Transregional Collaborative Research Center SFB-TR 84 - “Innate Immunity of the Lung: Mechanisms of Pathogen Attack and Host Defence in Pneumonia“


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Resolvin E1 and related lipid mediators programming the resolution of inflammation in pneumonia (Mayer / Witzenrath)


In pneumonia, actively controlled resolution of inflammation and repair of damaged barrier function are essential components of the innate immune response. Resolvin(Rv) E1 is generated from exogenously supplied n-3 fatty acids with 18R-HEPE as intermediate compound, based on the activity of lipoxygenases and cyclooxygenase II. RvE1 triggers monocytes and epithelial cells and thereby serves as resolution signal, preventing further recruitment of neutrophils and promoting the invasion of monocytes in the lung. Interaction of RvE1 with its cognate G-protein-coupled receptor ChemR23 results in attenuation of NF-B signaling, while competition with leukotriene B4 (LTB4) for binding to the LTB4 receptor, BLT1, may lead to suppression of the pro-inflammatory LTB4-BLT1 pathway. In the previous funding period we showed that 18R-HEPE and ChemR23 controlled the late phase of leukocyte recruitment and improved phagocytosis of pneumococci. Both pathways act in a concerted effort governing timely termination of inflammation and initiating resolution and repair, to remove detritus and re-establish barrier control in the lung. This program has to be compartment-specific, as the macro- and microcirculation as well as the alveolar space are in need for specific signaling. Interaction between invaded neutrophils and macrophages is essential to control bacterial killing but also to clear detritus, apoptotic cells, and to uphold the essential alveolar barrier and gas exchange functions. Therefore, we aim to unravel the spatio-temporal programs of resolution on a cellular and molecular level and to reveal diverging effects between 18R-HEPE and RvE1 on lung resident and circulating target cells such as PMN and monocytes. Wildtype mice treated with RvE1 or its precursors, as well as recently generated double-transgenic mice on the background of fat-1 mice which endogenously synthesize n-3 fatty acids (fat-1//ChemR23-/-; fat-1//BLT1-/-), will be infected with S. pneumoniae to dissect the different resolution pathways in pneumonia. Regulation of ChemR23- and BLT1-expression in monocytes and PMN as well as generation of resolvins in murine pneumonia will be determined. In addition, we will further proceed with human lung tissue studies in cooperation with B06/Z01a and analyze ChemR23 and BLT1 expression as well as interaction of endogenous and exogenous ligands upon stimulation with pneumococci using live cell imaging. To define  the impact of lipid mediator induced signaling in myeloid cells vs. lung parenchymal cells, adoptive cell transfer experiments will be carried out with wildtype, BLT1-/-, and ChemR23-/- mice. The resolution program dependent on macrophages will be selectively addressed by use of macrophage Fas-induced apoptosis (MAFIA) transgenic mice containing an inducible Fas suicide/apoptotic system. The experimental studies will be complemented by immunohistological analysis of healthy donor lungs (tissue bank of DZL, Gießen) and lungs of patients who deceased because of pneumonia (F. Klauschen, Dept. of Pathology, Charité, Berlin). Furthermore, we will analyze resolvins by lipidomics in serum of approximately 600 pneumonia patients (provided by the PROGRESS consortium), and correlate the findings with clinical and paraclinical patterns.