Immediate/early response to Trypanosoma cruzi infection involves minimal modulation of host cell transcription

Trypanosoma cruzi assembles host cytoplasmic processing bodies to evade the innate immune response

Processing bodies (P-bodies, PBs) are cytoplasmic foci formed by condensation of translationally inactivated messenger ribonucleoprotein particles (mRNPs). Infection with the protozoan parasite Trypanosoma cruzi (T. cruzi) promotes PB accumulation in host cells, suggesting their involvement in host mRNA metabolism during parasite infection. To identify PB-regulated mRNA targets during T. cruzi infection, we established a PB-defective human fibrosarcoma cell line by knocking out the enhancer of mRNA decapping 4 (EDC4), an essential component of PB assembly. Next-generation sequencing was used to establish transcriptome profiles for wild-type (WT) and EDC4 knockout (KO) cells infected with T. cruzi for 0, 3, and 24 h. Ingenuity pathway analysis based on the differentially expressed genes revealed that PB depletion increased the activation of several signaling pathways involved in the innate immune response. The proinflammatory cytokine IL-1β was significantly upregulated following infection of PB-deficient KO cells, but not in WT cells, at the mRNA and protein levels. Furthermore, the rescue of PB assembly in KO cells by GFP-tagged wild-type EDC4 (+WT) suppressed IL-1β expression, whereas KO cells with the C-terminal-deleted mutant EDC4 (+Δ) failed to rescue PB assembly and downregulate IL-1β production. Our results suggest that T. cruzi assembles host PBs to counteract antiparasitic innate immunity.

cGAS-STING Pathway Activation during Trypanosoma cruzi Infection Leads to Tissue-Dependent Parasite Control

Host cell invasion by Trypanosoma cruzi is a markedly silent process, with limited host transcriptional changes indicative of innate immune recognition, except for a modest type I IFN (IFN-I) response. In this study, we show that T. cruzi-induced IFN-β production was nearly abolished in primary murine cGAS-/- or stimulator of IFN genes (STING)-deficient (STINGGt) macrophages and fibroblasts. T. cruzi infection did not impact the ability of IFN-regulatory factor reporter macrophages to respond to classical cGAS-STING agonists, indicating that the limited IFN-β induction is not due to active parasite suppression. cGAS-/-, STINGGt, and IFN-α/β receptor-/- (IFNAR-/-) macrophages infected with T. cruzi yielded significantly higher numbers of amastigotes compared with wild-type macrophages; however, the impact of the STING pathway during infection in vivo is more complex. Despite an initial increase in parasite growth, STINGGt and IFNAR-/- mice ultimately had lower parasite burden in footpads as compared with wild-type mice, demonstrating a role for IFN-I expression in potentiating parasite growth at the infection site. STING pathway activation had little impact on parasite levels in the skeletal muscle; however, in the heart, cGAS-/- and STINGGt mice, but not IFNAR-/- mice, accumulated higher acute parasite loads, suggesting a protective role of STING sensing of T. cruzi in this organ that was independent of IFN-I. Together, these results demonstrate that host cGAS-STING senses T. cruzi infection, enhancing parasite growth at the site of entry, and contributes to acute-phase parasite restriction in the heart, a major site of tissue damage in chronic T. cruzi infection.

The transcriptome landscape of 3D-cultured placental trophoblasts reveals activation of TLR2 and TLR3/7 in response to low Trypanosoma cruzi parasite exposure

Vertical transmission of Trypanosoma cruzi (T. cruzi) become a globalized health problem accounting for 22% of new cases of Chagas disease (CD). Congenital infection is now considered the main route of CD spread in non-endemic countries where no routine disease testing of pregnant women is implemented. The main mechanisms that lead to fetal infection by T. cruzi remain poorly understood. Mother-to-child transmission may occur when bloodstream trypomastigotes interact with the syncytiotrophoblasts (SYNs) that cover the placenta chorionic villi. These highly specialized cells function as a physical barrier and modulate immune responses against pathogen infections. To model the human placenta environment, we have previously used a three-dimensional (3D) cell culture system of SYNs that exhibits differentiation characteristics comparable to placental trophoblasts. Further, we have shown that 3D-grown SYNs are highly resistant to T. cruzi infection. In this work, we used RNA sequencing and whole transcriptome analysis to explore the immunological signatures that drive SYNs' infection control. We found that the largest category of differentially expressed genes (DEGs) are associated with inflammation and innate immunity functions. Quantitative RT-PCR evaluation of selected DEGs, together with detection of cytokines and chemokines in SYNs culture supernatants, confirmed the transcriptome data. Several genes implicated in the Toll-like receptors signaling pathways were upregulated in 3D-grown SYNs. In fact, TLR2 blockade and TLR3/7 knockdown stimulated T. cruzi growth, suggesting that these molecules play a significant role in the host cell response to infection. Ingenuity Pathway Analysis of DEGs predicted the activation of canonical pathways such as S100 protein family, pathogen induced cytokine storm, wound healing, HIF1α signaling and phagosome formation after T. cruzi exposure. Our findings indicate that SYNs resist infection by eliciting a constitutive pro-inflammatory response and modulating multiple defense mechanisms that interfere with the parasite's intracellular life cycle, contributing to parasite killing and infection control.

The Complexity of Interferon Signaling in Host Defense against Protozoan Parasite Infection

Protozoan parasites, such as Plasmodium, Leishmania, Toxoplasma, Cryptosporidium, and Trypanosoma, are causative agents of health-threatening diseases in both humans and animals, leading to significant health risks and socioeconomic losses globally. The development of effective therapeutic and prevention strategies for protozoan-caused diseases requires a full understanding of the pathogenesis and protective events occurring in infected hosts. Interferons (IFNs) are a family of cytokines with diverse biological effects in host antimicrobial defense and disease pathogenesis, including protozoan parasite infection. Type II IFN (IFN-γ) has been widely recognized as the essential defense cytokine in intracellular protozoan parasite infection, whereas recent studies also revealed the production and distinct function of type I and III IFNs in host defense against these parasites. Decoding the complex network of the IFN family in host-parasite interaction is critical for exploring potential new therapeutic strategies against intracellular protozoan parasite infection. Here, we review the complex effects of IFNs on the host defense against intracellular protozoan parasites and the crosstalk between distinct types of IFN signaling during infections.

Modulation of STAT-1, STAT-3, and STAT-6 activities in THP-1 derived macrophages infected with two Trypanosoma cruzi strains

Trypanosoma cruzi is the causative protozoan of Chagas’ Disease, a neglected tropical disease that affects 6−7 million people worldwide. Interaction of the parasite with the host immune system is a key factor in disease progression and chronic symptoms. Although the human immune system is capable of controlling the disease, the parasite has numerous evasion mechanisms that aim to maintain intracellular persistence and survival. Due to the pronounced genetic variability of T. cruzi, co-infections or mixed infections with more than one parasite strain have been reported in the literature. The intermodulation in such cases is unclear. This study aimed to evaluate the co-infection of T. cruzi strains G and CL compared to their individual infections in human macrophages derived from THP-1 cells activated by classical or alternative pathways. Flow cytometry analysis demonstrated that trypomastigotes were more infective than extracellular amastigotes (EAs) and that strain G could infect more macrophages than strain CL. Classically activated macrophages showed lower number of infected cells and IL-4-stimulated cells displayed increased CL-infected macrophages. However, co-infection was a rare event. CL EAs decreased the production of reactive oxygen species (ROS), whereas G trypomastigotes displayed increased ROS detection in classically activated cells. Co-infection did not affect ROS production. Monoinfection by strain G or CL mainly induced an anti-inflammatory cytokine profile by decreasing inflammatory cytokines (IFN-γ, TNF-α, IL-1β) and/or increasing IL-4, IL-10, and TGF-β. Co-infection led to a predominant inflammatory milieu, with reduced IL-10 and TGF-β, and/or promotion of IFN-γ and IL-1β release. Infection by strain G reduced activation of intracellular signal transducer and activator of transcription (STAT) factors. In EAs, monoinfections impaired STAT-1 activity and promoted phosphorylation of STAT-3, both changes may prolong cell survival. Coinfected macrophages displayed pronounced activation of all STATs examined. These activations likely promoted parasite persistence and survival of infected cells. The collective results demonstrate that although macrophages respond to both strains, T. cruzi can modulate the intracellular environment, inducing different responses depending on the strain, parasite infective form, and co-infection or monoinfection. The modulation influences parasite persistence and survival of infected cells.

