Enteric helminth coinfection enhances host susceptibility to neurotropic flaviviruses via a tuft cell-IL-4 receptor signaling axis.

Although enteric helminth infections modulate immunity to mucosal pathogens, their effects on systemic microbes remain less established. Here, we observe increased mortality in mice coinfected with the enteric helminth Heligmosomoides polygyrus bakeri (Hpb) and West Nile virus (WNV). This enhanced susceptibility is associated with altered gut morphology and transit, translocation of commensal bacteria, impaired WNV-specific T cell responses, and increased virus infection in the gastrointestinal tract and central nervous system. These outcomes were due to type 2 immune skewing, because coinfection in Stat6-/- mice rescues mortality, treatment of helminth-free WNV-infected mice with interleukin (IL)-4 mirrors coinfection, and IL-4 receptor signaling in intestinal epithelial cells mediates the susceptibility phenotypes. Moreover, tuft cell-deficient mice show improved outcomes with coinfection, whereas treatment of helminth-free mice with tuft cell-derived cytokine IL-25 or ligand succinate worsens WNV disease. Thus, helminth activation of tuft cell-IL-4-receptor circuits in the gut exacerbates infection and disease of a neurotropic flavivirus.

Mechanisms of the host immune response and helminth-induced pathology during Trichobilharzia regenti (Schistosomatidae) neuroinvasion in mice.

Helminth neuroinfections represent serious medical conditions, but the diversity of the host-parasite interplay within the nervous tissue often remains poorly understood, partially due to the lack of laboratory models. Here, we investigated the neuroinvasion of the mouse spinal cord by Trichobilharzia regenti (Schistosomatidae). Active migration of T. regenti schistosomula through the mouse spinal cord induced motor deficits in hindlimbs but did not affect the general locomotion or working memory. Histological examination of the infected spinal cord revealed eosinophilic meningomyelitis with eosinophil-rich infiltrates entrapping the schistosomula. Flow cytometry and transcriptomic analysis of the spinal cord confirmed massive activation of the host immune response. Of note, we recorded striking upregulation of the major histocompatibility complex II pathway and M2-associated markers, such as arginase or chitinase-like 3. Arginase also dominated the proteins found in the microdissected tissue from the close vicinity of the migrating schistosomula, which unselectively fed on the host nervous tissue. Next, we evaluated the pathological sequelae of T. regenti neuroinvasion. While no demyelination or blood-brain barrier alterations were noticed, our transcriptomic data revealed a remarkable disruption of neurophysiological functions not yet recorded in helminth neuroinfections. We also detected DNA fragmentation at the host-schistosomulum interface, but schistosomula antigens did not affect the viability of neurons and glial cells in vitro. Collectively, altered locomotion, significant disruption of neurophysiological functions, and strong M2 polarization were the most prominent features of T. regenti neuroinvasion, making it a promising candidate for further neuroinfection research. Indeed, understanding the diversity of pathogen-related neuroinflammatory processes is a prerequisite for developing better protective measures, treatment strategies, and diagnostic tools.

Mechanistic perspectives on differential mitochondrial-based neuroprotective effects of several carnitine forms in Alzheimer's disease in vitro model.

Mitochondrial deregulation has emerged as one of the earliest pathological events in Alzheimer's disease (AD), the most common age-related neurodegenerative disorder. Improvement of mitochondrial function in AD has been considered a relevant therapeutic approach. L-carnitine (LC), an amino acid derivative involved in the transport of long-chain fatty acids into mitochondria, was previously demonstrated to improve mitochondrial function, having beneficial effects in neurological disorders; moreover, acetyl-L-carnitine (ALC) is currently under phase 4 clinical trial for AD (ClinicalTrials.gov NCT01320527). Thus, in the present study, we investigated the impact of different forms of carnitines, namely LC, ALC and propionyl-L-carnitine (PLC) on mitochondrial toxicity induced by amyloid-beta peptide 1-42 oligomers (AßO; 1 µM) in mature rat hippocampal neurons. Our results indicate that 5 mM LC, ALC and PLC totally rescued the mitochondrial membrane potential and alleviated both the decrease in oxygen consumption rates and the increase in mitochondrial fragmentation induced by AßO. These could contribute to the prevention of neuronal death by apoptosis. Moreover, only ALC ameliorated AßO-evoked changes in mitochondrial movement by reducing the number of stationary mitochondria and promoting reversal mitochondrial movement. Data suggest that carnitines (LC, ALC and PLC) may act differentially to counteract changes in mitochondrial function and movement in neurons subjected to AßO, thus counteracting AD-related pathological phenotypes.

