Abstract P3032: 15( R )-lipoxin A 4 Contributes To Splenic Erythrophagocytosis Via Activation Of ALX/FPR2

Abstract

Red blood cells (RBCs) are the most abundant cell type in the body and are traditionally appreciated for their role in respiration and gas exchange. Recently, however, RBCs have garnered new attention for their immunomodulatory effects which is primarily achieved via their interaction with resident macrophages in the spleen, known as red pulp macrophages. As RBCs enter the spleen, red pulp macrophages probe the cells for signs of mechanical and oxidative damage, as well as inflammatory stimuli bound to cell surface receptors (e.g., foreign pathogens, endogenous chemokines). Once recognized, red pulp macrophages prune damaged portions of RBC membranes or phagocytose the cell entirely, efficiently processing and recycling the cellular cargo of the RBC. In a healthy human, this process, termed erythrophagocytosis, accounts for the daily turnover of roughly 150-200 billion RBCs. Consequently, defects in the system can have wide-ranging health effects including anemia, impaired host defense, and even sepsis. Recent data suggest that arachidonic acid (AA)-derived prostaglandins promote erythrophagocytosis, yet the impact of other eicosanoid species on the process has not been well described. We performed targeted lipidomics analyses focused on the AA metabolome in two distinct models of erythrophagocytosis. First, mouse bone marrow-derived macrophages were incubated with freshly isolated RBCs; then, spleens from mice were collected following exogenous delivery of damaged RBCs. In both models, we found increased production of the 15( R )-epimer of lipoxin A 4 (15( R )-LXA 4 ), as well as its biosynthetic intermediate, 15-HETE. Similar to LXA 4 , 15( R )-LXA 4 has been shown to robustly promote the active resolution of inflammation by regulating leukocyte function via its interaction with the G protein-coupled receptor, ALX/FPR2. In mice genetically deficient in this receptor, we measured a significant decrease in splenic clearance of damaged RBCs. Together, these data suggest that 15( R )-LXA 4 activation of ALX/FPR2 on red pulp macrophages may be a critical aspect regulating erythrophagocytosis and maintaining RBC homeostasis.