Anionic Sites, Fucose Residues and Class I Human Leukocyte Antigen Fate During Interaction of Toxoplasma gondii with Endothelial Cells

Toxoplasma gondii invades and proliferates in human umbilical vein endothelial cells where it resides in a parasitophorous vacuole. In order to analyze which components of the endothelial cell plasma membrane are internalized and become part of the parasitophorous vacuole membrane, the culture of endothelial cells was labeled with cationized ferritin or UEA I lectin or anti Class I human leukocytte antigen (HLA) before or after infection with T. gondii. The results showed no cationized ferritin and UEA I lectin in any parasitophorous vacuole membrane, however, the Class I HLA molecule labeling was observed in some endocytic vacuoles containing parasite until 1 h of interaction with T. gondii. After 24 h parasite-host cell interaction, the labeling was absent on the vacuolar membrane, but presents only in small vesicles near parasitophorous vacuole. These results suggest the anionic site and fucose residues are excluded at the time of parasitophorous vacuole formation while Class I HLA molecules are present only on a minority of Toxoplasma-containig vacuoles.

B-cell infiltration and frequency of cytokine producing cells differ between localized and disseminated human cutaneous leishmaniases

Biopsies from human localized cutaneous lesions (LCL n = 7) or disseminated lesions (DL n = 8) cases were characterized according to cellular infiltration,frequency of cytokine (IFN-g, TNF-alpha) or iNOS enzyme producing cells. LCL, the most usual form of the disease with usually one or two lesions, exhibits extensive tissue damage. DL is a rare form with widespread lesions throughout the body; exhibiting poor parasite containment but less tissue damage. We demonstrated that LCL lesions exhibit higher frequency of B lymphocytes and a higher intensity of IFN-gamma expression. In both forms of the disease CD8+ were found in higher frequency than CD4+ T cells. Frequency of TNF-alpha and iNOS producing cells, as well as the frequency of CD68+ macrophages, did not differ between LCL and DL. Our findings reinforce the link between an efficient control of parasite and tissue damage, implicating higher frequency of IFN-gamma producing cells, as well as its possible counteraction by infiltrated B cells and hence possible humoral immune response in situ.

Screening and fractionation of plant extracts with antiproliferative activity on human peripheral blood mononuclear cells

Three hundred and thirteen extracts from 136 Brazilian plant species belonging to 36 families were tested for their suppressive activity on phytohemaglutinin (PHA) stimulated proliferation of human peripheral blood mononuclear cells (PBMC). The proliferation was evaluated by the amount of [³H]-thymidine incorporated by the cells. Twenty extracts inhibited or strongly reduced the proliferation in a dose-dependent manner at doses between 10 and 100 µg/ml. Three of these extracts appeared to be non-toxic to lymphocytes, according to the trypan blue permeability assay and visual inspection using optical microscopy. Bioassay-guided fractionation of Alomia myriadenia extract showed that myriadenolide, a labdane diterpene known to occur in this species, could account for the observed activity of the crude extract. Using a similar protocol, an active fraction of the extract from Gaylussacia brasiliensis was obtained. Analysis of the ¹H and13C NMR spectra of this fraction indicates the presence of an acetylated triterpene whose characterization is underway. The extract of Himatanthus obovatus is currently under investigation.