[Insertion of Trypanosoma cruzi DNA in the genome of mammal host cell through infection]

Correlation of Parasite Burden, kDNA Integration, Autoreactive Antibodies, and Cytokine Pattern in the Pathophysiology of Chagas Disease

Chagas disease (CD), caused by the protozoan Trypanosoma cruzi (T. cruzi), is the main parasitic disease in the Western Hemisphere. Unfortunately, its physiopathology is not completely understood, and cardiomegaly development is hard to predict. Trying to explain tissue lesion and the fact that only a percentage of the infected individuals develops clinical manifestations, a variety of mechanisms have been suggested as the provokers of CD, such as parasite persistence and autoimmune responses. However, holistic analysis of how parasite and host-related elements may connect to each other and influence clinical outcome is still scarce in the literature. Here, we investigated murine models of CD caused by three different pathogen strains: Colombian, CL Brener and Y strains, and employed parasitological and immunological tests to determine parasite load, antibody reactivity, and cytokine production during the acute and chronic phases of the disease. Also, we developed a quantitative PCR (qPCR) protocol to quantify T. cruzi kDNA minicircle integration into the mammalian host genome. Finally, we used a correlation analysis to interconnect parasite- and host-related factors over time. Higher parasite load in the heart and in the intestine was significantly associated with IgG raised against host cardiac proteins. Also, increased heart and bone marrow parasitism was associated with a more intense leukocyte infiltration. kDNA integration rates correlated to the levels of IgG antibodies reactive to host cardiac proteins and interferon production, both influencing tissue inflammation. In conclusion, our results shed light into how inflammatory process associates with parasite load, kDNA transfer to the host, autoreactive autoantibody production and cytokine profile. Altogether, our data support the proposal of an updated integrative theory regarding CD pathophysiology.

Myocardial inflammatory infiltrate in human chronic chagasic cardiomyopathy: Immunohistochemical findings

Chagas' disease is the most common form of chronic myocarditis in the world. It is characterized by a progressive chronic myocarditis that leads to cardiomegaly, arrhythmias, cardiac failure, and thromboembolic phenomena. This communication reports studies on the immunohistochemistry of chronic infiltrates in 30 endomyocardial biopsies and in contracting and specialized myocardium of autopsies of four patients suffering from Chagas' cardiomyopathy. Expression of the following antigens was studied: common leucocyte antigen (CLA-CD45R), L-26(CD20), CD68, kappa and lambda light chains and T-UCLH-1 (CD45RO), and MB-1. Streptavidin-peroxidase and streptavidin-alkaline phosphatase with biotinylated anti-mouse IgG were used as detection systems. Double immunostaining for the simultaneous demonstration of T lymphocytes (CD45R0) and macrophages was performed using both immunoenzymatic techniques consecutively. Expression of CD31 was detected for the demonstration of endothelial cells. In endomyocardial biopsies, tissue forms of trypanosomes were not found. The percentage of fibrous tissue was 24.1% ± 12.8% (range 8.2%-49%). Eosinophils were scarce (1/high-power field), but associated with necrotic areas of the myocardium. Mast cells were scarce or absent. They were always situated in fibrotic areas. The most remarkable finding was the presence of infiltrates consisting of macrophages and CLA-positive mononuclear cells. Twenty-six and one-half percent of them were T lymphocytes, and 10.5% were B lymphocytes. Lymphocytic infiltration was particularly associated with necrotic and degenerative myocardial lesions. Thirty percent of the infiltrate was composed of macrophages (positive CD68 cells). The remaining infiltrate was composed of mononuclear cells resembling macrophages and CLA-negative mononuclear cells. Contacts between CD68-positive cells and T lymphocytes were frequently found. CD31 antibodies clearly pointed out normal endothelial cells, in either normal or damaged vessels. No isolated cells positive for these antibodies were found within the mononuclear infiltrate. In autopsied hearts, myocardial lesions consisted of a chronic inflammatory process with fibrotic scars and extensive mononuclear infiltrates. No amastigote nests were found. A statistically significant difference (p < 0.05) was obtained when the percentage of fibrosis was compared in the specialized and contracting myocardiums (51.6% ± 18% vs. 43.4 % ± 8%). Eosinophils were scarce in infiltrates, reaching 5%, and they were associated with necrotic myocardium. Mast cells also were scarce or absent in specialized and in contracting myocardium. Almost all the lymphocytic population was T lymphocytes. Such infiltrates were more prominent in the working myocardium (39%) and in the specialized cells of the left branch of the His bundle than in the atrioventricular node and in the right Hisian branch (34.4%). The 31% of mononuclear cells were CD68 positive, thus corresponding to macrophages. Contacts among T lymphocytes and macrophages were frequently observed. Although much that is concerned with Chagas' cardiomyopathy is controversial, these may be the major ingredients for its pathogenesis: the parasite or a part of it, lymphocytes and macrophages, and fibrosis. Then a multifactorial or "combined theory" may be suggested to explain the sequence of events that lead to the chronic stage of the disease.