Toxoplasma infection induces microglia-neuron contact and the loss of perisomatic inhibitory synapses.

Infection and inflammation within the brain induces changes in neuronal connectivity and function. The intracellular protozoan parasite, Toxoplasma gondii, is one pathogen that infects the brain and can cause encephalitis and seizures. Persistent infection by this parasite is also associated with behavioral alterations and an increased risk for developing psychiatric illness, including schizophrenia. Current evidence from studies in humans and mouse models suggest that both seizures and schizophrenia result from a loss or dysfunction of inhibitory synapses. In line with this, we recently reported that persistent T. gondii infection alters the distribution of glutamic acid decarboxylase 67 (GAD67), an enzyme that catalyzes GABA synthesis in inhibitory synapses. These changes could reflect a redistribution of presynaptic machinery in inhibitory neurons or a loss of inhibitory nerve terminals. To directly assess the latter possibility, we employed serial block face scanning electron microscopy (SBFSEM) and quantified inhibitory perisomatic synapses in neocortex and hippocampus following parasitic infection. Not only did persistent infection lead to a significant loss of perisomatic synapses, it induced the ensheathment of neuronal somata by myeloid-derived cells. Immunohistochemical, genetic, and ultrastructural analyses revealed that these myeloid-derived cells included activated microglia. Finally, ultrastructural analysis identified myeloid-derived cells enveloping perisomatic nerve terminals, suggesting they may actively displace or phagocytose synaptic elements. Thus, these results suggest that activated microglia contribute to perisomatic inhibitory synapse loss following parasitic infection and offer a novel mechanism as to how persistent T. gondii infection may contribute to both seizures and psychiatric illness.

Neuronal impairment following chronic Toxoplasma gondii infection is aggravated by intestinal nematode challenge in an IFN-γ-dependent manner.

BACKGROUND: It has become increasingly evident that the immune and nervous systems are closely intertwined, relying on one another during regular homeostatic conditions. Prolonged states of imbalance between neural and immune homeostasis, such as chronic neuroinflammation, are associated with a higher risk for neural damage. Toxoplasma gondii is a highly successful neurotropic parasite causing persistent subclinical neuroinflammation, which is associated with psychiatric and neurodegenerative disorders. Little is known, however, by what means neuroinflammation and the associated neural impairment can be modulated by peripheral inflammatory processes. METHODS: Expression of immune and synapse-associated genes was assessed via quantitative real-time PCR to investigate how T. gondii infection-induced chronic neuroinflammation and associated neuronal alterations can be reshaped by a subsequent acute intestinal nematode co-infection. Immune cell subsets were characterized via flow cytometry in the brain of infected mice. Sulfadiazine and interferon-γ-neutralizing antibody were applied to subdue neuroinflammation. RESULTS: Neuroinflammation induced by T. gondii infection of mice was associated with increased microglia activation, recruitment of immune cells into the brain exhibiting Th1 effector functions, and enhanced production of Th1 and pro-inflammatory molecules (IFN-γ, iNOS, IL-12, TNF, IL-6, and IL-1ß) following co-infection with Heligmosomoides polygyrus. The accelerated cerebral Th1 immune response resulted in enhanced T. gondii removal but exacerbated the inflammation-related decrease of synapse-associated gene expression. Synaptic proteins EAAT2 and GABAAα1, which are involved in the excitation/inhibition balance in the CNS, were affected in particular. These synaptic alterations were partially recovered by reducing neuroinflammation indirectly via antiparasitic treatment and especially by application of IFN-γ-neutralizing antibody. Impaired iNOS expression following IFN-γ neutralization directly affected EAAT2 and GABAAα1 signaling, thus contributing to the microglial regulation of neurons. Besides, reduced CD36, TREM2, and C1qa gene expression points toward inflammation induced synaptic pruning as a fundamental mechanism. CONCLUSION: Our results suggest that neuroimmune responses following chronic T. gondii infection can be modulated by acute enteric nematode co-infection. While consecutive co-infection promotes parasite elimination in the CNS, it also adversely affects gene expression of synaptic proteins, via an IFN-γ-dependent manner.