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.

Differential Expression of Immune Response Genes in Asymptomatic Chronic Chagas Disease Patients Versus Healthy Subjects

Infection by the Trypanosoma cruzi parasite causes Chagas disease and triggers multiple immune mechanisms in the host to combat the pathogen. Chagas disease has a variable clinical presentation and progression, producing in the chronic phase a fragile balance between the host immune response and parasite replication that keeps patients in a clinically silent asymptomatic stage for years. Since the parasite is intracellular and replicates within cells, the cell-mediated response of the host adaptive immunity plays a critical role. This function is mainly orchestrated by T lymphocytes, which recognize parasite antigens and promote specific functions to control the infection. However, little is known about the immunological markers associated with this asymptomatic stage of the disease. In this large-scale analysis, the differential expression of 106 immune system-related genes has been analyzed using high-throughput qPCR in T. cruzi antigen-stimulated PBMC from chronic Chagas disease patients with indeterminate form (IND) and healthy donors (HD) from endemic and non-endemic areas of Chagas disease. This analysis revealed that there were no differences in the expression level of most genes under study between healthy donors from endemic and non-endemic areas determined by PCA and differential gene expression analysis. Instead, PCA revealed the existence of different expression profiles between IND patients and HD (p < 0.0001), dependent on the 32 genes included in PC1. Differential gene expression analysis also revealed 23 upregulated genes (expression fold change > 2) and 11 downregulated genes (expression fold change < 0.5) in IND patients versus HD. Enrichment analysis showed that several upregulated genes in IND patients participate in relevant immunological pathways such as antigen-dependent B cell activation, stress induction of HSP regulation, NO2-dependent IL12 pathway in NK cells, and cytokine-inflammatory response. The antigen-specific differential gene expression profile detected in these patients and the relevant immunological pathways that seem to be activated could represent potential biomarkers of the asymptomatic form of Chagas disease, helpful to diagnosis and infection control.

Transcriptome analysis of alternative splicing in the pathogen life cycle in human foreskin fibroblasts infected with Trypanosoma cruzi

Trypanosoma cruzi is an intracellular protozoan parasite that causes Chagas disease as a zoonotic pathogen. The parasite has been shown to remodel expression in the host transcriptome under different conditions. Although alternative splicing (AS) is involved in virtually every biological function in eukaryotes, including cellular differentiation and responses to immune reactions, host AS events that occur as a result of T. cruzi infection have yet to be explored. In this study, we bioinformatically investigated the transcriptome AS dynamics of T. cruzi (Y strain) infected human foreskin fibroblasts using RNA-Seq data captured over four timepoints (4, 24, 48, and 72 h post infection (hpi)). We identified 1768, 399, 250, and 299 differentially expressed exons (AS exons) at 4, 24, 48, and 72 hpi, respectively, showing that host AS mechanism may have a significant role in the intracellular life cycle of the parasite. We present an exon skipping event in HDAC7, which is a candidate gene that is important in the parasite’s cell cycle. To sum up, this bioinformatics analysis of transcriptome may provide new potential insight into AS regulation in human foreskin fibroblast (HFF) cells infected by T. cruzi and into its implication to the parasite life cycle. Moreover, identified AS genes may provide new potential molecular candidates for improving treatment.

Lipid metabolism in Trypanosoma cruzi: A review

The cellular membranes of Trypanosoma cruzi, like all eukaryotes, contain varying amounts of phospholipids, sphingolipids, neutral lipids and sterols. A multitude of pathways exist for the de novo synthesis of these lipid families but Trypanosoma cruzi has also become adapted to scavenge some of these lipids from the host. Completion of the TriTryp genomes has led to the identification of many putative genes involved in lipid synthesis, revealing some interesting differences to higher eukaryotes. Although many enzymes involved in lipid synthesis have yet to be characterised, completed experiments have shown the indispensability of some lipid metabolic pathways. Furthermore, the bioactive lipids of Trypanosoma cruzi and their effects on the host are becoming increasingly studied. Further studies on lipid metabolism in Trypanosoma cruzi will no doubt reveal some attractive targets for therapeutic intervention as well as reveal the interplay between parasite lipids, host response and pathogenesis.

Gene expression network analyses during infection with virulent and avirulent Trypanosoma cruzi strains unveil a role for fibroblasts in neutrophil recruitment and activation

Chagas disease is caused by Trypanosoma cruzi, a protozoan parasite that has a heterogeneous population composed of a pool of strains with distinct characteristics, including variable levels of virulence. In previous work, transcriptome analyses of parasite genes after infection of human foreskin fibroblasts (HFF) with virulent (CL Brener) and non-virulent (CL-14) clones derived from the CL strain, revealed a reduced expression of genes encoding parasite surface proteins in CL-14 compared to CL Brener during the final steps of the intracellular differentiation from amastigotes to trypomastigotes. Here we analyzed changes in the expression of host genes during in vitro infection of HFF cells with the CL Brener and CL-14 strains by analyzing total RNA extracted from cells at 60 and 96 hours post-infection (hpi) with each strain, as well as from uninfected cells. Similar transcriptome profiles were observed at 60 hpi with both strains compared to uninfected samples. However, at 96 hpi, significant differences in the number and expression levels of several genes, particularly those involved with immune response and cytoskeleton organization, were observed. Further analyses confirmed the difference in the chemokine/cytokine signaling involved with the recruitment and activation of immune cells such as neutrophils upon T. cruzi infection. These findings suggest that infection with the virulent CL Brener strain induces a more robust inflammatory response when compared with the non-virulent CL-14 strain. Importantly, the RNA-Seq data also exposed an unexplored role of fibroblasts as sentinel cells that may act by recruiting neutrophils to the initial site of infection. This role for fibroblasts in the regulation of the inflammatory response during infection by T. cruzi was corroborated by measurements of levels of different chemokines/cytokines during in vitro infection and in plasma from Chagas disease patients as well as by neutrophil activation and migration assays.

Trypanosoma cruzi is the causative agent of Chagas disease, a debilitating and often life-threatening illness that affects 6 to 7 million people mainly in Latin America. The parasite, transmitted to humans by an insect vector, needs to invade different cells from the infected person in order to multiply and spread the infection to various organs, including the heart and the gut. In this study, we investigated how the host cell responds to the infection by analyzing changes in the expression of human genes in fibroblasts infected with the CL Brener and CL-14 strains, which are strains that present highly distinct virulent phenotypes during infection in mice. We showed that human fibroblasts build a strong immune response upon infection by T. cruzi and that this response is different depending on the parasite strain: infection with the virulent CL Brener strain induces a more robust inflammatory response compared with the infection with the avirulent CL-14 strain. We also showed that, in response to the infection, fibroblasts produce molecules that can recruit and activate neutrophils, which are important immune cells that controls the infection.

Induction of Effective Immunity against Trypanosoma cruzi

Chagas disease, caused by Trypanosoma cruzi, is a major public health issue. Limitations in immune responses to natural T. cruzi infection usually result in parasite persistence with significant complications. A safe, effective, and reliable vaccine would reduce the threat of T. cruzi infections; however, no suitable vaccine is currently available due to a lack of understanding of the requirements for induction of fully protective immunity. We established a T. cruzi strain expressing green fluorescent protein (GFP) under the control of dihydrofolate reductase degradation domain (DDD) with a hemagglutinin (HA) tag, GFP-DDDHA, which was induced by trimethoprim-lactate (TMP-lactate), which results in the death of intracellular parasites. This attenuated strain induces very strong protection against reinfection. Using this GFP-DDDHA strain, we investigated the mechanisms underlying the protective immune response in mice. Immunization with this strain led to a response that included high levels of gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α), as well as a rapid expansion of effector and memory T cells in the spleen. More CD8⁺ T cells differentiate to memory cells following GFP-DDDHA infection than after infection with a wild-type (WT) strain. The GFP-DDDHA strain also provides cross-protection against another T. cruzi isolate. IFN-γ is important in mediating the protection, as IFN-γ knockout (KO) mice failed to acquire protection when infected with the GFP-DDDHA strain. Immune cells demonstrated earlier and stronger protective responses in immunized mice after reinfection with T. cruzi than those in naive mice. Adoptive transfers with several types of immune cells or with serum revealed that several branches of the immune system mediated protection. A combination of serum and natural killer cells provided the most effective protection against infection in these transfer experiments.

