Sequestration and tissue accumulation of human malaria parasites: can we learn anything from rodent models of malaria?

HIF-1α regulated pathomechanism of low birth weight through angiogenesis factors in placental Plasmodium vivax infection

Background

Malaria in pregnancy leads to placental malaria. The primary pathogenesis of the complex fetal implications in placental malaria is tissue hypoxia due to sequestrations of Plasmodium falciparum-infected erythrocytes in the placenta. However, the pathomechanism of placental Plasmodium vivax infection has not been thoroughly investigated. Hypoxia-inducible factor-1α (HIF-1α) is a key transcriptional mediator of the response to hypoxic conditions, which interacts with the change and imbalances of many chemical mediators, including angiogenic factors, leading to fetal growth abnormality.

Methods

This study was conducted cross-sectionally in Maumere, Sikka Regency, East Nusa Tenggara Province, previously known as one of the malaria endemic areas with a high incidence of low birth weight (LBW) cases. This study collected peripheral and umbilical blood samples and placental tissues from mothers who delivered their babies with LBW at the TC Hiller Regional Hospital. All of the blood samples were examined for parasites by microscopic and PCR techniques, while the plasma levels of VEGF, PlGF, VEGFR-1, VEGFR-2, and HIF-1α were determined using ELISA. The sequestration of infected erythrocytes and hemozoin was determined from placental histological slides, and the expression of placenta angiogenic factors was observed using the immunofluorescent technique.

Results

In this study, 33 cases had complete data to be analyzed. Of them, 19 samples were diagnosed as vivax malaria and none of falciparum malaria. There were significant differences in Δ 10th percentile growth curve of baby's body weights and also all angiogenic factors in placental tissues {VEGF, PlGF, and VEGFR-1, VEGFR-2, and HIF-1α} between those infected and not infected cases (p<0.05), but not for VEGF and VEGFR-2 in the plasma.

Conclusion

This study indicated that Plasmodium vivax sequestration may promote LBW through alterations and imbalances in angiogenic factors led by HIF-1α.

Time of day and circadian disruption influence host response and parasite growth in a mouse model of cerebral malaria

Malaria is a disease caused by infection with parasite Plasmodium spp. We studied the circadian regulation of host responses to the parasite, in a mouse model of cerebral malaria. The course of the disease was markedly affected by time of infection, with decreased parasitemia and increased inflammation upon infection in the middle of the night. At this time, there were fewer reticulocytes, which are target cells of the parasites. We next investigated the effects of desynchronization of host clocks on the infection: after 10 weeks of recurrent jet lags, mice showed decreased parasite growth and lack of parasite load rhythmicity, paralleled by a loss of glucose rhythm. Accordingly, disrupting host metabolic rhythms impacted parasite load rhythmicity. In summary, our findings of a circadian modulation of malaria parasite growth and infection shed light on aspects of the disease relevant to human malaria and could contribute to new therapeutic or prophylactic measures.

Acute response to pathogens in the early human placenta at single-cell resolution

The placenta is a selective maternal-fetal barrier that provides nourishment and protection from infections. However, certain pathogens can attach to and even cross the placenta, causing pregnancy complications with potential lifelong impacts on the child's health. Here, we profiled at the single-cell level the placental responses to three pathogens associated with intrauterine complications-Plasmodium falciparum, Listeria monocytogenes, and Toxoplasma gondii. We found that upon exposure to the pathogens, all placental lineages trigger inflammatory responses that may compromise placental function. Additionally, we characterized the responses of fetal macrophages known as Hofbauer cells (HBCs) to each pathogen and propose that they are the probable niche for T. gondii. Finally, we revealed how P. falciparum adapts to the placental microenvironment by modulating protein export into the host erythrocyte and nutrient uptake pathways. Altogether, we have defined the cellular networks and signaling pathways mediating acute placental inflammatory responses that could contribute to pregnancy complications.

