Epithelial defense in Hydra

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The phylum Cnidaria is one ofthe earliest branches in the animal tree of life. Cnidarians possess most of the gene families found in bilalerians and have relained many ancestral genes that have been lost in Drosophila and C. elegans. Characterisation of the innate immune repertoire of extant cnidarians is, therefore, of both fundamental and applied interest - it not only provides insights into the basic immunological tool kit of the common ancestor of all animals, but is also likely to be important in understanding human barrier disorders by describing ancient mechanisms of host/microbial interactions and the resulting evolutionary selection processes. In the last few years we have made considerable progress in characterizing the innate immune system in Hydra, one of the simplest multicellular animals known. In the complete absence of both protective mechanical barriers and mobile phagocytes. Hydra is remarkably well equipped to prevent pathogens infection. Our findings reveal highly active antimicrobial peptides and a complex genetic network involved in the interaction of host and microbiota at the beginning of metazoan evolution. The observations support the hypothesis that the epithelium represents the ancient system of host defense. Consistent with that, we have shown that epithelia in Hydra play an active role in selecting their microbiota and have proposed that antimicrobial peptides are key factors for host-bacteria coevolution. We now propose to study innate immune reactions in Hydra in more detail with the final goal of, (i) understanding the interactions of hydra epithelia with the associated microbial community; (ii) characterization of the glycocalix as a not yet understood physical barrier in microbial defence; (iii) characterizing the role of secretory gland cells in defence reactions; and (iv) identification of antifungal molecules.