Influence of a thymic hormone on cultured epithelial cells of the thymus

Addition of cortisone to primary cultures of mouse thymic stromal cells resulted in increased growth of medullary epithelial cells while cortical epithelial subpopulations were inhibited or destroyed. These adverse effects on cortical cells were ameliorated by the thymic hormone THF. Because thymocytes are also sensitive to both cortisone and THF we sought to eliminate them from the cultures by deoxyguanosine treatment. This treatment differentiated even more strongly between growth of cortical epithelial cells which were inhibited and medullary epithelium that was very strongly stimulated. These effects are discussed in relation to involution of the thymus with aging.