The innate immunity in the cnidarian Hydra vulgaris

Hydra vulgaris is currently receiving increased attention as a genetically tractable invertebrate model system for studying important processes of life such as the innate immune defense. Similar to complex animals, H. vulgaris polyps respond to injury by abrupt muscle contraction, by limited escape behavior, and by healing the damaged tissue. Simultaneously, cellular processes such as phagocytosis and programmed cell death as well as the massive production of antimicrobial peptides are induced. Recent studies identified several molecular pathways controlling these responses; however, the interdependence of innate immunity and, for example, regeneration and tissue remodeling is not well elucidated yet. H. vulgaris belongs to the Cnidaria representing the phylogenic sister group of bilaterian animals; hence, a better understanding of evolutionarily conserved as well as Hydra/Cnidaria-specific immune responses will provide deep insight into both origin and evolution of the animal innate immune syste