TheToxoplasma gondii-Shuttling Function of Dendritic Cells Is Linked to the Parasite Genotype

Abstract

Following intestinal invasion, the processes leading to systemic dissemination of the obligate intracellular protozoan Toxoplasma gondii remain poorly understood. Recently, tachyzoites representative of type I, II and III T. gondii populations were shown to differ with respect to their ability to transmigrate across cellular barriers. In this process of active parasite motility, type I strains exhibit a migratory capacity superior to those of the type II and type III strains. Data also suggest that tachyzoites rely on migrating dendritic cells (DC) as shuttling leukocytes to disseminate in tissue, e.g., the brain, where cysts develop. In this study, T. gondii tachyzoites sampled from the three populations were allowed to infect primary human blood DC, murine intestinal DC, or in vitro-derived DC and were compared for different phenotypic traits. All three archetypical lineages of T. gondii induced a hypermigratory phenotype in DC shortly after infection in vitro. Type II (and III) strains induced higher migratory frequency and intensity in DC than type I strains did. Additionally, adoptive transfer of infected DC favored the dissemination of type II and type III parasites over that of type I parasites in syngeneic mice. Type II parasites exhibited stronger intracellular association with both CD11c؉ DC and other leukocytes in vivo than did type I parasites. Altogether, these findings suggest that infected DC contribute to parasite propagation in a strain type-specific manner and that the parasite genotype (type II) most frequently associated with toxoplasmosis in humans efficiently exploits DC migration for parasite dissemination.The obligate intracellular parasite Toxoplasma gondii infects virtually any warm-blooded vertebrate and ϳ25% of the world's human population (27). Most infections generate few or no symptoms. Yet, acute infections are a concern in human medicine, since this opportunistic pathogen causes severe neurological complications in immunocompromised individuals, disseminated congenital infections in the developing fetus, and ocular manifestations in otherwise healthy individuals (27). After ingestion of the parasite, acute infection is characterized by the proliferation of fast-growing stages (tachyzoites) that rapidly disseminate and differentiate into slow-growing stages (bradyzoites) in peripheral tissues, where they may persist for the lifetime of the host (27). In contrast to pathogens that rely on uptake by host cells, T. gondii actively invades host cells, including cells of the immune system, and replicates in a nonfusigenic parasitophorous vacuole (45).Mounting evidence indicates that dendritic cells (DC) play critical roles during T. gondii infection as early sources of protective interleukin-12 responses and mediators of antigen presentation (32,35,37,41). In addition, based on their migratory properties (40) and permissiveness to Toxoplasma infection (6), DC have recently been identified as systemic carriers (Trojan horses) of T. gondii tachyzoites (2,7,30). Yet, the precise roles of ...

Avirulent strains of Toxoplasma gondii infect macrophages by active invasion from the phagosome

“…This interplay could then underlie a more robust innate and adaptive immune activation, leading to effective control of avirulent parasites. Additionally, avirulent T. gondii strains preferentially infect mononuclear cells, including naive resident macrophages (this report), monocytes (29,30) and neutrophils (31), and also differentially induce hypermigratory phenotype in infected macrophages and dendritic cells (10,32). It is tempting to speculate that these maneuvers together represent a constellation of adaptive responses characteristic of avirulent T. gondii.…”

“…The active penetration model was defined largely by using nonphagocytic host cells and hypervirulent strains of the parasite. Unlike their virulent counterparts, the interaction of avirulent Toxoplasma strains with macrophage and dendritic cell results in heightened innate cytokine and chemokine production (9) and the development of a "hypermotile" host cellular phenotype (10), which promotes the control of acute infection and mediates dissemination into sites of parasite latency (11,12). Here, we investigated whether avirulent parasites interact with phagocytic host cells in a fundamentally different way from the outset.…”

Motile invaded neutrophils in the small intestine ofToxoplasma gondii-infected mice reveal a potential mechanism for parasite spread

“…Cells of the immune system are often highly motile and represent attractive transport vessels for pathogens seeking to reach and enter tissues while being protected from the external environment. Consequently, recent studies have focused on the role of immune cells in transporting parasites between tissues (4,(16)(17)(18)(19)(20)(21)(22)(23). For example, cluster of differentiation 11b-positive (CD11b + ) cells have been implicated in the dissemination of T. gondii through the blood and across the blood-brain barrier (4,19).…”

Recombinant Adenovirus Vector Infection of Human Dendritic Cells

“…A series of sequential separations is necessary to yield sorted cells of high purity. We have developed two means of first enriching DC and monocytes from the total peripheral blood mononuclear cell (PBMC) population: (i) aphaeresis of donor leukocytes followed by counterflow centrifugation elutriation to separate monocytes and lymphocytes based on cell size and sedimentation density (Lore et al, 2003, Lore et al, 2005, or (ii) treatment of PBMC with RosetteSep CD14+ enrichment kit (Lambert et al, 2009). Both these methods result in a fraction of cells highly enriched of monocytes and DC, and depleted of lymphocytes.…”

“…Due to the rarity of DC subsets in blood and skin an alternative method was developed to more readily study DC (Sallusto & Lanzavecchia, 1994 , Lambert et al, 2009. Subsequent culture of monocytes with recombinant human interleukin (IL)-4 and granulocyte macrophage-colony stimulating factor (GM-CSF) at optimal concentrations over 6 days induces monocytes to differentiate into MDDC that display CD1a, DC-SIGN, HLA-DR, but lack CD14 (Fig.…”