Parasites have been shown to up- and downregulate host apoptosis, most likely facilitating their ability to successfully establish an infection in the host. It has been demonstrated that pathogens modulate well-established pathways, leading to cell death, including induction of the Fas–FasL system to promote apoptosis. In contrast, it has also been shown that in other instances a decrease in host cell apoptosis results after the upregulation of genes in the Bcl-2 family. The present study examined the ability of Trypanosoma cruzi to modulate expression of host cell genes of the TNFR1 apoptotic pathway. Using microarray technology, gene expression was compared between uninfected BALB/c fibroblasts and T. cruzi –infected BALB/c fibroblasts. After comparing expression patterns between uninfected and T. cruzi –infected BALB/c fibroblasts, it was concluded that genetic expression of genes in the TNFR1 apoptotic pathway is downregulated in T. cruzi –infected cells, indicating that in BALB/c fibroblasts the parasite decreases the expression of genes, leading to host cell apoptosis.

Trypanosoma cruzi , a protozoan parasite, is the etiologic agent of Chagas disease. The disease is characterized by acute and chronic phases, with high and low parasitemia, respectively. A strong immune activation is necessary for the host to enter the chronic phase; however, immune mechanisms participating in the reduction of parasites between the acute and chronic phases of the disease have been very difficult to elucidate. We report here the discovery of anti-egressin, an antibody present in serum from chronically infected BALB/c mice that is able to inhibit parasite egress from infected BALB/c fibroblast cultures in vitro. The antibody is very concentrated in serum from these mice; chronic serum may be diluted 1:20 while still maintaining functional activity. Isotype analysis of anti-egressin has suggested it to be IgG2a. Further analysis revealed that anti-egressin was specific for a component expressed on the surface of infected host cells. The specificity of anti-egressin toward the extracellular portion of infected host cells was demonstrated both by using a quantitative assay measuring released trypomastigotes and through immunocytochemical staining. The novel role of anti-egressin in the inhibition of parasite egress from infected host cells has not been described in the literature to date. We believe that anti-egressin plays an important role in achieving the low parasitemia characteristic of chronic Chagas disease.

Trypanosoma cruzi is the causative agent of Chagas disease, which is characterized by acute and chronic phases. During the former, parasitemia rises dramatically, then decreases significantly during the chronic phase. Immune mechanisms responsible for the parasitemia reduction have not been thoroughly elucidated. The goal of the present study was to further characterize the immune response during chronic infection. Previously, we described antiegressin, an antibody in sera from chronically infected mice. The in vitro presence of antiegressin inhibits parasite egress from infected host cells. Antiegressin appears by day 14 of an in vivo infection and is maintained through at least day 280 postinfection. The in vitro functional activity of antiegressin is initiated late in the 4–6 days intracellular growth cycle of T. cruzi ; antiegressin may be added at day 4, inhibiting parasite release at day 5. Immunocytochemical staining using antineuraminidase demonstrates the presence of mature parasites inside host BALB/c fibroblasts grown in the presence of antiegressin. These results demonstrate the ability of antiegressin to inhibit emergence of developmentally mature trypomastigotes from infected host cells late in their intracellular growth cycle. We believe this antibody plays an important and novel role in achieving the low-parasitemia characteristic of chronic Chagas disease.

Dicationic compounds, which are derivatives of pentamidine, are being developed for use as antiprotozoal drugs. These compounds bind to the minor groove of DNA and are thought to inhibit DNA-dependent enzymes and thereby prevent cellular replication by protozoans. The objective of this study was to test the ability of a group of these compounds to inhibit the intracellular and extracellular reproduction of Trypanosoma cruzi in vitro. At present, there are few drugs in use capable of inhibiting the intracellular stages of this parasite, and therefore compounds with this ability would be of value. Cultures of mouse fibroblasts were infected and treated with doses of dicationic compounds, and the numbers of parasites released at the end of the 5- to 7-day growth cycle were determined. Five of the compounds tested were found to be effective at inhibiting T. cruzi growth at doses that were not toxic to the host cells. The compound found most effective (DB709) inhibited parasite release at the low concentration of 0.8 ng/ml, justifying further study. These results suggest that dicationic compounds may have potential as chemotherapy against T. cruzi infection.