Immune control of mammalian aging: a T-cell model.

A competent immune response appears to play an important role in retarding aging. On the other hand, the aged immune system is assumed to accelerate the general aging process. In order to approach the underlying mechanism of this paradoxical immune response, the process of clonal deletion in the thymus is addressed under the aspect of aging. It is assumed that T-cell deletion in the thymus brings about a control of cell differentiation in the organism. For proper functioning, this control is suggested to be directed, in the sense of a feedback mechanism, primarily to thymic stromal cells involved in the process of clonal deletion. At the expense of a thymus atrophy, the control system can retard aging up into the reproductive period of life. With the progress of thymic involution, however, the control is predetermined to undergo a breakdown and, in consequence, through loss of self-tolerance it speeds up the whole aging process.