Susceptibility to acute Trypanosoma cruzi infection in autoimmune strains of mice

We previously observed that mice bearing the autoimmune associated lpr gene exhibit increased susceptibility to challenge with Trypanosoma cruzi, the causative agent of Chagas' disease. We have now tested two other autoimmune prone strains of mice, BXSB and NZB, and found that these animals also show increased sensitivity to acute T. cruzi infection. When challenged with a standard dose (10(2)) of Y strain trypomastigotes, BXSB males (BXSB-YSB), which develop early onset autoimmune disease, suffered high mortality, while late onset autoimmune BXSB females and minimally autoimmune male BXSB mice whose Y chromosome was derived from C57BL/6J mice (BXSB-YB/6) also recover. NZB mice were found to be highly susceptible to challenge while NZW and NZB/W were resistant. A finding common to all groups of susceptible autoimmune mice was increased plasma levels of T. cruzi specific antibody, especially IgM. The data indicate that in two of the three autoimmune prone strains examined, increased T. cruzi susceptibility appears to be linked to restricted genetic elements (i.e. lpr gene and the YSB associated factor) which also influence the rapidity of onset of autoimmunity.     

Protective effect of Trypanosoma rangeli against infections with a highly virulent strain of Trypanosoma cruzi

Summary We investigated the protective effect of Trypanosoma rangeli against infection with Trypanosoma cruzi in animal models of various ages and with different doses of inoculum. The age of the mice and the dose of parasites determined the course of the infection. When T. cruzi was inoculated into mice after challenge with T. rangeli , parasitaemia was more controlled, mortality decreased and histopathology showed lower inflammatory infiltration and pseudocysts. This study proposes a new murine model of the protective effect of recombinant proteins of T. rangeli for possible application in the vaccines field.     

CTLA-4 regulates the murine immune response to Trypanosoma cruzi infection

Infection with Trypanosoma cruzi causes a profound suppression of T cell responsiveness to polyclonal or antigenic stimuli. In this study, we quantified expression of the negative T cell regulatory molecule CTLA-4 in T. cruzi infected mice and analysed its influence on the immune suppression. Levels of splenic CTLA-4 expression were highest around day 10 after infection, reaching 5% in resistant B6D2F1 mice, but exceeding 10% of CD4(+) T cells in C57BL/6 mice that were susceptible to mortal disease. The proliferative response of explanted splenocytes to CD3-mediated stimulation was strongly suppressed in both the susceptible and the resistant strains. Blockade of CTLA-4 in vitro with a monoclonal antibody affected neither proliferative response nor cytokine production (IFN-gamma, IL-4 and IL-2) by splenic T cells from infected C57BL/6 mice. Treatment of mice with anti-CTLA-4 antibody on the day of infection decreased IFN-gamma production and reduced mortality by about 50%. We conclude that high CTLA-4 expression is a hallmark of severe disease in murine T. cruzi infection, and that CTLA-4 has a regulative influence at the early stages during priming of the immune reaction to the parasite, augmenting a strong Th1-biased response.     

Initial induction of immunity, followed by suppression of responses to parasite antigens during Trypanosoma cruzi infection of mice

Infection of a relatively resistant strain of mice (C57BL/6J) with the protozoan parasite Trypanosoma cruzi results in both the induction of parasite-specific T-helper cells and nonspecific suppressor cells. A time course study of the activation of help and suppression revealed that parasite-specific T-helper cell activity increases very early in infection (less than 12 days) at a time when suppression of non-parasite-specific responses and suppressor cell activity is increasing. Between 12 and 14 days of infection, the T-helper cell response to T. cruzi, as measured by the antibody response to hapten-T. cruzi in vitro, is suddenly and dramatically regulated. As reported previously, plastic and G-10 adherent cells appear to be responsible for the regulation of antibody responses to heterologous antigen during T. cruzi infection. These adherent suppressor cells are also responsible for the suppression of antibody responses to hapten-T. cruzi following the first 2 weeks of infection. Suppressor cells continue to regulate the parasite-specific response well into chronic infection even though the response to hapten-T. cruzi appears to return to normal levels. These results are the first to directly implicate nonspecific suppressor cells in the regulation of anti-T. cruzi humoral immune responses.     

Evaluation of IFN-gamma production by CD8 T lymphocytes in response to the K1 peptide from KMP-11 protein in patients infected with Trypanosoma cruzi

The cellular response mediated by MHC class I restricted CD8+ T cells has been shown to be crucial in the control of Chagas disease. The K1 peptide derived from T. cruzi KMP-11 protein has a high binding affinity to the HLA-A*0201 molecule. Nevertheless, it is not known whether this peptide is processed and displayed as an MHC class I epitope during natural infection by T. cruzi. The aim of this study was to evaluate, by ELISPOT assay, the ability of K1 peptide to activate CD8+ T lymphocytes to produce IFN-gamma. Therefore, CD8+ T lymphocytes from 22 HLA-A*0201+ individuals, 12 chronic chagasic patients and 10 uninfected controls, were analysed. The results revealed that two of the chagasic patients had IFN-gamma-secreting CD8+ T cells that were able to respond to K1 peptide with a relative frequency of 110 and 230 per million CD8+ T cells. In contrast, none of HLA-A*0201+ uninfected controls responded to K1 peptide. Responses to HLA-A*0201 restricted peptide from the influenza matrix protein were found in six chagasic patients and four uninfected controls with an average frequency of 175 and 111 cells per million CD8+ T cells, respectively. Moreover, a flow cytometric assay for degranulation showed that chagasic responders had K1-specific cytotoxic CD8+ T cells. It is shown here for the first time that the K1 peptide is efficiently processed, presented and recognized by CD8+ T lymphocytes during the natural course of Chagas disease.     

In-vivo treatment with benznidazole enhances phagocytosis, parasite destruction and cytokine release by macrophages during infection with a drug-susceptible but not with a derived drug-resistant Trypansoma cruzi population

To stuck the effect of chemotherapy on parasite-macrophage interaction we used the wild-type Y strain (drug-susceptible) of Trypanosoma cruzi and a drug-resistant parasite population derived from the same strain. Trypomastigotes isolated from untreated infected mice, as well as, 3 h after treatment with BZ were incubated with inflammatory macrophages and used to study phagocytosis, parasite destruction, cytokine release and reactive nitrogen intermediates (RN!) synthesis. Phagocytosis and destruction of the drug-susceptible parasites were significant/v enhanced by drug treatment. These enhancements were accompanied by an increase in cytokines [interleukin (IL)-12 and tumour necrosis factor (TNF)alpha] and RNI release by murine inflammatory macrophages primed with IFN-gamma. In contrast, BZ treatment of mice infected with drug-resistant T. cruzi population showed no effect whatsoever. The synthesis of IFN-gamma and RNI by splenocytes of mice infected with either susceptible and drug-resistant parasite populations, before and after treatment with BZ were also studied. On/v the splenocytes from mice infected with the drug-susceptible parasites treated with BZ produced high levels of IFN-gamma and RNI. Our findings indicate that BZ acts on the drug-susceptible T. cruzi parasites by enhancing the phagocytosis and the production of cytokines and RN!, thus, favouring the destruction of the intracellular parasites by the cellular compartment of the immune system.