Determinants of IgM mediated classical complement activation

Increasing antibiotic resistance among common pathogens underscores the need for alternative treatment methods, especially for bacterial infections. Antibody-based therapies are already being used successfully for the treatment of cancer and autoimmune diseases, and there is growing interest in applying these methods to fight bacteria as well. However, significant progress in this area is currently hampered by our limited understanding of the molecular mechanisms responsible for therapeutic success. Most pharmaceutical and academic antibody programs are focused on the development of immunoglobulin G (IgG) antibodies due to the extensive expertise in their large-scale manufacturing and clinical application available in this field. As an agent against bacterial infections, however, the larger IgM antibody is well known to be more effective than IgG, although its lower pathogen binding strength and shorter half-life in the blood have previously limited its use as a therapeutic. Recent studies have highlighted the importance of IgM for human immunity against various germs, including the largely antibiotic-resistant bacterium S. aureus and various SARS-CoV-2 variants. Understanding how IgM provides protection could therefore be crucial for the future development of antibody therapies. An important mechanism by which antibodies fight bacterial infections is the activation of the human complement system, which provides effective weapons for killing bacteria. When antibodies bind to a bacterial surface, they either cause direct killing of the bacterium by destroying its membrane, or to its improved uptake and destruction by the body`s own killer cells. Although the crucial role of IgM in human immunity against bacterial infections is widely recognized, and knowledge of the exact mechanisms behind its enhanced activity is essential for the future development of antibody therapies, IgMs exact properties remain unclear. In this project, we will comprehensively characterize these mechanisms using a combination of several state-of-the-art biophysical methods, including high-speed atomic force microscopy, 3D single-molecule fluorescence microscopy, and quartz crystal microbalance. Based on the experimental results, we will further develop a mechanistic model of the underlying molecular interactions, thereby laying the foundation for the optimization of IgM antibody development and pharmacokinetic/pharmacodynamic modeling in the context of future immunotherapies. The project is being carried out by Dr. Johannes Preiner (PI) and Dr. Jaroslaw Jacak at the University of Applied Sciences Upper Austria in close collaboration with Dr. Suzan Rooijakkers, UMC Utrecht.