Effect of interferon on the infectivity of Trypanosoma cruzi in cultured HeLa cells

Results are presented on the effects of human lymphoblastoid interferon (HUIFN-α-ly) on the infectivity of metacyclic culture forms of Trypanosoma cruzi in HeLa cells. When cells were pretreated with interferon the parasitisation ratios of the cultures increased with respect to controls. This phenomenon also occurs when interferon was added during the period of parasite-cell interaction. When parasites were pretreated with interferon but cells were not, no increase in the parasitisation ratios was observed.     

Isolation and purification of amastigotes of Trypanosoma cruzi from cultured vero cells

A method is described for the isolation and purification of the intracellular amastigotes of Trypanosoma cruzi from cultured Vero cells. Host cells were infected with metacyclic forms obtained in Grace's medium. Six days after infection, the cells wer subjected to treatment with trypsin to obtain the intracellular forms. The parasites were collected and purified by Percoll discontinuous gradient centrifugation.     

Presence of Trypanosoma cruzi antigen on the surface of both infected and uninfected cells in tissue culture

LLC-MK2 cell monolayers infected with Trypanosoma cruzi were shown by immunofluorescence to present parasite antigens on the surface of both parasitized and non-parasitized cells after completion of the first intracellular cycle and rupture of infected cells. The cell-culture supernatant fluid at this stage, as well as the supernatant fluid of parasites left overnight in culture medium were concentrated and contained antigen capable of binding to uninfected cell monolayers. The origin of this antigen, as well as its eventual role in the pathogenesis of Chagas' disease, are discussed.     

Human chagasic serum contains antibodies capable of inhibiting Trypanosoma cruzi egress from tissue culture cells

Previous studies at our laboratory have shown that an antibody (antiegressin) present in the serum of chronically infected mice is capable of inhibiting the egress of Trypanosoma cruzi from infected BALB/c fibroblasts. We have used this in vitro system to evaluate whether human chagasic serum is also capable of inhibiting T. cruzi egress. BALB/c fibroblasts were infected with tissue culture-derived parasites. Five-percent solutions of the individual human serum samples in culture medium were added to the wells, and the number of parasites released was determined at day 5 after infection. The cells cultured with serum from infected individuals released between 37% and 72% fewer parasites than those cultured with control serum. A similar reduction in parasite egress resulted from incubation with the protein-A purified IgG fraction from 3 of these human samples. Immunocytochemical staining employing antineuraminidase antibodies supported the notion that the reduction in parasite levels is due to inhibition at the point of parasite egress. These results indicate that human serum of individuals infected with T. cruzi is capable of inhibiting release of the parasite from infected tissue culture cells and that the phenomenon of egress-inhibition may be relevant during infection of human subjects.     

Intraspecific variation in Trypanosoma cruzi: effect of temperature on the intracellular differentiation in tissue culture.

Inhibition of T. cruzi amastigote-trypomastigote differentiation in tissue culture at 37 C is a strain-dependent event. When eight T. cruzi strains were submitted to two environmental temperatures (33 and 37 C), the following patterns of differentiation were obtained: in three strains, transformation was inhibited at 37 C but readily occurred at 33 C; in three other strains differentiation took place at both temperatures; finally, in the two remaining strains, a partial inhibition was detected at 37 C. The authors discuss the meaning of this intraspecific variation and the possible relationship with the occurrence of temperature-sensitive mutants among protozoa.     

Mechanism of action of a nitroimidazole-thiadiazole derivate upon Trypanosoma cruzi tissue culture amastigotes

Megazol (CL 64,855) a very effective drug in experimental infections by Trypanosoma cruzi, and also in in vitro assays with vertebrate forms of the parasite, had its activity upon macromolecule biosynthesis tested using tissue culture-derived amastigote forms. Megazol presented a drastic inhibition of [3H]-leucine incorporation, and only a partial inhibition of [3H]-thymidine and [3H]-uridine incorporation, suggesting a selective activity upon protein synthesis. Comparing the three drugs, megazol was more potent than nifurtimox and benznidazole in inhibiting protein and DNA synthesis. Megazol showed a 91% of inhibition of [3H]-leucine incorporation whereas nifurtimox and benznidazole, 0% and 2%, respectively. These latter two drugs inhibited the incorporation of all the precursors tested at similar levels, but the concentration of benznidazole was always three times higher, suggesting different mechanisms of action or, more probably, a greater efficiency of the 5-nitrofuran derivate in relation to the 2-nitroimidazole. So, we conclude that the mode of action of megazol is different from the ones of nifurtimox and benznidazole and that its primary effect is associated with an impairment of protein synthesis.     

The development of Trypanosoma cruzi in triatominae

Trypanosoma cruzi multiplies and differentiates in the digestive tract of triatomine insects. These insects ingest an enormous amount of blood, with ingestion followed very rapidly by a strong diuresis, slow digestion and occasionally long periods of starvation. Resulting changes in the intestinal environment induce the development of dominant stages of T. cruzi--epimastigotes and metacyclic trypomastigotes--and can be correlated with the appearance of specific developmental stages--spheromastigotes and giant cells--which otherwise are only rarely seen. Here, Astrid Kollien and Günter Schaub outline recent research on these developmental steps of T. cruzi in the vector, and the effects of different compounds acting against the parasite in the vector.     

Cytochrome P-450 in culture forms of Trypanosoma cruzi

Trypanosoma cruzi epimastigote and trypomastigote forms contain microsomal peptides in the 40-60,000 mol. wt region, some of which are heme-staining-positive and are induced by phenobarbital, as indicated by SDS-gel electrophoresis and by double-labeling experiments. Epimastigotes show induced peptides of mol. wt 56,000, 52,000, 49,000, 44,000, 42,000 and 40,500 whereas only one peptide (52,500 mol. wt) is increased in trypomastigotes. Fractionation of microsomes derived from epimastigotes by octylamine Sepharose-4B column chromatography reveals the presence of two heme peptides with mol. wt of 55,800 and 56,600. The pooled fraction has a typical cytochrome P-450 CO-difference spectrum and appears to correspond to a high spin form. The demonstration of the existence of this family of hemoproteins in T. cruzi further supports the idea that resistance to chemotherapeutic agents is due to active metabolism. The active metabolism, however, may not be similar in the various developmental forms of this organism since differences exist in the patterns of induction of heme-positive microsomal peptides.     

Effect of poly-L-lysine and neuraminidase on the infectivity of Trypanosoma cruzi in cultured HeLa cells

The percentage of parasitisation and index of adherence of Trypanosoma cruzi has been studied when host HeLa cells or metacyclic forms were pretreated with neuraminidase or with poly-L-lysine. The percentage of parasitisation was significatively reduced (P less than or equal to 0.001) when cells were pretreated with poly-L-lysine while pretreatment with neuraminidase caused no apparent effects. On the other hand, the adherence of the metacyclic forms pretreated with poly-L-lysine or neuraminidase was significantly higher than that of the control group.