Research

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.

Different species of Pseudomonas are used as plant protecting agents especially to bate potatoes. To achieve an admission from the authorities the Pseudomonas strains must be tested for their toxicological properties. To circumvent animal studies, test systems are developed to analyse the harmful potential on in vitro cultures of lung epithelial cells. Therefore Calu-3 cells are grown on transwell plates until tight junctions are formed. To classify the bacterial strains, the integrity of the tight junction is evaluated after incubation of Pseudomonas with cell cultures.

Different antibodies against HIV-1 have been developed at the Department of Biotechnology and have been tested in numerous in vitro studies and some of them also in clinical trials. Among others the mAb 4B3 demonstrated promising results in a macrophage assay infected with virus strain BaL and TV1. To test their potency in an in vitro mucosal system, it is necessary to swith the subclass from IgG to IgA specificity. Naturally occurring IgAs pass the epithelial barrier by cellular internalization via endocytosis with subsequent cleavage of the extracellular part of the receptor which remains at the IgA molecule, known as secretory component. This enables to transport the dimeric IgA from the site of application through the tight epithelial layer to the luminal surface. To test the IgA antibodies in an mucosal application the secretory component must be already coexpressed with the antibody. Therefore, this challenging project needs the expression of a heteropolymeric complex consisting of two antibody specific light and heavy chains connected by the common J-chain and associated with the secretory component. Afterwards the antibodies must be purified and, characterized and tested in different model systems.