FIG. 3.

Alternative hypotheses for the control of T. gondii tachyzoite replication in tissues of immunocompetent hosts. (A) The cellular immune response plays an active role in driving encystment of the parasite. Recent evidence suggests that production of RNI may promote tachyzoite-bradyzoite transformation. (B) Initiation of cyst formation occurs independently of host immunity. Once cysts are established, a low rate of conversion of bradyzoites to tachyzoites occurs continuously, but these reemergent parasites are effectively controlled by components of type 1 cytokine-based immunity such as RNI.