Stimulation of thymocytes in vitro by serum of 2-acetylaminofluorene (AAF)-treated rats

The serum of rats obtained at various time intervals after administration of AAF was tested for its action on the 3H-thymidine incorporation into the DNA of thymocytes in vitro. In comparison with untreated or solvent-treated controls, the sera of animals in the early phase after the AAF-treatment stimulate the incorporation of the nucleotide into the thymocytes of rats, mice and hamsters. This reaction shows an unequivocal dose-response relationship. The serum activity is dialysable and relatively thermostable. Spleen lymphocytes and peritoneal cells of rats are insensitve to the AAF-serum. A possible relationship between growth-stimulating serum activities in liver regeneration and in early carcinogen action is discussed.