RNAscope in situ hybridization reveals microvascular sequestration of Plasmodium relictum pSGS1 blood stages but absence of exo-erythrocytic dormant stages during latent infection of Serinus canaria

BACKGROUND

Birds chronically infected with avian malaria parasites often show relapses of parasitaemia after latent stages marked by absence of parasites in the peripheral circulation. These relapses are assumed to result from the activation of dormant exo-erythrocytic stages produced during secondary (post-erythrocytic) merogony of avian Plasmodium spp. Yet, there is no morphological proof of persistent or dormant tissue stages in the avian host during latent infections. This study investigated persistence of Plasmodium relictum pSGS1 in birds with latent infections during winter, with the goal to detect presumed persisting tissue stages using a highly sensitive RNAscope® in situ hybridization technology.

METHODS

Fourteen domestic canaries were infected with P. relictum pSGS1 by blood-inoculation in spring, and blood films examined during the first 4 months post infection, and during winter and spring of the following year. After parasitaemia was no longer detectable, half of the birds were dissected, and tissue samples investigated for persisting tissue stages using RNAscope ISH and histology. The remaining birds were blood-checked and dissected after re-appearance of parasitaemia, and their tissues equally examined.

RESULTS

Systematic examination of tissues showed no exo-erythrocytic stages in birds exhibiting latent infections by blood-film microscopy, indicating absence of dormant tissue stages in P. relictum pSGS1-infected canaries. Instead, RNAscope ISH revealed rare P. relictum blood stages in capillaries of various tissues and organs, demonstrating persistence of the parasites in the microvasculature. Birds examined after re-appearance of parasitemia showed higher numbers of P. relictum blood stages in both capillaries and larger blood vessels, indicating replication during early spring and re-appearance in the peripheral circulation.

CONCLUSIONS

The findings suggest that persistence of P. relictum pSGS1 during latent infection is mediated by continuous low-level erythrocytic merogony and possibly tissue sequestration of infected blood cells. Re-appearance of parasitaemia in spring seems to result from increased erythrocytic merogony, therefore representing recrudescence and not relapse in blood-inoculated canaries. Further, the study highlights strengths and limitations of the RNAscope ISH technology for the detection of rare parasite stages in tissues, providing directions for future research on persistence and tissue sequestration of avian malaria and related haemosporidian parasites.

Mycobacterium leprae is able to infect adipocytes, inducing lipolysis and modulating the immune response

Leprosy is a chronic infectious disease caused by the intracellular bacillus Mycobacterium leprae (M. leprae), which is known to infect skin macrophages and Schwann cells. Although adipose tissue is a recognized site of Mycobacterium tuberculosis infection, its role in the histopathology of leprosy was, until now, unknown. We analyzed the M. leprae capacity to infect and persist inside adipocytes, characterizing the induction of a lipolytic phenotype in adipocytes, as well as the effect of these infected cells on macrophage recruitment. We evaluated 3T3-L1-derived adipocytes, inguinal adipose tissue of SWR/J mice, and subcutaneous adipose tissue biopsies of leprosy patients. M. leprae was able to infect 3T3-L1-derived adipocytes in vitro, presenting a strong lipolytic profile after infection, followed by significant cholesterol efflux. This lipolytic phenotype was replicated in vivo by M. leprae injection into mice inguinal adipose tissue. Furthermore, M. leprae was detected inside crown-like structures in the subcutaneous adipose tissue of multibacillary patients. These data indicate that subcutaneous adipose tissue could be an important site of infection, and probably persistence, for M. leprae, being involved in the modulation of the innate immune control in leprosy via the release of cholesterol, MCP-1, and adiponectin.

NK cell-induced damage to P.falciparum-infected erythrocytes requires ligand-specific recognition and releases parasitophorous vacuoles that are phagocytosed by monocytes in the presence of immune IgG

