Gamma Irradiation-reduced IFN-γ Expression, STAT1 Signals, and Cell-mediated Immunity

Received 3 May 2002, Accepted 10 September 2002The signal transducer and activator of transcription(STAT)1 is a cytoplasmic-transcription factor that isphosphorylated by Janus kinases (Jak) in response tointerferon γ (IFN-γ). The phosphorylated STAT1translocates to the nucleus, where it turns on specific sets ofIFN-γ-inducible genes, such as the interferon regulatoryfactor (IRF)-1. We show here that gamma irradiationreduces the IFN-γ mRNA expression. The inhibition of theSTAT1 phosphorylation and the IRF-1 expression bygamma irradiation was also observed. In contrast, themRNA levels of IL-5 and transcription factor GATA-3were slightly induced by gamma irradiation whencompared to the non-irradiated sample. Furthermore, wedetected the inhibition of cell-mediated immunity bygamma irradiation in the allogenic-mixed lymphocytes’reaction (MLR). These results postulate that gammairradiation induces the polarized-Th2 response andinterferes with STAT1 signals, thereby causing theimmunosuppression of the Th1 response.Keywords: Gamma-irradiation, IFN-γ, STAT 1