Wirth, Delphine, Fabrice Bureau, Dorothée Melotte, Elisabeth Christians, and Pascal Gustin. Evidence for a role of heat shock factor 1 in inhibition of NF-B pathway during heat shock responsemediated lung protection. Am J Physiol Lung Cell Mol Physiol 287: L953-L961, 2004. First published June 25, 2004 doi:10.1152/ ajplung.00184.2003.-Heat shock transcription factor (HSF)-1 is recognized as a central component of the heat shock response, which protects against various harmful conditions. However, the mechanisms underlying the protection and the role of HSF-1 in these mechanisms have not yet been clearly elucidated. Using HSF-1 knockout mice (Hsf1 Ϫ/Ϫ ), we examined whether heat shock responsemediated lung protection involved an inhibition of the proinflammatory pathway via an interaction between HSF-1 and NF-B, in response to cadmium insult. The HSF-1-dependent protective effect against intranasal instillation of cadmium (10 and 100 g/mouse) was demonstrated by the higher protein content (1.2-and 1.4-fold), macrophage (1.6-and 1.9-fold), and neutrophil (2.6-and 1.8-fold) number in bronchoalveolar fluids, higher lung wet-to-dry weight ratio, and more severe lung damage evaluated by histopathology in Hsf1 Ϫ/Ϫ compared with wild-type animals. These responses were associated with higher granulocyte/macrophage colony-stimulating factor (GM-CSF; 1.7-fold) but not TNF-␣ concentrations in bronchoalveolar fluids of Hsf1 Ϫ/Ϫ mice compared with those of wild-type animals, indicating that HSF-1 behaved as a repressor of specific cytokine production in our model. To further investigate the mechanism of GM-CSF repression, we analyzed the NF-B activity and IB stability. The DNA binding NF-B activity, in particular p50 homodimer activity, was higher in Hsf1 Ϫ/Ϫ mice than in wild-type mice after cadmium exposure. These results provide a first line of evidence that mechanisms of lung protection depending on HSF-1 involve specific cytokine repression via inhibition of NF-B activation in vivo. knockout mice; cadmium; heat shock proteins; granulocyte/macrophage colony-stimulating factor; nuclear factor-B