Role of Aryl Hydrocarbon Receptor (AhR) in the Regulation of Immunity and Immunopathology During Trypanosoma cruzi Infection.

Resistance to Trypanosoma cruzi infection is dependent on a rapid induction of Th1-type and CD8+ T cell responses that should be promptly balanced to prevent immunopathology. T. cruzi-infected B6 mice are able to control parasite replication but show a limited expansion of Foxp3+regulatory T (Treg) cells that results in the accumulation of effector immune cells and the development of acute liver pathology. AhR is a ligand-activated transcription factor that promotes Treg cell development and suppression of pro-inflammatory cytokine production in dendritic cells, altering the course of adaptive immune response and the development of immunopathology. Here, we used different AhR-dependent activation strategies aiming to improve the Treg response, and B6 congenic mice carrying a mutant AhR variant with low affinity for its ligands (AhRd) to evaluate the role of AhR activation by natural ligands during experimental T. cruzi infection. The outcome of TCDD or 3-HK plus ITE treatments indicated that strong or weak AhR activation before or during T. cruzi infection was effective to regulate inflammation improving the Treg cell response and regularizing the ratio between CD4+ CD25- to Treg cells. However, AhR activation shifted the host-parasite balance to the parasite replication. Weak AhR activation resulted in Treg promotion while strong activation differentially modulated the susceptibility and resistance of cell death in activated T and Treg cells and the increase in TGF-ß-producing Treg cells. Of note, T. cruzi-infected AhRd mice showed low levels of Treg cells associated with strong Th1-type response, low parasite burden and absence of liver pathology. These mice developed a Treg- and Tr1-independent mechanism of Th1 constriction showing increased levels of systemic IL-10 and IL-10-secreting CD4+ splenocytes. In addition, AhR activation induced by exogenous ligands had negative effects on the development of memory CD8+ T cell subsets while the lack/very weak activation in AhRd mice showed opposite results, suggesting that AhR ligation restricts the differentiation of memory CD8+T cell subsets. We propose a model in which a threshold of AhR activation exists and may explain how activation or inhibition of AhR-derived signals by infection/inflammation-induced ligands, therapeutic interventions or exposure to pollutants can modulate infections/diseases outcomes or vaccination efficacy.

Trypanosoma cruzi Exploits Wnt Signaling Pathway to Promote Its Intracellular Replication in Macrophages.

During the acute phase of Trypanosoma cruzi infection, macrophages can act as host cells for the parasites as well as effector cells in the early anti-parasitic immune response. Thus, the targeting of specific signaling pathways could modulate macrophages response to restrict parasite replication and instruct an appropriate adaptive response. Recently, it has become evident that Wnt signaling has immunomodulatory functions during inflammation and infection. Here, we tested the hypothesis that during T. cruzi infection, the activation of Wnt signaling pathway in macrophages plays a role in modulating the inflammatory/tolerogenic response and therefore regulating the control of parasite replication. In this report, we show that early after T. cruzi infection of bone marrow-derived macrophages (BMM), ß-catenin was activated and Wnt3a, Wnt5a, and some Frizzled receptors as well as Wnt/ß-catenin pathway's target genes were upregulated, with Wnt proteins signaling sustaining the activation of Wnt/ß-catenin pathway and then activating the Wnt/Ca+2 pathway. Wnt signaling pathway activation was critical to sustain the parasite's replication in BMM; since the treatments with specific inhibitors of ß-catenin transcriptional activation or Wnt proteins secretion limited the parasite replication. Mechanistically, inhibition of Wnt signaling pathway armed BMM to fight against T. cruzi by inducing the production of pro-inflammatory cytokines and indoleamine 2,3-dioxygenase activity and by downregulating arginase activity. Likewise, in vivo pharmacological inhibition of the Wnts' interaction with its receptors controlled the parasite replication and improved the survival of lethally infected mice. It is well established that T. cruzi infection activates a plethora of signaling pathways that ultimately regulate immune mediators to determine the modulation of a defined set of effector functions in macrophages. In this study, we have revealed a new signaling pathway that is activated by the interaction between protozoan parasites and host innate immunity, establishing a new conceptual framework for the development of new therapies.

3-Hydroxykynurenine, a Tryptophan Metabolite Generated during the Infection, Is Active Against Trypanosoma cruzi.

The antiparasitic activity of 3-hydroxykynurenine (3-HK), one of the major tryptophan catabolites of the kynurenine pathway, against both Trypanosoma cruzi evolutive forms that are important for human infection, trypomastigotes (Tps) and amastigotes (Am), possible targets in the parasite and the drug toxicity to mammalian cells have been investigated. 3-HK showed a potent activity against Am with IC50 values in the micromolar concentration range, while the IC50 values to cause Tps death was ∼6000-times higher, indicating that the replicative form present in the vertebrate hosts is much more susceptible to 3-HK than bloodstream Tps. In addition, 3-HK showed activity against Tps and Am, at concentrations that did not exhibit toxicity to mammalian cells. Ultrastructural analysis and flow cytometry studies indicated that Am and Tps mitochondrion and nuclei contain 3-HK targets. The potency and selectivity of 3-HK, which is generated during T. cruzi infection in human and mice, suggest that 3-HK may be a suitable candidate for drug research and development for Chagas disease.