Natural killer (NK) cells lyse virus-infected cells and transformed cells through polarized delivery of lytic effector molecules into target cells. We have shown that NK cells lyse Plasmodium falciparum-infected red blood cells (iRBC) via antibody-dependent cellular cytotoxicity (ADCC). A high frequency of adaptive NK cells, with elevated intrinsic ADCC activity, in people chronically exposed to malaria transmission is associated with reduced parasitemia and resistance to disease. How NK cells bind to iRBC and the outcome of iRBC lysis by NK cells has not been investigated. We applied gene ablation in inducible erythrocyte precursors and antibody-blocking experiments with iRBC to demonstrate a central role of CD58 and ICAM-4 as ligands for adhesion by NK cells via CD2 and integrin αMβ2, respectively. Adhesion was dependent on opsonization of iRBC by IgG. Live imaging and quantitative flow cytometry of NK-mediated ADCC toward iRBC revealed that damage to the iRBC plasma membrane preceded damage to P. falciparum within parasitophorous vacuoles (PV). PV were identified and tracked with a P.falciparum strain that expresses the PV membrane-associated protein EXP2 tagged with GFP. After NK-mediated ADCC, PV were either found inside iRBC ghosts or released intact and devoid of RBC plasma membrane. Electron microscopy images of ADCC cultures revealed tight NK-iRBC synapses and free vesicles similar in size to GFP+ PV isolated from iRBC lysates by cell sorting. The titer of IgG in plasma of malaria-exposed individuals that bound PV was two orders of magnitude higher than IgG that bound iRBC. This immune IgG stimulated efficient phagocytosis of PV by primary monocytes. The selective NK-mediated damage to iRBC, resulting in release of PV, and subsequent phagocytosis of PV by monocytes may combine for efficient killing and removal of intra-erythrocytic P.falciparum parasite. This mechanism may mitigate the inflammation and malaria symptoms during blood-stage P. falciparum infection.

Neuropilin-1 identifies a subset of highly activated CD8+ T cells during parasitic and viral infections

Neuropilin-1 (Nrp-1) expression on CD8+ T cells has been identified in tumor-infiltrating lymphocytes and in persistent murine gamma-herpes virus infections, where it interferes with the development of long-lived memory T cell responses. In parasitic and acute viral infections, the role of Nrp-1 expression on CD8+ T cells remains unclear. Here, we demonstrate a strong induction of Nrp-1 expression on CD8+ T cells in Plasmodium berghei ANKA (PbA)-infected mice that correlated with neurological deficits of experimental cerebral malaria (ECM). Likewise, the frequency of Nrp-1+CD8+ T cells was significantly elevated and correlated with liver damage in the acute phase of lymphocytic choriomeningitis virus (LCMV) infection. Transcriptomic and flow cytometric analyses revealed a highly activated phenotype of Nrp-1+CD8+ T cells from infected mice. Correspondingly, in vitro experiments showed rapid induction of Nrp-1 expression on CD8+ T cells after stimulation in conjunction with increased expression of activation-associated molecules. Strikingly, T cell-specific Nrp-1 ablation resulted in reduced numbers of activated T cells in the brain of PbA-infected mice as well as in spleen and liver of LCMV-infected mice and alleviated the severity of ECM and LCMV-induced liver pathology. Mechanistically, we identified reduced blood-brain barrier leakage associated with reduced parasite sequestration in the brain of PbA-infected mice with T cell-specific Nrp-1 deficiency. In conclusion, Nrp-1 expression on CD8+ T cells represents a very early activation marker that exacerbates deleterious CD8+ T cell responses during both, parasitic PbA and acute LCMV infections.

Assessment of Liver Antioxidant Profile in Plasmodium Berghei Infected Mice Treated with Curative Ethanol Leaf extract of Musa paradisiaca

Background

The increasing resistance to most antimalarial drugs suggests a need for better alternatives. This study evaluated in vivo antimalarial and liver antioxidant profile of dry plantain leaf extract (Musa paradisiaca) on mice infected with Plasmodium berghei.

Methods

Six groups of ten mice each grouped as control, P. berghei, artesunate, and P. berghei infected mice were orally administered 250,500 and 1000mg/kg Musa paradisiaca leaf extract for 5 days. Blood smears were evaluated for parasitaemia on the 10th day and the mice sacrificed. Catalase, Malondialdehyde, protein, Glutathione peroxidase and reduced glutathione was estimated using Colorimetric, Biuret and spectrophotometric methods respectively with data analyzed using SPSS version 21.