The Neurotropic Parasite Toxoplasma gondii Induces Sustained Neuroinflammation with Microvascular Dysfunction in Infected Mice.

Toxoplasmosis is one of the leading parasitic diseases worldwide. Some data suggest that chronic acquired toxoplasmosis could be linked to behavioral alterations in humans. The parasite infects neurons, forming immunologically silent cysts. Cerebral microcirculation homeostasis is determinant to brain functions, and pathologic states can alter capillarity or blood perfusion, leading to neurodegeneration and cognitive deficits. Albino mice were infected with Toxoplasma gondii (ME49 strain) and analyzed after 10, 40, and 180 days. Infected mice presented decreased cerebral blood flow at 10 and 40 days post infection (dpi), which were restored at 180 dpi, as shown by laser speckle contrast imaging. Intravital microscopy demonstrated that infection led to significant capillary rarefaction, accompanied by neuroinflammation, with microglial activation and increased numbers of rolling and adherent leukocytes to the wall of cerebral capillaries. Acetylcholine-induced vasodilation was altered at all time points, and blood brain barrier permeability was evident in infected animals at 40 dpi. Infection reduced angiogenesis, with a decreased number of isolectin B4-stained blood vessels and a decrease in length and branching of laminin-stained capillaries. Sulfadiazine reduced parasite load and partially repaired microvascular damages. We conclude that T. gondii latent infection causes a harmful insult in the brain, promoting neuroinflammation and microcirculatory dysfunction in the brain, with decreased angiogenesis and can contribute to a neurodegenerative process.

Neurons are the Primary Target Cell for the Brain-Tropic Intracellular Parasite Toxoplasma gondii.

Toxoplasma gondii, a common brain-tropic parasite, is capable of infecting most nucleated cells, including astrocytes and neurons, in vitro. Yet, in vivo, Toxoplasma is primarily found in neurons. In vitro data showing that interferon-γ-stimulated astrocytes, but not neurons, clear intracellular parasites suggest that neurons alone are persistently infected in vivo because they lack the ability to clear intracellular parasites. Here we test this theory by using a novel Toxoplasma-mouse model capable of marking and tracking host cells that directly interact with parasites, even if the interaction is transient. Remarkably, we find that Toxoplasma shows a strong predilection for interacting with neurons throughout CNS infection. This predilection remains in the setting of IFN-γ depletion; infection with parasites resistant to the major mechanism by which murine astrocytes clear parasites; or when directly injecting parasites into the brain. These findings, in combination with prior work, strongly suggest that neurons are not incidentally infected, but rather they are Toxoplasma's primary in vivo target.

Investigation of tissue cysts in the retina in a mouse model of ocular toxoplasmosis: distribution and interaction with glial cells.

The conversion of tachyzoites into bradyzoites is a way for Toxoplasma gondii to establish a chronic and asymptomatic infection and achieve lifelong persistence in the host. The bradyzoites form tissue cysts in the retina, but not much is known about the horizontal distribution of the cysts or their interactions with glial cells in the retina. A chronic ocular toxoplasmosis model was induced by per oral administration of T. gondii Me49 strain cysts to BALB/c mice. Two months after the infection, retinas were flat-mounted and immunostained to detect cysts, ganglion cells, Müller cells, astrocytes, and microglial cells, followed by observation under fluorescence and confocal microscope. The horizontal distribution showed a rather clustered pattern, but the clusters were not restricted to certain location of the retina. Axial distribution was confined to the inner retina, mostly in ganglion cell layer or the inner plexiform layer. Both ganglion cells, a type of retinal neurons, and Müller cells, predominant retinal glial cells, could harbor cysts. The cysts were spatially separated from astrocytes, the most abundant glial cells in the ganglion cell layer, while close spatial distribution of microglial cells was observed in two thirds of retinal cysts. In this study, we demonstrated that the retinal cysts were not evenly distributed horizontally and were confined to the inner retina axially. Both neurons and one type of glial cells could harbor cysts, and topographic analysis of other glial cells suggests role of microglial cells in chronic ocular toxoplasmosis.

