昆虫免疫进化的研究进展

昆虫在长期的进化过程中发展出了一套独特的免疫系统,由细胞免疫和体液免疫组成。随着分子生物学研究技术的发展,人们发现昆虫具有复杂的免疫系统,在病原体识别、信号转导途径及效应机制等方面与哺乳动物均高度相似,这些防御机制有着共同的进化起源。越来越多的研究表明昆虫的免疫具有特异性,不仅有免疫记忆,还能改变自身的免疫细胞去对付不同类型的微生物。     

The economics of overexploitation

The general economic analysis of a biological resource presented in this article suggests that overexploitation in the physical sense of reduced productivity may result from not one, but two social conditions: common-property competitive exploitation on the one hand, and private-property maximization of profits on the other. For populations that are economically valuable but possess low reproductive capacities, either condition may lead even to the extinction of the population. In view of the likelihood of private firms adopting high rates of discount, the conservation of renewable resources would appear to require continual public surveillance and control of the physical yield and the condition of the stocks.     

The ins and outs of body surface immunology

Rather than being confined to the secondary lymphoid tissue of the spleen and lymph nodes, large numbers of lymphocytes are intrinsically associated with the epithelial surfaces of the body. The best studied is gut-associated lymphoid tissue, but distinct epithelium-associated lymphoid tissue also exists in the reproductive tract, the lung, and the skin. The multiple cell types and functions composing these lymphoid tissues are increasingly seen as the key to how antigens delivered to body surfaces can elicit either immunogenic or tolerogenic responses. In some instances, these responses occur purely within the local body surface tissue, yet in other cases both local and systemic responses are elicited.     

The economics of pesticide use and regulation

Pesticides enhance agricultural productivity, but the environmental and health side effects of their use justify government regulation, a subject of continuing societal debate. Bans on pesticide use are the principal regulatory device used in the United States. The economic impacts of such bans depend on the availability of substitutes, supply and trade conditions, and research and development. Without substitutes, pesticide bans result in reduced production levels and higher prices, a substantial loss of discretionary income to consumers, and a redistribution of income among agricultural producers. Most food safety concerns can be addressed by establishing standards and markets for pesticide-differentiated products, but worker safety and clean water concerns will require direct controls. Pesticide-use fees are shown to be more efficient than outright pesticide bans as a mechanism to obtain environmental goals.     

The economics of small farms

The role of the small farm in American agriculture has been the focus of much public discussion since Secretary of Agriculture Bob Bergland elevated farm structure to the national political agenda during the Carter Administration. Eight hypotheses based on common assertions concerning the alleged advantages of the small farm were tested in the light of available empirical evidence. No basis was found to accept any of the eight hypotheses. There may be reasons to preserve and even encourage small farms but they are not the reasons commonly given for political initiatives and public policies favoring small farms. Although it is questionable whether any size of farm can be viewed as optimal, the strongest case is for the typical moderate-size family farm of today rather than for small farms or large industrial-type farms.     

The economics of information security

The economics of information security has recently become a thriving and fast-moving discipline. As distributed systems are assembled from machines belonging to principals with divergent interests, we find that incentives are becoming as important as technical design in achieving dependability. The new field provides valuable insights not just into "security" topics (such as bugs, spam, phishing, and law enforcement strategy) but into more general areas such as the design of peer-to-peer systems, the optimal balance of effort by programmers and testers, why privacy gets eroded, and the politics of digital rights management.