ENHANCEMENT OF DNA SYNTHETIC ACTIVITY OF THYMIC LYMPHOCYTES BY THE CULTURE SUPERNATANT OF THYMUS EPITHELIAL-CELLS STIMULATED BY GROWTH-HORMONE

The authors examined the effect of the culture supernatant of growth h ormone (GH)-stimulated thymus epithelial cells (TECs) on DNA synthetic activity of thymic lymphocytes (TLs) and then examined TL proliferati on-inducing factors released from the TECs. TEC line, IT-45R1 derived from Wistar strain rat, was used. It was revealed that the supernatant from TECs treated with GH enhanced significantly DNA synthetic activi ty of TLs and that the activity of the least dense subset of TLs, cont aining undifferentiated lymphoid cells and the most immature TLs, was significantly increased by the supernatant as compared with other subs ets. Anti-insulin like growth factor-I (IGF-I) monoclonal antibody (MA b) binding specifically to C region of IGF-I molecule was added to the culture supernatant from the GH-treated TECs, and then the supernatan t was treated with ultrafiltration (MW cutting off; more than 50 kDa). When TLs were incubated with the ultrafiltered supernatant, the enhan cement of TL proliferation induced by the supernatant of GH-treated TE Cs was significantly suppressed. However, the suppression did not desc end to the level of TL-proliferative response observed in the supernat ant of GH non-stimulated TECs. These results suggested that IGF-I rele ased into the supernatant from GH-stimulated TECs enhances markedly th e DNA synthetic activity of TLs and that the TL-proliferation-inducing , factors (PIFs) other than IGF-I possibly exist in the supernatant of GH-stimulated TECs.