On a causal mechanism of chronic thymic involution in man.

The age-associated chronic thymus involution is interpreted to occur due to cytolytic depletion of thymic stromal tissue whose cells present altered self-peptides. Using simplified assumptions and based on morphometric data on thymic involution in man, the chance for a single protein to be altered is estimated to be in the range of 2-4 x 10(-6) per year. The corresponding mutation rate is compatible with that derived from both evolutionary and direct studies, thus supporting the proposed model.