Fig. 1.

Macrophage polarization. Exposure to different cytokine milieu promotes the differentiation of monocytes into polarised macrophage subsets. When exposed to LPS, IFN-γ or other microbial products, monocytes differentiate into M1 macrophages. When exposed to IL-4, IL-10, IL-13 and immuno-suppressive agents, monocytes differentiate into M2 macrophages. M1 and M2 subsets share different characteristics in their function and phenotype. M1 cells have bactericidal activity, immuno-stimulatory functions and display tumour cytotoxicity. M2 cells promote tissue repair and angiogenesis and have high scavenging ability, favouring tumour progression. Abbreviations are: RNI, reactive nitrogen intermediates; ROI, reactive oxygen intermediates; IL, interleukin; TNF, tumour necrosis factor; CXCL, chemokine (C-X-C motif) ligand; IFN, interferon; LPS, lipopolysaccharide; IC, immune complexes; TLR, toll-like receptor; MR, mannose receptor; SR, scavenger receptor; CCL, CC chemokine ligand; TGF, transforming growth factor.