Although both AMCase and CHIT1 are upregulated in certain bacterial and nematode infections [68, 69] only AMCase was significantly increased in the brain following Toxoplasma infection ( Figure 2C ). To confirm that AMCase is responsible for the observed chitinase activity, we performed a chitinase assay similar to that in Figure 1D using BMDM from WT and AMCase null mice ( Figure 5A ). Our results reveal a severe defect in chitinase production by AMCase null macrophages. Indeed, these cells showed a significantly lower baseline level of chitinase and were unresponsive to the addition of cysts. To test whether the ability to destroy cysts is dependent on this enzyme, BMDM from WT and AMCase2/2 mice were fluorescently labeled and cultured with Me49-RFP expressing cysts and cyst lysis time imaged as before. Using fluorescently labeled parasites enhanced the ability to see escaping parasites from lysing cysts. Results, as before, demonstrated that WT non-polarized macrophages were able to lyse cysts in ,10 hours ( Figures 5B and 5D ; Videos S6 and S10). In contrast, cysts cultured with AMCase2/2 macrophages had a significantly increased survival time over WT macrophages consistent with AMCase being the source of chitinase activity required to lyse cysts ( Figures 5C and 5D ; Videos S7 and S11). To determine the requirement for macrophage polarization in their ability to lyse cysts, macrophages were treated with cytokines to polarize them to classical or alternative phenotypes prior to cyst addition. In line with the lack of chitinase induction, IL-4 priming had no effect on cyst survival time, suggesting that cytokineinduced alternative activation does not enhance the ability to destroy cysts ( Figures 5D; Video S9) . In contrast, macrophages that were classically polarized with LPS and IFN-c showed a defect in chitinase activity and cyst destruction (Figures 5D and  5E ; Video S9). Suggesting that polarization of macrophages is required but that chitin is the most likely source of alternative activation and not IL-4. Taken together, these data demonstrate that macrophages lyse cysts in an AMCase-dependent manner in vitro.