[Mechanism of thymic involution (analysis of intrinsic and extrinsic aspects)]

The mechanisms of thymic involution with age are analyzed in terms of both intrinsic and extrinsic aspects. The intrinsic factors include: decrease in the number of thymocyte-precursors (pro-T cells) in the bone marrow, in emigration of pro-T cells into the thymus, in proliferation of thymic lymphocytes and decrease in extrathymic factors promoting proliferation of thymic lymphocytes. The extrinsic factors capable to exert modulating effects on the thymic function are humoral factors of the hypothalamic-pituitary origin. It seems much easier to manipulate the extrinsic factors by controlling neuro-endocrine stimulation, and to restore the thymic involution. This is quite encouraging, because it permits restoring the impaired immune functions of the aged people.