Microdomains in the immune system control cell adhesion and pathogen uptake.

Abstract

DCs are the sentinels of the immune system and act at the interface between innate and aquired immunity. DCs establish several dynamic interactions with invading microorganisms, extracellular matrix, endothelial cells, and lymphocytes. All these interactions are mediated by specific membrane receptors, among which the 2 integrin LFA-1 and the C-type lectin DC-SIGN. These receptors have two common ligands, ICAM-2 and -3. The aim of this thesis was to investigate the relation between organization at the cell surface and functional activity of LFA-1 and DC-SIGN. Particularly, Transmission Electron Microscopy (TEM) and Near-field Scanning Optical Microscopy (NSOM) were employed to study these receptors at high resolution. Moreover, the interactions of these receptors with other components of the cell membrane, such as lipid rafts, was determined. In Chapter 1, a general introduction is given about characteristics and properties of DCs and their monocytic precursors. Chapter 2 describes several high-resolution microscopies and their applications in cell biology. Chapter 3 shows that LFA-1 activation state changes during DCs development along with major modifications of its organization within the cell membrane. In Chapter 4, the distribution of DC-SIGN in well-defined microdomains at the cell surface of immature DCs is described. In Chapter 5, the distribution of DC-SIGN in microdomains on DCs was determined by NSOM, which for the first time imaged sub-micron sized microdomains on whole cells under liquid conditions. In Chapter 6, we demonstrated that DC-SIGN is also able to recognize fungi such as C. albicans. In Chapter 7, the carbohydrate structure recognized by DC-SIGN on the cell wall of C. albicans was identified. Finally, in Chapter 8, general discussion and future prospective on the topics described in this thesis are given.