Abstract
ABSTRACTToxoplasma gondii is an obligate intracellular parasite capable of invading any nucleated cell. Three main clonal lineages (type I, II, III) exist and murine models have driven the understanding of general and strain-specific immune mechanisms underlying Toxoplasma infection. However, murine models are limited for studying parasite-leukocyte interactions in vivo, and discrepancies exist between cellular immune responses observed in mouse versus human cells. Here, we developed a zebrafish infection model to study the innate immune response to Toxoplasma in vivo. By infecting the zebrafish hindbrain ventricle, and using high-resolution microscopy techniques coupled with computer vision-driven automated image analysis, we reveal that Toxoplasma invades brain cells and replicates inside a parasitophorous vacuole to which type I and III parasites recruit host cell mitochondria. We also show that type II and III strains maintain a higher infectious burden than type I strains. To understand how parasites are cleared in vivo, we further analyzed Toxoplasma-macrophage interactions using time-lapse microscopy and three-dimensional correlative light and electron microscopy (3D CLEM). Time-lapse microscopy revealed that macrophages are recruited to the infection site and play a key role in Toxoplasma control. High-resolution 3D CLEM revealed parasitophorous vacuole breakage in brain cells and macrophages in vivo, suggesting that cell-intrinsic mechanisms may be used to destroy the intracellular niche of tachyzoites. Together, our results demonstrate in vivo control of Toxoplasma by macrophages, and highlight the possibility that zebrafish may be further exploited as a novel model system for discoveries within the field of parasite immunity.This article has an associated First Person interview with the first author of the paper.
Highlights
Toxoplasma gondii is a successful human pathogen that often remains asymptomatic, complications can arise in the immunocompromised and in neonates if infection is contracted during pregnancy (Pappas et al, 2009)
We demonstrate that macrophages are crucial in the clearance of viable parasites, and use high-resolution three-dimensional correlative light and electron microscopy (3D CLEM) techniques to reveal a discontinuous parasitophorous vacuole (PV) in brain cells and macrophages
Intracellular Toxoplasma replicate in the zebrafish hindbrain ventricle To develop a Toxoplasma-zebrafish infection model, we tested whether tachyzoites could replicate in zebrafish larvae
Summary
Toxoplasma gondii is a successful human pathogen that often remains asymptomatic, complications can arise in the immunocompromised and in neonates if infection is contracted during pregnancy (Pappas et al, 2009). Toxoplasma exist as invasive rapidly replicating tachyzoites in intermediate hosts (such as rodents and livestock), and convert into bradyzoite cysts in immune-privileged sites and long-lived cells (such as the brain and muscle tissue) during chronic infection (Pittman and Knoll, 2015). Once inside the host cell, parasites reside in a non-fusogenic parasitophorous vacuole (PV), where Toxoplasma asexually replicates (Clough and Frickel, 2017). Predation of intermediate hosts by the definitive feline host completes the Toxoplasma life cycle. Control of infection by the host immune response is critical for host survival and for continued parasite transmission. As a result of its well-understood life cycle, Toxoplasma has emerged as a valuable model organism to understand the balance between pathogen survival and innate cellular immune control
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
