CD14-dependent internalization and metabolism of extracellular phosphatidylinositol by monocytes

We report that membrane CD14 (mCD14), a cell surface receptor found princip ally on leukocytes, can mediate the uptake and metabolism of extracellular phosphatidylinositol (PtdIns), mCD14 facilitates PtdIns internalization, ta rgeting it to intracellular sites where, following stimulation with a calci um ionophore, it can be acted upon by cytosolic phospholipase A(2). The [C- 14]arachidonate released from mCD14-acquired [C-14]arachidonyl-PtdIns is ei ther esterified to triacylglycerol and retained in the cell or secreted as free arachidonate or leukotrienes. Although less than 10% of the arachidona te-derived lipids secreted from endogenous cellular stores are Ei-lipoxygen ase metabolites, over one-half of the secreted C-14-lipids derived from mCD 14-acquired PtdIns are hydroxyeicosatetraenoic acids or leukotriene B-4, mC D14 may allow these highly active blood cells to acquire and use extracellu lar Pt-dIns as a source of arachidonate for leukotriene synthesis.