Crystal‐induced neutrophil activation. II. evidence for the activation of a phosphatidylcholine‐specific phospholipase D

Objective. To investigate the involvement of phospholipase D in the signaling pathways activated by 2 pathologically relevant inflammatory microcrystals, monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD). Methods. Human peripheral blood neutrophils were used throughout. Phospholipase D activity was monitored by measuring 3 separate indices: 1) the mass of phosphatidic acid, 2) the levels of alkyl‐phosphatidic acid, and 3) the levels of formation, in the presence of ethanol, of phosphatidylethanol. The latter 2 parameters were measured in cells labeled with 1‐0‐ 3 H–alkyl‐2‐acetyl‐sn‐glycero‐3‐phosphocholine. The cells were stimulated with microcrystals of triclinic morphology. Results. Both MSU and CPPD crystals induced a time‐ and concentration‐dependent accumulation of phosphatidic acid mass and elevation in levels of alkyl‐phosphatidic acid and phosphatidylethanol in prelabeled cells. The activation of phospholipase D by the microcrystals was partially sensitive to colchicine and largely resistant to pertussis toxin. Inhibition of phosphatidic acid formation by wortmannin or ethanol reduced the microcrystal‐stimulated production of superoxide anions. Conclusion. These results indicate that microcrystals stimulate phospholipase D in human neutrophils and that at least some of the functional consequences of neutrophil‐microcrystal interactions may be dependent on this biochemical pathway.