Table 1.

Natural Killer and Natural Killer T Cells

	Age-Associated Defects	Refs.
NK Cells	↓ bone marrow production	[98]
	↑ CD56dim cell population	[95, 99–102]
	↓ cytotoxicity	[94, 100, 103–106]
	↓ or ↔perforin	[107–108]
	↓ IFN-γ, TNF-α, IL-2 and IL-12 production	[95]
	↓ chemokine production in response to IL-2 and IL-12	[109]
	Improved cytotoxicity and IFN-γ production after zinc or hormone treatment	[111–113]
NKT Cells	↓ iNKTpopulation in human peripheral blood and liver	[114–115]
	↑ iNKTpopulation in murinespleen and lymph node	[117]
	↑ NKT-like cell population in human peripheral blood	[114, 116–119]
	↓ iNKTcell proliferation after α-Gal Cerstimulation	[116]
	↓ IFN-γafter IL-12 stimulation	[113]
	↑ IL-4, IL-10 and IL-17	[31, 120]
	Role in age-associated defective T cell proliferation	[117]

Arrows (↑, ↓ or ↔) denote increased, decreased or unaltered levels in the aged compared to the young.

Abbreviations: NK, natural killer cell; NKT, natural killer T cell; iNKT, invariant natural killer T cell; NKT-like, natural killer like T cells; TNF-α, tumor necrosis factor-alpha; IL, interleukin; IFN-γ, interferon-gamma; α-GalCer, a CD1d ligand.