Inflammation underlies a wide variety of physiological and pathological processes. Although the pathological aspects of many types of inflammation are well appreciated, their physiological functions are mostly unknown. The classic instigators of inflammation — infection and tissue injury — are at one end of a large range of adverse conditions that induce inflammation, and they trigger the recruitment of leukocytes and plasma proteins to the affected tissue site. Tissue stress or malfunction similarly induces an adaptive response, which is referred to here as para-inflammation. This response relies mainly on tissue-resident macrophages and is intermediate between the basal homeostatic state and a classic inflammatory response. Para-inflammation is probably responsible for the chronic inflammatory conditions that are associated with modern human diseases.
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I apologize to the many authors whose work could not be cited directly because of space limitations. I thank I. Brodsky, T. Horng, A. Iwasaki, E. Kopp, N. Palm and D. Stetson for critical reading of the manuscript. R.M. is an investigator of the Howard Hughes Medical Institute.
The author declares no competing financial interests.
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Medzhitov, R. Origin and physiological roles of inflammation. Nature 454, 428–435 (2008). https://doi.org/10.1038/nature07201
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