Close encounters between Trypanosoma cruzi and the host mammalian cell: Lessons from genome-wide expression studies

Trypanosoma cruzi is the etiologic agent of Chagas disease, a life-threatening disease that affects different tissues. Within its mammalian host, T. cruzi develops molecular strategies for successful invasion of different cell types and adaptation to the intracellular environment. Conversely, the host cell responds to the infection by activating intracellular pathways to control parasite replication. Here, we reviewed genome-wide expression studies based on microarray and RNA-seq data from both parasite and host genes generated from animal models of infection as well as from Chagas disease patients. As expected, analyses of T. cruzi genes highlighted changes related to parasite energy metabolism and cell surface molecules, whereas host cell transcriptome emphasized the role of immune response genes. Besides allowing a better understanding of mechanisms behind the pathogenesis of Chagas disease, these studies provide essential information for the development of new therapies as well as biomarkers for diagnosis and assessment of disease progression.

Limited Foxp3+ Regulatory T Cells Response During Acute Trypanosoma cruzi Infection Is Required to Allow the Emergence of Robust Parasite-Specific CD8+ T Cell Immunity

While it is now acknowledged that CD4⁺ T cells expressing CD25 and Foxp3 (Treg cells) regulate immune responses and, consequently, influence the pathogenesis of infectious diseases, the regulatory response mediated by Treg cells upon infection by Trypanosoma cruzi was still poorly characterized. In order to understand the role of Treg cells during infection by this protozoan parasite, we determined in time and space the magnitude of the regulatory response and the phenotypic, functional and transcriptional features of the Treg cell population in infected mice. Contrary to the accumulation of Treg cells reported in most chronic infections in mice and humans, experimental T. cruzi infection was characterized by sustained numbers but decreased relative frequency of Treg cells. The reduction in Treg cell frequency resulted from a massive accumulation of effector immune cells, and inversely correlated with the magnitude of the effector immune response as well as with emergence of acute immunopathology. In order to understand the causes underlying the marked reduction in Treg cell frequency, we evaluated the dynamics of the Treg cell population and found a low proliferation rate and limited accrual of peripheral Treg cells during infection. We also observed that Treg cells became activated and acquired a phenotypic and transcriptional profile consistent with suppression of type 1 inflammatory responses. To assess the biological relevance of the relative reduction in Treg cells frequency observed during T. cruzi infection, we transferred in vitro differentiated Treg cells at early moments, when the deregulation of the ratio between regulatory and conventional T cells becomes significant. Intravenous injection of Treg cells dampened parasite-specific CD8⁺ T cell immunity and affected parasite control in blood and tissues. Altogether, our results show that limited Treg cell response during the acute phase of T. cruzi infection enables the emergence of protective anti-parasite CD8⁺ T cell immunity and critically influences host resistance.

Phospho-proteomic analysis of primary human colon epithelial cells during the early Trypanosoma cruzi infection phase

The protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease, causes severe morbidity and mortality in afflicted individuals. About 30% of T. cruzi-infected individuals present with cardiac, gastrointestinal tract, and/or neurological disorders. Megacolon, one of the major pathologies of Chagas disease, is accompanied by gastrointestinal motility disorders. The molecular mechanism of T. cruzi-mediated megacolon in Chagas disease is currently unknown. To decipher the molecular mechanism of T. cruzi-induced alteration in the colon during the early infection phase, we exposed primary human colonic epithelial cells (HCoEpiC) to invasive T. cruzi trypomastigotes at multiple time points to determine changes in the phosphoprotein networks in the cells following infection using proteome profiler Human phospho-kinase arrays. We found significant changes in the phosphorylation pattern that can mediate cellular deregulations in colonic epithelial cells after infection. We detected a significant increase in the levels of phosphorylated heat shock protein (p-HSP) 27 and transcription factors that regulate various cellular functions, including c-Jun and CREB. Our study confirmed significant upregulation of phospho (p-) Akt S473, p-JNK, which may directly or indirectly modulate CREB and c-Jun phosphorylation, respectively. We also observed increased levels of phosphorylated CREB and c-Jun in the nucleus. Furthermore, we found that p-c-Jun and p-CREB co-localized in the nucleus at 180 minutes post infection, with a maximum Pearson correlation coefficient of 0.76±0.02. Increased p-c-Jun and p-CREB have been linked to inflammatory and profibrotic responses. T. cruzi infection of HCoEpiC induces an increased expression of thrombospondin-1 (TSP-1), which is fibrogenic at elevated levels. We also found that T. cruzi infection modulates the expression of NF-kB and JAK2-STAT1 signaling molecules which can increase pro-inflammatory flux. Bioinformatics analysis of the phosphoprotein networks derived using the phospho-protein data serves as a blueprint for T. cruzi-mediated cellular transformation of primary human colonic cells during the early phase of T. cruzi infection.

Cardiomyocyte oxidants production may signal to T. cruzi intracellular development

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, presents a variable clinical course, varying from asymptomatic to serious debilitating pathologies with cardiac, digestive or cardio-digestive impairment. Previous studies using two clonal T. cruzi populations, Col1.7G2 (T. cruzi I) and JG (T. cruzi II) demonstrated that there was a differential tissue distribution of these parasites during infection in BALB/c mice, with predominance of JG in the heart. To date little is known about the mechanisms that determine this tissue selection. Upon infection, host cells respond producing several factors, such as reactive oxygen species (ROS), cytokines, among others. Herein and in agreement with previous data from the literature we show that JG presents a higher intracellular multiplication rate when compared to Col1.7G2. We also showed that upon infection cardiomyocytes in culture may increase the production of oxidative species and its levels are higher in cultures infected with JG, which expresses lower levels of antioxidant enzymes. Interestingly, inhibition of oxidative stress severely interferes with the intracellular multiplication rate of JG. Additionally, upon H2O2-treatment increase in intracellular Ca2+ and oxidants were observed only in JG epimastigotes. Data presented herein suggests that JG and Col1.7G2 may sense extracellular oxidants in a distinct manner, which would then interfere differently with their intracellular development in cardiomyocytes.

Participation of TLR2 and TLR4 in Cytokines Production by Patients with Symptomatic and Asymptomatic Chronic Chagas Disease

Chagas disease (CD), caused by the protozoan Trypanosoma cruzi, is a serious public health issue. Its evolution involves an acute stage, characterized by no specific symptoms, and the chronic stage during most individuals are asymptomatic, but about 30-40% of them become symptomatic presenting the cardiac or digestive disease. Host immune response mechanisms involved in symptomatic or asymptomatic chronic disease are not fully understood. The pro-inflammatory cytokines are crucial in host resistance. However, a fine control of this inflammatory process, by action of anti-inflammatory cytokines, is necessary to avoid tissue injury. This control was found to be responsible for no clinical manifestations in asymptomatic individuals. Toll-like receptors (TLRs) are extremely important in defining the cytokine profile released in response to a micro-organism. We found that patients with the cardiac form predominantly released the pro-inflammatory cytokines: IFN-γ, TNF-α and IL-17 with the involvement of both, TLR2 and TLR4. In contrast, patients with asymptomatic disease release predominantly the anti-inflammatory cytokines IL-10 and TGF-β, but also with TLR2 and TLR4 participation. The mechanisms by which stimulation of the same TLRs results in release of different pattern of cytokines, depending on the patients group that is being evaluated, are discussed.

Protozoan Parasites and Type I IFNs

For many years, the role of interferon (IFN)-I has been characterized primarily in the context of viral infections. However, regulatory functions mediated by IFN-I have also been described against bacterial infections and in tumor immunology. Only recently, the interest in understanding the immune functions mediated by IFN-I has dramatically increased in the field of protozoan infections. In this review, we discuss the discrete role of IFN-I in the immune response against major protozoan infections: Plasmodium, Leishmania, Trypanosoma, and Toxoplasma.

