Studies on thymus products. 3. Epithelial origin of the serum thymic factor.

Serum thymic factor (TF) has been tested by its action on spleen rosette-forming cells from adult thymectomized mice. It has been confirmed in a blind study using coded serum samples that TF disappeared early after adult thymectomy and reappeared after grafting a thymus, either as a free graft or enclosed in cell impermeable diffusion chambers. Similar reconstitution was also obtained by grafting a non-lymphoid epithelial thymoma or pure epithelial thymus, obtained by incubation of a thymus within a diffusion chamber in an intermediate host. Conversely, TF levels were not restored in thymectomized animals treated with dispersed spleen cells or with dispersed thymic lymphocytes.