A Novel Ligand of the Formyl Peptide Receptor

The glucocorticoid-regulated protein annexin I (lipocortin I) has been shown to mediate antiinflammatory activities of glucocorticoids, but the molecular basis of its action has remained elusive. Here we show that annexin I acts through the formyl peptide receptor (FPR) on human neutrophils. Peptides derived from the unique N-terminal domain of annexin I serve as FPR ligands and trigger different signaling pathways in a dose-dependent manner. Lower peptide concentrations possibly found in inflammatory situations elicit Ca2+ transients without fully activating the MAP kinase pathway. This causes a specific inhibition of the transendothelial migration of neutrophils and a desensitization of neutrophils toward a chemoattractant challenge. These findings identify annexin I peptides as novel, endogenous FPR ligands and establish a mechanistic basis of annexin I–mediated antiinflammatory effects.