Results

Catalase activity (umol/ml/mins) was 24.62 ± 0.99, 10.04 ± 0.50, 19.35 ± 0.38, 22.13 ± 0.00, 22.79 ± 0.00 and 23.66 ± 0.20 while Glutathione Peroxidase(u/l) was 332.34± 0.64, 205.22± 4.61, 218.26± 0.63, 310.59± 0.00, 305.20± 0.00. and 295.97± 0.02 at Control, P.berghei, artesunate, 250mg, 500mg and1000mg extracts. Glutathione (mM) was 1.60 ± 0.12, 0.64 ± 0.09, 1.06 ± 0.16, 0.72 ± 0.00, 0.92 ± 0.00 and 1.26 ± 0.08 while Malondialdehye (uM) was 16.93 ± 3.59, 61.65 ± 1.72, 27.80 ± 0.26, 36.90 ± 0.00, 34.30 ± 0.00 and 32.68 ± 0.27 and Protein(g/dl) was 22.37 ± 1.87, 7.91 ± 0.13, 11.78 ± 1.19, 11.79 ± 0.00, 13.20 ± 0.00 and 17.04 ±0.03 at control, P.berghei, artesunate, 250mg, 500mg and1000mg respectively.

Conclusion

The study suggested that ethanolic extract of Musa paradisiaca reduced liver oxidative stress caused by P.berghei.

Beyond energy balance regulation: The underestimated role of adipose tissues in host defense against pathogens

Although the adipose tissue (AT) is a central metabolic organ in the regulation of whole-body energy homeostasis, it is also an important endocrine and immunological organ. As an endocrine organ, AT secretes a variety of bioactive peptides known as adipokines - some of which have inflammatory and immunoregulatory properties. As an immunological organ, AT contains a broad spectrum of innate and adaptive immune cells that have mostly been studied in the context of obesity. However, overwhelming evidence supports the notion that AT is a genuine immunological effector site, which contains all cell subsets required to induce and generate specific and effective immune responses against pathogens. Indeed, AT was reported to be an immune reservoir in the host's response to infection, and a site of parasitic, bacterial and viral infections. In addition, besides AT's immune cells, preadipocytes and adipocytes were shown to express innate immune receptors, and adipocytes were reported as antigen-presenting cells to regulate T-cell-mediated adaptive immunity. Here we review the current knowledge on the role of AT and AT's immune system in host defense against pathogens. First, we will summarize the main characteristics of AT: type, distribution, function, and extraordinary plasticity. Second, we will describe the intimate contact AT has with lymph nodes and vessels, and AT immune cell composition. Finally, we will present a comprehensive and up-to-date overview of the current research on the contribution of AT to host defense against pathogens, including the respiratory viruses influenza and SARS-CoV-2.

Cerebral Malaria and Neuronal Implications of Plasmodium Falciparum Infection: From Mechanisms to Advanced Models

Reorganization of host red blood cells by the malaria parasite Plasmodium falciparum enables their sequestration via attachment to the microvasculature. This artificially increases the dwelling time of the infected red blood cells within inner organs such as the brain, which can lead to cerebral malaria. Cerebral malaria is the deadliest complication patients infected with P. falciparum can experience and still remains a major public health concern despite effective antimalarial therapies. Here, the current understanding of the effect of P. falciparum cytoadherence and their secreted proteins on structural features of the human blood-brain barrier and their involvement in the pathogenesis of cerebral malaria are highlighted. Advanced 2D and 3D in vitro models are further assessed to study this devastating interaction between parasite and host. A better understanding of the molecular mechanisms leading to neuronal and cognitive deficits in cerebral malaria will be pivotal in devising new strategies to treat and prevent blood-brain barrier dysfunction and subsequent neurological damage in patients with cerebral malaria.

Mouse Models for Unravelling Immunology of Blood Stage Malaria

Malaria comprises a spectrum of disease syndromes and the immune system is a major participant in malarial disease. This is particularly true in relation to the immune responses elicited against blood stages of Plasmodium-parasites that are responsible for the pathogenesis of infection. Mouse models of malaria are commonly used to dissect the immune mechanisms underlying disease. While no single mouse model of Plasmodium infection completely recapitulates all the features of malaria in humans, collectively the existing models are invaluable for defining the events that lead to the immunopathogenesis of malaria. Here we review the different mouse models of Plasmodium infection that are available, and highlight some of the main contributions these models have made with regards to identifying immune mechanisms of parasite control and the immunopathogenesis of malaria.

