The differential characterization of GPR55 receptor in human peripheral blood reveals a distinctive expression in monocytes and NK cells and a proinflammatory role in these innate cells

G protein-coupled receptor 55 (GPR55) is activated by endogenous, plant-derived and synthetic cannabinoids. Recent studies reported a broad tissue distribution for GPR55 and found prominent roles for this receptor in inflammatory pain, gut and bone physiology, as well as cancer. However, little is known about the expression and function of GPR55 in immune cells. To address this question, we performed a detailed characterization of GPR55 in different human innate and adaptive immune populations using polychromatic flow cytometry and we found that monocytes and NK cells expressed remarkable levels of this receptor compared to several cells of adaptive immunity. GPR55 activation by the specific agonist O-1602 boosted IL-12 and TNF-alpha production, and decreased endocytic activity, in LPS-activated monocytes. In addition, it increased CD69 activation marker expression, granzyme B and CD107a-dependent cytotoxicity and IFN-gamma and TNF-alpha production in NK cells activated by both IL-2 and IL-12. These over-stimulatory effects of GPR55 were antagonized by its selective antagonist cannabidiol. Altogether, our data thus unveil a proinflammatory role for GPR55 in innate immunity that may be important for the design of new immune therapeutic strategies.