Figure 3.

Spectrum of macrophage polarization. Depending on the signals perceived in its milieu (microbial products, damaged cells, cytokines), a naive M0 macrophage can be activated and polarize towards a plethora of different phenotypes. The two extremes of this continuous polarization spectrum are, on the one hand, M1 macrophages, known to have pro-inflammatory activity, and on the other hand, M2 macrophages, known to have anti-inflammatory function. These two extremes were obtained in in vitro models where their polarization markers (such as membrane receptors, transcription factors, cytokines) were identified. However, in vivo, macrophages present in an organism, or in a tumor, will tend towards an M1 or M2 phenotype. Due to the great complexity of the in vivo milieu, these macrophages will never reach the level of polarization that macrophages obtained in vitro. These macrophages in vivo will thus be called M1-like or M2-like [149,150,151,152]. Created with BioRender.com.