Adhesion of parasitized red blood cells (RBCs) to vascular endothelium is thought to be a key factor in the pathology of falciparum malaria. However, quantitative analyses of the intercellular forces and of the effects of flow on adhesion have been lacking. We have characterized cytoadhesion of RBCs parasitized by the strains ITO4 (which can bind to receptors ICAM-1 or CD36) and FCR3A2 (which can bind to CD36 only) using micropipette manipulation and flow chamber techniques. Target cells were unfixed or glutaraldehyde-fixed human umbilical vein endothelial cells (HUVEC, bearing ICAM-1 only) or human amelanotic melanoma cells (C32, bearing CD36 and ICAM-1). In the static, micropipette assay, 60% to 70% of parasitized cells would adhere when tested at up to three successive sites. The percentage of cells adhering and the force required for their detachment (approximately 10(- 10) N) were similar for each combination of parasite strain and adhesion target (ITO4/HUVEC, ITO4/C32, FCR3A2/C32). In the flow chamber, efficiency of initial adhesion of parasitized cells was essentially constant (at about 1%) up to a stress of 0.1 Pa, and then decreased rapidly with increasing stress. Either receptor (ICAM-1 or CD36) could immobilize flowing cells at a physiologic flow stress (0.1 Pa), but the numbers of cells adhering varied for the different combinations (ITO4/C32 greater than ITO4/HUVEC greater than FCR3A2/C32). When flow was increased in steps, adhered cells were gradually washed off but many could withstand stresses at which they would not initially adhere. The force for detachment estimated in this way was similar to the pipette value, and again, was similar for the different combinations of strains and targets. Adhesion from flow depends on the affinity between surfaces being above a critical level, and once adhesion is established, the fracture energy determines resistance to disruption of adhesion. The results show that the fracture energy is greater than the affinity (ie, that adhesion becomes stabilized after it is initially established) and that the ratio of affinity to fracture energy is different for different receptor/ligand pairs, with ICAM-1 appearing to be the more efficient immobilizing receptor. Also, static and flow-based assays of adhesion clearly differ; the affinity is less critical in the static situation, so that most parasitized cells were capable of adhering in a static assay, but fewer did so under flow. Adhesiveness varied markedly from cell to cell, both for targets and parasitized cells.(ABSTRACT TRUNCATED AT 400 WORDS).

Abnormal adhesion of sickle cells to vascular endothelium may be a factor in the initiation of painful vaso-occlusive crisis. The sickle cell population contains an unusually large number of less dense reticulocytes that are known to be more adhesive than mature red cells, but there is contradictory evidence regarding the adhesiveness of dense sickle cells. We used a flow-based assay of adhesion to cultured human umbilical vein endothelial cells to test the properties of density fractions of sickle cells, prepared either by density gradient or by centrifugation of packed cells. We also examined the effects of incubating sickle cells with or without cyclical deoxygenation on their adhesion. After fractionation on a Percoll-lsopaque gradient, the less dense 10% (reticulocyte-rich) cells and the most dense 10% cells adhered in greater number than the remainder (by about twofold). However, after centrifugation of packed cells, the less dense 10% were again more adhesive than the "middle" cells, but the most dense were not. Exposing sickle cells to constituents of the gradient had no consistent effect on adhesion, while centrifugal packing induced a degree of hemolysis, and tended to reduce adhesiveness of the dense fraction previously obtained from a gradient. Incubation in air at 37°C for 15 hr reduced the number of reticulocytes and the adhesiveness of less dense sickle cells compared to those held at 4°C. On the other hand, incubation at 37°C for 15 hr with cyclical deoxygenation caused formation of dense cells and increased adhesiveness compared to incubation without cyclical deoxygenation. We conclude that young, less dense sickle cells are unusually adhesive, but that this adhesiveness is reduced during maturation. However, repeated sickling in vivo causes formation of an abnormally dense subpopulation of cells which either redevelop an increased tendency to adhere to endothelial cells or preserve their initial adhesiveness. Both adhesive cell populations may be implicated in promoting vascular obstruction.

The past decade has seen a rapid increase in the number of studies employing psychophysiological methods to explain variation in political attitudes and behavior. However, the collection, analysis, and interpretation of physiological data present novel challenges for political scientists unfamiliar with the underlying biological concepts and technical skills necessary for utilizing this approach. Our objective in this article is to maximize the effectiveness of future work utilizing psychophysiological measurement by providing guidance on how the techniques can be employed most fruitfully as a complement to, not a replacement for, existing methods. We develop clear, step-by-step instructions for how physiological research should be conducted and provide a discussion of the issues commonly faced by scholars working with these measures. Our hope is that this article will be a useful resource for both neophytes and experienced scholars in lowering the start-up costs to doing this work and assessing it as part of the peer review process. More broadly, in the spirit of the open science framework, we aim to foster increased communication, collaboration, and replication of findings across political science labs utilizing psychophysiological methods.

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