The Yin and Yang of Innate Immunity in Stroke

Table 1

Activation and function of innate immune cells.

	Activation	Function
Microglia	Within minutes	M1 phenotype promotes inflammation by secreting cytokines like IL-1𝛽, TNF-𝛼 and presenting antigens to T cell; M2 phenotype quells inflammation by secreting cytokines like IL-10, TGF-𝛽, and tissue repair [38, 46].
Macrophages	2 days	View point 1: M1 phenotype promotes inflammation and M2 phenotype quells inflammation (similar with microglia) [29, 49].; View point 2: macrophages originating from peripheral monocytes are cytotoxic, while those from microglia are protective [50].
Neutrophils	30 minutes	N1 phenotype exacerbates the damage, whereas N2 is protective [51].
Dendritic cells	1 hour	Generally deleterious, suggested by researches to date [42–45].