Transcriptome Remodeling in Trypanosoma cruzi and Human Cells during Intracellular Infection

Intracellular colonization and persistent infection by the kinetoplastid protozoan parasite, Trypanosoma cruzi, underlie the pathogenesis of human Chagas disease. To obtain global insights into the T. cruzi infective process, transcriptome dynamics were simultaneously captured in the parasite and host cells in an infection time course of human fibroblasts. Extensive remodeling of the T. cruzi transcriptome was observed during the early establishment of intracellular infection, coincident with a major developmental transition in the parasite. Contrasting this early response, few additional changes in steady state mRNA levels were detected once mature T. cruzi amastigotes were formed. Our findings suggest that transcriptome remodeling is required to establish a modified template to guide developmental transitions in the parasite, whereas homeostatic functions are regulated independently of transcriptomic changes, similar to that reported in related trypanosomatids. Despite complex mechanisms for regulation of phenotypic expression in T. cruzi, transcriptomic signatures derived from distinct developmental stages mirror known or projected characteristics of T. cruzi biology. Focusing on energy metabolism, we were able to validate predictions forecast in the mRNA expression profiles. We demonstrate measurable differences in the bioenergetic properties of the different mammalian-infective stages of T. cruzi and present additional findings that underscore the importance of mitochondrial electron transport in T. cruzi amastigote growth and survival. Consequences of T. cruzi colonization for the host include dynamic expression of immune response genes and cell cycle regulators with upregulation of host cholesterol and lipid synthesis pathways, which may serve to fuel intracellular T. cruzi growth. Thus, in addition to the biological inferences gained from gene ontology and functional enrichment analysis of differentially expressed genes in parasite and host, our comprehensive, high resolution transcriptomic dataset provides a substantially more detailed interpretation of T. cruzi infection biology and offers a basis for future drug and vaccine discovery efforts.

In-depth knowledge of the functional processes governing host colonization and transmission of pathogenic microorganisms is essential for the advancement of effective intervention strategies. This study focuses on Trypanosoma cruzi, the vector-borne protozoan parasite responsible for human Chagas disease and the leading cause of infectious myocarditis worldwide. To gain global insights into the biology of this parasite and its interaction with mammalian host cells, we have exploited a deep-sequencing approach to generate comprehensive, high-resolution transcriptomic maps for mammalian-infective stages of T. cruzi with the simultaneous interrogation of the human host cell transcriptome across an infection time course. We demonstrate that the establishment of intracellular T. cruzi infection in mammalian host cells is accompanied by extensive remodeling of the parasite and host cell transcriptomes. Despite the lack of transcriptional control mechanisms in trypanosomatids, our analyses identified functionally-enriched processes within sets of developmentally-regulated transcripts in T. cruzi that align with known or predicted biological features of the parasite. The novel insights into the biology of intracellular T. cruzi infection and the regulation of amastigote development gained in this study establish a unique foundation for functional network analyses that will be instrumental in providing functional links between parasite dependencies and host functional pathways that have the potential to be exploited for intervention.

Evasion of the Immune Response by Trypanosoma cruzi during Acute Infection

Trypanosoma cruzi is the etiologic agent of Chagas disease, a neglected tropical disease that affects millions of people mainly in Latin America. To establish a life-long infection, T. cruzi must subvert the vertebrate host's immune system, using strategies that can be traced to the parasite's life cycle. Once inside the vertebrate host, metacyclic trypomastigotes rapidly invade a wide variety of nucleated host cells in a membrane-bound compartment known as the parasitophorous vacuole, which fuses to lysosomes, originating the phagolysosome. In this compartment, the parasite relies on a complex network of antioxidant enzymes to shield itself from lysosomal oxygen and nitrogen reactive species. Lysosomal acidification of the parasitophorous vacuole is an important factor that allows trypomastigote escape from the extremely oxidative environment of the phagolysosome to the cytoplasm, where it differentiates into amastigote forms. In the cytosol of infected macrophages, oxidative stress instead of being detrimental to the parasite, favors amastigote burden, which then differentiates into bloodstream trypomastigotes. Trypomastigotes released in the bloodstream upon the rupture of the host cell membrane express surface molecules, such as calreticulin and GP160 proteins, which disrupt initial and key components of the complement pathway, while others such as glycosylphosphatidylinositol-mucins stimulate immunoregulatory receptors, delaying the progression of a protective immune response. After an immunologically silent entry at the early phase of infection, T. cruzi elicits polyclonal B cell activation, hypergammaglobulinemia, and unspecific anti-T. cruzi antibodies, which are inefficient in controlling the infection. Additionally, the coexpression of several related, but not identical, epitopes derived from trypomastigote surface proteins delays the generation of T. cruzi-specific neutralizing antibodies. Later in the infection, the establishment of an anti-T. cruzi CD8(+) immune response focused on the parasite's immunodominant epitopes controls parasitemia and tissue infection, but fails to completely eliminate the parasite. This outcome is not detrimental to the parasite, as it reduces host mortality and maintains the parasite infectivity toward the insect vectors.

Interfering with immunity: detrimental role of type I IFNs during infection

Type I IFNs are known to inhibit viral replication and mediate protection against viral infection. However, recent studies revealed that these cytokines play a broader and more fundamental role in host responses to infections beyond their well-established antiviral function. Type I IFN induction, often associated with microbial evasion mechanisms unique to virulent microorganisms, is now shown to increase host susceptibility to a diverse range of pathogens, including some viruses. This article presents an overview of the role of type I IFNs in infections with bacterial, fungal, parasitic, and viral pathogens and discusses the key mechanisms mediating the regulatory function of type I IFNs in pathogen clearance and tissue inflammation.

CD8+ T cells in Trypanosoma cruzi infection

Trypanosoma cruzi infection and Chagas disease remains among the most neglected of the neglected tropical diseases. Despite this, studies of the immune response to T. cruzi have provided new insights in immunology and guidance for approaches for prevention and treatment of the disease. T. cruzi represents one of the very best systems in which to study CD8(+) T cell biology; mice, dogs, and primates (and many other mammals) are all natural hosts for this parasite, the robust T cell responses generated in these hosts can be readily monitored using the full range of cutting edge techniques, and the parasite can be easily modified to express (or not) a variety of tags, reporters, immune enhances, and endogenous or model antigens. The infection in most hosts is characterized by vigorous and largely effective immune responses, including CD8(+) T cells capable of controlling T. cruzi at the level of the infected host cells. However, this immune control is only partially effective and most hosts maintain a low level infection for life. This review addresses the interplay of highly effective CD8(+) T cell responses with elaborate pathogen immune evasion mechanisms, including the generation and simultaneous expression of highly variant CD8(+) T cell targets and a host cell invasion mechanisms that largely eludes innate immune detection.

Trypanosoma cruzi parasites fight for control of the JAK-STAT pathway by disarming their host

The zoonotic Chagas' disease is caused by infections with the hemoflagellate Trypanosoma cruzi (T. cruzi) which is endemic in Latin America. Despite recent advances in our understanding of the pathogenesis of the disease, the underlying molecular processes involved in host-parasite interactions are only poorly understood. In particular, the mechanisms for parasite persistence in host cells remain largely unknown. Cytokine-driven transcription factors from the family of STAT (signal transducer and activator of transcription) proteins appear to play a central role in the fight against T. cruzi infection. However, amastigotes proliferating in the cytoplasm of infected host cells develop effective strategies to circumvent the attack executed by STAT proteins. This review highlights the interactions between T. cruzi parasites and human host cells in terms of cytokine signaling and, in particular, discusses the impact of STATs on the balance between parasite invasion and clearance.

