Involvement of cannabinoid receptor CB2 in dectin-1-mediated macrophage phagocytosis

Cannabinoid receptors are expressed in macrophages, but little is known of their roles. We here examined their involvement in phagocytosis. The presence of 2-arachidonylglycerol, an endocannabinoid, augmented the phagocytosis of zymosan by mouse macrophages, while the phagocytosis of Escherichia coli, Staphylococcus aureus, apoptotic cells or latex beads remained unaffected. An agonist of the cannabinoid receptors CB1 and CB2 also stimulated the phagocytosis of zymosan. The stimulatory effect of 2-arachidonylglycerol was abolished when phagocytosis reactions were carried out in the presence of an antagonist of CB2 but not of CB1. Furthermore, the phagocytosis of zymosan in the presence of 2-arachidonylglycerol was severely inhibited by the addition of a beta-glucan-containing carbohydrate or antibody neutralizing dectin-1, a beta-glucan-recognizing phagocytosis receptor. These results suggested that the activation of CB2 in macrophages leads to the stimulation of dectin-1-mediated phagocytosis.