[First report of complete genome sequence and phylogenetic analysis of Human Bocavirus 1 isolated in Argentina]. / Primer reporte de secuencia genómica completa y análisis filogenético de Bocavirus Humano 1 aislado en Argentina.

ANTECEDENTS: Human bocavirus (HBoV) is a parvovirus identified for the first time in 2005 associated to upper- and lower- acute respiratory tract infection (ARI), which is one of the main causes of morbimortality in infant population worldwide. Currently four genotypes have been described named HBoV1-4, of which HBoV1 is the one predominantly related to ARI. OBJECTIVE: To obtain the complete genome of respiratory HBoV locally isolated. METHODS: By means of bioinformatics tools such as ClustalW and NCBI Primer-Blast, primers were designed to amplify overlapping DNA fragments altogether spanning the complete genome of HBoV. Fragments were amplified by PCR and sequenced by BigDye Terminator capillary technology. Sequence editing and phylogenetic analysis were accomplished using MEGA v6 software. RESULTS: Complete genome sequence of HBoV1 strain 307AR09 was obtained after isolation from respiratory secretion of a pediatric patient with bronchiolitis. The sequence was deposited in the GenBank public database (accession number KJ634207). The phylogenetic analysis including complete genome sequences of all four genotypes from around the world shows similarity close to 100% between the local strain and the virus originally discovered in Sweden (DQ000495). The four genotypes clustered in 2 groups of high internal homology: HBoV1-HBoV3 and HBoV2-HBoV4. CONCLUSIONS: We provide local molecular data that can be used in future technological developments for research and diagnostic tests intended for medical practice. Our results add support to the proposed redistribution of the four genotypes into 2 species.

Antecedentes. El Bocavirus humano (HBoV) es un parvovirus descripto por primera vez en 2005, asociado a cuadros leves y graves de infección respiratoria aguda (IRA), una de las principales causas de morbimortalidad en la población infantil en todo el mundo. Al presente se han identificado 4 genotipos, nombradas HBoV1 a 4, de los cuales el primero es el que se asocia a IRA con predominancia. Objetivo. Obtener el genoma completo de HBoV respiratorio aislado localmente. Métodos. Se diseñaron primers para fragmentos superpuestos del genoma completo de HBoV, empleando las herramientas informáticas ClustalW y NCBI Primer-Blast. Los fragmentos se amplificaron por PCR convencional y se secuenciaron mediante tecnología capilar BigDye Terminator. La edición de las secuencias y análisis filogenético se realizó con el programa MEGA v6. Resultados. Se obtuvo la secuencia genómica completa de HBoV1 cepa 307AR09, aislada de secreción respiratoria de paciente pediátrico con bronquiolitis. La misma fue depositada en la base de datos GenBank con número de acceso KJ634207. El análisis filogenético con secuencias genómicas completas de los 4 genotipos obtenidas en distintas regiones del mundo muestra similitud cercana al 100% con la secuencia original descubierta en Suecia (DQ000495), así como el agrupamiento de los 4 genotipos en 2 clusters de alta homología interna: HBoV1-HBoV3 y HBoV2-HBoV4. Conclusiones. Se aportan datos locales para futuros desarrollos tecnológicos destinados tanto a la investigación como al diseño de métodos diagnósticos para la práctica médica. Por otra parte, los resultados sustentan la propuesta de redistribución taxonómica de los 4 genotipos en 2 especies.

Comorbidity and high viral load linked to clinical presentation of respiratory human bocavirus infection.

Human bocavirus (HBoV) is a new parvovirus associated with acute respiratory tract infection (ARTI). In order to evaluate HBoV significance as an agent of acute respiratory disease, we screened 1,135 respiratory samples from children and adults with and without symptoms during two complete calendar years. HBoV1 prevalence in patients with ARTI was 6.33 % in 2011 and 11.64 % in 2012, including neonatal and adult patients. HBoV1 was also detected in 3.77 % of asymptomatic individuals. The co-detection rate was 78.1 %. Among children, 87 % were clinically diagnosed with lower respiratory infection (no significant differences between patients with and without coinfection), and 31 % exhibited comorbidities. Pediatric patients with comorbidities were significantly older than patients without comorbidities. Patients with ARTI had either high or low viral load, while controls had only low viral load, but there were no clinical differences between patients with high or low viral load. In conclusion, we present evidence of the pathogenic potential of HBoV1 in young children with ARTI. Since patients with HBoV1-single infection are not significantly different from those with coinfection with respect to clinical features, the virus can be as pathogenic by itself as other respiratory agents are. Furthermore, an association between high HBoV1 load and disease could not be demonstrated in this study, but all asymptomatic individuals had low viral loads. Also, children with comorbidities are susceptible to HBoV1 infection at older ages than previously healthy children. Thus, the clinical presentation of infection may occur depending on both viral load and the particular interaction between the HBoV1 and the host.