Dynamics and participation of type II phospholipase A2 in rat zymosan-induced pleurisy

Intrapleural injection of zymosan into rats induces acute inflammation characterized by plasma leakage and cellular influx. The level of type II phospholipase A2 (PLA2) increased in the pleural fluid as well as in exudating leukocytes after the injection of zymosan. Rather low PLA2 activity was found in cell lysates, though treatment of such lysates at low pH increased the PLA2 activity drastically. The appearance of "acid-extracted" PLA2 activity in leukocytes preceded that of the extracellular enzyme activity, suggesting that pleural leukocytes might be one of the origins of the extracellular enzyme. Treatment of exudating pleural leukocytes with purified rat type II PLA2 elicited the production of prostaglandin E2, but not platelet-activating factor appreciably. These findings indicate that type II PLA2 might play a role in the progression of inflammation through the production of eicosanoids in the present inflammation model.