Trypanosoma cruzi evades the protective role of interferon-gamma-signaling in parasite-infected cells

The protozoan parasite Trypanosoma cruzi is responsible for the zoonotic Chagas disease, a chronic and systemic infection in humans and warm-blooded animals typically leading to progressive dilated cardiomyopathy and gastrointestinal manifestations. In the present study, we report that the transcription factor STAT1 (signal transducer and activator of transcription 1) reduces the susceptibility of human cells to infection with T. cruzi. Our in vitro data demonstrate that interferon -γ (IFNγ) pre-treatment causes T. cruzi-infected cells to enter an anti-parasitic state through the activation of the transcription factor STAT1. Whereas stimulation of STAT1-expressing cells with IFNγ significantly impaired intracellular replication of parasites, no protective effect of IFNγ was observed in STAT1-deficient U3A cells. The gene encoding indoleamine 2, 3-dioxygenase (ido) was identified as a STAT1-regulated target gene engaged in parasite clearance. Exposure of cells to T. cruzi trypomastigotes in the absence of IFNγ resulted in both sustained tyrosine and serine phosphorylation of STAT1 and its increased DNA binding. Furthermore, we found that in response to T. cruzi the total amount of intracellular STAT1 increased in an infectious dose-dependent manner, both at the mRNA and protein level. While STAT1 activation is a potent strategy of the host in the fight against the invading pathogen, amastigotes replicating intracellularly antagonize this pathway by specifically promoting the dephosphorylation of STAT1 serine 727, thereby partially circumventing its protective effects. These findings point to the crucial role of the IFNγ/STAT1 signal pathway in the evolutionary combat between T. cruzi parasites and their host.

Protozoan parasites and type I interferons: a cold case reopened

Protozoan parasites, such as Plasmodium, Toxoplasma, Cryptosporidium, trypanosomes, and Leishmania, are a major cause of disease in both humans and other animals, highlighting the need to understand the full spectrum of strategies used by the host immune system to sense and respond to parasite infection. Although type II interferon (IFN-γ) has long been recognized as an essential antiparasite immune effector, much less is known about the role of type I interferons (IFN-α and -β) in host defense, particularly in vivo. Recent studies are reviewed which collectively highlight that type I IFN can be induced in response to parasite infection and influence the outcome of infection.

The acute phase of Trypanosoma cruzi infection is attenuated in 5-lipoxygenase-deficient mice

In the present work we examine the contribution of 5-lipoxygenase- (5-LO-) derived lipid mediators to immune responses during the acute phase of Trypanosoma cruzi infection in 5-LO gene knockout (5-LO(-/-)) mice and wild-type (WT) mice. Compared with WT mice, the 5-LO(-/-) mice developed less parasitemia/tissue parasitism, less inflammatory cell infiltrates, and a lower mortality. This resistance of 5-LO(-/-) mice correlated with several differences in the immune response to infection, including reduced PGE2 synthesis; sustained capacity of splenocytes to produce high levels of interleukin (IL)-12 early in the infection; enhanced splenocyte production of IL-1β, IL-6, and IFN-γ; rapid T-cell polarization to secrete high quantities of IFN-γ and low quantities of IL-10; and greater numbers of CD8(+)CD44(high)CD62L(low) memory effector T cells at the end of the acute phase of infection. The high mortality in WT mice was associated with increased production of LTB4/LTC4, T cell bias to produce IFN-γ, high levels of serum nitrite, and marked protein extravasation into the peritoneal cavity, although survival was improved by treatment with a cys-LT receptor 1 antagonist. These data also provide evidence that 5-LO-derived mediators negatively affect host survival during the acute phase of T. cruzi infection.

Early Trypanosoma cruzi infection reprograms human epithelial cells

Trypanosoma cruzi, the causative agent of Chagas disease, has the peculiarity, when compared with other intracellular parasites, that it is able to invade almost any type of cell. This property makes Chagas a complex parasitic disease in terms of prophylaxis and therapeutics. The identification of key host cellular factors that play a role in the T. cruzi invasion is important for the understanding of disease pathogenesis. In Chagas disease, most of the focus is on the response of macrophages and cardiomyocytes, since they are responsible for host defenses and cardiac lesions, respectively. In the present work, we studied the early response to infection of T. cruzi in human epithelial cells, which constitute the first barrier for establishment of infection. These studies identified up to 1700 significantly altered genes regulated by the immediate infection. The global analysis indicates that cells are literally reprogrammed by T. cruzi, which affects cellular stress responses (neutrophil chemotaxis, DNA damage response), a great number of transcription factors (including the majority of NFκB family members), and host metabolism (cholesterol, fatty acids, and phospholipids). These results raise the possibility that early host cell reprogramming is exploited by the parasite to establish the initial infection and posterior systemic dissemination.

Microarray in parasitic infections

Modern biology and genomic sciences are rooted in parasitic disease research. Genome sequencing efforts have provided a wealth of new biological information that promises to have a major impact on our understanding of parasites. Microarrays provide one of the major high-throughput platforms by which this information can be exploited in the laboratory. Many excellent reviews and technique articles have recently been published on applying microarrays to organisms for which fully annotated genomes are at hand. However, many parasitologists work on organisms whose genomes have been only partially sequenced. This review is mainly focused on how to use microarray in these situations.

The MASP family of Trypanosoma cruzi: changes in gene expression and antigenic profile during the acute phase of experimental infection

BACKGROUND

Trypanosoma cruzi is the etiological agent of Chagas disease, a debilitating illness that affects millions of people in the Americas. A major finding of the T. cruzi genome project was the discovery of a novel multigene family composed of approximately 1,300 genes that encode mucin-associated surface proteins (MASPs). The high level of polymorphism of the MASP family associated with its localization at the surface of infective forms of the parasite suggests that MASP participates in host-parasite interactions. We speculate that the large repertoire of MASP sequences may contribute to the ability of T. cruzi to infect several host cell types and/or participate in host immune evasion mechanisms.

METHODS

By sequencing seven cDNA libraries, we analyzed the MASP expression profile in trypomastigotes derived from distinct host cells and after sequential passages in acutely infected mice. Additionally, to investigate the MASP antigenic profile, we performed B-cell epitope prediction on MASP proteins and designed a MASP-specific peptide array with 110 putative epitopes, which was screened with sera from acutely infected mice.

FINDINGS AND CONCLUSIONS

We observed differential expression of a few MASP genes between trypomastigotes derived from epithelial and myoblast cell lines. The more pronounced MASP expression changes were observed between bloodstream and tissue-culture trypomastigotes and between bloodstream forms from sequential passages in acutely infected mice. Moreover, we demonstrated that different MASP members were expressed during the acute T. cruzi infection and constitute parasite antigens that are recognized by IgG and IgM antibodies. We also found that distinct MASP peptides could trigger different antibody responses and that the antibody level against a given peptide may vary after sequential passages in mice. We speculate that changes in the large repertoire of MASP antigenic peptides during an infection may contribute to the evasion of host immune responses during the acute phase of Chagas disease.

Mild Plasmodium falciparum malaria following an episode of severe malaria is associated with induction of the interferon pathway in Malawian children

Infection with Plasmodium falciparum can lead to a range of severe to minimal symptoms, occasionally resulting in death in young children or nonimmune adults. In areas of high transmission, older children and adults generally suffer only mild or asymptomatic malaria infections and rarely develop severe disease. The immune features underlying this apparent immunity to severe disease remain elusive. To gain insight into host responses associated with severe and mild malaria, we conducted a longitudinal study of five children who first presented with severe malaria and, 1 month later, with mild malaria. Employing peripheral blood whole-genome profiling, we identified 68 genes that were associated with mild malaria compared to their expression in the severe malaria episode (paired Students t test, P < 0.05). These genes reflect the interferon (IFN) pathway and T cell biology and include IFN-induced protein transcripts 1 to 3, oligoadenylate synthetases 1 and 3, and the T cell markers cathepsin W and perforin. Gene set enrichment analysis identified Gene Ontology (GO) pathways associated with mild malaria to include the type I interferon-mediated signaling pathway (GO 0060337), T cell activation (GO 0042110), and other GO pathways representing many aspects of immune activation. In contrast, only six genes were associated with severe malaria, including thymidine kinase 1, which was recently found to be a biomarker of cerebral malaria susceptibility in the murine model, and carbonic anhydrase, reflecting the blood's abnormal acid base environment during severe disease. These data may provide potential insights to inform pathogenesis models and the development of therapeutics to reduce severe disease outcomes due to P. falciparum infection.