Inhibition of autoimmune Chagas-like heart disease by bone marrow transplantation

BACKGROUND

Infection with the protozoan Trypanosoma cruzi manifests in mammals as Chagas heart disease. The treatment available for chagasic cardiomyopathy is unsatisfactory.

METHODS/PRINCIPAL FINDINGS

To study the disease pathology and its inhibition, we employed a syngeneic chicken model refractory to T. cruzi in which chickens hatched from T. cruzi inoculated eggs retained parasite kDNA (1.4 kb) minicircles. Southern blotting with EcoRI genomic DNA digests revealed main 18 and 20 kb bands by hybridization with a radiolabeled minicircle sequence. Breeding these chickens generated kDNA-mutated F1, F2, and F3 progeny. A targeted-primer TAIL-PCR (tpTAIL-PCR) technique was employed to detect the kDNA integrations. Histocompatible reporter heart grafts were used to detect ongoing inflammatory cardiomyopathy in kDNA-mutated chickens. Fluorochromes were used to label bone marrow CD3+, CD28+, and CD45+ precursors of the thymus-dependent CD8α+ and CD8β+ effector cells that expressed TCRγδ, vβ1 and vβ2 receptors, which infiltrated the adult hearts and the reporter heart grafts.

CONCLUSIONS/SIGNIFICANCE

Genome modifications in kDNA-mutated chickens can be associated with disruption of immune tolerance to compatible heart grafts and with rejection of the adult host's heart and reporter graft, as well as tissue destruction by effector lymphocytes. Autoimmune heart rejection was largely observed in chickens with kDNA mutations in retrotransposons and in coding genes with roles in cell structure, metabolism, growth, and differentiation. Moreover, killing the sick kDNA-mutated bone marrow cells with cytostatic and anti-folate drugs and transplanting healthy marrow cells inhibited heart rejection. We report here for the first time that healthy bone marrow cells inhibited heart pathology in kDNA+ chickens and thus prevented the genetically driven clinical manifestations of the disease.

Applying horizontal gene transfer phenomena to enhance non-viral gene therapy

Horizontal gene transfer (HGT) is widespread amongst prokaryotes, but eukaryotes tend to be far less promiscuous with their genetic information. However, several examples of HGT from pathogens into eukaryotic cells have been discovered and mimicked to improve non-viral gene delivery techniques. For example, several viral proteins and DNA sequences have been used to significantly increase cytoplasmic and nuclear gene delivery. Plant genetic engineering is routinely performed with the pathogenic bacterium Agrobacterium tumefaciens and similar pathogens (e.g. Bartonella henselae) may also be able to transform human cells. Intracellular parasites like Trypanosoma cruzi may also provide new insights into overcoming cellular barriers to gene delivery. Finally, intercellular nucleic acid transfer between host cells will also be briefly discussed. This article will review the unique characteristics of several different viruses and microbes and discuss how their traits have been successfully applied to improve non-viral gene delivery techniques. Consequently, pathogenic traits that originally caused diseases may eventually be used to treat many genetic diseases.

