Immunoglobulin G‐mediated phagocytosis activates a calcium‐independent, phosphatidylethanolamine‐specific phospholipase

Inhibition of arachidonate release down‐ regulates immunoglobulin G‐mediated phagocytosis. This arachidonate requirement is selective for IgG‐ opsonized targets, suggesting that arachidonate may act as a second messenger for Fcγ receptor‐mediated phagocytosis. Here we report the characterization of a phospholipase, activated during phagocytosis, that releases arachidonate from phosphatidylethanolamine in the absence of intracellular calcium ([Ca] i ≤ 2 nM). In vitro, a phospholipase with these characteristics was detected in soluble and particulate fractions of human monocyte homogenates. ( E )‐6‐(Bromomethylene)tetrahydro‐3‐(l‐ naphthalenyl)‐2H‐pyran‐2‐one, a drug that selectively inhibits Ca‐independent phospholipase A 2 S, is shown to inhibit IgG‐mediated phagocytosis and its associated arachidonate release in intact monocytes as well as the in vitro enzyme activity. These findings provide a link between the whole‐cell and in vitro data and present the initial characterization of a receptor‐activated, calcium‐ independent phospholipase from human monocytes.