Resolvin D1 binds human phagocytes with evidence for proresolving receptors

Endogenous mechanisms that act in the resolution of acute inflammation are essential for host defense and the return to homeostasis. Resolvin D1 (RvD1), biosynthesized during resolution, displays potent and stereoselective anti-inflammatory actions, such as limiting neutrophil infiltration and proresolving actions. Here, we demonstrate that RvD1 actions on human polymorphonuclear leukocytes (PMNs) are pertussis toxin sensi-tive, decrease actin polymerization, and block LTB4-regulated adhesion molecules (beta 2 integrins). Synthetic [H-3]-RvD1 was prepared, which revealed specific RvD1 recognition sites on human leukocytes. Screening systems to identify receptors for RvD1 gave two candidates-ALX, a lipoxin A(4) receptor, and GPR32, an orphan -that were confirmed using a beta-arrestin-based ligand receptor system. Nuclear receptors including retinoid X receptor-alpha and peroxisome proliferator-activated receptor -alpha, -delta, -gamma were not activated by either resolvin E1 or RvD1 at bioactive nanomolar concentrations. RvD1 enhanced macrophage phagocytosis of zymosan and apoptotic PMNs, which increased with overexpression of human ALX and GPR32 and decreased with selective knockdown of these G-protein-coupled receptors. Also, ALX and GPR32 surface expression in human monocytes was up-regulated by zymosan and granulocyte-monocyte-colony-stimulating factor. These results indicate that RvD1 specifically interacts with both ALX and GPR32 on phagocytes and suggest that each plays a role in resolving acute inflammation.