Apoptosis is a form of programmed cell death that is essential in such processes as organ and tissue remodeling and maturation of hematopoietic cells. The clearance of apoptotic cells is essential to prevent autoimmune responses to sequestered antigens. This process is mediated by phagocytes of the monocyte lineage. Before phagocytosis can occur, macrophages must be recruited to the apoptotic cells through chemotaxis. Products of the reaction catalyzed by the phospholipases A2 (PLA2) have been shown to induce monocyte chemotaxis either directly or indirectly. Some investigators have implicated a cytosolic calcium-independent PLA2 (iPLA2) in the production of these products during apoptosis. However, a recent report suggests that the secreted group IIa (sPLA2) binds to surfaces of apoptotic cells. The "receptor" for this pool of sPLA2 is the rod domain of vimentin, an intermediate filament protein that is exposed by caspase activity when cells undergo apoptosis. Based on these observations, we hypothesize that the exposure of vimentin on apoptotic cells traps a pool of catalytically active sPLA2 that then generates the bioactive lipids that induce macrophage chemotaxis. In our methods, [3H]-oleate labeled E-coli is used as a substrate for sPLA2 and enzyme activity is quantified by scintillation counting of released radiolabeled oleic acid. Apoptosis is induced with anti-fas (CD-95) on Jurkat cells and monitored through annexin-V binding and propidium iodide(PI) staining followed by flow cytometric analyses. THP-1 monocytes are employed in chemotaxis assay with monocyte chemotactic protein (MCP-1) as a positive control. The preliminary data show equivalent group IIa sPLA2 association with anti-fas treated and control cells, and the enzyme remains catalytically active when bound. In line with the hypothesis, trapped sPLA2 generated soluble molecules that directly or indirectly induced migration of THP-1 monocytes. However, the similar binding effect observed with apoptotic or control cells is surprising and experiments are being planned to determine if the interaction between IIa sPLA2 and apoptotic cells is vimentin dependent.