Definition: "Immune system that responds broadly and fast (e.g., within hours) upon infection or injury, producing and secreting various compounds (antimicrobial peptides, interferon) and activating cellular defense such as cell-mediated cytotoxicity by natural killer (NK) cells and phagocytosis by neutrophils and macrophages. Innate immunity generally refers to any type of host responses elicited by receptor-encoded genes/gene families."