Malaria parasite heme biosynthesis promotes and griseofulvin protects against cerebral malaria in mice

Heme-biosynthetic pathway of malaria parasite is dispensable for asexual stages, but essential for mosquito and liver stages. Despite having backup mechanisms to acquire hemoglobin-heme, pathway intermediates and/or enzymes from the host, asexual parasites express heme pathway enzymes and synthesize heme. Here we show heme synthesized in asexual stages promotes cerebral pathogenesis by enhancing hemozoin formation. Hemozoin is a parasite molecule associated with inflammation, aberrant host-immune responses, disease severity and cerebral pathogenesis. The heme pathway knockout parasites synthesize less hemozoin, and mice infected with knockout parasites are protected from cerebral malaria and death due to anemia is delayed. Biosynthetic heme regulates food vacuole integrity and the food vacuoles from knockout parasites are compromised in pH, lipid unsaturation and proteins, essential for hemozoin formation. Targeting parasite heme synthesis by griseofulvin-a FDA-approved antifungal drug, prevents cerebral malaria in mice and provides an adjunct therapeutic option for cerebral and severe malaria.

The Phosphodiesterase Inhibitor Tadalafil Promotes Splenic Retention of Plasmodium falciparum Gametocytes in Humanized Mice

The persistence of erythrocytes infected with Plasmodium falciparum gametocytes in the bloodstream is closely related to the modulation of their mechanical properties. New drugs that increase the stiffness of infected erythrocytes may thus represent a novel approach to block malaria parasite transmission. The phosphodiesterase inhibitor tadalafil has been shown to impair the ability of infected erythrocytes to circulate in an in vitro model for splenic retention. Here, we used a humanized mouse model to address in vivo the effect of tadalafil on the circulation kinetics of mature gametocyte-infected erythrocytes. We show that stiff immature gametocyte-infected erythrocytes are retained in the spleen of humanized mice at rates comparable to that of the in vitro model. Accordingly, tadalafil-induced stiffening of mature gametocyte-infected erythrocytes impairs their circulation in the bloodstream and triggers their retention by the spleen. These in vivo results validate that tadalafil is a novel drug lead potentially capable of blocking malaria parasite transmission by targeting GIE mechanical properties.

Experimental Models to Study the Pathogenesis of Malaria-Associated Acute Respiratory Distress Syndrome

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is increasingly gaining recognition as a severe malaria complication because of poor prognostic outcomes, high lethality rate, and limited therapeutic interventions. Unfortunately, invasive clinical studies are challenging to conduct and yields insufficient mechanistic insights. These limitations have led to the development of suitable MA-ARDS experimental mouse models. In patients and mice, MA-ARDS is characterized by edematous lung, along with marked infiltration of inflammatory cells and damage of the alveolar-capillary barriers. Although, the pathogenic pathways have yet to be fully understood, the use of different experimental mouse models is fundamental in the identification of mediators of pulmonary vascular damage. In this review, we discuss the current knowledge on endothelial activation, leukocyte recruitment, leukocyte induced-endothelial dysfunction, and other important findings, to better understand the pathogenesis pathways leading to endothelial pulmonary barrier lesions and increased vascular permeability. We also discuss how the advances in imaging techniques can contribute to a better understanding of the lung lesions induced during MA-ARDS, and how it could aid to monitor MA-ARDS severity.

Improving the Molecular Diagnosis of Malaria: Droplet Digital PCR-Based Method Using Saliva as a DNA Source

