR methods for quantitating gene expression and compares the different kinetic RT-PCR systems. It illustrates the usefulness of these assays by demonstrating the significantly different levels of transcription between individuals of the housekeeping gene family, glyceraldehyde-3-phosphate-dehydrogenase (GAPDH).

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Absolute quantification of mRNA using real-time reverse transcription polymerase chain reaction assays.

Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

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Microfluidics: Fluid physics at the nanoliter scale

An expert meeting was organized by the World Health Organization (WHO) and held in Stockholm on 15-18 June 1997. The objective of this meeting was to derive consensus toxic equivalency factors (TEFs) for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxinlike polychlorinated biphenyls (PCBs) for both human, fish, and wildlife risk assessment. Based on existing literature data, TEFs were (re)evaluated and either revised (mammals) or established (fish and birds). A few mammalian WHO-TEFs were revised, including 1,2,3,7,8-pentachlorinated DD, octachlorinated DD, octachlorinated DF, and PCB 77. These mammalian TEFs are also considered applicable for humans and wild mammalian species. Furthermore, it was concluded that there was insufficient in vivo evidence to continue the use of TEFs for some di-ortho PCBs, as suggested earlier by Ahlborg et al. [Chemosphere 28:1049-1067 (1994)]. In addition, TEFs for fish and birds were determined. The WHO working group attempted to harmonize TEFs across different taxa to the extent possible. However, total synchronization of TEFs was not feasible, as there were orders of a magnitude difference in TEFs between taxa for some compounds. In this respect, the absent or very low response of fish to mono-ortho PCBs is most noticeable compared to mammals and birds. Uncertainties that could compromise the TEF concept were also reviewed, including nonadditive interactions, differences in shape of the dose-response curve, and species responsiveness. In spite of these uncertainties, it was concluded that the TEF concept is still the most plausible and feasible approach for risk assessment of halogenated aromatic hydrocarbons with dioxinlike properties.

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Toxic equivalency factors (TEFs) for PCBs, PCDDs, PCDFs for humans and wildlife

▪ Abstract Soft lithography, a set of techniques for microfabrication, is based on printing and molding using elastomeric stamps with the patterns of interest in bas-relief. As a technique for fabricating microstructures for biological applications, soft lithography overcomes many of the shortcomings of photolithography. In particular, soft lithography offers the ability to control the molecular structure of surfaces and to pattern the complex molecules relevant to biology, to fabricate channel structures appropriate for microfluidics, and to pattern and manipulate cells. For the relatively large feature sizes used in biology (≥50 μm), production of prototype patterns and structures is convenient, inexpensive, and rapid. Self-assembled monolayers of alkanethiolates on gold are particularly easy to pattern by soft lithography, and they provide exquisite control over surface biochemistry.

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Soft Lithography in Biology and Biochemistry

ModesIntroduction to Capillary Electrophoresis, R.P. Oda and J.P. LandersMicellar Electrokinetic Chromatography, J.R. MazzeoCapillary Electrophoresis Separation of Enantiomers by Cyclodextrin Array Chiral Analysis, A. GuttmanCapillary Isoelectric Focusing, R. Rodr guez-D az, T. Wehr, M. Zhu, and V. LeviTheory and Practice of Capillary Electrochromatography, M.M. Dittmann and G.P. RozingAnalyteCapillary Ion Electrophoresis, W.R. JonesAnalysis of Small Organic Molecules by Capillary Electrophoresis, K.D. AltriaCapillary Electrophoresis of Peptides, T. van de Goor, A. Apffel, J. Chakel, and W. HancockCapillary Electrophoresis of Proteins, T. Pritchett and F.A. RobeyCarbohydrate Analysis by Capillary Electrophoresis, J.D. Olechno and J.A. NolanSeparation of DNA by Capillary Electrophoresis, K.J. Ulfelder and B.R. McCordEssential Aspects of Capillary ElectrophoresisOptical Detection Techniques for Capillary Electrophoresis, S.L. Pentoney, Jr. and J.V. SweedlerElectrochemical Detection in Capillary Electrophoresis, C. HaberData Analysis in Capillary Electrophoresis, B.J. WandersEffects of Sample Matrix on Capillary Electrophoretic Analysis, Z.K. ShihabiOn-Line Sample Preconcentration for Capillary Electrophoresis, D.S. Burgi and R.-L. ChienApplicationsCapillary Electrophoresis for the Analysis of Single Cells: Electrochemical, Mass Spectrometric, and Radiochemical Detection, F.D. Swanek, S.S. Ferris, and A.G. EwingCapillary Electrophoresis for the Analysis of Single Cells: Laser-Induced Fluorescence Detection, S.J. Lillard and E.S. YeungCapillary Gel Electrophoresis for Large Scale DNA Sequencing: Separation and Detection, N.J. DovichiCapillary Electrophoresis for the Analysis of Drugs in Biological Fluids, R.P. Oda, M.E. Roche, J.P. Landers, and Z.K. ShihabiUse of Capillary Electrophoresis for Binding Studies, F.A. RobeyImmunoassays and Enzyme Assays Using Capillary Electrophoresis, N.M. Schultz, L. Tao, D.J. Rose, Jr., and R.T. KennedyClinical Applications of Capillary Electrophoresis, R.P. Oda, V.J. Bush, and J.P. LandersSpecialized Aspects of Capillary ElectrophoresisCapillary Surface Modification in Capillary Electrophoresis, A.M. Dougherty, N. Cooke, and P. ShiehImproved Capillary Electrophoretic Separations Associated with Controlling Electroosmotic Flow, C.S. LeeContinuous Separations by Electrophoresis in Rectangular Channels, P.F. Gavin and A.G. EwingTwo-Dimensional Liquid Chromatography-Capillary Electrophoresis, D.J. Jeffery, T.F. Hooker, and J.W. JorgensonCapillary Electrophoresis-Mass Spectrometry, J.C. Severs and R.D. SmithMicrofabricated Devices for Performing Capillary Electrophoresis, S.C. Jacobson and J.M. RamseyFraction Collection with Micro-Preparative Capillary Electrophoresis, M.A. Strausbauch and P.J. WettsteinAppendix 1: Calculations for Practical UseAppendix 2: TroubleshootingAppendix 3: Seperation Conditions for Classes of AnalytesIndex

