The Innate Immune System

The innate immune system recognizes infectious danger and launches an immediate anti-infective response. It relies on recognition systems (receptors) that were selected during phylogeny and which in part are shared with non-vertebrate organisms. Receptors of innate immunity are encoded within the germ-line and do not undergo somatic recombination. Humoral as well as cellular mechanisms are involved, which interact at multiple levels and are expressed on immune and non-immune cells to ensure an appropriate and efficient defense response. Innate and adaptive immunity are interconnected. Activation of innate immune cells is a necessary prerequisite for induction of adaptive immune responses. Multiple effector mechanisms of adaptive immunity ultimately rely on the clearance function of innate immune cells. Moreover, the products of the adaptive immune system will enhance the efficacy of innate immune responses. Thus, in vertebrates, innate and adaptive immunity act in a well-tuned concert to ascertain an effective antipathogen response.