Abstract
This presentation offers a brief review of the bone marrow‐thymus axis in senescence, a putatitive model for thymocyte differentiation, and recent results of our work on the status of pre‐thymic stem cells in aged mice. The data presented here provide further evidence for a thymus endocrine influence on the bone marrow stem cells, specifically lymphocyte precursors. It has been pstulated that the thymic hormones may act on lymphocyte precursors in the bone marrow and that the loss of thymic factors during senescence may be a contributing factor to the decreased cellular immune function. This study used Haar's in vitro model to investigate the bone marrow‐thymus axis in aged mice. Erythroid‐depleted bone‐marrow cells from 3‐month‐ and 24‐month‐old CBA (Thy 1.2) mice were placed in the upper half of a blind‐well chamber with thymus supernatant in the lower half. Experimental cells were treated with thymus supernatant for 1 hr prior to migration. This study confirmed that pre‐thymic stem cells in aged bone marrow are deficient in their ability to migrate to the thymus supernatant. It also revealed that treatment of the old bone marrow with thymus supernatant, made from neonatal thymus cultures, could dramatically improve the thymus migrating ability of the aged bone‐marrow stem cells.