Page 575 - Veterinary Immunology, 10th Edition

high levels of IL-2Rβ, a receptor that binds both IL-2 and IL-15.
VetBooks.ir They express increased amounts of adhesion molecules, so they can

bind more efficiently to antigen-presenting cells. They produce
more IL-4 and IFN-γ and respond more strongly to stimulation of

their TCR. They continue to divide very slowly in the absence of
antigen. This division requires cell-bound IL-15 and is inhibited by
soluble IL-2. IL-15 is a unique cytokine that persists for very long
periods attached to its receptor on T cells. It thus acts as a persistent

stimulus for the memory cell microenvironment and stimulates
nearby cells by cell-cell contact. The balance between IL-15 and IL-2
regulates the persistence of memory T cells. In the absence of IL-15,
+
memory cells undergo apoptosis. In humans the CD8 memory cell
half-life is 8 to 15 years.
Over an animal's lifetime, immunological memories accumulate.
Older animals have more memory cells than young animals and are
thus much better prepared to respond to antigens than younger

animals. Repeated vaccination generates new memory cells.
However, the size of the memory cell compartment expands to
accommodate them. Previously generated memory cells are not
removed to make space for the newcomers.

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