The prevailing view is that cysts in the brain remain intracellular within neurons and that CD8+ T cell production of perforin is responsible for cyst clearance in the brain although the exact mechanism of cyst destruction has yet to be described [17, 18] . In order to determine whether or not macrophage chitinase activity could be responsible for the direct lysis of cysts, BMDM were co-cultured with cysts; with and without the chitinase inhibitor allosamidin. Cultures were observed for 14 hours capturing images every 10 minutes. Cysts observed in the absence of macrophages remained intact for the entire time course suggesting no parasite intrinsic mechanism of cyst destruction ( Figure 4A ; Video S2). In contrast, the addition of 20 mg/ml trichoderma chitinase to cyst cultures led to rapid rupture of the cysts within an average of 4 hrs, releasing bradyzoites into the media ( Figure 4B ; Video S3). Strikingly, cysts that were cultured with macrophages came under vigorous attack. This involved efficient and rapid migration of macrophages toward the cyst creating clusters of macrophages that could be seen pulling at the cyst wall ( Figure 4C ; Video S4). In these cultures most of the cysts were destroyed during the observation period with the average survival time of 9.5 hours ( Figure 4E ). In contrast cysts cultured in the presence of macrophages and the chitinase inhibitor allosamidin survived significantly longer than in untreated cultures. Although there appeared to be no defect in the recruitment and activity of macrophages to cysts with similar clustering and 'pulling' of the cyst wall, the majority of cysts survived the entire 14 hour period when treated with either 100 mM or 10 mM allosamidin ( Figure 4D ; Video S5). Decreasing concentrations of allosamidin led to a dose dependent decrease in cyst survival time ( Figure 4E ). These results demonstrate that macrophages can induce cyst lysis in a chitinase dependent manner.