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All forms of life need to be able to simultaneously cooperate with other life forms in their environment, while defending themselves from harmful interactions, such as infection or parasitism. The physical and chemical mechanisms that have evolved to negotiate these interactions constitute the immune system of an organism. The immune system can be divided into two functional components – innate and adaptive. Innate immunity includes evolved strategies to avoid harmful confrontations through erection of standing physical and chemical barriers along with the ability to actively and immediately respond to threats that circumvent the standing mechanisms by focusing on evolutionarily conserved signatures of pathogen and tissue injury. These mechanisms have evolved through mutation and selection over many generations and are elaborated by all self-replicating organisms from single cell organisms to plants and animals. Vertebrate animals developed an elaborate adaptive immune strategy in which new molecules are built to allow chemical recognition and responses to novel threats over the life of an individual. When present, the adaptive system evolved to work closely with the innate system. Innate and adaptive immune strategies build on coevolving systems of the organism that are involved in control of metabolism, the cell cycle, and cell death. In this article we will provide an overview of the functional cell biology section and organize these into Innate and Adaptive components.

Original publication





Book title

Encyclopedia of Cell Biology: Volume 1-6, Second Edition

Publication Date





336 - 349