Evolution of the Human Immune System

Abstract

Human immune system is an orchestra of various defence mechanisms functioning at different levels, from individual cells to the whole body. Specialised immune mechanisms can be subdivided into innate and adaptive immune systems. Innate immune mechanisms use receptors recognising conserved molecular patterns of pathogens. Adaptive immune system depends on the production of vast repertoires of immune receptors and selective expansion of pathogenā€specific ones. Some basic cellular functions such as ubiquitination and autophagy as well as stress response pathways also contribute to the immune defence. Various immune defence systems work autonomously but in communication with each other. All responses are coordinated at the body level by hormones and other mediators. Layered and redundant structure of the human immune system offers great efficiency in the detection and elimination of pathogens. All immune mechanisms evolve interactively in concordance with human environment and history.

Key Concepts:

  • Human immune system is a multilayered structure that includes various mechanisms.

  • Basic cellular mechanisms may contribute to immune defence.

  • Specialised immune mechanisms are subdivided into innate and adaptive based on the receptors used for antigen recognition.

  • Immune mechanisms comprise those based on humoral factors and those based on cells.

  • Most immune defence mechanisms work semiautonomously in interaction with other systems.

  • Immune mechanisms can be controlled at the body level by hormones and other mediators.

  • Immune receptors evolve by gene duplication, balancing selection, changes in coding and regulatory sequences, and other mechanisms.

  • Human immune system continues to evolve.

  • Individual immune mechanisms evolve in interaction with other mechanisms and basic cellular machinery.

Keywords: innate; adaptive; defence mechanisms; pathogen; positive selection

Figure 1. Human immune system is a multilayered network of various defence mechanisms. Each cell in a human body has various means to fight pathogens. Basic cellular mechanisms such as ubiquitination, RNAi and apoptosis contribute to immune defence. Specialised immune cells such as B cells and macrophages and humoral systems such as complement work autonomously but in communication with other mechanisms. All responses are coordinated at the body level by various mediators. Skin and epithelial barriers of the body are protected by the secretion of antimicrobial substances.
Figure 2.

Coevolution of humans and Staphylococcus aureus. FcaR1, a receptor for IgA‐Fc, expressed on myeloid cells mediates phagocytosis of IgA‐coated pathogens. S. aureus produces a bacterial decoy SSL7 that binds IgA‐Fc region preventing FcaR1 binding and phagocytosis. Immunoglobulin duplication and diversification took place in primates (step 1). FcaR1 was positively selected for binding with the new IgA (step 2). Bacterial decoy proteins developed high affinity to this IgA (step 3). Next, IgA forms with low binding to the bacterial decoy were selected (step 4). Now, FcaR1 needs to change again to bind the new IgA (step 5) and so on. If FcaR1 fails to keep up, it may be lost from the genome.

Figure 3.

IgG4 is a regulatory antibody inhibiting the formation of immune complexes, inflammation and allergy. It is under the dual selection pressure. Pressure from pathogens requiring stronger immune response can lead to loss of G4, whereas pressure from inflammatory/allergic diseases can lead to its duplication.

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Further Reading

Janeway CA , Travers P , Walport M and Shlomchik M (2005) Immunobiology: The Immune System in Health and Disease. New York: Garland Science. http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=imm.TOC&depth=10.

Larrea CL (ed.) (2011) Self and Non‐self. Austin: Landes Bioscience.

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How to Cite close
Danilova, Nadia(Sep 2013) Evolution of the Human Immune System. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0020781.pub2]