Force spectroscopy to understand cell surface receptor interactions in the immune system.

Abstract

Contains fulltext : 77577.pdf (publisher's version ) (Open Access)Since the invention of the atomic force microscope (AFM) in 1986, the application of the instrument has shifted from a pure physicist’s tool to a useful instrument for physicists, chemists and biologists. The AFM is not a classical microscope in the sense that light or electrons are used to obtain an image, it is rather a mechanical microscope. The imaging is purely based on a physical probing of the surface topography by raster scanning (zigzag movements) of a sharp tip on a cantilever across the sample. Furthermore, the AFM can probe forces with ultra-high sensitivity by moving the cantilever in the vertical direction, which is especially interesting for biological applications. The probing of forces with AFM is known as AFM force spectroscopy. These AFM measurements can be performed under physiological conditions and make it possible to study dynamical processes, such as the adhesion of a living cell to an adjacent cell or the extracellular matrix, from the single cell to single molecular level. In the immune system diverse dynamical processes, such as the recognition of a pathogen by a dendritic cell (DC) or the transmigration of a leukocyte through the endothelium of a blood vessel, happen all the time throughout the human body. In the latter case during initial binding of these cells, bonds between different cell adhesion molecules (CAMs) are formed. These interactions have to be highly dynamic to withstand forces induced by for example the blood flow. These CAM bonds associate and dissociate at rates that change considerably under conditions of cell stress. The combination of molecular cell biology and AFM single molecule force spectroscopy provides a powerful tool to explore the complexity of these cell adhesion processes. In this thesis, we explored the versatility of the AFM in the context of biomaterial science, nano-chemistry and cell biology. The high spatial resolution of the AFM was exploited to measure and manipulate samples at the nanoscale. Moreover, the high force sensitivity of the AFM was applied to measure adhesive properties of CAMs on cells and to address the two distinct adhesive regulation processes of a CAM: affinity and avidity.RU Radboud Universiteit Nijmegen, 21 juni 2010Promotores : Speller, S.E., Figdor, C.G. Co-promotor : Cambi, A.176 p