A Laminar-Flow Chamber Assay for Measuring Bacterial Adhesion Under Shear Stress
Shear stress levels generated by circulating blood have a strong impact on biological processes taking place in the vasculature. It is therefore important to take them into account when studying infectious agents targeting the endothelium. Here we describ
- PDF / 237,268 Bytes
- 11 Pages / 504.57 x 720 pts Page_size
- 35 Downloads / 176 Views
Introduction The importance of blood flow generated drag forces can be clearly illustrated by the physiological interaction of lymphocytes with endothelial cells. Lymphocytes and platelets have developed efficient systems allowing adhesion to the vascular wall despite high forces, through the interaction of selectins with its ligands (1). In addition, the presence of shear stress for extended periods of time alters endothelial cell physiology, and studies in vascular biology extensively take advantage of experimental designs that allow the study of cell behavior under shear stress conditions (2). Blood flow in the vessels generates hydrodynamic forces on vessel walls and on circulating objects. The shear stress reports the tangential force exerted per unit area by a fluid moving near a stationary wall.
Myron Christodoulides (ed.), Neisseria meningitidis: Advanced Methods and Protocols, Methods in Molecular Biology, vol. 799, DOI 10.1007/978-1-61779-346-2_12, © Springer Science+Business Media, LLC 2012
185
186
M. Soyer and G. Duménil
This is a quantity similar to a pressure and may be expressed in dynes/cm2. It depends on blood velocity, viscosity, and vessel diameter. An analogous situation is a river bank that is submitted to a shear stress that depends on how fast the river flows (3). All blood components are submitted to forces induced by blood flow that tend to prevent their attachment to the vessel wall. Such forces are called hydrodynamic forces and depend on shear stress and cell geometry. Since most objects do not display regular shapes, hydrodynamic forces are not easy to determine and shear stress is more commonly used as a reference during laminar-flow assays. The importance of mechanical forces is not only found for physiological processes, but also in the case of pathological processes such as septicemia and meningitis where infectious agents interact with endothelial cells in the bloodstream. In particular, these forces have an impact on contact establishment between the pathogen and the endothelium. Although the general interest in studying the connection between microcirculation and infectious diseases (4) is rising, there are still only a few appropriate experimental models for these specific infection processes. To address this issue we have designed a simple in vitro experimental approach using disposable flow channels to study the bloodstream phase of bacterial infections (Fig. 1). Our main study was focused on Neisseria meningitidis (meningococcus) infection and we have shown that initial adhesion of individual bacteria only occurs in small brain capillaries, where transient blood flow arrests take place, even in physiological conditions (5). The mechanical properties of microcirculation are therefore a determining factor for pathogenesis. We also found that this adhesion is “irreversible,” as adhering bacteria resist blood flow returning to normal values. Shear stress does not interfere with bacterial growth, as large microcolonies grow out of individual adhering bacteria over extended periods of tim
Data Loading...
