RESUMEN
The protozoan parasite Trypanosoma cruzi circulates in the blood as trypomastigotes and invades a variety of cells to multiply intracellularly as amastigotes. The acute phase triggers an immune response that restricts the proliferation of the parasite. However, parasites are able to persist in different tissues causing the pathology of Chagas' disease. Natural killer (NK) cells play an important role in innate resistance to a variety of pathogens. In the present study we demonstrate that NK cells trigger trypanocidal mechanisms in infected L929 cells that are critically dependent on inducible nitric oxide (NO) synthase (iNOS) induction which is, to a major degree, triggered by interferon (IFN)-gamma provided by NK cells. This work provides a more detailed analysis of how NK cells as a part of the innate immune system participate in the control of parasites that reside intracellularly in fibroblast-like L929 cells.
Asunto(s)
Enfermedad de Chagas/inmunología , Fibroblastos/inmunología , Células Asesinas Naturales/inmunología , Trypanosoma cruzi , Animales , Línea Celular , Inducción Enzimática , Inhibidores Enzimáticos/farmacología , Fibroblastos/parasitología , Guanidinas/farmacología , Humanos , Interferón gamma/genética , Interferón gamma/inmunología , Interferón gamma/metabolismo , Interleucina-12/inmunología , Activación de Linfocitos , Depleción Linfocítica , Ratones , Ratones Endogámicos CBA , Óxido Nítrico Sintasa de Tipo II/antagonistas & inhibidores , Óxido Nítrico Sintasa de Tipo II/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
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.
Asunto(s)
Antígenos de Diferenciación/biosíntesis , Antígenos de Diferenciación/inmunología , Enfermedad de Chagas/inmunología , Trypanosoma cruzi/inmunología , Animales , Antígenos CD , Antígenos CD4/análisis , Linfocitos T CD4-Positivos/inmunología , Linfocitos T CD4-Positivos/metabolismo , Antígenos CD8/análisis , Linfocitos T CD8-positivos/inmunología , Linfocitos T CD8-positivos/metabolismo , Antígeno CTLA-4 , Enfermedad de Chagas/parasitología , Modelos Animales de Enfermedad , Regulación de la Expresión Génica , Interferón gamma/análisis , Interferón gamma/biosíntesis , Interleucina-2/análisis , Interleucina-2/biosíntesis , Interleucina-4/análisis , Interleucina-4/biosíntesis , Subgrupos Linfocitarios/inmunología , Subgrupos Linfocitarios/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Bazo/citología , Bazo/inmunología , Trypanosoma cruzi/patogenicidadRESUMEN
Chagas' disease is caused by the protozoan parasite Trypanosoma cruzi and commonly modelled in inbred mice. Susceptibility of mouse strains to experimental infection varies considerably. We quantified parasite tissue burdens in resistant and susceptible strains by real time PCR and applied a backcross strategy to map the genomic loci linked to susceptibility in inbred mice. Resistant B6D2F1 mice were backcrossed with susceptible C57BL/6 mice, and 46 of a total 192 offspring died after infection. Their genomes were scanned with microsatellite markers. One region on chromosome 17 was significantly linked to susceptibility, while another on chromosome 5 was suggestive of linkage.