Table 1.

Microglial polarization states and substances produced.

Activation type/function	Source	Substances produced	Reference
M1 (classical activation): pro-inflammatory and pro-killing	LPS, IFN-γ	Cytokines: IL-1β, IL-6, IL-12, IL-17, IL-18, IL-23, TNF-α	Mahad and Ransohoff, 2003; Kawanokuchi et al., 2006 Kawanokuchi et al., 2008; Loane and Byrnes, 2010; Benarroch, 2013; Chhor et al., 2013; Franco and Fernandez-Suarez, 2015; Nakagawa and Chiba, 2015
		Markers: CD86, MHC-II
		Chemokines: CCL2
		Metabolic enzyme/redox molecules: iNOS, COX-2, reactive oxygen species and reactive nitrogen species prostaglandin E2
M2a (alternative activation): tissue repair and phagocytosis	IL-4, IL-13	Cytokines: IL-10	Mahad and Ransohoff, 2003; Loane and Byrnes, 2010, Benarroch, 2013; Chhor et al., 2013; Franco and Fernandez-Suarez, 2015; Nakagawa and Chiba, 2015
		Markers: CD206, SR-A1, SR-B1, Arg1, Ym1, Fizz1
		Others: extracellular matrix proteins, PPAR
M2b (alternative activation): recruitment of regulatory T cells	Fcγ receptors, TLRs and immune complexes (IgG)	Cytokines: IL-1β, IL-6, IL-10, TNF-α
		Markers: CD86, MHC-II
		Others: SOCS3, COX-2, Sphk
M2c (alternative activation): anti-inflammatory and healing	IL-10, TGF-β and glucocorticoids	Cytokines: IL-10, TGF-β
		Markers: CD163

Arg1, arginase 1; CCL, chemokine (C-C motif) ligand; CD, cluster of differentiation; COX-2, cyclooxygenase-2; Fizz1, found in inflammatory zone; IFN-γ, interferon-γ; IL, interleukin; iNOS, inducible nitric oxide synthase; MHC-II, major histocompatibility complex II; SOCS3, suppressor of cytokine signaling-3; Sphk, sphingosine kinase; SR-A1, scavenger receptor class A1; SR-B1, scavenger receptor class B1; TGF, transforming growth factor; TNF-α, tumor necrosis factor-α; Ym1, chitinase-like protein.