PROJECT SUMMARY/ABSTRACT Interleukin-1 (IL-1) plays an important role in the host defense against Mycobacterium tuberculosis (Mtb), the bacterium that causes human disease tuberculosis (TB). IL-1 is essential for anti-bacterial immunity during Mtb infection in mice and genetic polymorphisms in IL-1 receptor (IL-1R1) signaling are associated with greater risk from active pulmonary TB. IL-1R1 is expressed by both the hematopoietic-derived and stromal cells in the lung, but the cell-type specific roles of IL-1R1-signaling in protective immunity against TB remains unclear. Supported by a R56 Bridge grant from NIAID, we investigated the contribution of different lung cells to the IL- 1R1 mediated protective immunity. We used bone marrow chimaeras and discovered that IL-1R1 expression on stromal cells is crucial for protecting mice against severe disease. We generated a panel of knock-in and knock out mouse strains where IL-1R1 expression is conditionally deleted- or restored in specific cells either in a wild type or IL-1R1-deficient host background. Our preliminary results indicated that expression of IL-1R1 on type II alveolar epithelial cells (AECII) is both necessary and sufficient for controlling bacterial replication, inflammation in the lung and preventing wasting disease. AECII-intrinsic IL-1R1 signaling is critical for anti- mycobacterial immunity and preventing type I IFN (IFN-I) dependent neutrophil influx. Depleting neutrophils or IFN-I significantly reduced bacterial load, immunopathology. Moreover, AECII-restricted overproduction of GM- CSF in the lung protected the highly susceptible GM-CSF deficient animals by reducing bacterial load, weight loss and lung pathology. Importantly, IFN-I blockade rescued alveolar type I (AEC-I) and type II (AECII) epithelial cells that were otherwise damaged during progressive disease. Based on our preliminary results, we hypothesize that IL-1R1 signaling in AECII potentiates the anti-microbial function of myeloid cells by GM-CSF production and restrains the pathological level of IFN-I production to maintain epithelial barrier integrity. We have three specific aims. In aim1, we will investigate the role of GM-CSF in regulating antimicrobial immunity by examining bacterial fitness and replication dynamics in myeloid cells obtained from mice that lack or express IL-1R1 expression in AECII. In aim2, we will investigate the role of AECII-derived prostaglandin E2 (PGE2) in regulating IFN-I response and consequent pathogenic neutrophil influx to prevent tissue damage. Finally, in aim3, we will investigate the impact of IFN-I on alveolar epithelial cell repair and regeneration by performing lineage tracing and spatial analysis of lung epithelial cells in the infected lung samples. Overall, the completion of these aims will provide mechanistic basis for IL-1R1 mediated protective immunity and reveal principles to target airway epithelial cells for boosting antimicrobial immunity and limiting the inexorable lung d...