Research Topics

A major concern of Comparative Immunology is to compare the complex mechanisms that various species from different parts of the animal phylogeny use to function – from the level of the organism down to the level of the molecule. Our research is concerned with comparative immunobiology and molecular parasitology. 

We are studying the evolution of the immune systems by comparing well-established model systems such as the free-living amoeboid protozoon Dictyostelium discoideum and the nematode Caenorhabditis elegans, and, in addition, marine invertebrates. 
We analyze the biological function of immune effector proteins such as antimicrobial peptides, pore-forming proteins and lysozymes from various animal taxa, including their activity spectrum, mode of action and structure-function relationships. Based on the comprehensive characterization of these ancient defensive weapons, we aim to identify natural templates for the design of new antibiotics.

We are elucidating the other side of host-pathogen interactions by investigating molecularly pathogenicity mechanisms of eukaryotic parasites and medically important human pathogens such as free-living and enteric amoebic parasites. Using a wide variety of methods, we particularly focus on the quantitative identification of proteins from cellular compartments (proteomics) and perform fundamental research on novel anti-infectives. 


Comparative Immunobiology:

• Ancient weapons – cytolytic and antimicrobial polypeptides as defence effector molecules of animals

Antimicrobial systems in animals have been characterized at the molecular level primarily for vertebrates and arthropods. A variety of active peptides have been found and they possess highly diverse structures. The majority of them share the common feature of amphipathicity and appear to act by physical disruption of the membranes of their targets. As the mode of action suggests that their application will not create resistant strains of pathogens, such peptides are currently used as natural templates to design new antibiotics. 

Among the several groups of membrane-permeabilizing peptides classified so far, the one to which the subjects of our studies belong is extraordinary; its members are relatively large polypeptides and are characterized by a compact alpha-helical and disulfide-bonded fold. Such polypeptides can be found in species of amoeboid protozoa (e.g. amoebapores), organisms which may be viewed primarily as insatiable phagocytic cells that uses bacteria as a nutrient source, in invertebrates and in vertebrates. Porcine and human cytotoxic lymphocytes contain similar peptides, termed NK-lysin and granulysin, respectively, which appear to be an important constituents of the internal defence against pathogens, e.g. intracellular bacteria. We are comparing the structures of the various antimicrobial and/or cytotoxic polypeptides and monitor their biological activities to extract the similarities and differences of effector molecules from evolutionarily highly divergent animals.



We also are characterizing antimicrobial and cytolytic proteins from body fluids of invertebrate species, such as bacteria-degrading lysozymes or various cytolysins, some of which create electron microscopically visible ring-like lesions on target cell membranes reminiscent of bacterial pore-forming toxins and of the complement system of mammals. These proteins may be viewed as broad spectrum defensive weapons against prokaryotic and eukaryotic pathogens.

Moreover, with the nematode Caenorhabditis elegans a multicellular model organism has been introduced in our project. As the entire genome of the worm has been elucidated and sophisticated techniques to manipulate the organism have been established, it is possible to analyze the antimicrobial system at the molecular and organismal level using DNA array technology and functional knock-out mutants. We are focussing on the molecular basis of the epithelial defense in C. elegans. Here, we are characterizing the molecular mechanisms which combat infections of epithels that are constantly exposed to potential pathogens, from target recognition to signal transduction and eventually synthesis and secretion of effector molecules.


Caenorhabditis elegans

Ursprüngliche Waffen im Tierreich: Membran-durchlöchernde Peptide für Verteidigung und Angriff [PDF]

go back

• Comparative and quantitative proteomics of microbe-challenged versus unchallenged Caenorhabditis elegans, an invertebrate model organism for innate immunity and inflammation

The consensus view is that the intestinal epithelium of animals forms a physical barrier to limit access of enteric microbes to the inner milieu of the host and contributes to innate host defense by producing effector molecules, e.g. antimicrobial peptides and enzymes, against particular luminal microbes. Classical studies on processes involved in innate immunity, inflammation, and pathology are often time-consuming, costly, and ethically problematic. In recent years, invertebrate model organisms have been employed to get out of this dilemma.
C. elegans can be infected by a plethora of pathogens, most of them are pathogenic also for humans. Consequently, the nematode has emerged as a powerful surrogate host for the study of innate immunity and host-pathogen interactions and to model microbial human infectious diseases in a non-vertebrate. Signalling cascades are well investigated that face bacterial or fungal pathogens. In our project we want to focus on the downstream processes of these cascades, i. e. the differential expression of effector and regulatory molecules due to a microbial challenge. Here, comparative and quantitative proteomic techniques including tandem mass spectrometric methods are introduced into the molecular analysis of infection. Recently, we have identified a series of different lysozymes in C. elegans total extracts by a proteomic approach as a snapshot of the physiological condition of the worm at a specific time-point. It is unknown what are the effector molecules in the intestine responsible for nutrition on microbes and for defense against pathogens that may became extraintestinal and how the antimicrobial armamentarium, e. g. lysozymes, is regulated at the proteinaceous level upon infection with different pathogens. It can be hypothesized that the lysozymes, comprising several subclasses, are differentially regulated upon infection with different potential pathogens. This may also hold true for the members of other antimicrobial peptides, e. g. the family of saposin-like peptides. We are analyzing proteins and peptides of the proteome that are down- or upregulated upon microbial infection by a set of microbial pathogens for humans and C. elegans. The output of these analyses will describe the “C. elegans infectome”. The project is unique in concerns of analyzing the global proteome of the nematode as a response to the challenge of the innate immune system. The venture is supposed to decipher the response pattern to different pathogens and will bring yet uncharacterized proteins to their functional annotation.



• Archaic cytolytic and antimicrobial mechanisms of free-living and pathogenic protozoa compared to those of higher eukaryotes

Many natural cytotoxic and antimicrobial proteins act by permeabilizing the target cell membranes. Presumably the most ancient phylogenetic location of such membrane-active polypeptides in eukaryotes has been found in amoebae. We found cytotoxic and antimicrobial polypeptides in enteric human pathogens (Entamoeba histolytica) and in free-living amoeboid protozoa (Naegleria, Acanthamoeba, Balamuthia) which are potentially highly pathogenic for humans. We are analyzing the structures of these amoebic proteins and determine their biological activities to elucidate the similarities and differences of these effector molecules. As an intensively studied and genetically tractable cellular model system, we are using the free-living and non-pathogenic amoeboid protozoon Dictyostelium discoideum to study the molecular armament which such a primitive phagocyte may use to combat growth of phagocytozed bacteria inside its digestive vacuoles.


Left figure: Entamoeba histolytica represented as a bacteria-phagocytozing (at the left) and cytolytic effector cell (at the right). In both scenarios, granule proteins such as the amoebapores are considered instrumental in killing the target cell.
Right figure: REM image of Acanthamoeba trophozoites.

Dictyostelium can transform from the amoebic phase upon streaming (1) into multicellular aggregates that migrate and are termed slugs (2) which eventually will become `fruiting bodies´ (3). These slugs contain specialized phagocytosing cells that are proposed to fullfil functions comparable to those of immune cells of higher organisms. Accordingly, slugs are valuable objects for infection experiments.





go back