Intracellular membrane trafficking plays key roles in cell signalling and innate and adaptive immunity. Endocytosis and subsequent endolysosomal trafficking of growth factor receptors constitute a crucial mechanism for receptor signal attenuation and tumo ur suppression. For innate immunity against gram-negative bacteria and viruses, Toll-like receptors such as TLR4 and TLR9 need to traffic intracellularly in response to extracellular triggers in order to orchestrate appropriate cellular responses. Likewis e, MHC class II mediated adaptive immunity requires correct biosynthetic trafficking of MHC-II molecules as well as endo- or phagocytic trafficking of the pathogen. In spite of their importance, we have only fragmentary knowledge of the molecular mechanis ms that govern these endocytic and biosynthetic trafficking pathways and their interactions. Nevertheless, it is clear that these pathways share common basic mechanisms yet involve specific sets of structural and regulatory components whose identities and interactions remain to be clarified. The aim of the present project is to identify lipids, proteins and pathways that mediate and regulate the intracellular trafficking of TLRs, MHC-II and growth factor receptors, and to describe the mechanisms by which these molecules contribute to immunity and tumour suppression. The development and implementation of advanced imaging methods such as high-sensitivity and live-cell confocal microscopy, high-throughput imaging and electron tomography, in close collaborati on with the FUGE imaging platform, will be an integral part of the project. Microarray analyses will be performed with assistance from the FUGE microarray platform, whereas their interpretation will involve the FUGE bioinformatics platform. For proteomic analyses of posttranslational protein modifications the FUGE proteomics platform will be employed.