Soluble tachyzoite antigen (STAg) was obtained using a previously described protocol [45] . Briefly, tachyzoites of T. gondii (RH strain) were maintained by serial passage in BALB/c mice and obtained from peritoneal exudates from mice infected 48 h earlier. Only exudates containing 100% of free-ranging tachyzoites were used for antigen preparation. Parasite suspension was washed in phosphate buffered saline (PBS, pH 7.2), added to a protease inhibitor cocktail (Complete Ultra tablets, Roche, USA), processed through lysis by repeated freezing and thawing cycles, sonicated, and centrifuged at 14,0006g for 30 min at 4uC. After supernatant recovery, total protein was estimated by the Bicinchoninic acid kit (BCA, Sigma, St. Louis, MO, USA) and aliquots were stored at 280uC until use. The same protocol was performed with cells extracted from the peritoneal cavity of mice, used as experimental controls.