Purification and biological activity of thymosin, a hormone of the thymus gland

The purification and chemical properties of thymosin, obtained from bovine thymus tissue, are described. The biological activity of the thymic hormone has been assessed by a newly developed rosette assay, which permits measurement of thymus-dependent lymphoid cells. Thymosin activity is associated with a physico-chemically homogeneous protein of molecular weight 12,600. The hormonal activity is evident in in vitro incubation assay, after injection into adult thymectomized mice, and in prolonging survival of neonatally thymectomized mice and the reconstitution of their response to a skin allograft.