Platelet aggregation by a phospholipase C from Pseudomonas aeruginosa.

The effects and mechanism of action of a phospholipase C (PLC) from Pseudomonas aeruginosa on human platelet rich plasma were examined to better understand the interaction of PLC with human platelets. PLC caused platelet aggregation in a concentration-dependent manner. Enzymatic activity of PLC was necessary for aggregation since heat-denatured PLC had no effect on platelets. P-nitrophenolphosphorylcholine, a substrate for PLC, was unable to cause platelet aggregation and inhibited PLC-induced aggregation if added to platelets prior to the addition of PLC. In addition, phosphorylcholine, a product of PLC action on phospholipid substrates, was unable to aggregate platelets. When PLC was tested on the aggregation response to known aggregating agents such as ADP, epinephrine, collagen or ristocetin, no inhibitory effect was seen. Studies with aspirin or nordihydroguairetic acid (NDGA) indicated that the action of PLC was independent of the prostaglandin and lipooxygenase pathways, respectively. The studies described herein point to a novel pathway of platelet aggregation by P. aeruginosa PLC.