Use of L-proline and ATP production by Trypanosoma cruzi metacyclic forms as requirements for host cell invasion.

The process of host cell invasion by Trypanosoma cruzi depends on parasite energy. What source of energy is used for that event is not known. To address this and other questions related to T. cruzi energy requirements and cell invasion, we analyzed metacyclic trypomastigote forms of the phylogenetically distant CL and G strains. For both strains, the nutritional stress experienced by cells starved for 24, 36, or 48 h in phosphate-buffered saline reduced the ATP content and the ability of the parasite to invade HeLa cells proportionally to the starvation time. Inhibition of ATP production by treating parasites with rotenone plus antimycin A also diminished the infectivity. Nutrient depletion did not alter the expression of gp82, the surface molecule that mediates CL strain internalization, but increased the expression of gp90, the negative regulator of cell invasion, in the G strain. When L-proline was given to metacyclic forms starved for 36 h, the ATP levels were restored to those of nonstarved controls for both strains. Glucose had no such effect, although this carbohydrate and L-proline were transported in similar fashions. Recovery of infectivity promoted by L-proline treatment of starved parasites was restricted to the CL strain. The profile of restoration of ATP content and gp82-mediated invasion capacity by L-proline treatment of starved Y-strain parasites was similar to that of the CL strain, whereas the Dm28 and Dm30 strains, whose infectivity is downregulated by gp90, behaved like the G strain. L-Proline was also found to increase the ability of the CL strain to traverse a gastric mucin layer, a property important for the establishment of T. cruzi infection by the oral route. Efficient translocation of parasites through gastric mucin toward the target epithelial cells in the stomach mucosa is an essential requirement for subsequent cell invasion. By relying on these closely associated ATP-driven processes, the metacyclic trypomastigotes effectively accomplish their internalization.

Co-infection with Trypanosoma cruzi protects mice against early death by neurological or pulmonary disorders induced by Plasmodium berghei ANKA.

OBJECTIVE: The objective of this study was to investigate whether the infection of C57BL/6 mice by P. berghei ANKA, which causes severe malaria, was modulated by co-infection with Trypanosoma cruzi. METHODS: Groups of C57BL/6 mice were infected either with P. berghei ANKA, T. cruzi strain G, or with both parasites. The presence of parasites was checked by microscopic examination of blood samples. Symptoms of neurological or respiratory disorders, as well as mortality, were registered. Breakdown of the blood brain barrier was determined by injecting the dye Evans blue. Histological sections of the lung were prepared and stained with hematoxilin-eosin. RESULTS: All mice infected only with P. berghei ANKA died within 7-11 days post-infection, either with symptoms of cerebral malaria or with respiratory abnormalities. The animals co-infected with T. cruzi strain G survived longer, without any of the referred to symptoms. Protection against the early death by severe malaria was effective when mice were given T. cruzi 15 days before P. berghei inoculation. Breakdown of the blood brain barrier and extensive pulmonary oedema, caused by malaria parasites, were much less pronounced in co-infected mice. The degree of protection to severe malaria and early death, conferred by co-infection with T. cruzi, was comparable to that conferred by treatment with anti-CD8 antibodies. CONCLUSION: Co-infection with T. cruzi protects C57BL/6 against the early death by malaria infection, by partially preventing either the breakdown of the blood brain, and cerebral malaria as a consequence, or the pulmonary oedema.

Interaction with host factors exacerbates Trypanosoma cruzi cell invasion capacity upon oral infection.

Outbreaks of severe acute Chagas' disease acquired by oral infection, leading to death in some cases, have occurred in recent years. Using the mouse model, we investigated the basis of such virulence by analyzing a Trypanosoma cruzi isolate, SC, from a patient with severe acute clinical symptoms, who was infected by oral route. It has previously been shown that, upon oral inoculation into mice, T. cruzi metacyclic trypomastigotes invade the gastric mucosal epithelium by engaging the stage-specific surface glycoprotein gp82, whereas the surface molecule gp90 functions as a down-modulator of cell invasion. We found that, when orally inoculated into mice, metacyclic forms of the SC isolate, which express high levels of gp90, produced high parasitemias and high mortality, in sharp contrast with the reduced infectivity in vitro. Upon recovery from the mouse stomach 1h after oral inoculation, the gp90 molecule of the parasites was completely degraded, and their entry into HeLa cells, as well as into Caco-2 cells, was increased. The gp82 molecule was more resistant to digestive action of the gastric juice. Host cell invasion of SC isolate metacyclic trypomastigotes was augmented in the presence of gastric mucin. No alteration in infectivity was observed in T. cruzi strains CL and G which were used as references and which express gp90 molecules resistant to degradation by gastric juice. Taken together, our findings suggest that the exacerbation of T. cruzi infectivity, such as observed upon interaction of the SC isolate with the mouse stomach components, may be responsible for the severity of acute Chagas' disease that has been reported in outbreaks of oral T. cruzi infection.