Pneumonia is the leading cause of infectious deaths in the U.S. and the most common factor underlying acute lung injury. Community acquired pneumonias are most often caused by Streptococcus pneumoniae, whereas nosocomial pneumonias are commonly caused by Gram-negative enteric bacteria such as Escherichia coli. Fighting bacteria while preventing lung injury requires precisely regulated gene expression mediated by cytokine-transcription factor networks. Our long-term goals are to elucidate these signaling networks so that cytokines and transcription factors may be manipulated to improve host defense and prevent lung injury. The cytokine IL-6 is essential to neutrophil recruitment and bacterial clearance during bacterial pneumonia. The transcription factor STAT3 can be activated by IL-6, and is critical to preventing lung injury after hyperoxia. Our broad objectives are to determine whether STAT3 is activated in the lungs during pneumonia, to decipher the upstream pathways regulating STAT3 activation during pneumonia, and to determine whether increasing STAT3 activity protects the lungs during pneumonia. Based on results from our preliminary studies, we have formulated the central hypothesis that STAT3 is activated by different upstream cytokine pathways during E. coli and S. pneumoniae pneumonias to increase neutrophil recruitment and prevent lung injury. To test this central hypothesis, we have developed strategies for studying gene induction and transcription factor function in the lungs in vivo, using plasmid transfection, and for identifying transcription factors activated in the lungs in vivo, using proteomics. With these approaches, we will pursue the following specific aims: (1) to test the hypothesis that STAT3 activation requires IL-6 during E. coli pneumonia, (2) to test the hypothesis that, during S. pneumoniae pneumonia, STAT3 is activated by multiple IL-6 family cytokines whose expression requires NF-KappaB activation from receptors for TNFalpha and IL-1, (3) to test the hypothesis that STAT3 activity in the lungs increases neutrophil recruitment and decreases lung injury during pneumonia, and (4) to identify transcriptional regulators other than STAT3 that depend on IL-6 during pneumonia. Elucidating the regulation and function of IL-6 and STAT3 during pneumonia will provide molecular targets for improving host defense and preventing lung injury in patients with or at risk for lung infections.