Table 1.

Physiologic changes in the immune system that occur with aging (1–4).

	Inappropriate elevation with age	Inappropriate decrease with age
Innate immune system	NK cells: CD56dim NK cell number	Anatomical and biochemical barriers: Regeneration, sweat production, and barrier function of skin and mucus
		Hematopoietic tissue: total number of hematopoietic stem cells (HSCs) in the bone marrow, total bone marrow hematopoietic tissue, the proliferative capacity of HSCs
		Macrophages: Bone marrow precursors, phagocytic capacity, and oxidative killing activity of macrophages
		Neutrophils: chemotactic responses, migration capacity, phagocytic capacity, and superoxide generation
		NK cells: CD56bright NK cell number
Adaptive immune system
T cells	Number of CD8 T cells	Involution of the thymus gland
		Number of thymic precursors
		Number of naïve T cells
		T cell repertoire
		Functional activity of Regulatory T cells (Treg)
		Number of CD4 T cells
		Number of CD28 T cells
B cells	Autoreactive serum antibodies	B cell precursors in the bone marrow
		Number of B cells
		Plasma cell differentiation
		Specific antibody production
		B cells' response to antigen exposure
		The diversity of the B cell repertoire
		Opsonizing capacity of immunglobulins