Nuclear receptors for 1,25(OH)2 vitamin D3 in thymus reticular cells studied by autoradiography

After injection of 3H 1,25(OH)2 vitamin D3 to rats fed a vitamin D-deficient diet, nuclear concentration and retention of radioactivity exists in reticular cells of the thymus medulla and cortex, as well as outer cells of developing Hassal's corpuscles. Lymphocytes do not show nuclear concentration of radioactivity. Nuclear concentration in reticular cells is prevented by prior injection of excess 1,25(OH)2 vitamin D3. The results indicate that reticular-endothelial cells contain nuclear receptors for 1,25(OH)2 vitamin D3 and suggest that effects of 1,25(OH)2 vitamin D3 on immune response and lymphocyte differentiation are indirect and mediated through genomic modulation of reticular cell functions such as messenger secretion.