CNS macrophage/monocytes differentiate into polarized macrophage subsets when exposed to different cytokine milieu. In the presence of granulocyte-macrophage colony stimulating factor (GM-CSF), interferon-(IFN) γ, lipopolysaccharide (LPS) and other microbial products, monocytes differentiate into M1 macrophages. In the presence of macrophage colony stimulating factor (M-CSF), interleukin-(IL) 4, IL-6, IL-10 and immune suppressive molecules (corticosteroids, vitamin D3, prostaglandins), monocytes differentiate into M2 macrophages. M1 and M2 subsets differ in terms of phenotype and functions. M1 cells have high anti-microbial activity, immune stimulatory functions and tumor cytotoxicity and express the signal transducer and activator of transcription 1 (STAT-1). M2 cells have high scavenging ability, promote tissue repair and angiogenesis, favor tumor progression and express STAT-3.