Handbook of Capillary Electrophoresis

We describe a microfluidic genetic analysis system that represents a previously undescribed integrated microfluidic device capable of accepting whole blood as a crude biological sample with the endpoint generation of a genetic profile. Upon loading the sample, the glass microfluidic genetic analysis system device carries out on-chip DNA purification and PCR-based amplification, followed by separation and detection in a manner that allows for microliter samples to be screened for infectious pathogens with sample-in-answer-out results in < 30 min. A single syringe pump delivers sample/reagents to the chip for nucleic acid purification from a biological sample. Elastomeric membrane valving isolates each distinct functional region of the device and, together with resistive flow, directs purified DNA and PCR reagents from the extraction domain into a 550-nl chamber for rapid target sequence PCR amplification. Repeated pressure-based injections of nanoliter aliquots of amplicon (along with the DNA sizing standard) allow electrophoretic separation and detection to provide DNA fragment size information. The presence of Bacillus anthracis (anthrax) in 750 nl of whole blood from living asymptomatic infected mice and of Bordetella pertussis in 1 microl of nasal aspirate from a patient suspected of having whooping cough are confirmed by the resultant genetic profile.

https://www.pnas.org/content/pnas/103/51/19272.full.pdf

A fully integrated microfluidic genetic analysis system with sample-in–answer-out capability

A microchip solid-phase extraction method for purification of DNA from biological samples, such as blood, is demonstrated. Silica beads were packed into glass microchips and the beads immobilized with sol−gel to provide a stable and reproducible solid phase onto which DNA could be adsorbed. Optimization of the DNA loading conditions established a higher DNA recovery at pH 6.1 than 7.6. This lower pH also allowed for the flow rate to be increased, resulting in a decrease in extraction time from 25 min to less than 15 min. Using this procedure, template genomic DNA from human whole blood was purified on the microchip platform with the only sample preparation being mixing of the blood with load buffer prior to loading on the microchip device. Comparison between the microchip SPE (μchipSPE) procedure and a commercial microcentrifuge method showed comparable amounts of PCR-amplifiable DNA could be isolated from cultures of Salmonella typhimurium. The greatest potential of the μchipSPE device was illustrated by...

Microchip-based purification of DNA from biological samples.

Over the last several decades, dioxins have become the subject of intense public and scientific scrutiny. This is the result of not only their widespread presence in the environment but also their great toxicity. The environmental issue has been addressed through the study of the production, release and fate of dioxins and related substances, as well as the development of analytical techniques to detect and quantify these compounds in environmental matrices. The toxicology of dioxins has been addressed principally through studies of their mechanism of toxic action using animal models and is the focus of this review. In addition, the potential threat that dioxins present to human health has been addressed in a limited manner through epidemiological studies of populations known to have been exposed to dioxins.

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James P. Landers

Papers

Handbook of Capillary Electrophoresis

A fully integrated microfluidic genetic analysis system with sample-in–answer-out capability

Microchip-based purification of DNA from biological samples.

The Ah receptor and the mechanism of dioxin toxicity.

Polymerase chain reaction in polymeric microchips: DNA amplification in less than 240 seconds.