To observe the interaction of macrophages and cysts in vitro, cysts were isolated from the brains of chronically infected mice as described above. 50 cysts were added per well to 96 well plates containing 2610 5 bone marrow derived macrophages. Cysts and cells were viewed using a BD HT Pathway 855 microscope (BD Biosciences, San Jose, CA) in a climate-controlled chamber (37uC, 5% CO 2 ). Nine cysts were identified per condition and photographed every 10 minutes for 14 or 16 hours. Movies were compiled using ImageJ software (NIH, Bethesda, MD) and cyst survival time was determined.