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

Mediation is said to occur when a causal effect of some variable X on an outcome Y is explained by some intervening variable M. The authors recommend that with small to moderate samples, bootstrap methods (B. Efron & R. Tibshirani, 1993) be used to assess mediation. Bootstrap tests are powerful because they detect that the sampling distribution of the mediated effect is skewed away from 0. They argue that R. M. Baron and D. A. Kenny's (1986) recommendation of first testing the X --> Y association for statistical significance should not be a requirement when there is a priori belief that the effect size is small or suppression is a possibility. Empirical examples and computer setups for bootstrap analyses are provided.

/pdf/mediation-in-experimental-and-nonexperimental-studies-new-36pi5vkg4y.pdf

Mediation in experimental and nonexperimental studies: New procedures and recommendations.

Emotion-regulation strategies across psychopathology: A meta-analytic review.

The goals of this article are to (a) describe differences between moderator and mediator effects; (b) provide nontechnical descriptions of how to examine each type of effect, including study design, analysis, and interpretation of results; (c) demonstrate how to analyze each type of effect; and (d) provide suggestions for further reading. The authors focus on the use of multiple regression because it is an accessible data-analytic technique contained in major statistical packages. When appropriate, they also note limitations of using regression to detect moderator and mediator effects and describe alternative procedures, particularly structural equation modeling. Finally, to illustrate areas of confusion in counseling psychology research, they review research testing moderation and mediation that was published in the Journal of Counseling Psychology during 2001.

Testing Moderator and Mediator Effects in Counseling Psychology Research.

Ten per cent of the world’s school-aged children are estimated to be carrying excess body fat (Fig. 1), with an increased risk for developing chronic disease. Of these overweight children, a quarter are obese, with a significant likelihood of some having multiple risk factors for type 2 diabetes, heart disease and a variety of other co-morbidities before or during early adulthood. The prevalence of overweight is dramatically higher in economically developed regions, but is rising significantly in most parts of the world. In many countries the problem of childhood obesity is worsening at a dramatic rate. Surveys during the 1990s show that in Brazil and the USA, an additional 0.5% of the entire child population became overweight each year. In Canada, Australia and parts of Europe the rates were higher, with an additional 1% of all children becoming overweight each year. The burden upon the health services cannot yet be estimated. Although childhood obesity brings a number of additional problems in its train – hyperinsulinaemia, poor glucose tolerance and a raised risk of type 2 diabetes, hypertension, sleep apnoea, social exclusion and depression – the greatest health problems will be seen in the next generation of adults as the present childhood obesity epidemic passes through to adulthood. Greatly increased rates of heart disease, diabetes, certain cancers, gall bladder disease, osteoarthritis, endocrine disorders and other obesityrelated conditions will be found in young adult populations, and their need for medical treatment may last for their remaining life-times. The costs to the health services, the losses to society and the burdens carried by the individuals involved will be great. The present report has been written to focus attention on the issue and to urge policy-makers to consider taking action before it is too late. Specifically, the report:

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1467-789X.2004.00133.x

Obesity in children and young people: a crisis in public health.

This meta-analytic review of prospective and experimental studies reveals that several accepted risk factors for eating pathology have not received empirical support (e.g., sexual abuse) or have received contradictory support (e.g.. dieting). There was consistent support for less-accepted risk factors(e.g., thin-ideal internalization) as well as emerging evidence for variables that potentiate and mitigate the effects of risk factors(e.g., social support) and factors that predict eating pathology maintenance(e.g., negative affect). In addition, certain multivariate etiologic and maintenance models received preliminary support. However, the predictive power of individual risk and maintenance factors was limited, suggesting it will be important to search for additional risk and maintenance factors, develop more comprehensive multivariate models, and address methodological limitations that attenuate effects.

http://web4.uwindsor.ca/users/j/jarry/main.nsf/032ecd0df8f83bdf8525699900571a93/aa9ed943e56182bf85256abe005bc3f6/$FILE/Stice%20(2002).pdf

Risk and maintenance factors for eating pathology: a meta-analytic review

OBJECTIVE: The authors developed a methodological basis for investigating how risk factors work together. Better methods are needed for understanding the etiology of disorders, such as psychiatric syndromes, that presumably are the result of complex causal chains. METHOD: Approaches from psychology, epidemiology, clinical trials, and basic sciences were synthesized. RESULTS: The authors define conceptually and operationally five different clinically important ways in which two risk factors may work together to influence an outcome: as proxy, overlapping, and independent risk factors and as mediators and moderators. CONCLUSIONS: Classifying putative risk factors into these qualitatively different types can help identify high-risk individuals in need of preventive interventions and can help inform the content of such interventions. These methods may also help bridge the gaps between theory, the basic and clinical sciences, and clinical and policy applications and thus aid the search for early diagnoses and ...

/pdf/how-do-risk-factors-work-together-mediators-moderators-and-310ywlv77b.pdf

How Do Risk Factors Work Together? Mediators, Moderators, and Independent, Overlapping, and Proxy Risk Factors

http://web4.uwindsor.ca/users/j/jarry/main.nsf/032ecd0df8f83bdf8525699900571a93/aa9ed943e56182bf85256abe005bc3f6/$FILE/Stice%20&%20Shaw%20(2002).pdf

Role of body dissatisfaction in the onset and maintenance of eating pathology: a synthesis of research findings.

Body-image disturbance and eating disorders are a significant physical and mental health problem in Western countries. We describe emerging work on one newly identified variable that appears to be a potent risk factor for the development of these problems internalization of societal standards of attractiveness. Work conducted independently in our labs over the past decade has included scale development, correlational studies, prospective risk-factor studies, randomized experiments, and randomized prevention trials. Findings collectively suggest that internalization is a causal risk factor for body-image and eating disturbances, and that it appears to operate in conjunction with other established risk factors for these outcomes, including dieting and negative affect. Future research is needed to examine the specific familial, peer, and media influences that promote internalization and to replicate and extend our prospective and experimental studies.

Thin-Ideal Internalization: Mounting Evidence for a New Risk Factor for Body-Image Disturbance and Eating Pathology:

Because there have been few longitudinal investigations of integrative etiological theories of bulimia nervosa, this study prospectively tested the dual-pathway model using random regression growth curve models and data from a 3-wave community sample of adolescent girls (N = 231). Initial pressure to be thin and thin-ideal internalization predicted subsequent growth in body dissatisfaction, initial body dissatisfaction predicted growth in dieting and negative affect, and initial dieting and negative affect predicted growth in bulimic symptoms. There was prospective evidence for most of the hypothesized mediational effects. Results are consistent with the assertion that pressure to be thin, thin-ideal internalization, body dissatisfaction, dieting, and negative affect are risk factors for bulimic pathology and provide support for the dual-pathway model.

Eric Stice

Papers

Risk and maintenance factors for eating pathology: a meta-analytic review

How Do Risk Factors Work Together? Mediators, Moderators, and Independent, Overlapping, and Proxy Risk Factors

Role of body dissatisfaction in the onset and maintenance of eating pathology: a synthesis of research findings.

Thin-Ideal Internalization: Mounting Evidence for a New Risk Factor for Body-Image Disturbance and Eating Pathology:

A prospective test of the dual-pathway model of bulimic pathology: mediating effects of dieting and negative affect.