In recent years, our understanding of macrophages has expanded and we now appreciate these cells' remarkable plasticity. Thus, although whole populations of macrophages can become polarized to classical or alternative phenotypes associated with protection against protozoan and helminth pathogens respectively, the ability to respond and adapt to local stimuli in the environment is paramount [20] [21] [22] [23] [24] . The role of classically activated macrophages in the control of T. gondii infection is well documented. These cells are a source of IL-12, reactive oxygen and nitrogen species, and GTPases that enable the direct killing of the parasite [6, [25] [26] [27] [28] [29] [30] . However, here we describe a population of CXCR3+ macrophages in the brain following T. gondii infection. These cells express the scavenger receptors MMR and stabilin-1 and produce arginase in response to the presence of Toxoplasma cysts. In addition to these traditional signs of alternative activation, these studies demonstrate that macrophages respond to chitin present in the cyst wall and produce the true mammalian chitinase, AMCase. Finally we show that this chitinase activity destroys cysts and is essential for the control of cyst burden within the chronically infected brain.