Table 1 Basal regional features of microglia in the healthy rodent and human brains

Density

High-average [30, 31, 33, 34]; Lower in human cerebral GM than WM [39]

High [30, 31]; Lower in CA3 than CA1 [21]

High in CVOs [49]

Average [30, 31] or high [32]; Higher in SNr than VTA [65]

Low [30, 31, 33, 34]; Higher in cerebellar nuclei and granular layers [30, 40]; Less CD68+ & MHCII+ in human cerebellum [38, 39]

Low [136, 137]

Morphology (ramification)

High [33, 34]

High [33, 34]

Amoeboid [30, 49, 52]

Higher in SNr than VTA [65]

Low [33, 34]

Average; Cell smaller in dorsal horn [138]

Molecular expression CX3CR1

High (Fig. 1)

High (Fig. 1)

Unknown

Low-median (Fig. 1)

Low (Fig. 1)

Unknown

TREM-2

High [58]

High [58];

Low [58]

Low (Fig. 1)

Low (Fig. 1)

Unknown

Phagocytic or immune activating genes (Trem 3 etc.)

Low [28, 65, 68]

Low-median [28, 68]

High [49, 52, 67]

High in VTA [65]

High [28, 68]

Unknown

Immune inhibitory genes (Sirpa etc.), Cd206, P2ry12

High [68]; Higher in human GM [67];

Median [68]

High IL-4 [49, 52]; Low P2ry12 [58]

Low P2ry12 (Fig. 1)

Low P2ry12 (Fig. 1)

Low Sirpa [136]

Others (NF-κB, CD11b, MHCII, Tim3, etc.)

Higher in human WM [66, 75, 76]

Median [59, 62, 63, 136]

High [49]

Median [59, 62, 63, 136]

Median [59, 62, 63, 136]

High [59, 62, 63, 136]

Cellular functions: Proliferation/replenish after ablation

Both fast [42]

Both fast [46, 48]

Both fast [44, 45, 104]

Replenish fast [42]

Fast [48] /replenish slower [42]

Replenish fast [42]

Protrusion toward ATP/Phagocytosis/pruning

Fast protrusion [52]/Low lysosome content in NAc [65]

High surveillance [74, 82]

Slow protrusion [52]

High lysosome content in SNr [65]/High pruning in thalamus [117]

Less surveillance [34]/High clearance [77]

High pruning [139]

Ontogenesis

Hoxb8^± [101]; Sensitive to IL-34 [111, 112] but not CSF1 [113]

Sensitive to IL-34 [111, 112];

Unknown

Hoxb8⁻, [101]; Insensitive to IL-34 [111, 112]

Hoxb8⁻, [101]; Sensitive to CSF1 [113] but not IL-34 [111, 112]

 Unknown