HUMAN NEUTROPHILS STORE TYPE-II 14-KDA PHOSPHOLIPASE A(2) IN GRANULESAND SECRETE ACTIVE ENZYME IN RESPONSE TO SOLUBLE STIMULI

Although ''secretory'' type II 14-kDa phospholipase A(2) (sPLA(2)) act ivity has been described in neutrophils, direct evidence of enzyme sec retion has been elusive. We have used immunogold electron microscopy w ith polyclonal and monoclonal antibodies to sPLA(2) to demonstrate loc alization of the enzyme to granules of resting human neutrophils and t ranslocation to phagolysosomes. Soluble stimuli such as calcium ionoph ore A23187 stimulate loss of cell-associated enzymatic activity. Super natant fluids from stimulated neutrophils lack measurable PLA(2) but c ontain proteases which inactivate exogenous sPLA(2). The use of alpha- 1-antitrypsin as a protease inhibitor permitted this first demonstrati on of secretion of PLA(2) activity from stimulated human neutrophils.