Dynamics of Toxoplasma gondii Oocyst Phagocytosis by Macrophages

Abstract

Oocysts are the environmentally resistant stage of the protozoan parasite Toxoplasma gondii. They are responsible for foodborne infections in humans and animals worldwide. Infectious oocysts contain sporozoites that have to exit the sporocyst and oocyst walls to initiate replication of the parasite within the host tissues. Given their robustness and resistance to chemical degradation, it is still unclear how the oocyst and sporocyst walls release the sporozoites. This process called excystation is thought to occur in the small intestine as a result of the combined action of digestive agents, yet to be identified. By using an oocyst-macrophage co-culture platform, we previously demonstrated in vitro that the excystation of sporozoites and their differentiation into replicative tachyzoites could occur in absence of digestive factors, following phagocytosis by macrophages. Here, we further characterize the dynamics of the oocyst phagocytosis at the single-cell level by using optical tweezers and micropipette aspiration techniques. Our results show that the oocyst internalization kinetics can vary among a given population of macrophages, but similar processes and dynamics could be observed. Most of the cells manipulate oocysts for ∼15 min before internalizing them in typically 30 min. This process mainly involves the actin cytoskeleton of the macrophages. Liberated sporozoites within macrophages then differentiate into tachyzoites within 4-6 h following oocyst-macrophage contact. Tachyzoites appear to develop better in macrophages challenged with free sporocysts or sporozoites than with whole oocysts, suggesting that opening of the oocyst wall is one of the most limiting steps for sporozoite excystation completion.

Recombinant Toxoplasma gondii Ribosomal Protein P2 Modulates the Functions of Murine Macrophages In Vitro and Provides Immunity against Acute Toxoplasmosis In Vivo

“…Many proinflammatory agents are generated during early and acute T. gondii invasion, and, largely, cytokines are released. Cytokine IFN-γ can efficiently activate M1 macrophages through the NF-κB signaling pathway and promote M1 macrophages to secrete proinflammatory cytokines (IL-1β, TNF-α, IL-6, and IL-23), inducible nitric oxide synthase (iNOS), and nitric oxide (NO), even enhancing the ability of phagocytes to resist T. gondii [ 23 , 24 ]. Interestingly, although macrophages play an important role in resisting the replications of T. gondii [ 25 ], T. gondii has developed multistrategies to limit the antimicrobial activities of macrophages [ 26 , 27 ].…”

Expanding the Known Repertoire of C-Type Lectin Receptors Binding to Toxoplasma gondii Oocysts Using a Modified High-Resolution Immunofluorescence Assay

“…It results in induction of the cellular phagocytosis machinery, generation of reactive oxygen species, and inflammasome activation ( 63 ). Previous in vitro studies showed that oocysts are taken up by a mouse macrophage cell line in a phagocytic manner, and evidence was provided for subsequent oocyst wall rupture and occasional sporozoite release and intracellular differentiation into tachyzoites ( 64 , 65 ). Freppel et al speculated that oocyst phagocytosis might be a way of parasite dissemination in the host if similar processes with inhaled oocysts would occur in alveolar macrophages.…”

Comparative Phosphoproteomic Analysis of Sporulated Oocysts and Tachyzoites of Toxoplasma gondii Reveals Stage-Specific Patterns

“…It was reported that 21% of waterborne toxoplasmosis outbreaks between 1976 and 2009 were derived from oocysts [ 10 , 17 ]. Disappointingly, the mechanism of the unclosing of the oocyst walls that is triggered by digestive agents, followed by the release of sporozoites from oocysts in the small intestine is still unclear [ 10 , 18 ]. Heather et al first identified the profile of the proteome of sporulated oocyst walls and sporocysts/sporozoites, as well as an inventory of oocyst inner wall proteins and outer wall proteins [ 19 ].…”