Initiation of the complement cascade by pentameric and hexameric IgMs

Theoretical framework One of the first specific defense mechanisms against invading pathogens and self-antigens is the complement system, activated by immunoglobulins (Igs). Igs bind specifically to the antigen on the pathogen and thereby enable the docking of the C1q-complement initiation complex. Two factors influencing the complement activation were so far not investigated in detail. First, the format of the antigen, described by the chemical nature, the molecular size and the mode of presentation (as soluble substance or embedded in vesicles for mimicking the cell surface). Second, the huge difference in complement activation resulting from the degree of oligomerization of the IgMs. Objectives The overall goal of the pent/hexIgM project is to elucidate the activation sites of C1q and the IgM-Fc after binding of pentameric and hexameric IgMs to different antigen formats. Approach/methods We will produce recombinant IgMs and the C1q protein in mammalian cells and generate mutants thereof by yeast surface display. Next, we will confirm the biological activities of generated proteins in vitro by immunochemical and biophysical analyses as well as functionality tests. Most important, we will elucidate in influence of the antigen format and the degree of oligomerization of the IgMs (pentameric versus hexameric IgMs) on the activation of the complement system. Level of originality Although IgMs in combination with complement proteins have an important function in the human body, these proteins are not yet widely used in therapy and diagnosis. The results of the pent/hexIgM project will contribute to understanding the complex mechanisms underlying the activation of the complement cascade and will provide data of particular importance for developing new diagnostics and efficient treatment methods for various infectious, inflammatory, chronical and cancerous diseases.