Decreased levels of both Stat1 and Stat3 in T lymphocytes from mice bearing mammary tumors

Background: Lymphocytes from tumor-bearing animals have been shown to lack antitumor function. The objective of this study was to investigate the status of the signal transducers, Stat1 and Stat3, in T lymphocytes of animals bearing D1-DMBA-3 mammary tumors and to elucidate if any alterations in these signal transducers can be explained by the presence of tumor-derived factors and correlated with the lack of antitumor function in these cells. Materials and Methods: T Lymphocytes from spleens of normal and tumor-bearing mice were purified and assayed for the presence of Stat1 and Stat3 by Western blot analysis. Results: It was found that levels of both Stat1 and Stat3 were reduced in T lymphocytes of tumor-bearers not only in their active, phosphorylated form but in total protein levels. Conclusion: These findings indicate that during mammary tumor progression, alteration of various transcription factors may contribute to the down-regulation of immune function.