IgG titers of mouse sera. Groups of mice were intraperitoneally immunized twice (↑) with PLG-rSAG1 microparticles (■ ), rSAG1 (Vet L-10)(● ), soluble rSAG1 alone (□ ), PLG (◊ ), or PBS (○ ). Sera were collected from three mice per group every two weeks and their anti-Toxoplasma IgG titers were determined by ELISA. Results were presented as the mean of log10 titers ± SD. *P<0.05 when comparing the PLG-rSAG1 group to the rSAG1 (Vet L-10) group.