One of the major fundamental causes for the aging of the immune system is the structural
and functional involution of the thymus, and the associated decline in de novo naïve T-
lymphocyte output. This loss of naïve T-cell production weakens the ability of the adaptive
immune system to respond to new antigenic stimuli and eventually leads to a peripheral T-
cell bias to the memory phenotype. While the precise mechanisms responsible for age-
associated thymic involution remain unknown, a variety of theories have been forwarded …