Gamma Interferon Mediates Experimental Cerebral Malaria by Signaling within Both the Hematopoietic and Nonhematopoietic Compartments.

Experimental cerebral malaria (ECM) is a gamma interferon (IFN-γ)-dependent syndrome. However, whether IFN-γ promotes ECM through direct and synergistic targeting of multiple cell populations or by acting primarily on a specific responsive cell type is currently unknown. Here, using a panel of cell- and compartment-specific IFN-γ receptor 2 (IFN-γR2)-deficient mice, we show that IFN-γ causes ECM by signaling within both the hematopoietic and nonhematopoietic compartments. Mechanistically, hematopoietic and nonhematopoietic compartment-specific IFN-γR signaling exerts additive effects in orchestrating intracerebral inflammation, leading to the development of ECM. Surprisingly, mice with specific deletion of IFN-γR2 expression on myeloid cells, T cells, or neurons were completely susceptible to terminal ECM. Utilizing a reductionist in vitro system, we show that synergistic IFN-γ and tumor necrosis factor (TNF) stimulation promotes strong activation of brain blood vessel endothelial cells. Combined, our data show that within the hematopoietic compartment, IFN-γ causes ECM by acting redundantly or by targeting non-T cell or non-myeloid cell populations. Within the nonhematopoietic compartment, brain endothelial cells, but not neurons, may be the major target of IFN-γ leading to ECM development. Collectively, our data provide information on how IFN-γ mediates the development of cerebral pathology during malaria infection.

Beneficial immunomodulatory and neuro digestive effect in Trypanosoma cruzi infection after Lycopodium clavatum 13c treatment.

Studies show that highly diluted medications demonstrate benefits in treating infections, constituting an alternative for their treatment. The present study evaluated the effects of Lycopodium clavatum, dynamization 13c, in Wistar rats infected with T. cruzi. In this study 42 male rats were intraperitoneally inoculated with T. cruzi - Y strain and allocated into groups: IC (infected control group) and Ly (treated with L. clavatum 13c). The cytokines dosage (IFN-γ, IL-12, IL-10, IL-4), quantification and morphometry of myenteric neurons were evaluated. The treatment with L. clavatum modifies the immune response, with increase of IFN-γ on day 10 a.i. and IL-12 on day 24 a.i., decrease of IL-10 concentration on day 10 a.i. and subsequent increase of this cytokine and IL-4 on day 24 a.i., affording a bigger number of myenteric neurons compared to IC group. Thus, L. clavatum 13c promoted on rats infected with T. cruzi a beneficial immunomodulatory action reducing the pathogenic progression of digestive Chagas disease.

Astrocytic TGF-ß signaling limits inflammation and reduces neuronal damage during central nervous system Toxoplasma infection.

The balance between controlling infection and limiting inflammation is particularly precarious in the brain because of its unique vulnerability to the toxic effects of inflammation. Astrocytes have been implicated as key regulators of neuroinflammation in CNS infections, including infection with Toxoplasma gondii, a protozoan parasite that naturally establishes a chronic CNS infection in mice and humans. In CNS toxoplasmosis, astrocytes are critical to controlling parasite growth. They secrete proinflammatory cytokines and physically encircle parasites. However, the molecular mechanisms used by astrocytes to limit neuroinflammation during toxoplasmic encephalitis have not yet been identified. TGF-ß signaling in astrocytes is of particular interest because TGF-ß is universally upregulated during CNS infection and serves master regulatory and primarily anti-inflammatory functions. We report in this study that TGF-ß signaling is activated in astrocytes during toxoplasmic encephalitis and that inhibition of astrocytic TGF-ß signaling increases immune cell infiltration, uncouples proinflammatory cytokine and chemokine production from CNS parasite burden, and increases neuronal injury. Remarkably, we show that the effects of inhibiting astrocytic TGF-ß signaling are independent of parasite burden and the ability of GFAP(+) astrocytes to physically encircle parasites.

Irf8-regulated genomic responses drive pathological inflammation during cerebral malaria.

