Type 2 Immune Responses in Endotoxemia-induced Lung Injury - PROJECT SUMMARY/ABSTRACT Acute lung injury (ALI)/acute respiratory distress (ARDS) is major cause of mortality in emergency rooms and intensive care units in hospitals. Identifying a role for eosinophils in ARDS has been limited, in part due to the technological difficulties in studying these cells, their association as destructive degranulating cells in asthma, and their low numbers in the lungs in some forms of ARDS. Rather, eosinophils are pleiotropic cells with complex immune activities in health and disease, where even small numbers of eosinophils may have a large impact on the immune responses in situ. In agreement with this, recent studies have found that an increase in eosinophil numbers in the lung correlated with survival in some patients with ALI/ARDS. In translational models of ALI/ARDS, lung eosinophils were necessary for reduced injury, improved resolution, and better survival. In particular, the type 2 immune responses of eosinophils were suggested to promote resolution of injury. In this proposal we will define and investigate two novel methods to amplify type 2 immune responses of eosinophils in ALI/ARDS to better understand how these cells may contribute to repair/resolution of injury. We hypothesize that increasing type 2 immune responses of eosinophils through activation by IL-33 or suppression of transcription factor IRF1 will result in reduced injury and increased resolution of ALI/ARDS. In models of ALI, increased IL-33 promoted recruitment and activation of eosinophils and group 2 innate lymphoid cells (ILC2s) that correlated with improved neutrophil resolution and survival. IL-33 binds the ST2 receptor on eosinophils and ILC2s and increases their type 2 effector functions. We recently identified IL- 33-activated eosinophils significantly promoted ILC2 type 2 effector functions in vitro and in vivo. We propose IL-33 signaling is critical for the eosinophil-ILC2 nexus that promotes type 2 responses, and enhancing this response in endotoxemia-induced ALI will be beneficial to resolution. In Aim 1 we will test the role of IL-33 with eosinophil and ILC2-specific knockouts of ST2 to define their role in endotoxemia induced ALI. In Aim 2, we will induce eosinophil type 2 immune responses by knocking out the transcription factor interferon regulatory factor 1 (IRF1) in eosinophils. We identified IRF1 as a novel major regulatory transcription factor of eosinophil immune phenotype in vivo and in vitro. IRF1 knockout eosinophils become type 2 immune cells in response to IFNγ. Our preliminary findings show IRF1 knockout mice have increased airway eosinophilia and eosinophil-specific IRF1 knockout mice have reduced neutrophilia during the resolution phase of endotoxin-induced ALI. We will complete studies with IRF1 knockout and eosinophil specific IRF1 knockout mice in endotoxemia-induced ALI. Importantly we will complete novel single cell analysis of the composition and phenotypes of lung immune cells using mass cytometry (CyToF). These pathways are critical to define in order to identify the beneficial and/or negative consequences of eosinophil responses in ALI/ARDS.
