Function and regulation of GPR84 in human neutrophils.

Human neutrophils belong to the innate immune system and are the most abundant white blood cells in circulation. They are professional phagocytes and express several G protein-coupled receptors (GPCRs) which are essential for proper neutrophil functions. So far, the two formyl peptide receptors (FPR1 and FPR2) have been the most extensively studied group of neutrophil GPCRs, but recently a new group, the free fatty acid sensing receptors (FFARs), has gained growing attention. Neutrophils express GPR84 and FFA2 (sensing medium- and short-chain fatty acids, respectively) which display similar activation profiles. The exact pathophysiological role of GPR84 is not yet fully understood, but it is generally regarded as a pro-inflammatory receptor that mediate neutrophil activation. In this review, we summarize current knowledge of how GPR84 affects human neutrophil functions and discuss the regulatory mechanisms that control these responses, focusing on the similarities and differences in comparison to the two FPRs and FFA2.