Endocannabinoid content in fetal bovine sera - Unexpected effects on mononuclear cells and osteoclastogenesis

► The endocannabinoid 2-AG is a major residual lipid in commercial FBS. ► 2-AG in FBS can induce significant cellular activation of primary monocytes/macrophages and increase RANKL-stimulated osteoclastogenesis. ► LPS-stimulated U937 cells show differential IL-6 expression depending on FBS batch. ► Polymyxin B beads bind to and selectively remove 2-AG.