TRANSFORMING GROWTH-FACTOR-BETA (TGF-BETA) IS PRODUCED BY AND INFLUENCES THE PROLIFERATIVE RESPONSE OF XENOPUS-LAEVIS LYMPHOCYTES

Both TGFbeta2 and 5 have been described in the South African clawed fr og Xenopus laevis and have been cloned from the tadpole-derived fibrob last cell line, XTC. Because TGFbeta has such a profound inhibitory ef fect on the mammalian immune system, this study was performed to deter mine whether TGFbeta: (a) has any in vitro effects on the growth of Xe nopus lymphoblasts, and (b) is produced by mitogen-activated Xenopus l ymphocytes. Following stimulation with mitogen or alloantigen, T lymph ocytes from Xenopus secrete a T-cell growth factor (TCGF) that is func tionally homologous to mammalian interleukin-2 (IL-2). Both recombinan t human TGFbeta1 and Xenopus TGFbeta5 inhibit TCGF-induced proliferati on of Xenopus splenic blasts and this inhibition can be reversed with anti-pan TGFbeta antiserum. The Xenopus mitogen-induced saturated ammo nium sulfate precipitated TCGF-containing supernatant (SAS TCGF SN) al so contains latent TGFbeta as assayed on mink lung fibroblasts and Xen opus splenic blasts, and experiments utilizing anti-TGFbeta antiserum showed that only TGFbeta5 is present in this supernatant.