A pituitary-thymus connection during aging.

Abstract

Thymic involution is a normal consequence of aging. It has often been speculated that if this age-associated atrophy of the thymus gland could be prevented, the natural decline that occurs in a number of T-cell-mediated immune responses could be reversed. It has recently become clear that thymic involution can indeed be reversed by altering the hormonal environment of aged animals. These data support the concept of an active and functional pituitary-thymus axis. Since thymic reconstitution can result in restoration of some T-cell responses, it would appear that intrinsic defects which exist in T cells of aged animals can be at least partially reversed. This suggests that the aged environment plays a greater role in the decline of T-cell functions than has been previously recognized. Furthermore, phorbol esters and calcium ionophores can restore suppressed proliferative responses of T cells from aged rodents, so we speculate that intrinsic defects in T cells of aged subjects lie between the recognition system for antigen/lectin and intracellular transmission of this signal.