PROJECT SUMMARY Researchers still do not understand the mechanisms behind the progressive and irreversible lung structural damage that ultimately causes respiratory failure in patients with cystic fibrosis (CF). We have developed a CF mouse model of chronic inflammation that recapitulates the progressive and irreversible lung tissue remodeling in late-stage CF lung disease. The overall goal here is to understand the cellular mechanisms that lead to progressive and irreversible CF lung deterioration. The objective is to study how inflammatory monocytes and monocyte-derived MΦs (MΦs) contribute to the development of irreversible lung tissue remodeling in CF. Our central hypothesis is that, in CF, chronic lung exposure to lipopolysaccharide (LPS) increases recruitment of inflammatory monocytes to the lungs and that these monocytes are programmed to cause tissue damage while failing to effectively fight the infection. Moreover, we hypothesize that this is initiated by the loss of CFTR function in hematopoietic stem/progenitor cells in the bone marrow. The rationale is based on observations that an increased number of inflammatory monocytes and monocyte-derived MΦs are found in the lungs of patients with CF. This feature is recapitulated by our CF mouse model when chronically exposed to LPS. Moreover, after six weeks of recovery from chronic LPS exposure, monocytes from CF lungs maintain a “pro-inflammatory” signature, suggesting a permanent change in CF monocyte functions. Furthermore, we conducted studies using a mouse model in which migration of inflammatory monocytes is impaired (Ccr2-/- mice). These studies suggest that the inflammatory monocytes drive the lung tissue remodeling caused by chronic exposure to LPS. Our specific aims will test the following hypotheses: (aim 1) that lowering the recruitment of circulating inflammatory monocytes to CF lungs during chronic exposure to LPS is sufficient to reduce TGFβ signaling and mitigate tissue remodeling in CF lungs without compromising host defense against bacteria; (aim 2) that the innate immune memory acquisition in CF myeloid progenitor stem cells, caused by chronic LPS exposure, will generate inflammatory monocytes that fail to effectively clear infections and that cause profound lung tissue damage; (aim 3) that cell-autonomous CFTR dysfunction in hematopoietic stem/progenitor cells and monocytes contributes to pathogenic responses to chronic lung exposure to LPS. The contribution is significant because it will result in a better understanding of the pathogenesis of immune-mediated diseases in CF and in other chronic inflammatory diseases with persistent bacterial lung infections. Our proposed research is innovative because we will use novel mouse models, we will bridge together methodologies in lung immunology and hematopoietic stem cell fields, and we will use unbiased cutting-edge technologies. At the completion of this work, we will have identified novel mechanisms by which chronic instigat...