Vascular endothelial cells and macrophages coordinate neutrophil trafficking in inflammation

Title: Vascular endothelial cells and macrophages coordinate neutrophil trafficking in inflammation Abstract Many pathological conditions occur due to or involve deregulated immune cell trafficking and/or effector function. In particular, tissue accumulation of innate immune cells termed neutrophils (PMN) while essential for host defense and tissue homeostasis, often leads to exacerbated inflammation. Crossing of the endothelial barrier is the first critical regulatory step in tissue PMN effector function. Many receptor-ligand interactions involved this cascade have been well-defined, however, cues that initiate and terminate this process are less understood. Our data identified a novel synergistic function of endothelial cells (ECs) and interstitial macrophages (Mϕs) in regulating this importnant process in inflamed mucosa. We found that EC-specific cues attract Mϕs to the vessel wall, and that Mϕs extend cellular protrusions to form transient junctions with ECs. Through these binding interactions and the release of extracellular vesicles (EVs), which transport regulatory microRNAs, Mϕs can transduce the necessary signaling events in ECs to preferentially accommodate PMN TEM. Thus, the overall goal of this proposal is to define mechanisms and signaling events that regulate interstitial Mϕ recruitment and contact with the vessel wall to locally prime EC responses and guide PMN TEM in inflamed mucosa. We will utilize state-of-the-art 2-photon intravital microscopy (2pIVM), relevant reporter and KO mice in models of mucosal inflammation to 1. Determine how interstitial Mϕs are recruited to interact with vascular ECs in inflamed tissue. 2. Define mechanisms by which Mϕs prime vascular ECs to form PMN TEM hot spots. 3. Determine the extent to which Mϕ-priming of vascular ECs (hot spot formation) is required for PMN TEM and resolution of tissue inflammation. Our studies will define new mechanisms of PMN trafficking, and likely identify new molecular targets to improve resolution of inflammation.