General introduction to innate immunity: Dr. Jekyl/Mr. Hyde quality of the innate immune system.

The innate immunity plays a critical role in host protection against pathogens and transformed cells. It relies amongst others on pattern recognition receptors such as Toll-like receptors, C-type lectin receptors, and nucleotide-binding oligomerization domain proteins to alert and activate defense pathways including the activation of the complement system. Innate immunity represents a trait common to plants and animals, and besides the humoral factors different cell types e.g. subspecies of dendritic cells (plasmacytoid dendritic cells), phagocytic cells, mast cells, glia cells, Kupffer cells, neutrophils and natural killer cells are involved to orchestrate the anti-infectious and antitumor response. Studies in plants, in fruit flies and in mammals reveal that the defensive strategies of invertebrates and vertebrates are highly conserved at the molecular level, which raises the exciting prospects of an increased understanding of innate immunity in a healthy or diseased organism. However, the molecular machinery, e.g. cytokines and chemokines, which triggers, amplifies, and sustains the different phases of the innate immune response could also promote a substantial imbalance between danger and inflammatory response when an infectious challenge is either chronic or not properly declining.