A Soluble Phospholipase of Toxoplasma gondii Associated with Host Cell Penetration

We previously reported that phospholipase increases host cell penetration by Toxoplasma gondii . Here we show that calcium-dependent phospholipase A (PLA) activity is found in the supernatant of sonically disrupted T. gondii . When fractions of disrupted T. gondii were incubated with host cells, the release of fatty acids and lysolipids was detected. Fractions of sonically disrupted T. gondii with PLA activity increased T. gondii host cell penetration in a bioassay. In addition, a protein of approximately 20 kDa was detected by immunoblot of T. gondii antigens with horse antiserum to snake venom, the major antibody of which recognizes PLA₂. Incubation of T. gondii with exogenous PLA₂ resulted in increased solubility of a rhoptry protein. This protein, which we previously characterized as involved with enhanced parasite invasion of host cells and which is recognized by monoclonal antibody Tg49, was detected in increased amounts in supernatant fractions of extracellular parasites treated with PLA₂. Whereas without PLA₂ treatment, it is only slightly soluble under physiological conditions. This raises the possibility that PLA may be implicated in the release of rhoptry proteins.