Pathogenesis of chagas' disease: parasite persistence and autoimmunity

Acute Trypanosoma cruzi infections can be asymptomatic, but chronically infected individuals can die of Chagas' disease. The transfer of the parasite mitochondrial kinetoplast DNA (kDNA) minicircle to the genome of chagasic patients can explain the pathogenesis of the disease; in cases of Chagas' disease with evident cardiomyopathy, the kDNA minicircles integrate mainly into retrotransposons at several chromosomes, but the minicircles are also detected in coding regions of genes that regulate cell growth, differentiation, and immune responses. An accurate evaluation of the role played by the genotype alterations in the autoimmune rejection of self-tissues in Chagas' disease is achieved with the cross-kingdom chicken model system, which is refractory to T. cruzi infections. The inoculation of T. cruzi into embryonated eggs prior to incubation generates parasite-free chicks, which retain the kDNA minicircle sequence mainly in the macrochromosome coding genes. Crossbreeding transfers the kDNA mutations to the chicken progeny. The kDNA-mutated chickens develop severe cardiomyopathy in adult life and die of heart failure. The phenotyping of the lesions revealed that cytotoxic CD45, CD8(+) γδ, and CD8α(+) T lymphocytes carry out the rejection of the chicken heart. These results suggest that the inflammatory cardiomyopathy of Chagas' disease is a genetically driven autoimmune disease.

Trypanosoma cruzi in the chicken model: Chagas-like heart disease in the absence of parasitism

BACKGROUND

The administration of anti-trypanosome nitroderivatives curtails Trypanosoma cruzi infection in Chagas disease patients, but does not prevent destructive lesions in the heart. This observation suggests that an effective treatment for the disease requires understanding its pathogenesis.

METHODOLOGY/PRINCIPAL FINDINGS

To understand the origin of clinical manifestations of the heart disease we used a chicken model system in which infection can be initiated in the egg, but parasite persistence is precluded. T. cruzi inoculation into the air chamber of embryonated chicken eggs generated chicks that retained only the parasite mitochondrial kinetoplast DNA minicircle in their genome after eight days of gestation. Crossbreeding showed that minicircles were transferred vertically via the germ line to chicken progeny. Minicircle integration in coding regions was shown by targeted-primer thermal asymmetric interlaced PCR, and detected by direct genomic analysis. The kDNA-mutated chickens died with arrhythmias, shortness of breath, cyanosis and heart failure. These chickens with cardiomyopathy had rupture of the dystrophin and other genes that regulate cell growth and differentiation. Tissue pathology revealed inflammatory dilated cardiomegaly whereby immune system mononuclear cells lyse parasite-free target heart fibers. The heart cell destruction implicated a thymus-dependent, autoimmune; self-tissue rejection carried out by CD45(+), CD8γδ(+), and CD8α lymphocytes.

CONCLUSIONS/SIGNIFICANCE

These results suggest that genetic alterations resulting from kDNA integration in the host genome lead to autoimmune-mediated destruction of heart tissue in the absence of T. cruzi parasites.

Inheritance of DNA transferred from American trypanosomes to human hosts

Interspecies DNA transfer is a major biological process leading to the accumulation of mutations inherited by sexual reproduction among eukaryotes. Lateral DNA transfer events and their inheritance has been challenging to document. In this study we modified a thermal asymmetric interlaced PCR by using additional targeted primers, along with Southern blots, fluorescence techniques, and bioinformatics, to identify lateral DNA transfer events from parasite to host. Instances of naturally occurring human infections by Trypanosoma cruzi are documented, where mitochondrial minicircles integrated mainly into retrotransposable LINE-1 of various chromosomes. The founders of five families show minicircle integrations that were transferred vertically to their progeny. Microhomology end-joining of 6 to 22 AC-rich nucleotide repeats in the minicircles and host DNA mediates foreign DNA integration. Heterogeneous minicircle sequences were distributed randomly among families, with diversity increasing due to subsequent rearrangement of inserted fragments. Mosaic recombination and hitchhiking on retrotransposition events to different loci were more prevalent in germ line as compared to somatic cells. Potential new genes, pseudogenes, and knockouts were identified. A pathway of minicircle integration and maintenance in the host genome is suggested. Thus, infection by T. cruzi has the unexpected consequence of increasing human genetic diversity, and Chagas disease may be a fortuitous share of negative selection. This demonstration of contemporary transfer of eukaryotic DNA to the human genome and its subsequent inheritance by descendants introduces a significant change in the scientific concept of evolutionary biology and medicine.

Chagas disease

Chagas disease is the clinical condition triggered by infection with the protozoan Trypanosoma cruzi. The infection is transmitted by triatomine insects while blood feeding on a human host. Field studies predict that one third of an estimated 18 million T cruzi-infected humans in Latin America will die of Chagas disease. Acute infections are usually asymptomatic, but the ensuing chronic T cruzi infections have been associated with high ratios of morbidity and mortality: Chagas heart disease leads to unexpected death in 37.5% of patients, 58% develop heart failure and die and megacolon or megaoesophagus has been associated with death in 4.5%. The pathogenesis of Chagas disease appears to be related to a parasite-induced mutation of the vertebrate genome. Currently, treatment is unsatisfactory.

