New thymocyte growth factor from thymic epithelial cell line.

Three polypeptide fractions were separated from the culture supernatant of a thymic epithelial cell line, TAD3, by high-pressure liquid chromatography (HPLC) equipped with gel-filtration column (GFC). One (estimated molecular weight: 10 kD) of the polypeptide fractions possessed the capacity to induce thymocyte proliferation. The sensitive cells for the growth factor in the fraction seem to be immature thymocytes which exist in the outer-cortical or the subcapsular area of thymic lobule. Furthermore, the mechanism to proliferate the thymocytes appears to differ from that of other cytokines. Thus, the fraction might possibly contain a previously unidentified thymocyte growth factor.