Although it has been shown that MAG1 antigen is expressed during both tachyzoite and bradyzoite development [26], we found MAG1 antibody level was highly associated with cyst burden within the chronically infected brain, determined by the number of tissue cysts, by the average size of cysts, and by the bradyzoite prevalence in the mouse prefrontal cortex. This evidence concerns the gene GPAT3 and cyst.