Macrophage activation and polarization: nomenclature and experimental guidelines.
Murray PJ., Allen JE., Biswas SK., Fisher EA., Gilroy DW., Goerdt S., Gordon S., Hamilton JA., Ivashkiv LB., Lawrence T., Locati M., Mantovani A., Martinez FO., Mege JL., Mosser DM., Natoli G., Saeij JP., Schultze JL., Shirey KA., Sica A., Suttles J., Udalova I., van Ginderachter JA., Vogel SN., Wynn TA.
Description of macrophage activation is currently contentious and confusing. Like the biblical Tower of Babel, macrophage activation encompasses a panoply of descriptors used in different ways. The lack of consensus on how to define macrophage activation in experiments in vitro and in vivo impedes progress in multiple ways, including the fact that many researchers still consider there to be only two types of activated macrophages, often termed M1 and M2. Here, we describe a set of standards encompassing three principles-the source of macrophages, definition of the activators, and a consensus collection of markers to describe macrophage activation-with the goal of unifying experimental standards for diverse experimental scenarios. Collectively, we propose a common framework for macrophage-activation nomenclature.