Interferon Regulatory Factor 8 (IRF8) is required for development, maturation and expression of anti-microbial defenses of myeloid cells. BXH2 mice harbor a severely hypomorphic allele at Irf8 (Irf8(R294C)) that causes susceptibility to infection with intracellular pathogens including Mycobacterium tuberculosis. We report that BXH2 are completely resistant to the development of cerebral malaria (ECM) following Plasmodium berghei ANKA infection. Comparative transcriptional profiling of brain RNA as well as chromatin immunoprecipitation and high-throughput sequencing (ChIP-seq) was used to identify IRF8-regulated genes whose expression is associated with pathological acute neuroinflammation. Genes increased by infection were strongly enriched for IRF8 binding sites, suggesting that IRF8 acts as a transcriptional activator in inflammatory programs. These lists were enriched for myeloid-specific pathways, including interferon responses, antigen presentation and Th1 polarizing cytokines. We show that inactivation of several of these downstream target genes (including the Irf8 transcription partner Irf1) confers protection against ECM. ECM-resistance in Irf8 and Irf1 mutants is associated with impaired myeloid and lymphoid cells function, including production of IL12p40 and IFNγ. We note strong overlap between genes bound and regulated by IRF8 during ECM and genes regulated in the lungs of M. tuberculosis infected mice. This IRF8-dependent network contains several genes recently identified as risk factors in acute and chronic human inflammatory conditions. We report a common core of IRF8-bound genes forming a critical inflammatory host-response network.

Toxoplasma gondii-induced neuronal alterations.

The zoonotic pathogen Toxoplasma gondii infects over 30% of the human population. The intracellular parasite can persist lifelong in the CNS within neurons modifying their function and structure, thus leading to specific behavioural changes of the host. In recent years, several in vitro studies and murine models have focused on the elucidation of these modifications. Furthermore, investigations of the human population have correlated Toxoplasma seropositivity with changes in neurological functions; however, the complex underlying mechanisms of the subtle behavioural alteration are still not fully understood. The parasites are able to induce direct modifications in the infected cells, for example by altering dopamine metabolism, by functionally silencing neurons as well as by hindering apoptosis. Moreover, indirect effects of the peripheral immune system and alterations of the immune status of the CNS, observed during chronic infection, might also contribute to changes in neuronal connectivity and synaptic plasticity. In this review, we will provide an overview and highlight recent advances, which describe changes in the neuronal function and morphology upon T. gondii infection.

Persistence of Toxoplasma gondii in the central nervous system: a fine-tuned balance between the parasite, the brain and the immune system.

Upon infection of humans and animals with Toxoplasma gondii, the parasites persist as intraneuronal cysts that are controlled, but not eliminated by the immune system. In particular, intracerebral T cells are crucial in the control of T. gondii infection and are supported by essential functions from other leukocyte populations. Additionally, brain-resident cells including astrocytes, microglia and neurons contribute to the intracerebral immune response by the production of cytokines, chemokines and expression of immunoregulatory cell surface molecules, such as major histocompatibility (MHC) antigens. However, the in vivo behaviour of these individual cell populations, specifically their interaction during cerebral toxoplasmosis, remains to be elucidated. We discuss here what is known about the function of T cells, recruited myeloid cells and brain-resident cells, with particular emphasis on the potential cross-regulation of these cell populations, in governing cerebral toxoplasmosis.

Moderate physical exercise protects myenteric metabolically more active neurons in mice infected with Trypanosoma cruzi.

