Project Summary Neutrophil recruitment to sites of inflammation is a multi-step process mediated by the interactions between several receptors and ligands. Although the major receptors and ligands mediating neutrophil-endothelial cell interactions have been identified, it remains poorly understood how receptor-ligand interactions are regulated under inflammatory conditions. This project will provide novel fundamental knowledge of how neutrophil surface- localized ERO1?-thiol isomerase complexes target allosteric disulfide bonds in different surface receptors and promote the ligand-binding function under inflammatory conditions. Our preliminary data demonstrated that neutrophil surface-bound ERp57 and PDI cooperatively and distinctly regulate the process of neutrophil recruitment and extracellular ERO1? coordinates this regulatory mechanism. Using biochemical, cellular, and in vivo studies with novel blocking antibodies, peptides and mouse models, we will test the hypothesis that two structurally-similar thiol isomerases, ERp57 and PDI and their oxidase ERO1? facilitate modification of allosteric disulfide bonds in different surface molecules and enhance neutrophil adhesive function, contributing to tissue damage under thromboinflammatory conditions. In Aim 1, we will determine how PDI and ERp57 distinctly regulate the adhesive function of different neutrophil receptors. Also, we will test whether extracellular ERO1? controls the activity of those thiol isomerases. In Aim 2, we will test how inflammatory environments influence the function of extracellular PDI, ERp57 and ERO1?. In Aim 3, using in vivo live imaging techniques, we will study the pathological roles of extracellular PDI, ERp57 and ERO1? in intravascular cell-cell interactions and tissue damage in thromboinflammation. Our studies will provide insights into novel molecular and cellular mechanisms of neutrophil-endothelial cell interactions, which can be used to design new strategies for the treatment of thromboinflammatory disease.