SECRETION OF PHOSPHOLIPASE A(2) INDUCED BY INTERACTIONS OF HUMAN PLATELETS WITH MONOCYTES

Phospholipase A(2) (PLA(2)) activity was found and measured in the cel l-free supernatants of human mononuclear cells (monocytes and lymphocy tes) cultured with platelets for 48 h at 37 degrees C. The relative mo lecular mass of purified, calcium-dependent PLA(2) was 14 kD. The amou nt of PLA(2) in the supernatants correlated positively with the number of monocytes and platelets in the cultures. Electron microscopically, direct cell-to-cell interactions of monocytes and platelets were obse rved. Cultivation of suspensions of human mononuclear cells with plate lets in serum-free medium was found to be an efficient way to produce and purify human secretable PLA(2). In the release of secretable PLA(2 ) in peripheral blood, the interactions between platelets and monocyte s may play a considerable role.