Elucidation of IgG oligomer mediated Fc receptor clustering

Antibodies are one of the most important molecules of our immune system and are at the forefront in the fight against pathogens and tumor cells. These Y-shaped proteins recognize and tightly bind specific structures on the surface of viruses, bacteria or tumor cells via their two "arms", the so- called Fab fragments, and thus mark them for destruction through other components of the immune system. In particular, the stem of the Y-shaped antibody, the so-called Fc-fragment, which then protrudes from the surface of the target cell, is recognized by special immune cells, activates them and leads to the elimination of the antibody-tagged target cells. Binding partners of the Fc-fragments on the surface of the immune cells, so-called Fc-receptors, play an important role in this process: they ensure the specific recognition of the antibodies Fc-fragments and activate the immune cells through their local clustering (i.e. the accumulation of Fc-receptors within the contact area of the two cells) on the surface of the immune cells, which consequently kills the target cell through the release of cytotoxic proteins or direct phagocytosis (i.e. the immune cell "eats" the target cell directly). Within the present project, a combination of several high-end microscopic techniques (high-speed atomic force microscopy, cryo-electron microscopy, single-molecule fluorescence microscopy) and a technique for quantifying the interactions between antibodies and Fc-receptors (quartz-crystal microbalance) will be employed to structurally and dynamically investigate the mechanism of Fc- receptor clustering through the binding to antibodies. We are particularly interested in the role of a recently discovered property of antibodies to arrange themselves into antibody-hexamers (i.e. snowflake-like structures of six Y-shaped antibodies each) upon binding to a target cell under certain conditions, and whether the clustering of Fc-receptors on the immune cell is actually caused by binding to pre-formed antibody-hexamers. In this case, the activation of the immune cell would be a direct consequence of antibody hexamerization on the target cell, which could have far-reaching consequences for the development of new Fc-receptor- based immune therapies. The project is conducted by Dr. Johannes Preiner (PI) in collaboration with Dr. Birgit Plochberger and Dr. Mario Mairhofer at the University of Applied Sciences Upper Austria, Department of Medical Technology, Campus Linz, and Dr. Thomas H. Sharp, University Hospital Leiden, Netherlands.