Intracellular life of protozoan Toxoplasma gondii:Parasitophorous vacuole establishment and survival strategies

Toxoplasma gondii is a protozoan of worldwide distribution and the agent of toxoplasmosis.It is estimated that 30%–50%of the world population could be infected with this parasite.Although the infection in immunocompetent individuals is mostly asymptomatic,the disease in immunosuppressed and pregnant is a risk condition.As a member of the phylum Apicomplexa,T.gondii has an obligatory intracellular lifestyle;therefore,invading a host cell and establishing it inside a parasitophorous vacuole(PV)are mandatories for the survival of this parasite.The construction of a perfect intracellular niche for T.gondii requires the secretion of an arsenal of proteins from unique secretory organelles.These proteins will remodel the vacuolar environment and the host cell organization and functions,allowing the parasite to access essential nutrients and stay“invisible”inside a host cell.In the present review,we will discuss the main steps involved in the PV formation and its differentiation to tissue cyst,focusing mainly on the strategies employed in the acquisition of nutrients and proteins involved in host cell modification.

Trichomonas vaginalis perturbs the junctional complex in epithelial cells

Trichomonas vaginalis,a protist parasite of the urogenital tract in humans,is the causative agent of trichomonosis,which in recent years have been associated with the cervical cancer development.In the present study we analyzed the modifications at the junctional complex level of Caco-2 cells after interaction with two isolates of T.vaginalis and the influence of the iron concentration present in the parasite’s culture medium on the interaction effects.Our results show that T.vaginalis adheres to the epithelial cell causing alterations in the junctional complex,such as:(a)a decrease in transepithelial electrical resistance;(b)alteration in the pattern of junctional complex proteins distribution as observed for E-cadherin,occludin and ZO-1;and(c)enlargement of the spaces between epithelial cells.These effects were dependent on(a)the degree of the parasite virulence isolate,(b)the iron concentration in the culture medium,and(c)the expression of adhesin proteins on the parasite surface.

Trypanosoma cruzi invasion in non-phagocytic cells:an ultrastructural study

Trypanosoma cruzi is the causative agent of Chagas disease.This parasite requires the intracellular niche in order to proliferate and disseminate the infection.After invasion,T.cruzi resides temporarily in an acidic vacuole which is lysed by a not well-understood mechanism.Transmission electron microscopy was used to describe the process of T.cruzi escape from the parasitophorous vacuole over the time.Using HeLa(non-professional phagocytic cells)as host cell,we observed that recently internalized parasites reside in a membrane-bounded vacuole.A few hours later,the first sign of vacuole disruption appeared as membrane discontinuities.This observation was followed by a progressive vacuole swelling as evidenced by an electron-lucent halo between the parasite and the vacuole membrane.Apparently,the vacuole membrane remnants reorganized as small vesicles that eventually disappeared from the vicinity of the parasites.Finally,parasites reach the host cell cytosol where replication takes place.The thorough ultrastructural description of this process set the base for a comprehensive understanding of the parasite-host cell interaction and,thus open the possibility of new therapeutic intervention strategies.

Tritrichomonas foetus:New structures by high-resolution scanning helium ion microscopy

Helium ion scanning microscopy(HIM)is a novel high-resolution scanning microscopy technique that uses helium ions instead of electrons to form images of the highest quality and resolution,providing a sub-nanometer resolution sputter uncoated biological cell.Here,we took advantage of HIM to explore the cell surface of Tritrichomonas foetus,a protist parasite of cattle that provokes hard infection and abortion in cows.We describe thin protrusions,like nanotubes described in other cells,with different sizes(27 nm to 81 nm in thickness)and various lengths(from 73 nm to 2μm),as well bulbous structures either budding from the cell surface or present in the extremities of some protrusions.The flagella also presented these thin protrusions and different protein decoration,similar to those previously described using freeze-fracture techniques.Nanotubes between two cells were also seen,and their role in infection is discussed.The cell surface was also examined and showed several pits indicative of endocytic activity and other types of arrays of particles.These observations were confirmed using Scanning Electron Microscopy(SEM),negative staining,and conventional thin sectioning for observation by transmission electron microscopy.Our findings provide new and relevant information that may contribute to a better understanding of protozoan biology and its interaction with mammalian cells.