IL-12p40 deficiency leads to uncontrolled Trypanosoma cruzi dissemination in the spinal cord resulting in neuronal death and motor dysfunction

SOCS2 expression in hematopoietic and non-hematopoietic cells during Trypanosoma cruzi infection: Correlation with immune response and cardiac dysfunction

Chagas disease has a complex pathogenesis wherein the host immune response is essential for controlling its development. Suppressor of cytokine signaling(SOCS)2 is a crucial protein that regulates cytokine production. In this study, SOCS2 deficiency resulted in an initial imbalance of IL12- and IL-10-producing neutrophils and dendritic cells (DCs), which caused a long-lasting impact reducing inflammatory neutrophils and DCs, and tolerogenic DCs at the peak of acute disease. A reduced number of inflammatory and pro-resolving macrophages, and IL17A-producing CD4⁺ T cells, and increased lymphocyte apoptosis was found in SOCS2-deficient mice. Electrocardiogram analysis of chimeric mice showed that WT mice that received SOCS2 KO bone marrow transplantation presented increased heart dysfunction. Taken together, the results demonstrated that SOCS2 is a crucial regulator of the immune response during Trypanosoma cruzi infection, and suggest that a SOCS2 genetic polymorphism, or failure of its expression, may increase the susceptibility of cardiomyopathy development in Chagasic patients.

Experimental Trypanosoma cruzi Infection Induces Pain in Mice Dependent on Early Spinal Cord Glial Cells and NFκB Activation and Cytokine Production

The neglected tropical infirmity Chagas disease (CD) presents high mortality. Its etiological agent T. cruzi is transmitted by infected hematophagous insects. Symptoms of the acute phase of the infection include fever, fatigue, body aches, and headache, making diagnosis difficult as they are present in other illnesses as well. Thus, in endemic areas, individuals with undetermined pain may be considered for CD. Although pain is a characteristic symptom of CD, its cellular and molecular mechanisms are unknown except for demonstration of a role for peripheral TNF-α in CD pain. In this study, we evaluate the role of spinal cord glial cells in experimental T. cruzi infection in the context of pain using C57BL/6 mice. Pain, parasitemia, survival, and glial and neuronal function as well as NFκB activation and cytokine/chemokine production were assessed. T. cruzi infection induced chronic mechanical and thermal hyperalgesia. Systemic TNF-α and IL-1β peaked 14 days postinfection (p.i.). Infected mice presented increased spinal gliosis and NFκB activation compared to uninfected mice at 7 days p.i. Glial and NFκB inhibitors limited T. cruzi–induced pain. Nuclear phosphorylated NFκB was detected surrounded by glia markers, and glial inhibitors reduced its detection. T. cruzi–induced spinal cord production of cytokines/chemokines was also diminished by glial inhibitors. Dorsal root ganglia (DRG) neurons presented increased activity in infected mice, and the production of inflammatory mediators was counteracted by glial/NFκB inhibitors. The present study unveils the contribution of DRG and spinal cord cellular and molecular events leading to pain in T. cruzi infection, contributing to a better understanding of CD pathology.

Microglia in neuropathology caused by protozoan parasites

Involvement of the central nervous system (CNS) is the most severe consequence of some parasitic infections. Protozoal infections comprise a group of diseases that together affect billions of people worldwide and, according to the World Health Organization, are responsible for more than 500000 deaths annually. They include African and American trypanosomiasis, leishmaniasis, malaria, toxoplasmosis, and amoebiasis. Mechanisms underlying invasion of the brain parenchyma by protozoa are not well understood and may depend on parasite nature: a vascular invasion route is most common. Immunosuppression favors parasite invasion into the CNS and therefore the host immune response plays a pivotal role in the development of a neuropathology in these infectious diseases. In the brain, microglia are the resident immune cells active in defense against pathogens that target the CNS. Beside their direct role in innate immunity, they also play a principal role in coordinating the trafficking and recruitment of other immune cells from the periphery to the CNS. Despite their evident involvement in the neuropathology of protozoan infections, little attention has given to microglia-parasite interactions. This review describes the most prominent features of microglial cells and protozoan parasites and summarizes the most recent information regarding the reaction of microglial cells to parasitic infections. We highlight the involvement of the periphery-brain axis and emphasize possible scenarios for microglia-parasite interactions.

