MODULE SUPPLEMENT: IMMUNE SYSTEM
What Happens to Specific Immunity With Age?

Data are somewhat conflicting on whether the total number of T & B cells change (at least in peripheral blood), but it is felt that these cells may not be as functionally competent in older persons as in younger persons. What is currently supported most strongly is that cellular immunity is affected to a greater extent than humoral immunity. Yet, because they are so inter-related, the changes in cellular immunity impact the functioning of the humoral system.

One reason given for the change in cellular immunity is thymic involution--that is, it keeps getting smaller and smaller after birth so that it almost disappears by age 60. Because thyosin is generally considered important to the maturation of T-cells, a decrease in its levels could be important. However, it is still controversial regarding whether this is the most important factor in the decline in cellular immunity and more data are certainly needed.

General changes in humoral and cellular immunity are presented below.

Age Changes in Select Components of Specific Immunity^{1, 2}

Immune System	Component of Immune System	Age Related Change
Humoral Immunity B-Cells Plasma Cells Antibodies (IgG, IgM, IgA, IgE)
B-Cells	Bone Marrow	Less reserve
	Circulating #s and %	No or minimal change but altered repertoire which affects type/amount of antibody produced
	Production of antibodies	Decreased
	Auto-antibodies	Increased
	Anti-idiotype antibodies	Increased suppression of Antibody production
	Memory phenotype	? Decreased
Cellular Immunity T-Cells T-Helper (CD4+), Cytotoxic (CD8+)
T-Cells	Thymus	Involutes starting after puberty
	Circulating #s and %	Some decrease or no change but altered functional capacity
	Memory phenotype	Increases
	Delayed type hypersensitivity Reaction (DTH)	Decreased; delayed
	Cytotoxicity (lytic capacity of CD8(+) cells)	Diminished
	Proliferative response	Decreased
	Response to IL-1 (from APCs)	Diminished
	Cytokines: Variable changes (data are still limited and often contradictory but data suggest there may be a subtle shift in T-cell repertoire to more Th2 cytokine dominance with age)
	IL-2 (from Th1 T-cells; proinflammatory)	? Decreased & have less feedback T-cell proliferatory capacity
	IL-4 & IL-6 (from Th2 T-cells & other cells; proimmune/B-cell stimulation effect)	? Increased
	IL-10 (from Th2 T-cells; proimmune)	? Decreased or no change
	IFN- (from Th1 T-cells, CTL, & NK cells; proinflammatory)	Increased, decreased or no change
1 Components included represent a number of key aspects of the immune system but are far from inclusive; as this is an expanding area, understanding about components and how they change are continuing to evolve. 2 Adapted from: Boon, et al, 2002; Breitbart, et al, 2002; Groer, 2001; Murasko & Bernstein, 1999; Sandmand, et al., 2002; Weksler, 2000.