Table 1 Differences of microglia in the M0/M1/M2 phenotype

M0

(Homeostatic microglia)

CD11b, P2ry12, Cx3cr1, Tmem119, Sall1, Tgfbr1, Fcrls, Hexb, Mertk, Gpr34, Olfml3, Siglech [32]

Branched, have small somata and multiple fine processes [33])

–

Have housekeeping functions and typically express genes involved in synaptic pruning, remodeling, and phagocytosis [34]

Soluble factors, including TNF-α and BDNF

–

CCL2

–

M1

(pro-inflammatory microglia)

CD86, CD16/32, MHC-11, CD40, IFN-γ

CD11b, CCL2

iNOS, Cox-2, IL‐1β, IL‐6, TNF‐α [35, 36]

Larger somata and still branched compared with M0

LPS and IFN-γ [37]

Pro-inflammatory and pro-killing functions

TNF-α, IL-6, IL-12, IL-1β, IL-18, CXCL10, NO, ROS, iNOS, and proteolytic enzymes (MMP9, MMP3) [38]

saturated fatty acids increase the pro-inflammatory microglial phenotype

CCL2、CCL3、CCL4、CCL5、CXCL1、CXCL8、CXCL9、CXCL10

Preferentially use glycolysis [39]

M1½

co-expressing M1 makers and M2 markers [40]

Bipolar-shaped microglia [41]

--

improve cognition [42]

--

--

--

--

M2 (anti-inflammatory microglia) [43, 44]

M2a

CD206, SRs Arg1, Fizz-1

, YM1, CCL22

Amoeboid morphology [45]

IL-4 or IL-13 [46]

Involved in phagocytosis, tissue restoration, and tissue regeneration

IL-10, IGF-1, and trophic polyamines

Unsaturated fatty acids influence the anti-inflammatory microglial phenotype [46]

CCL22、CXCL8、CXCL12、CX3CL1

Oxidative phosphorylation and fatty acid oxidation [39]

M2b

CD86, MHC II

TNF-α, IL-6, IL-10, COX2

TLRs, FCγ and IL-1 receptors [47]

Involved in the recruitment of regulatory T cells

TNF-α, IL-1β, IL-10, and IL-6

M2c

SLAM, CD206

TGFβ, IL-10, CD163 [48]

IL-10, TGF-β, and glucocorticoid hormones, sphingosine kinase, and CD163. A membrane-bound receptor for haptoglobin/hemoglobin complexes [49]

Involved in anti-inflammatory and therapeutic functions

TGF-β, IL-10, sphingosine lipid kinase