Toxoplasma gondii secretes a calcium-independent phospholipase A(2)

Phospholipases A(2) (PLA(2)) play an important role in Toxoplasma gondii host cell penetration. They are also key enzymes in the host cell response to the parasite invasion. PLA(2) hydrolyse cellular phospholipids, releasing multiple inflammatory lipidic mediators. We have investigated the biochemical characterisation of T. gondii PLA(2) activity in a mouse-cultured tachyzoite homogenate and in the peritoneal exudate from infected mice, using the hydrolysis of a fluorescent phosphatidylglycerol labelled at the sn-2 position. Spectrofluorimetry and thin-layer chromatography showed a PLA(2) activity (about 0.5-2 nmol/min per mg), calcium-independent, secreted into infected mice peritoneal exudate, with a broad pH activity ranging between 6.5 and 9.5 and resistant to a great number of potential PLA(2) inhibitors except dithio-nitrobenzoic acid (1 mM). An associated phospholipase A(1) activity was also displayed. These results suggest that Toxoplasma gondii displays specific phospholipases different from host enzymes and probably involved at critical steps of infectious cycle.