PerspectiveImmunology

No Need to Coax Monocytes

Science  10 Jun 2011:
Vol. 332, Issue 6035, pp. 1268-1269
DOI: 10.1126/science.1208480

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Summary

Macrophages are among the immune system's most important line of innate defense. They engulf and kill microorganisms and secrete factors that afford them key roles in tissue repair and remodeling. Macrophages are found in all resting tissues at low amounts; local demand dictates that their numbers increase in response to inflammatory signals. In many chronic diseases including heart disease, asthma, and cancer, inflammation overstays its welcome and drives disease. In many of these scenarios, accumulated macrophages are unwanted, and suppressing this build-up has therapeutic potential. Monocytes that circulate in the bloodstream are recruited to inflamed tissues and give rise to macrophages, and therapies to control inflammation often focus on interrupting this recruitment. However, on page 1284 of this issue, Jenkins et al. (1) reveal that the accumulation of certain macrophages—called M2 macrophages or alternatively activated macrophages (AAMs)—occurs not through coaxing their precursors from the bloodstream, but by local proliferation of macrophages (see the figure).

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