Studies on Thymic Involution: Growth Potential and DNA Repair of the Stromal Cells

Abstract

Involution of the thymus is reflected in primary cultures of mouse thymic stromal cells which we have described at the previous Germinal Center Conference (1,2). When these cultures are grown from preinvolution mice, the majority of the cells arrange themselves into networks with long cytoplasmic interconnections between the cells. In cultures from older mice, cellularity is considerably reduced especially of the cells with processes. Correspondingly, in the post involution cultures an increased proportion of cells grow as confluent carpets of paving stones (1,2). The present study was carried out a) to Identify which cells each of these are and b) to use these cultures to test the hypothesis that involution, as an accelerated form of aging may result from failure to repair damaged DNA. For cell identification we used fluorescent antibody staining, and for studies of DNA repair, autoradiography of unscheduled DNA synthesis after irradiation with UV. Cortical epithelial cells turned out to be those with decreased growth in cultures from aging mice, but the cells which remain continue to repair UV-induced damage to their DNA.