Infection by Trypanosoma cruzi in the central nervous system in non-human mammals: a systematic review

Currently, the types and distribution of the lesions induced in the central nervous system (CNS) by Trypanosoma cruzi remain unclear as the available evidence is based on fragmented data. Therefore, we developed a systematic review to analyse the main characteristics of the CNS lesions in non-human hosts infected. From a structured search on the PubMed/Medline and Scopus platforms, 32 studies were retrieved, subjected to data extraction and methodological bias analysis. Our results show that the most frequent alterations in the CNS are the presence of different forms of T. cruzi and intense lymphocytes infiltrates. The encephalon is the main target of T. cruzi, and inflammatory changes in the CNS are more frequent and severe in the acute phase of infection. The parasite's genotype and phenotype are associated with the tropism and severity of the CNS lesions. The methodological limitations found in the studies were divergences in inoculation pathways, under-reporting of animal age and weight, sample calculation strategies and histopathological characterization. Since the changes were dependent on the pathogenicity and virulence of the T. cruzi strains, the genotype and phenotype characterization of the parasite are extremely relevant to predict changes in the CNS and the neurological manifestations associated with Chagas' disease.

Disease Tolerance and Pathogen Resistance Genes May Underlie Trypanosoma cruzi Persistence and Differential Progression to Chagas Disease Cardiomyopathy

Chagas disease is caused by infection with the protozoan Trypanosoma cruzi and affects over 8 million people worldwide. In spite of a powerful innate and adaptive immune response in acute infection, the parasite evades eradication, leading to a chronic persistent infection with low parasitism. Chronically infected subjects display differential patterns of disease progression. While 30% develop chronic Chagas disease cardiomyopathy (CCC)—a severe inflammatory dilated cardiomyopathy—decades after infection, 60% of the patients remain disease-free, in the asymptomatic/indeterminate (ASY) form, and 10% develop gastrointestinal disease. Infection of genetically deficient mice provided a map of genes relevant for resistance to T. cruzi infection, leading to the identification of multiple genes linked to survival to infection. These include pathogen resistance genes (PRG) needed for intracellular parasite destruction, and genes involved in disease tolerance (protection against tissue damage and acute phase death—DTG). All identified DTGs were found to directly or indirectly inhibit IFN-γ production or Th1 differentiation. We hypothesize that the absolute need for DTG to control potentially lethal IFN-γ PRG activity leads to T. cruzi persistence and establishment of chronic infection. IFN-γ production is higher in CCC than ASY patients, and is the most highly expressed cytokine in CCC hearts. Key DTGs that downmodulate IFN-γ, like IL-10, and Ebi3/IL27p28, are higher in ASY patients. Polymorphisms in PRG and DTG are associated with differential disease progression. We thus hypothesize that ASY patients are disease tolerant, while an imbalance of DTG and IFN-γ PRG activity leads to the inflammatory heart damage of CCC.

Importance of major histocompatibility complex of class I (MHC-I) expression for astroglial reactivity and stability of neural circuits in vitro

MHC-I molecules are involved in the antigenic presentation of cytosol-derived peptides to CD8T lymphocytes. In the nervous system, MHC-I expression is low to absent, occurring only during certain phases of development and aging or after injuries. The involvement of MHC-I in synaptic plasticity has been reported and, following lesion, astrocytes become reactive, limiting tissue damage. Such cells also attempt to restore homeostasis by secreting cytokines and neurotrophic factors. Moreover, astrocytes modulate synapse function, by taking up and releasing neurotransmitters and by limiting the synaptic cleft. Thus, the aim of the present study was to evaluate if astrocyte activation and reactivity are related to MHC I expression and if astrogliosis can be downregulated by silencing MHC-I mRNA synthesis. Given that, we evaluated astrocyte reactivity and synaptogenesis in co-cultures of astrocytes and spinal neurons under MHC-I RNA interference. For that, the MHC-I β2-microglobulin subunit (β2m) was knocked-down by siRNA in co-cultures (β2m expression <60%, p<0.001). As measured by qRT-PCR, silencing of β2m decreased expression of the astrocytic marker GFAP (<60%, p<0.001), as well as neurotrophic factors (BDNF and GDNF) and pro-inflammatory cytokines (TNF-α, IL-1, IL-6, IL-12 and IL-17). No significant changes in synaptic stability indicate that neuron-neuron interaction was preserved after β2m silencing. Overall, the present data reinforce the importance of MHC-I expression for generation of astrogliosis, what may, in turn, become a target for future CNS/PNS therapies following injury.