Current millennium biotechniques for biomedical research on parasites and host-parasite interactions

The development of biotechnology in the last three decades has generated the feeling that the newest scientific achievements will deliver high standard quality of life through abundance of food and means for successfully combating diseases. Where the new biotechnologies give access to genetic information, there is a common belief that physiological and pathological processes result from subtle modifications of gene expression. Trustfully, modern genetics has produced genetic maps, physical maps and complete nucleotide sequences from 141 viruses, 51 organelles, two eubacteria, one archeon and one eukaryote (Saccharomices cerevisiae). In addition, during the Centennial Commemoration of the Oswaldo Cruz Institute the nearly complete human genome map was proudly announced, whereas the latest Brazilian key stone contribution to science was the publication of the Shillela fastidiosa genomic sequence highlythed on a Nature cover issue. There exists a belief among the populace that further scientific accomplishments will rapidly lead to new drugs and methodological approaches to cure genetic diseases and other incurable ailments. Yet, much evidence has been accumulated, showing that a large information gap exists between the knowledge of genome sequence and our knowledge of genome function. Now that many genome maps are available, people wish to know what are we going to do with them. Certainly, all these scientific accomplishments will shed light on many more secrets of life. Nevertheless, parsimony in the weekly announcements of promising scientific achievements is necessary. We also need many more creative experimental biologists to discover new, as yet un-envisaged biotechnological approaches, and the basic resource needed for carrying out mile stone research necessary for leading us to that "promised land" often proclaimed by the mass media.

Integration of Trypanosoma cruzi kDNA minicircle sequence in the host genome may be associated with autoimmune serum factors in Chagas disease patients

Integration of kDNA sequences within the genome of the host cell shown by PCR amplification with primers to the conserved Trypanosoma cruzi kDNA minicircle sequence was confirmed by Southern hybridization with specific probes. The cells containing the integrated kDNA sequences were then perpetuated as transfected macrophage subclonal lines. The kDNA transfected macrophages expressed membrane antigens that were recognized by antibodies in a panel of sera from ten patients with chronic Chagas disease. These antigens barely expressed in the membrane of uninfected, control macrophage clonal lines were recognized neither by factors in the control, non-chagasic subjects nor in the chagasic sera. This finding suggests the presence of an autoimmune antibody in the chagasic sera that recognizes auto-antigens in the membrane of T. cruzi kDNA transfected macrophage subclonal lines.

Possible integration of Trypanosoma cruzi kDNA minicircles into the host cell genome by infection

Infection with Trypanosoma cruzi is known to induce the division of peritoneal macrophages in BALB/c mice. We have demonstrated, by cytogenetic analysis, that accessory DNA elements are associated with the metaphase macrophage chromosomes of such infected macrophages. The identification of these accessory DNA elements with T. cruzi DNA is strongly supported by the association of 3H-label with some chromatids in macrophages previously infected with T. cruzi which had been labelled with 3H-methyl-thymidine. The karyotyping consistently showed preferential associations of T. cruzi DNA with chromosomes 3, 6 and 11. A conclusive demonstration of the parasite origin of the integrated DNA came from fluorescein in situ hybridization studies using specific parasite DNAs as probes. In order to determine the identity of the inserted DNA and to investigate the nature of the integration mechanism, Southern blot analyses were performed on DNA extracted from both uninfected and infected (but parasite-free) macrophages. Hybridizations of BamHI, EcoRI and TaqI digests of DNA from T. cruzi-infected host cells all revealed the presence of a 1.7-kb DNA fragment when probed with kDNA. The covalent association of kDNA with that of the host was confirmed by the fact that AluI and Hinf-I digests of DNA from infected host cells produced a number of bands, in a size range of 0.8-3.6 kb, which hybridized with kDNA minicircles. None of these bands was found in DNA purified from cell-free preparations of the parasite and thus it must be concluded that they represent insertion fragments between parasite and host cell DNA. These results strongly suggest that kDNA minicircles from T. cruzi have been integrated into the genome of the host cell following infection.