An <i>ex vivo</i> model of <i>Toxoplasma</i> recrudescence reveals developmental plasticity of the bradyzoite stage

Abstract

The classical depiction of the <i>Toxoplasma</i> lifecycle is bradyzoite excystation conversion to tachyzoites, cell lysis, and immune control, followed by the reestablishment of bradyzoites and cysts. In contrast, we show that tachyzoite growth slows independent of the host immune response at a predictable time point following excystation. Furthermore, we demonstrate a host cell-dependent pathway of continuous amplification of the cyst-forming bradyzoite population. The developmental plasticity of the excysted bradyzoites further underlines the critical role the cyst plays in the flexibility of the lifecycle of this ubiquitous parasite. This revised model of <i>Toxoplasma</i> recrudescence uncovers previously unknown complexity in the clinically important bradyzoite stage of the parasite, which opens the door to further study these novel developmental features of the <i>Toxoplasma</i> intermediate life cycle.