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  • Review Article
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Complement: a key system for immune surveillance and homeostasis

Abstract

Nearly a century after the significance of the human complement system was recognized, we have come to realize that its functions extend far beyond the elimination of microbes. Complement acts as a rapid and efficient immune surveillance system that has distinct effects on healthy and altered host cells and foreign intruders. By eliminating cellular debris and infectious microbes, orchestrating immune responses and sending 'danger' signals, complement contributes substantially to homeostasis, but it can also take action against healthy cells if not properly controlled. This review describes our updated view of the function, structure and dynamics of the complement network, highlights its interconnection with immunity at large and with other endogenous pathways, and illustrates its multiple roles in homeostasis and disease.

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Figure 1: Immune surveillance functions of complement.
Figure 2: Detailed view of complement activation, amplification, signaling and regulation.
Figure 3: Integrative role of complement in host defense and homeostasis.
Figure 4: Emerging roles of complement in health and disease.

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Acknowledgements

The scope of research into complement over the past decade makes it impossible to cover every important aspect; we have had to focus on certain areas, and we acknowledge the research that we could not mention specifically. We thank D. McClellan for editorial assistance and A. Tenner for comments. Supported by US Public Health Service grants CA112162, AI68730, AI30040, AI72106, EB3968, GM62134 (to J.D.L.), and DE015254 and DE018292 (to G.H.).

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Ricklin, D., Hajishengallis, G., Yang, K. et al. Complement: a key system for immune surveillance and homeostasis. Nat Immunol 11, 785–797 (2010). https://doi.org/10.1038/ni.1923

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