A soluble factor from Trypanosoma cruzi inhibits transforming growth factor-ß-induced MAP kinase activation and gene expression in dermal fibroblasts

The protozoan parasite Trypanosoma cruzi, which causes human Chagas' disease, exerts a variety of effects on host extracellular matrix (ECM) including proteolytic degradation of collagens and dampening of ECM gene expression. Exposure of primary human dermal fibroblasts to live infective T. cruzi trypomastigotes or their shed/secreted products results in a rapid down-regulation of the fibrogenic genes collagenIα1, fibronectin and connective tissue growth factor (CTGF/CCN2). Here we demonstrate the ability of a secreted/released T. cruzi factor to antagonize ctgf/ccn2 expression in dermal fibroblasts in response to TGF-ß, lysophosphatidic acid or serum, where agonist-induced phosphorylation of the mitogen-activated protein (MAP) kinases Erk1/2, p38 and JNK was also inhibited. Global analysis of gene expression in dermal fibroblasts identified a discrete subset of TGF-ß-inducible genes involved in cell proliferation, wound repair, and immune regulation that are inhibited by T. cruzi secreted/released factors, where the genes exhibiting the highest sensitivity to T. cruzi are known to be regulated by MAP kinase-activated transcription factors. Consistent with this observation, the Ets-family transcription factor binding site in the proximal promoter region of the ctgf/ccn2 gene (−91 bp to −84 bp) was shown to be required for T. cruzi-mediated down-regulation of ctgf/ccn2 reporter expression. The cumulative data suggest a model in which T. cruzi-derived molecules secreted/released early in the infective process dampen MAP kinase signaling and the activation of transcription factors that regulate expression of fibroblast genes involved in wound repair and tissue remodelling, including ctgf/ccn2. These findings have broader implications for local modulation of ECM synthesis/remodelling by T. cruzi during the early establishment of infection in the mammalian host and highlight the potential for pathogen-derived molecules to be exploited as tools to modulate the fibrogenic response.

The Trypanosoma cruzi protease cruzain mediates immune evasion

Trypanosoma cruzi is the causative agent of Chagas' disease. Novel chemotherapy with the drug K11777 targets the major cysteine protease cruzain and disrupts amastigote intracellular development. Nevertheless, the biological role of the protease in infection and pathogenesis remains unclear as cruzain gene knockout failed due to genetic redundancy. A role for the T. cruzi cysteine protease cruzain in immune evasion was elucidated in a comparative study of parental wild type- and cruzain-deficient parasites. Wild type T. cruzi did not activate host macrophages during early infection (<60 min) and no increase in ∼P iκB was detected. The signaling factor NF-κB P65 colocalized with cruzain on the cell surface of intracellular wild type parasites, and was proteolytically cleaved. No significant IL-12 expression occurred in macrophages infected with wild type T. cruzi and treated with LPS and BFA, confirming impairment of macrophage activation pathways. In contrast, cruzain-deficient parasites induced macrophage activation, detectable iκB phosphorylation, and nuclear NF-κB P65 localization. These parasites were unable to develop intracellularly and survive within macrophages. IL 12 expression levels in macrophages infected with cruzain-deficient T. cruzi were comparable to LPS activated controls. Thus cruzain hinders macrophage activation during the early (<60 min) stages of infection, by interruption of the NF-κB P65 mediated signaling pathway. These early events allow T. cruzi survival and replication, and may lead to the spread of infection in acute Chagas' disease.

Type I interferons increase host susceptibility to Trypanosoma cruzi infection

Trypanosoma cruzi, the protozoan parasite that causes human Chagas' disease, induces a type I interferon (IFN) (IFN-α/β) response during acute experimental infection in mice and in isolated primary cell types. To examine the potential impact of the type I IFN response in shaping outcomes in experimental T. cruzi infection, groups of wild-type (WT) and type I IFN receptor-deficient (IFNAR(-/-)) 129sv/ev mice were infected with two different T. cruzi strains under lethal and sublethal conditions and several parameters were measured during the acute stage of infection. The results demonstrate that type I IFNs are not required for early host protection against T. cruzi. In contrast, under conditions of lethal T. cruzi challenge, WT mice succumbed to infection whereas IFNAR(-/-) mice were ultimately able to control parasite growth and survive. T. cruzi clearance in and survival of IFNAR(-/-) mice were accompanied by higher levels of IFN-γ production by isolated splenocytes in response to parasite antigen. The suppression of IFN-γ in splenocytes from WT mice was independent of IL-10 levels. While the impact of type I IFNs on the production of IFN-γ and other cytokines/chemokines remains to be fully determined in the context of T. cruzi infection, our data suggest that, under conditions of high parasite burden, type I IFNs negatively impact IFN-γ production, initiating a detrimental cycle that contributes to the ultimate failure to control infection. These findings are consistent with a growing theme in the microbial pathogenesis field in which type I IFNs can be detrimental to the host in a variety of nonviral pathogen infection models.

Trypanosoma cruzi infection induces a global host cell response in cardiomyocytes

Chagas' disease, caused by the hemoflagellate protozoan Trypanosoma cruzi, affects millions of people in South and Central America. Chronic chagasic cardiomyopathy, the most devastating manifestation of this disease, occurs in approximately one-third of infected individuals. Events associated with the parasite's tropism for and invasion of cardiomyocytes have been the focus of intense investigation in recent years. In the present study, we use murine microarrays to investigate the cellular response caused by invasion of primary murine cardiomyocytes by T. cruzi trypomastigotes. These studies identified 353 murine genes that were differentially expressed during the early stages of invasion and infection of these cells. Genes associated with the immune response, inflammation, cytoskeleton organization, cell-cell and cell-matrix interactions, apoptosis, cell cycle, and oxidative stress are among those affected during the infection. Our data indicate that T. cruzi induces broad modulations of the host cell machinery in ways that provide insight into how the parasite survives, replicates, and persists in the infected host and ultimately defines the clinical outcome of the infection.

Gene network analysis during early infection of human coronary artery smooth muscle cells by Trypanosoma cruzi and Its gp83 ligand

Trypanosoma cruzi, the causative agent of Chagas' disease, infects heart and muscle cells leading to cardiac arrest, followed by death. The genetic architectures in the early T. cruzi infection process of human cells are unknown. To understand the genetic architectures of the early invasion process of T. cruzi, we conducted gene transcription microarray analysis, followed by gene network construction of the host cell response in primary human coronary artery smooth muscle (HCASM) cells infected with T. cruzi or exposed to T. cruzi gp83, a ligand used by the trypanosome to bind host cells. Using seven RT-PCR verified up-regulated genes (FOSB, ATF5, INPP1, CCND2, THBS1, LAMC1, and APLP2) as the seed for network construction, we built an interaction network of the early T. cruzi infection process containing 165 genes, connected by 598 biological interactions. This interactome network is centered on the BCL6 gene as a hub. Silencing the expression of two seed genes (THBS1 and LAMC1) by RNAi reduced T. cruzi infection. Overall, our results elucidate the significant and complex process involved in T. cruzi infection of HCASM cells at the transcriptome level. This is the first elucidation into the interactome network in human cells caused by T. cruzi and its gp83 ligand.

Developmental expression of a Trypanosoma cruzi phosphoinositide-specific phospholipase C in amastigotes and stimulation of host phosphoinositide hydrolysis

Phosphoinositide phospholipase C (PI-PLC) plays an essential role in cell signaling. A unique Trypanosoma cruzi PI-PLC (TcPI-PLC) is lipid modified in its N terminus and localizes to the outer surface of the plasma membrane of amastigotes. We show here that TcPI-PLC is developmentally regulated in amastigotes and shows two peaks of surface expression during the developmental cycle of T. cruzi, the first immediately after differentiation of trypomastigotes into amastigotes and the second before differentiation of amastigotes into trypomastigotes. Surface expression of TcPI-PLC coincides with phosphatidylinositol 4,5-bisphosphate (PIP(2)) depletion in the host cell membrane and with an increase in the levels of its product, inositol 1,4,5-trisphosphate. During extracellular differentiation, PI-PLC is secreted into the incubation medium. Maximal early expression of TcPI-PLC on the surface of amastigotes and PIP(2) depletion coincide with host cytoskeletal changes, Ca(2+) signaling, and transcriptional responses described previously. The presence of TcPI-PLC on the outer surface of the plasma membrane of the parasite and the capacity to be secreted and to alter host phospholipids are novel mechanisms of the host-parasite interaction.

c-di-AMP secreted by intracellular Listeria monocytogenes activates a host type I interferon response

Intracellular bacterial pathogens, such as Listeria monocytogenes, are detected in the cytosol of host immune cells. Induction of this host response is often dependent on microbial secretion systems and, in L. monocytogenes, is dependent on multidrug efflux pumps (MDRs). Using L. monocytogenes mutants that overexpressed MDRs, we identified cyclic diadenosine monophosphate (c-di-AMP) as a secreted molecule able to trigger the cytosolic host response. Overexpression of the di-adenylate cyclase, dacA (lmo2120), resulted in elevated levels of the host response during infection. c-di-AMP thus represents a putative bacterial secondary signaling molecule that triggers a cytosolic pathway of innate immunity and is predicted to be present in a wide variety of bacteria and archea.

