Nicholson, L. (2016). The Immune System. Essays in Biochemistry, 60(3), 275-301. https://doi.org/10.1042/EBC20160017 Publisher's PDF, also known as Version of record License (if available): CC BY Link to published version (if available): 10.1042/EBC20160017 Link to publication record in Explore Bristol Research PDF-document This is the final published version of the article (version of record). It first appeared online via Portland Press at http://doi.org/10.1042/EBC20160017. Please refer to any applicable terms of use of the publisher. University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/ Essays in Biochemistry (2016) 60 275–301 DOI: 10.1042/EBC20160017 The immune system Lindsay B. Nicholson Cellular and Molecular Medicine, University of Bristol, Bristol, U.K. Correspondence: Lindsay B. Nicholson (email
[email protected]). All organisms are connected in a complex web of relationships. Although many of these are benign, not all are, and everything alive devotes significant resources to identifying and neutralizing threats from other species. From bacteria through to primates, the presence of some kind of effective immune system has gone hand in hand with evolutionary success. This article focuses on mammalian immunity, the challenges that it faces, the mechanisms by which these are addressed, and the consequences that arise when it malfunctions. “Great fleas have little fleas upon their backs to bite ’em, And little fleas have lesser fleas, and so ad infinitum.” Augustus De Morgan (1872) Introduction The problems that the mammalian immune system solves are not restricted to higher animals; they are faced by all forms of life and are ignored by none.