No abstract

Protective immunity against Toxoplasma gondii is known to be mediated mainly by T lymphocytes and gamma interferon (IFN-␥). The contribution of CD4؉ and CD8 ؉ T-lymphocyte subsets to protective immune responses against T. gondii infection, triggered by a GRA1 (p24) DNA vaccine, was assessed in this study. In vitro T-cell depletion experiments indicated that both CD4؉ and CD8 ؉ T-cell subsets produced IFN-␥ upon restimulation with a T. gondii lysate. In addition, the GRA1 DNA vaccine elicited CD8 ؉ T cells that were shown to have cytolytic activity against parasite-infected target cells and a GRA1-transfected cell line. C3H mice immunized with the GRA1 DNA vaccine showed 75 to 100% protection, while 0 to 25% of the mice immunized with the empty control vector survived challenge with T. gondii cysts. In vivo T-cell depletion experiments indicated that CD8 ؉ T cells were essential for the survival of GRA1-vaccinated C3H mice during the acute phase of T. gondii infection, while depletion of CD4 ؉ T cells led to an increase in brain cyst burden during the chronic phase of infection.

In a previous study, single-gene vaccination with GRA1, GRA7 or ROP2 was shown to elicit partial protection against Toxoplasma gondii. In this study, the contribution of each antigen in the evoked humoral and cellular immune responses was evaluated after vaccination with plasmid mixtures containing GRA1, GRA7 and ROP2. Cocktail DNA vaccinated mice developed high antibody titers against the antigens from two-gene DNA vaccine cocktails, but lower titres when immunized with the three-gene cocktail. High numbers of IFN-gamma secreting splenocytes were generated predominantly against GRA7. Brain cyst burden was reduced by 81% in mice vaccinated with the three-gene mixture and they were completely protected against acute toxoplasmosis. Similar high levels of brain cyst reductions were obtained after vaccination with cocktails composed of GRA1 and GRA7 (89% reduction), or GRA7 and ROP2 (79% reduction), but not with the cocktail composed of GRA1 and ROP2. In low dose single-gene vaccinations, IFN-gamma and strong protection could only be elicited by GRA7. Hence, the presence of GRA7 in the DNA vaccine formulation was important for optimal protection and this was correlated with GRA7-specific IFN-gamma production. We propose GRA7 as a main component in cocktail DNA vaccines for vaccination against T. gondii.

No abstract

The aim of our study was to investigate whether the level of actin polymerization plays a role in the motile and tissue infiltrating behavior of malignant lymphoma cells. For a panel of cell lines derived from the murine BW5147 T-cell lymphoma, we had previously shown a correlation between experimental metastasis formation and in vitro monolayer invasion. We have analyzed the motility and the F-actin content of six nonmetastatic, noninvasive (meta-inv-) and five metastatic, invasive (meta+inv+) variants of BW5147. Fourier analysis of cell contours was used to quantify shape changes of cells. All meta+inv+ lines rapidly protruded and retracted pseudopodia, whereas only one of the six meta-inv- lines showed this type of motility. Flow cytometry of cells stained with fluorescein-labeled phalloidin showed that the motile meta+inv+ cell lines have a higher F-actin content than their nonmotile meta-inv- counterparts. The results indicate that in lymphoma cells a high level of actin polymerization is a prerequisite for the formation of pseudopodia, which in turn are necessary for infiltration of the cells into tissues, and eventually for efficient metastasis formation. A corollary of this conclusion is that regulation of actin polymerization is a possible target for intervention aimed at moderating the spread of malignant lymphoma.