Effect of cortisone in delineating thymus cell subsets in advanced age.

The mixed lymphocyte reactivity of thymus cells from normal and cortisone-treated, young and old C57BL/6J mice was evaluated. The results indicated that while in the young mice cortisone treatment caused a 12-fold increase in the reactivity of thymus cells, it had no effect on the response of thymus cells from old mice. The significance of the disappearance of cortisone-resistant mature thymus cells in old mice is discussed regarding the general decline in immunocompetence and the increase of autoimmune manifestations in old age.