The Thymus in Relation to Ageing

Abstract

Increasing vulnerability to infection is one aspect of ageing which may well be responsible for the terminal breakdown in a majority of natural deaths. Enough direct evidence is available that various measurable functions of the immune system show progressive weakening and inefficiency with age. Presumably this must in some way be related to accumulating somatic mutational changes in lymphocytes and their derivates, perhaps particularly in T-immunocytes. At one stage I was inclined to look on the striking atrophy and eventual almost complete disappearance of the thymus as an index of the process by which T-cell immune function faded out. That may well be partially true, but for the present it is probably better to concentrate attention on the lymphocytes as a model system of clonally proliferating cells and try to understand the manifestations of cumulative somatic mutational changes in such a system.