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

Summary for policymakers Technical summary 1. The climate system - an overview 2. Observed climate variability and change 3. The carbon cycle and atmospheric CO2 4. Atmospheric chemistry and greenhouse gases 5. Aerosols, their direct and indirect effects 6. Radiative forcing of climate change 7. Physical climate processes and feedbacks 8. Model evaluation 9. Projections of future climate change 10. Regional climate simulation - evaluation and projections 11. Changes in sea level 12. Detection of climate change and attribution of causes 13. Climate scenario development 14. Advancing our understanding Glossary Index Appendix.

Climate change 2001: the scientific basis

Identifying and quantifying planetary boundaries that must not be transgressed could help prevent human activities from causing unacceptable environmental change, argue Johan Rockstrom and colleagues.

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A safe operating space for humanity

Drafting Authors: Neil Adger, Pramod Aggarwal, Shardul Agrawala, Joseph Alcamo, Abdelkader Allali, Oleg Anisimov, Nigel Arnell, Michel Boko, Osvaldo Canziani, Timothy Carter, Gino Casassa, Ulisses Confalonieri, Rex Victor Cruz, Edmundo de Alba Alcaraz, William Easterling, Christopher Field, Andreas Fischlin, Blair Fitzharris, Carlos Gay García, Clair Hanson, Hideo Harasawa, Kevin Hennessy, Saleemul Huq, Roger Jones, Lucka Kajfež Bogataj, David Karoly, Richard Klein, Zbigniew Kundzewicz, Murari Lal, Rodel Lasco, Geoff Love, Xianfu Lu, Graciela Magrín, Luis José Mata, Roger McLean, Bettina Menne, Guy Midgley, Nobuo Mimura, Monirul Qader Mirza, José Moreno, Linda Mortsch, Isabelle Niang-Diop, Robert Nicholls, Béla Nováky, Leonard Nurse, Anthony Nyong, Michael Oppenheimer, Jean Palutikof, Martin Parry, Anand Patwardhan, Patricia Romero Lankao, Cynthia Rosenzweig, Stephen Schneider, Serguei Semenov, Joel Smith, John Stone, Jean-Pascal van Ypersele, David Vaughan, Coleen Vogel, Thomas Wilbanks, Poh Poh Wong, Shaohong Wu, Gary Yohe

Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change

This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

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The HITRAN 2008 molecular spectroscopic database

Bulk freezing experiments have been performed with binary and ternary HNO3/H2SO4/H2O solutions containing original micrometeorites, ground samples of representative larger meteorites and other freezing nuclei of potential stratospheric importance. The experiments enable us to determine upper bounds for the heterogeneous freezing rates of sulfuric and nitric acid hydrates. Based on an analysis, of the meteoritic mass flux from space and of the modifications meteorites undergo when entering the atmosphere, the resulting morphology and surface area of extraterrestrial material in the stratosphere are estimated. From this micrometeorites gained from Antarctica are shown to be a good proxy for meteoritic surfaces in the stratosphere. In combination with this analysis the freezing experiments suggest that heterogeneous nucleation rates on micrometeorites ale too low to enhance freezing of polar stratospheric clouds above the frost point.

The unsuitability of meteoritic and other nuclei for polar stratospheric cloud freezing

High levels of ionising radiation in the Earth's stratosphere will lead to increased concentrations of nitrogen oxides and decreased concentrations of ozone. Changes in the surface environment will include an increased level of biologically harmful UV radiation, caused by the ozone depletion, and a decreased level of visible solar radiation, due to the presence of major enhancements in the stratospheric concentration of nitrogen dioxide. These changes are studied quantitatively, using the passage of the Solar System through a supernova remnant shell as an example. Some of the potential environmental changes are a substantial global cooling, abnormally dry conditions, a reduction in global photosynthesis and a large increase in the flux of atmospheric fixed nitrogen to the surface of the Earth. Such events might have been the cause of mass extinctions in the distant past.

Effects of intense stratospheric ionisation events

Stratospheric air samples have been obtained at 17.7, 22.3, and 26.2 km using balloon borne sampling spheres launched from Laramie, Wyo. These samples have been analyzed for CFCl3, CF2Cl2 and N2O, using electron capture detector gas chromatography. The concentrations of all three constituents are compared with theoretical models and found to be in excellent agreement. The dissociation products of N2O, CFCl3, and CF2Cl2 (NO and chlorine atoms) catalytically destroy ozone in the stratosphere. A knowledge of the concentrations of these species in the stratosphere is therefore essential to an understanding of the ozone balance.

Measurements of stratospheric CFCl3, CF2Cl2, and N2O

Two tropospheric, meridional sets of OH distribution are calculated with a two-dimensional model. One of the solutions represents the expected minimum OH concentrations in the absence of radical scavenging by aerosol particles in the atmosphere. The other solution provides excellent descriptions of the observed CFCl3, CF2Cl2 distributions, good approximations of the ozone observations, and a very good agreement with the global observations of CH3CCl3 by Rasmussen and co-workers (22). The derived distributions of hydroxyl may, therefore, represent reasonable approximations to the average meridional OH distributions in the atmosphere. However, if the methylchloroform observations of other workers are also considered, up to two times larger OH concentrations are possible. Despite rough approximation, rather fortuitously, it may, therefore, be possible to propose OH distributions which may approximate the average meridional OH distributions to within a factor of two. The OH concentrations are most difficult to estimate in the continental boundary layer because of reactions with effluents from biological and anthropogenic processes which are most pronounced over land. For gases with average residence times of less than a few weeks, the removal rates from the atmosphere are determined by photochemical processes taking place over the continents, so that for such gases a three-dimensional treatment is required.

The Global Distribution of Hydroxyl

Among the N compounds released to the atmosphere, NH$\_3$ and the oxides N$\_2$O, NO and NO$\_2$ are most important. Various microbial and human activities constitute the main sources of these compounds. NH$\_3$ strongly influences precipitation chemistry, but its role in atmospheric photochemistry is probably not very important. The oxides of N, however, must be regarded as key compounds. N$\_2$O seems to be inert in the troposphere, but its oxidation is the main source of NO in the stratosphere. The more reactive NO and NO$\_2$ act as catalysts in various photochemical reaction chains which affect the residence times of many carbon, sulphur and halogen compounds in the atmosphere through the role that they play in the ozone balance of the atmosphere. The atmospheric abundance of N$\_2$O, NO, NO$\_2$ and a variety of halogen compounds is increasingly influenced by man. As one of the consequences one may expect changes in the abundance of atmospheric ozone, perhaps leading to increased intensity of ultraviolet radiation at ground level or climatic changes.

Paul J. Crutzen

Papers

The unsuitability of meteoritic and other nuclei for polar stratospheric cloud freezing

Effects of intense stratospheric ionisation events

Measurements of stratospheric CFCl3, CF2Cl2, and N2O

The Global Distribution of Hydroxyl

The role of fixed nitrogen in atmospheric photochemistry