BACKGROUND: Trypanosoma cruzi causes neuronal myenteric depopulation compromising intestinal function. AIM: The purpose of this study was to evaluate the influence of moderate physical exercise on NADH diaphorase (NADH-d)-positive neurons in the myenteric plexus and intestinal wall of the colon in mice infected with T. cruzi. MATERIALS AND METHODS: Forty 30-day-old male Swiss mice were divided into the following groups: trained infected (TI), sedentary infected (SI), trained control (TC), and sedentary control. The TC and TI groups were subjected to a moderate physical exercise program on a treadmill for 8 weeks. Three days after finishing physical exercise, the TI and SI groups were intraperitoneally inoculated with 1,300 blood trypomastigotes of the Y strain of Trypanosoma cruzi. Parasitemia was evaluated from days 4 to 61 after inoculation. On day 75 of infection, myenteric neurons in the colon were quantified (NADH-d), and inflammatory foci were counted. Tumor necrosis factor-α (TNF-α) and transforming growth factor-ß (TGF-ß) levels were evaluated in plasma. The results were compared using analysis of variance and the Kruskal-Wallis test at a 5 % significance level. RESULTS: Moderate physical exercise reduced the parasite peak on day 8 of infection (p = 0.0132) and total parasitemia (p = 0.0307). It also prevented neuronal depopulation (p < 0.01), caused hypertrophy of these cells (p < 0.05), prevented the formation of inflammatory foci (p < 0.01), and increased the synthesis of TNF-α (p < 0.01) and TGF-ß (p > 0.05). CONCLUSION: These results reinforce the therapeutic benefits of moderate physical exercise for T. cruzi infection.

Modelling amoebic brain infection caused by Balamuthia mandrillaris using a human cerebral organoid.

The lack of disease models adequately resembling human tissue has hindered our understanding of amoebic brain infection. Three-dimensional structured organoids provide a microenvironment similar to human tissue. This study demonstrates the use of cerebral organoids to model a rare brain infection caused by the highly lethal amoeba Balamuthia mandrillaris. Cerebral organoids were generated from human pluripotent stem cells and infected with clinically isolated B. mandrillaris trophozoites. Histological examination showed amoebic invasion and neuron damage following coculture with the trophozoites. The transcript profile suggested an alteration in neuron growth and a proinflammatory response. The release of intracellular proteins specific to neuronal bodies and astrocytes was detected at higher levels postinfection. The amoebicidal effect of the repurposed drug nitroxoline was examined using the human cerebral organoids. Overall, the use of human cerebral organoids was important for understanding the mechanism of amoeba pathogenicity, identify biomarkers for brain injury, and in the testing of a potential amoebicidal drug in a context similar to the human brain.

A translational in vivo model of trigeminal autonomic cephalalgias: therapeutic characterization.

Trigeminal autonomic cephalalgias are highly disabling primary headache disorders, characterized by severe unilateral head pain and associated ipsilateral cranial autonomic features. There is limited understanding of their pathophysiology and how and where treatments act to reduce symptoms; this is significantly hindered by a lack of animal models. We have developed the first animal model to explore trigeminal autonomic cephalalgias, using stimulation within the brainstem, at the level of the superior salivatory nucleus, to activate the trigeminal autonomic reflex arc. Using electrophysiological recording of neurons of the trigeminocervical complex and laser Doppler blood flow changes around the ipsilateral lacrimal duct, superior salivatory nucleus stimulation exhibited both neuronal trigeminovascular and cranial autonomic manifestations. These responses were specifically inhibited by the autonomic ganglion blocker hexamethonium bromide. These data demonstrate that brainstem activation may be the driver of both sensory and autonomic symptoms in these disorders, and part of this activation may be via the parasympathetic outflow to the cranial vasculature. Additionally, both sensory and autonomic manifestations were significantly inhibited by highly effective treatments for trigeminal autonomic cephalalgias, such as oxygen, indomethacin and triptans, and some part of their therapeutic action appears to be specifically on the parasympathetic outflow to the cranial vasculature. Treatments more used to migraine, such as naproxen and a calcitonin gene-related peptide receptor inhibitor, olcegepant, were less effective in this model. This is the first model to represent the phenotype of trigeminal autonomic cephalalgias and their response to therapies, and indicates the parasympathetic pathway may be uniquely involved in their pathophysiology and targeted to relieve symptoms.

Toxoplasma gondii infection causes morphological changes in caecal myenteric neurons.