4-Nitrobenzaldehyde thiosemicarbazone: a new compound derived from S-(-)-limonene that induces mitochondrial alterations in epimastigotes and trypomastigotes of Trypanosoma cruzi

Trypanosoma cruzi is the causative agent of Chagas’ disease, a parasitic disease that remains a serious health concern with unsatisfactory treatment. Drugs that are currently used to treat Chagas’ disease are partially effective in the acute phase but ineffective in the chronic phase of the disease. The aim of the present study was to evaluate the antitrypanosomal activity and morphological, ultrastructural and biochemical alterations induced by a new molecule, 4-nitrobenzaldehyde thiosemicarbazone (BZTS), derived from S-(-)-limonene against epimastigote, trypomastigote and intracellular amastigote forms of T. cruzi. BZTS inhibited the growth of epimastigotes (IC50 = 9·2 μm), intracellular amastigotes (IC50 = 3·23 μm) and inhibited the viability of trypomastigotes (EC50 = 1·43 μm). BZTS had a CC50 of 37·45 μm in LLCMK2 cells. BZTS induced rounding and distortion of the cell body and severely damaged parasite mitochondria, reflected by extensive swelling and disorganization in the inner mitochondrial membrane and the presence of concentric membrane structures inside the organelle. Cytoplasmic vacuolization, endoplasmic reticulum that surrounded organelles, the loss of mitochondrial membrane potential, and increased mitochondrial O2•ˉ production were also observed. Our results suggest that BZTS alters the ultrastructure and physiology of mitochondria, which could be closely related to parasite death.

Chagas disease: still many unsolved issues

Over the past 20 years, the immune effector mechanisms involved in the control of Trypanosoma cruzi, as well as the receptors participating in parasite recognition by cells of the innate immune system, have been largely described. However, the main questions on the physiopathology of Chagas disease remain unanswered: “Why does the host immune system fail to provide sterile immunity?” and “Why do only a proportion of infected individuals develop chronic pathology?” In this review, we describe the mechanisms proposed to explain the inability of the immune system to eradicate the parasite and the elements that allow the development of chronic heart disease. Moreover, we discuss the possibility that the inability of infected cardiomyocytes to sense intracellular T. cruzi contributes to parasite persistence in the heart and the development of chronic pathology.

Contribution of interleukin-12 p35 (IL-12p35) and IL-12p40 to protective immunity and pathology in mice infected with Chlamydia muridarum

The p35 molecule is unique to interleukin-12 (IL-12), while p40 is shared by both IL-12 and IL-23. IL-12 promotes Th1 T cell responses, while IL-23 promotes Th17 T cell responses. The roles of IL-12p35- and IL-12p40-mediated responses in chlamydial infection were compared in mice following an intravaginal infection with Chlamydia muridarum. Mice deficient in either IL-12p35 or p40 both developed similar but prolonged infection time courses, confirming the roles of IL-12-mediated immune responses in clearing primary infection. However, all mice, regardless of genotype, cleared reinfection within 2 weeks, suggesting that an IL-12- or IL-23-independent adaptive immunity is protective against chlamydial infection. All infected mice developed severe oviduct hydrosalpinx despite the increased Th2 responses in IL-12p35- or IL-12p40-deficient mice, suggesting that Th2-dominant responses can contribute to Chlamydia-induced inflammatory pathology. Compared to IL-12p35 knockout mice, the IL-12p40-deficient mice exhibited more extensive spreading of chlamydial organisms into kidney tissues, leading to significantly increased incidence of pyelonephritis, which both confirms the role of IL-12 or IL-23-independent host responses in Chlamydia-induced pathologies and suggests that in the absence of IL-12/IFN-γ-mediated Th1 immunity, an IL-23-mediated response may play an important role in restricting chlamydial organisms from spreading into distal organs. These observations together provide important information for both understanding chlamydial pathogenesis and developing anti-Chlamydia vaccines.