Immunological alterations with aging-laying a stress on recent progress in Japan

Age-related decline of immune functions mainly occurs in the T-cell-dependent immune system and this is precede by physiological thymic involution starting after puberty. Age-related alterations of T cells are seen in their number, subsets and qualities. In relation to the qualitative change of aging T cells, disturbance of intracellular signal transduction is responsible for the impairment of proliferation and cytokine production upon antigenic stimulation. Thymus, but not bone marrow, is responsible for aging of the T-cell-dependent immune system. The thymic capacity to induce T cells starts to decline early in life. Older thymus induces different subsets of T cells which are functionally less active T cells than those of young thymus. In association with a decline in immune functions to exogenous antigens, autoimmune phenomena increase with advance of age, which are observed as production of autoantibodies and auto-reactive T cells. The possible site for controlling thymic function is discussed.