Table 1.

Overview of innate immune memory mechanisms described for various types of innate immune cells.

Innate immune cell type	Primary challenge	Type of memory	Pathway involved	Mechanism	References
Monocytes - macrophages	LPS	tolerance / trained immunity	TLR4/MAPK-dependent ATF7-dependent	Epigenetic changes: latent enhancers (H3K4me1), other modifications (H3K4me3, H2K27me, H3K9me2)	Foster & Medzhitov (50) Ostuni et al (74) Yoshida et al (79)
Monocytes - macrophages	β-glucan, Candida infection	trained immunity	Dectin-1/Raf1/Akt-dependent STAT1-dependent	Epigenetic changes (H3K4me1, H3K4me3, H2K27Ac, H3K9me2), metabolic rewiring	Quintin et al (26) Saeed et al (51) Cheng et al (78) Yoshida et al (79)
NK-cells	Hapten-induced Influenza A Vaccinia virus HIV-1 infection	antigen-specific		CXCR6-dependent NKG2D-dependent	O’Leary et al (30) Paust et al. (57) Gillard et al (58) Reeves et al (63)
NK-cells	CMV infection	antigen-dependent	Atg3-mediated mitophagy	BNIP3-/BNIP3L-dependent	Sun et al (31) O’Sullivan et al (59)
NK-cells	CMV infection	trained immunity	Stable downregulation of adaptors and transcription factors (e.g. Syk, PLZF)	Epigenetic modification of gene promotors DNA methylation	Lee et al (64) Schlums et al (34)