. 2015 Jan 14;8:461. doi: 10.3389/fncel.2014.00461

Table 1.

Different activation states of neutrophils, circulating monocytes and tissue macrophages in mice.

	Neutrophils	Circulating monocytes		Monocyte-derived macrophages		Resident microglia
Subsets	N1/N2	“Inflammatory” monocytes	“Patrolling” monocytes	M1	M2 (M2a,b,c)	Surveying microglia	Microglia-derived macrophages
Marker genes	iNOS			iNOS	Arg1, CD206, Chil3 (Ym1)	DAP12
Receptor expression	CD45^high CD11b⁺ Ly6G⁺	CD45^high Ly6C^high CD115⁺ CCR2⁺ CX3CR1^int Ly6G-	CD45^high Ly6C^low CD115⁺ CCR2⁻ CX3CR1⁺ Ly6G-	CD45^high CD115⁺ CD11b⁺ F4/80⁺ CD68 (ED-1) CCR2⁺	CD45^high CD115⁺ CD11b⁺ F4/80⁺ CD68 (ED-1) CX3CR1⁺	CD45^int CD11b⁺ CX3CR1 Ibal⁺ IB4	CD45^high CD11b⁺ CD115⁺ F4/80⁺ CD68 (ED-1) CX3CR1⁺ Iba1⁺ IB4
Activated by [cells]	Platelets, Endothelial cells	Neutrophils, Dying neurons		Th1, NK	Th2	Neurons	Dying neurons
Activated by [molecules]	IL-1α	CCL2		LPS, IFNγ, TNF	IL- 4 and IL-13 (M2a), IL-10, Glucocorticoid, TGFβ (M2c), CCL2 (MCP1)		DAMPs, CX3CL1
Function	Neurotoxic (N1), Neuroprotection (N2)	Recruited at sites of inflammation, Precursors of peripheral mononuclear phagocytes	Endothelium integrity	Cytotoxic effect	Phagocytic capacity, Promote neurite outgrowth	Synaptic pruning and remodeling during development, Homeostatic functions	Phagocytosis, Neurotoxicity
Cell products	ROS, NO, RNS, MMP-9, NE	TNF, ROS, NO, IL-1β, Little IL-10	IL-10, VEGF	IL-12, IL-23, TNF, IL-1β, IL-6, ROS	TGFβ, Arg1 and scavenger receptors (M2a), IL-10 (M2c).	TGFβ	IL-1β, TNF, IL-6, Chemokines, IFNγ

The dichotomy in the function of each cell type shown here is an oversimplified view of their activation state. They rather undergo multiple activation phenotypes at a given time making the interpretation of their neuroprotective or/and deleterious effect in cerebral ischemia complex. Whether N1/N2 and M1/M2 phenotypes may apply to neutrophils and microglia, respectively, would need further investigation.

Abbreviations: Arginase 1 (Arg1), Chemokine (C-C motif) ligand 2 (CCL2), C-C chemokine receptor type 2 (CCR2), Chitinase-like 3 (Chil3 or Ym1), CX3C chemokine receptor 1 (CX3CR1), Damage-associated molecular pattern molecules (DAMPs), DNAX activation protein of 12 kDa (DAP12), inducible nitric oxide synthase (iNOS), Interferon gamma (IFNγ), Interleukin-1,4,6,10,12,23 (IL-1, IL-4, IL-6, IL-10, IL-12, IL-23), Ionized calcium binding adaptor molecule 1 (Iba1), Isolectin B4 (IB4), Lipopolysaccharide (LPS), Lymphocyte antigen 6G (Ly6G), Matrix metallopeptidase 9 (MMP-9), monocyte chemotactic protein 1 (MCP1), Natural Killer (NK), Neutrophil elastase (NE), Nitric oxide (NO), Reactive nitrogen species (RNS), Reactive oxygen species (ROS), Transforming growth factor beta (TGF-β), Tumor necrosis factor (TNF), Type 1 T helper (Th1), Type 2 T helper (Th2), Vascular Endothelial Growth Factor (VEGF).