Generation of Trypanosoma cruzi-specific CD8+ T-cell immunity is unaffected by the absence of type I interferon signaling

Trypanosoma cruzi is a protozoan parasite that causes human Chagas' disease, a leading source of congestive heart failure in Central and South America. CD8+ T cells are critical for control of T. cruzi infection, and CD8+ T cells recognizing the immunodominant trans-sialidase gene-encoded peptide TSKB20 (ANYKFTLV) account for approximately 30% of the total CD8+ T-cell population at the peak of infection in C57BL/6 mice. Type I interferons (IFN-I) are pleiotropic cytokines that play a critical role in both innate and adaptive immunity against a variety of infections, but their induction and their role in infection are dictated by the infectious agent. Because type I IFNs and IFN-responsive genes are evident early after T. cruzi infection of host cells, we examined the influence of IFN-I on the development of CD8+ T-cell responses during this infection. Mice lacking the receptor for IFN-I (IFNARKO) and their wild-type counterparts both developed chronic infections and generated similar frequencies of immunodominant TSKB20- and subdominant TSKB18-specific CD8+ T cells following T. cruzi infection. In contrast, peak TSKB20-specific CD8+ T-cell responses generated during infection with vaccinia virus engineered to express TSKB20 were approximately 2.5-fold lower in IFNARKO mice than B6 mice, although after viral clearance, the frequencies of TSKB20-specific CD8+ T cells stabilized at similar levels. Together, these data suggest that IFN-I induction and biology are dependent upon the microbial context and emphasize the need to investigate various infection models for a full understanding of CD8+ T-cell development.

The Lyme disease spirochete Borrelia burgdorferi utilizes multiple ligands, including RNA, for interferon regulatory factor 3-dependent induction of type I interferon-responsive genes

We recently discovered a critical role for type I interferon (IFN) in the development of murine Lyme arthritis. Borrelia burgdorferi-mediated induction of IFN-responsive genes by bone marrow-derived macrophages (BMDMs) was dependent upon a functional type I IFN receptor but independent of Toll-like receptor 2 (TLR2), TLR4, TLR9, and the adapter molecule MyD88. We now demonstrate that induction of the IFN transcriptional profile in B. burgdorferi-stimulated BMDMs occurs independently of the adapter TRIF and of the cytoplasmic sensor NOD2. In contrast, B. burgdorferi-induced transcription of these genes was dependent upon a rapid STAT1 feedback amplification pathway. IFN profile gene transcription was IRF3 dependent but did not utilize B. burgdorferi-derived DNA or DNase-sensitive ligands. Instead, IFN-responsive gene expression could be induced by B. burgdorferi-derived RNA. Interferon regulatory factor 3 (IRF3)-dependent IFN profile gene transcription was also induced by sonicated bacteria, by the lipoprotein OspA, and by factors released into the BSKII medium during culture of B. burgdorferi. The IFN-stimulatory activity of B. burgdorferi culture supernatants was not destroyed by nuclease treatment. Nuclease digestion also had no effect on IFN profile induction mediated by sonicated B. burgdorferi. Thus, B. burgdorferi-derived RNA, OspA, and non-nucleic acid ligands present in both sonicated bacteria and B. burgdorferi culture medium contribute to type I IFN-responsive gene induction. These findings suggest that B. burgdorferi invasion of joint tissue and the resultant type I IFN induction associated with Lyme arthritis development may involve multiple triggering ligands.

Delineation of diverse macrophage activation programs in response to intracellular parasites and cytokines

Background

The ability to reside and proliferate in macrophages is characteristic of several infectious agents that are of major importance to public health, including the intracellular parasites Trypanosoma cruzi (the etiological agent of Chagas disease) and Leishmania species (etiological agents of Kala-Azar and cutaneous leishmaniasis). Although recent studies have elucidated some of the ways macrophages respond to these pathogens, the relationships between activation programs elicited by these pathogens and the macrophage activation programs elicited by bacterial pathogens and cytokines have not been delineated.

Methodology/Principal Findings

To provide a global perspective on the relationships between macrophage activation programs and to understand how certain pathogens circumvent them, we used transcriptional profiling by genome-wide microarray analysis to compare the responses of mouse macrophages following exposure to the intracellular parasites T. cruzi and Leishmania mexicana, the bacterial product lipopolysaccharide (LPS), and the cytokines IFNG, TNF, IFNB, IL-4, IL-10, and IL-17. We found that LPS induced a classical activation state that resembled macrophage stimulation by the Th1 cytokines IFNG and TNF. However, infection by the protozoan pathogen L. mexicana produced so few transcriptional changes that the infected macrophages were almost indistinguishable from uninfected cells. T. cruzi activated macrophages produced a transcriptional signature characterized by the induction of interferon-stimulated genes by 24 h post-infection. Despite this delayed IFN response by T. cruzi, the transcriptional response of macrophages infected by the kinetoplastid pathogens more closely resembled the transcriptional response of macrophages stimulated by the cytokines IL-4, IL-10, and IL-17 than macrophages stimulated by Th1 cytokines.

Conclusions/Significance

This study provides global gene expression data for a diverse set of biologically significant pathogens and cytokines and identifies the relationships between macrophage activation states induced by these stimuli. By comparing macrophage activation programs to pathogens and cytokines under identical experimental conditions, we provide new insights into how macrophage responses to kinetoplastids correlate with the overall range of macrophage activation states.

Macrophages are a type of immune cell that engulf and digest microorganisms. Despite their role in protecting the host from infection, many pathogens have developed ways to hijack the macrophage and use the cell for their own survival and proliferation. This includes the parasites Trypanosoma cruzi and Leishmania mexicana. In order to gain further understanding of how these pathogens interact with the host macrophage, we compared macrophages that have been infected with these parasites to macrophages that have been stimulated in a number of different ways. Macrophages can be activated by a wide variety of stimuli, including common motifs found on pathogens (known as pathogen associated molecular patterns or PAMPs) and cytokines secreted by other immune cells. In this study, we have delineated the relationships between the macrophage activation programs elicited by a number of cytokines and PAMPs. Furthermore, we have placed the macrophage responses to T. cruzi and L. mexicana into the context of these activation programs, providing a better understanding of the interactions between these pathogens and macrophages.

REGULATION of the EXTRACELLULAR MATRIX INTERACTOME by Trypanosoma cruzi

It has been shown that the invasive trypomastigote forms of Trypanosoma cruzi use and modulate components of the extracellular matrix (ECM) during the initial process of infection. Infective trypomastigotes up-regulate the expression of laminin γ-1 (LAMC1) and thrombospondin (THBS1) to facilitate the recruitment of trypomastigotes to enhance cellular infection. Silencing the expression of LAMC1 and THBS1 by stable RNAi dramatically reduces trypanosome infection. T. cruzi gp83, a ligand that mediates the attachment of trypanosomes to cells to initiate infection, up-regulates LAMC1 expression to enhance cellular infection. Infective trypomastigotes interact with LAMC1 through galectin-3 (LGALS3), a human lectin, to enhance cellular infection. Silencing the expression of LGALS3 also reduces cellular infection. Some trypanosome surface molecules also interact with the ECM to facilitate infection. Despite the role of the ECM in T. cruzi infection, almost nothing is known about the ECM interactome networks operating in the process of T. cruzi infection. In this mini review, we critically analyze and discuss the regulation of the ECM by T. cruzi and its gp83 ligand, and present the first elucidation of the human ECM interactome network, regulated by T. cruzi and its gp83 ligand, to facilitate cellular infection. The elucidation of the human ECM interactome regulated by T. cruzi is critically important to the understanding of the molecular pathogenesis of T. cruzi infection and developing novel approaches of intervention in Chagas' disease.

