ABSTRACT
Transforming growth factor-B1 (TGF-B1) is well known to be one of the most potent Immunosuppressive cytokines. To determine whether TGF-B1 secreted in the latent form can be immunoregulatory, TGF-B1 cDNA driven by the human -actin promotor was transfected into a murine thymoma cell line, EL4 cells. The transfectants (ELJ4) secreted a latent torm of TGF-B1 at a concentration of 5 ng/ml under the influence of TPA. Transfected TGF-b1 transcripts was readily detected by RT-PCR in ELJ4 cells regardless of the presence of TPA, but not in EL4 cells. In addition, we found the degree of Thy-B1 expression, IL-2 secretion and the proliferation rate are not altered by the transfection. Finally, EL4 and ELJ4 cells were injected into C57BU6 mice (syngenic strain), subcutaneously. Tumor cell masses derived from both cell populations survived longer than 1 wk, and the size of tumor derived from ELJ4 was three times larger (2.5 cm of diameter) than that from EL4. Virtually, there was no histopathological difference between two tumors. Taken together, the results from the present study indicates that EL4 thymomas transfected with TGF-1 secretes a latent form of TGF-B1 which may suppress host immune defence system.