Project Summary Idiopathic pulmonary fibrosis (IPF) is a progressive pulmonary disorder with no known cure and poorly understood pathogenesis. IPF results in significant reductions in quality of life, recurrent hospitalizations and is fatal. We and others have shown that pulmonary immunity is dysregulated in IPF. The bacteria and host environment of the human gut - the gut microbiome - has a profound impact on human immunity. The gut microbiome is a key regulator of pulmonary immunity, a consistent biological observation across several experimental models. In a key finding, recently published, we have shown that germ free (GF) mice – experimental mice devoid of a microbiome – are protected from pulmonary fibrosis related mortality. In human patients with IPF, the bacterial burden of the lung predicts mortality and the lungs bacterial diversity correlates with pulmonary inflammation. While the microbiome predicts outcomes, key regulatory interactions between the host, lung and gut microbiota remain unknown. The central hypothesis of this proposal is that key gut microbiota, namely Bifidobacterium spp, act as master regulators of pulmonary immunity in lung fibrosis, shaping host defense, associated inflammation and modifying parenchymal repair after lung injury. The rationale for this proposal is that this work will augment our current knowledge of IPF pathogenesis and further the foundational basis for microbiome based therapies in chronic lung disease. We will accomplish this through the following experimental aims: Specific Aim 1: To determine key Bifidobacteria by-products and metabolites that contribute to outcomes in pre-clinical models of pulmonary fibrosis using pre-biotic diet modifications, germ free (GF) and gnotobiotic mice, 16S rRNA gene sequencing, functional metagenomics and metabolomics. Specific Aim 2: To determine the host related cellular and molecular mechanisms through which Bifidobacterium spp modify outcomes in pulmonary fibrosis using pre-clinical models of pulmonary fibrosis in conventional and GF derived T cell, IL-10 and IL-17 transgenic models, T cell adoptive transfer and multicolor flow cytometry mediated characterization of lung cellular immunity. Specific Aim 3: To determine the immunogenic and fibrogenic effects of gut microbiota from patients with IPF. Gut microbiota from patients with IPF will be identified and correlated with disease severity and clinical outcomes. Regulatory T cell phenotype from patients with IPF will be correlated with gut diversity and taxa. This translational approach will use advanced mechanistic tools to 1) improve our understanding of complex immune-microbiota interactions that occur in pre-clinical models of lung fibrosis, 2) identify modifiable host and microbiota related targets in lung fibrosis and finally 3) advance the foundation for microbiome based therapies in chronic lung disease.