The role of DNA microarrays in Toxoplasma gondii research, the causative agent of ocular toxoplasmosis

Ocular toxoplasmosis, which is caused by the protozoan parasite Toxoplasma gondii, is the leading cause of retinochoroiditis. Toxoplasma is an obligate intracellular pathogen that replicates within a parasitophorous vacuole. Infections are initiated by digestion of parasites deposited in cat feces or in undercooked meat. Parasites then disseminate to target tissues that include the retina where they then develop into long-lived asymptomatic tissue cysts. Occasionally, cysts reactivate and growth of newly emerged parasites must be controlled by the host’s immune system or disease will occur. The mechanisms by which Toxoplasma grows within its host cell, encysts, and interacts with the host’s immune system are important questions. Here, we will discuss how the use of DNA microarrays in transcriptional profiling, genotyping, and epigenetic experiments has impacted our understanding of these processes. Finally, we will discuss how these advances relate to ocular toxoplasmosis and how future research on ocular toxoplasmosis can benefit from DNA microarrays.

Transcriptomic alterations in Trypanosoma cruzi-infected cardiac myocytes

Trypanosoma cruzi infection is a major cause of cardiomyopathy. Previous gene profiling studies of infected mouse hearts have revealed prominent changes in gene expression within many functional pathways. This variety of transcriptomic changes in infected mice raises the question of whether gene expression alterations in whole hearts are due to changes in infected cardiac myocytes or other cells or even to systemic effects of the infection on the heart. We employed microarrays to examine infected cardiac myocyte cultures 48 h post-infection. Statistical comparison of gene expression levels of 7624 well annotated unigenes in four independent cultures of infected and uninfected myocytes detected substantial (>or=1.5 absolute fold changes) in 420 (5.5%) of the sampled genes. Major categories of affected genes included those involved in immune response, extracellular matrix and cell adhesion. These findings on infected cardiac myocytes in culture reveal that alterations in cardiac gene expression described in Chagas disease are the consequence of both direct infection of the myocytes themselves as well as resulting from the presence of other cell types in the myocardium and systemic effects of infection.

CD8+ T cells in Trypanosoma cruzi infection

CD8(+) T cells have emerged as crucial players in the control of a number of protozoan pathogens, including Trypanosoma cruzi, the agent of human Chagas disease. The recent identification of the dominant targets of T. cruzi-specific T cells has allowed investigators to follow the generation of and document the functionality of T cell responses in both mice and humans. Although slow to develop in the early stages of the infection, T. cruzi-specific CD8(+) T cells reach prodigious levels and remain highly functional throughout chronic infections in mice. Following drug-induced cure during either the acute or chronic stage, these immunodominant T cells persist as stable, antigen-independent memory populations. T. cruzi-specific CD8(+) T cells in humans are less-well-studied but appear to lose functionality and decline in numbers in these decades-long infections. Changes in the frequency of parasite-specific T cell upon therapeutic treatment in humans may provide a new metric for determining treatment efficacy.

Insufficient TLR activation contributes to the slow development of CD8+ T cell responses in Trypanosoma cruzi infection

During experimental infection with Trypanosoma cruzi, mice develop a strong CD8(+) T cell response focused mainly on a few immunodominant peptides encoded in trans-sialidase family genes. Despite the potency of this response, the initial emergence and peak of parasite-specific CD8(+) T cells has been noted to be relatively slow. In this study, we further document this delayed onset of T cell responses to T. cruzi as measured by the increase in frequency of parasite-specific T cells, the effector function of these cells, T cell proliferation in general, and the recruitment of cells into the draining lymph nodes. This delay does not appear to be the result of general immunosuppressive effects of the infection, a limitation in parasite numbers, or parasite trafficking to lymph nodes or to the specific epitope. Increasing the initial infecting dose or the density of parasite epitopes on APCs can modestly speed the generation of anti-T. cruzi T cell responses. Given these characteristics of the response, we propose that T. cruzi is a stealth invader, largely avoiding recognition by components of the innate immune system until the infection is well established. This conclusion is supported by the ability to accelerate the induction of T cell responses to T. cruzi by administration of ligands for TLR2 and TLR9 at the time of infection. These studies highlight a previously unappreciated mechanism of immune evasion, the surreptitious establishment of infection, by the protozoan T. cruzi.

Cytokine-dependent and-independent gene expression changes and cell cycle block revealed in Trypanosoma cruzi-infected host cells by comparative mRNA profiling

Background

The requirements for growth and survival of the intracellular pathogen Trypanosoma cruzi within mammalian host cells are poorly understood. Transcriptional profiling of the host cell response to infection serves as a rapid read-out for perturbation of host physiology that, in part, reflects adaptation to the infective process. Using Affymetrix oligonucleotide array analysis we identified common and disparate host cell responses triggered by T. cruzi infection of phenotypically diverse human cell types.

Results

We report significant changes in transcript abundance in T. cruzi-infected fibroblasts, endothelial cells and smooth muscle cells (2852, 2155 and 531 genes respectively; fold-change ≥ 2, p-value < 0.01) 24 hours post-invasion. A prominent type I interferon response was observed in each cell type, reflecting a secondary response to secreted cytokine in infected cultures. To identify a core cytokine-independent response in T. cruzi-infected fibroblasts and endothelial cells transwell plates were used to distinguish cytokine-dependent and -independent gene expression profiles. This approach revealed the induction of metabolic and signaling pathways involved in cell proliferation, amino acid catabolism and response to wounding as common themes in T. cruzi-infected cells. In addition, the downregulation of genes involved in mitotic cell cycle and cell division predicted that T. cruzi infection may impede host cell cycle progression. The observation of impaired cytokinesis in T. cruzi-infected cells, following nuclear replication, confirmed this prediction.

Conclusion

Metabolic pathways and cellular processes were identified as significantly altered at the transcriptional level in response to T. cruzi infection in a cytokine-independent manner. Several of these alterations are supported by previous studies of T. cruzi metabolic requirements or effects on the host. However, our methods also revealed a T. cruzi-dependent block in the host cell cycle, at the level of cytokinesis, previously unrecognized for this pathogen-host cell interaction.

Perspectives on the Trypanosoma cruzi-host cell receptor interactions

Chagas disease is caused by the parasite Trypanosoma cruzi. The critical initial event is the interaction of the trypomastigote form of the parasite with host receptors. This review highlights recent observations concerning these interactions. Some of the key receptors considered are those for thromboxane, bradykinin, and for the nerve growth factor TrKA. Other important receptors such as galectin-3, thrombospondin, and laminin are also discussed. Investigation into the molecular biology and cell biology of host receptors for T. cruzi may provide novel therapeutic targets.

TLR-independent type I interferon induction in response to an extracellular bacterial pathogen via intracellular recognition of its DNA

Type I interferon (IFN) is an important host defense cytokine against intracellular pathogens, mainly viruses. In assessing IFN production in response to group B streptococcus (GBS), we find that IFN-beta was produced by macrophages upon stimulation with both heat-killed and live GBS. Exposure of macrophages to heat-killed GBS activated a Toll-like receptor (TLR)-dependent pathway, whereas live GBS activated a TLR/NOD/RIG-like receptor (RLR)-independent pathway. This latter pathway required bacterial phagocytosis, proteolytic bacterial degradation, and phagolysosomal membrane destruction by GBS pore-forming toxins, leading to the release of bacterial DNA into the cytosol. GBS DNA in the cytosol induced IFN-beta production via a pathway dependent on the activation of the serine-threonine kinase TBK1 and phosphorylation of the transcription factor IRF3. Thus, activation of IFN-alpha/-beta production during infection with GBS, commonly considered an extracellular pathogen, appears to result from the interaction of GBS DNA with a putative intracellular DNA sensor or receptor.