Table 1.

Effects of aging on phagocytes and antigen-presenting cells

Functional activity	Cell type
	Neutrophils	Monocytes/Macrophages	Dendritic cells
Reduced	Signal transduction (Ca2+ influx, phosphorylation of ERK, p38, Akt, PLC-γ) Receptor recruitment to lipid rafts (TLR4, TREM-1) Chemotaxis (fMLP, GM-CSF) CD16 expression Phagocytosis Microbicidal activity Reactive oxygen species (LPS, fMLP, GM-CSF, opsonized bacteria)	Signal transduction (e.g., total levels and/or activation of STAT-1α, p38 & JNK MAPKs, MyD88, NF-κB) Cytokine production (IL-12, IL-6, TNF, MIP-1α, MIP-1β, MIP-2) Chemotaxis Phagocytosis Reactive oxygen species Reactive nitrogen species Intracellular killing Expression of costimulatory molecules (CD80 and CD86), MHC Class II, Expression of CD14, TLR1, and TLR3*	Antigen presentation Chemotaxis Endocytosis Production of IFN type I and III (pDC) IL-12 PI3K activity and Akt phosphorylation Expression of TLR-1,-3,-5, -7, and -8
Maintained	Total number of circulating neutrophils Basal levels of receptor expression (GM-CSFR, TLR2, TLR4, CD14, CD11b) Expression of adhesion molecules and adhesion to endothelial cells Apoptosis (spontaneous)	Expression of IFN-γ receptor and TLR2 Expression of TLR negative regulators (e.g., SOCS-1, IRAK-M, A20, PPAR-γ)**	Expression of TLR2 (mDC) and TLR9 (pDC)
Increased	Apoptosis (under priming conditions; e.g., impaired anti-apoptotic signals after exposure to GM-CSF) Activity of cytokine-signaling inhibitory molecules (SHP-1, SOCS)	PGE2 production TLR5 expression	TNF, IL-6, IL-23 Basal expression of CD80, CD83, CD86*** Basal NF-κB activity

^*Basal levels only

^**In mice, not yet reported for humans

^***DC isolated directly from peripheral blood