Effect of age on T cell differentiation.

A brief overview of the area of T cell aging is presented by first discussing the age-related changes in T cell activities, and then by focusing attention on the possible mechanisms that may be responsible for the decline. Present evidence indicates that thymic involution precedes and therefore may be responsible for the age-dependent decline in the ability of the immune system to generate functional T cells. At this time, it appears that the primary effect of thymic involution is on a T cell differentiation pathway affecting the more mature T cells first with time, and then the less mature T cells. Thus, the thymus may be the aging clock for the immune system. Further studies should be centered around processes regulating growth and atrophy of the thymus.