The aim of this study was to evaluate the effects of chronic infection of Toxoplasma gondii (with genotype I and genotype III strains) on the population density and morphometry of caecal myenteric neurons in rats. Fifteen, 60-day-old, male Wistar rats (Rattus norvegicus) were used. The animals were assigned into three groups: Control Group (CG), Experimental Group 1 (EG1) and Experimental Group 2 (EG2). EG1 animals received 10(5) tachyzoites of the genotype I (BTU IV) T. gondii strain orally, and the EG2 animals received 10(5) tachyzoites of the genotype III (BTU II) strain orally. Thirty days after inoculation, caecal whole-mount preparations were stained by Giemsa technique. The caecal preparations were then analysed by assessing the population density and morphometry of myenteric neurons in specific regions of the caecum: mesenteric apical (MA), antimesenteric apical (AA), antimesenteric basal (AB) and next to caecal ampulla (NA). Myenteric neurons from the AA region were more clustered in EG1 animals (P<0.05). The EG1 animals presented a 16.8% reduction in the area of the nucleus, whereas the EG2 animals showed 18.4% increase (P<0.05). There was a more marked reduction in the cytoplasm of the animals in EG1 (↓23.2%) compared to EG2 (↓6.2%). There was 35.8% neuronal atrophy in the AB region and 16.8% in the region NA of the EG1 animals (P<0.05). In conclusion, different strains of T. gondii cause morphometric changes in caecal myenteric neurons of rats. Only the genotype I strain was able to cause neuronal density changes.

Myenteric neuronal plasticity induced by Toxoplasma gondii (genotype III) on the duodenum of rats.

The effects of acute and chronic infection caused by Toxoplasma gondii on duodenal myenteric neurons were analyzed. Eighteen rats were assigned into four groups: Acute Control Group (ACG, n=4); Acute Experimental Group (AEG, n=4); Chronic Control Group (CCG, n=5); and Chronic Experimental Group (CEG, n=5). Rats from the AEG and CEG were inoculated orally with 105 genotype III (BTU-II strain) tachyzoites of T. gondii isolated from a dog with neurological signs. Acute groups were killed after 24 hours after the inoculation and the chronic groups after 30 days. Whole-mount from the duodenum were stained with Giemsa. The population density of myenteric neurons, as well the body cell, nuclear and cytoplasmic area were analyzed. Both acute and chronic toxoplasmic infection did not provoke neuronal loss. On the other hand, plastic alterations were observed: decreasing of the nuclear and cytoplasmic area during the acute phase and neuronal hypertrophy during the chronic phase.

Neurotrophin receptor TrkC is an entry receptor for Trypanosoma cruzi in neural, glial, and epithelial cells.

Trypanosoma cruzi, the agent of Chagas' disease, infects a variety of mammalian cells in a process that includes multiple cycles of intracellular division and differentiation starting with host receptor recognition by a parasite ligand(s). Earlier work in our laboratory showed that the neurotrophin-3 (NT-3) receptor TrkC is activated by T. cruzi surface trans-sialidase, also known as parasite-derived neurotrophic factor (PDNF). However, it has remained unclear whether TrkC is used by T. cruzi to enter host cells. Here, we show that a neuronal cell line (PC12-NNR5) relatively resistant to T. cruzi became highly susceptible to infection when overexpressing human TrkC but not human TrkB. Furthermore, trkC transfection conferred an ∼3.0-fold intracellular growth advantage. Sialylation-deficient Chinese hamster ovarian (CHO) epithelial cell lines Lec1 and Lec2 also became much more permissive to T. cruzi after transfection with the trkC gene. Additionally, NT-3 specifically blocked T. cruzi infection of the TrkC-NNR5 transfectants and of naturally permissive TrkC-bearing Schwann cells and astrocytes, as did recombinant PDNF. Two specific inhibitors of Trk autophosphorylation (K252a and AG879) and inhibitors of Trk-induced MAPK/Erk (U0126) and Akt kinase (LY294002) signaling, but not an inhibitor of insulin-like growth factor 1 receptor, abrogated TrkC-mediated cell invasion. Antibody to TrkC blocked T. cruzi infection of the TrkC-NNR5 transfectants and of cells that naturally express TrkC. The TrkC antibody also significantly and specifically reduced cutaneous infection in a mouse model of acute Chagas' disease. TrkC is ubiquitously expressed in the peripheral and central nervous systems, and in nonneural cells infected by T. cruzi, including cardiac and gastrointestinal muscle cells. Thus, TrkC is implicated as a functional PDNF receptor in cell entry, independently of sialic acid recognition, mediating broad T. cruzi infection both in vitro and in vivo.