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.