Malaria is an acute febrile disease caused by a protozoan of the genus Plasmodium. Light microscopy (LM) is the gold standard for the diagnosis of malaria. Despite this method being rapid and inexpensive, it has a low limit of detection, which hampers the identification of low parasitemia infections. By using multicopy targets and highly sensitive molecular techniques, it is possible to change this scenario. In this study, we evaluated the performance of droplet digital PCR (ddPCR) to detect Plasmodium DNA obtained from saliva samples (whole saliva and buccal swab) of 157 individuals exposed to malaria transmission from the Brazilian Amazon region. We used the highly sensitive ddPCR method with non-ribosomal multicopy targets for Plasmodium vivax (Pvr47) and Plasmodium falciparum (Pfr364). There was good concordance between the quantitative real-time PCR (qPCR) results from the saliva and blood, except for mixed-species infections. The sensitivity of qPCR was 93% for blood, 77% for saliva, and 47% for swabs. Parasite DNA was not detected in saliva samples in low-density infections compared with the detection in blood samples. ddPCR showed increased sensitivity for detecting Plasmodium in the blood and swabs (99% in blood, 73% in saliva, and 59% in swabs). Notably, ddPCR detected more mixed infections in the blood (15%), saliva (9%), and swabs (18%) than qPCR. Our data showed that the differences between ddPCR and qPCR were the result of a higher number of P. falciparum infections detected by ddPCR. Overall, there was a moderate correlation between parasite densities estimated by the different methods in the blood. Our findings highlight the possibility of using non-invasive sample collection methods for malaria diagnosis by targeting multicopy sequences combined with highly sensitive molecular methods.

Host cell maturation modulates parasite invasion and sexual differentiation in Plasmodium berghei

Malaria remains a global health problem causing more than 400,000 deaths annually. Plasmodium parasites, the causative agents of malaria, replicate asexually in red blood cells (RBCs) of their vertebrate host, while a subset differentiates into sexual stages (gametocytes) for mosquito transmission. Parasite replication and gametocyte maturation in the erythropoietic niches of the bone marrow and spleen contribute to pathogenesis and drive transmission, but the mechanisms underlying this organ enrichment remain unknown. Here, we performed a comprehensive analysis of rodent P. berghei infection by flow cytometry and single-cell RNA sequencing. We identified CD71 as a host receptor for reticulocyte invasion and found that parasites metabolically adapt to the host cell environment. Transcriptional analysis and functional assays further revealed a nutrient-dependent tropism for gametocyte formation in reticulocytes. Together, we provide a thorough characterization of host-parasite interactions in erythropoietic niches and define host cell maturation state as the key driver of parasite adaptation.

Role of sphingosine kinase and sphingosine-1-phosphate receptor in the liver pathology of mice infected with Plasmodium berghei ANKA

Decreased serum sphingosine 1-phosphate (S1P) has been reported in severe malaria patients, but the expression of receptors and enzymes associated with S1P has not been investigated in the liver of malaria patients. Therefore, this study aimed to investigate the expression of sphingosine kinase (SphK) and S1P receptors (S1PRs) in the liver of malaria-infected mice. C57BL/6 male mice were divided into a control group (n = 10) and a Plasmodium berghei (PbA)-infected group (n = 10). Mice in the malaria group were intraperitoneally injected with 1×10⁶P. berghei ANKA-infected red blood cells, whereas control mice were intraperitoneally injected with normal saline. Liver tissues were collected on Day 13 of the experiment to evaluate histopathological changes by hematoxylin and eosin staining and to investigate SphK and S1PR expression by immunohistochemistry and real-time PCR. Histological examination of liver tissues from the PbA-infected group revealed sinusoidal dilatation, hemozoin deposition, portal tract inflammation and apoptotic hepatocytes, which were absent in the control group. Immunohistochemical staining showed significant increases in the expression of SphK1 and SphK2 and significant decreases in the expression of S1PR1, S1PR2, and S1PR3 in the endothelium, hepatocytes, and Kupffer cells in liver tissue from the PbA-infected group compared with the control group. Real-time PCR analysis showed the upregulation of SphK1 and the downregulation of S1PR1, S1PR2, and S1PR3 in the liver in the PbA-infected group compared with the control group. In conclusion, this study demonstrates for the first time that SphK1 mRNA expression is upregulated and that S1PR1, S1PR2, and S1PR3 expression is decreased in the liver tissue of PbA-infected mice. Our findings suggest that the decreased levels of S1PR1, S1PR2, and S1PR3 might play an important role in liver injury during malaria infection.

Autophagy Pathways in the Genesis of Plasmodium-Derived Microvesicles: A Double-Edged Sword?

Malaria, caused by Plasmodium species (spp.), is a deadly parasitic disease that results in approximately 400,000 deaths per year globally. Autophagy pathways play a fundamental role in the developmental stages of the parasite within the mammalian host. They are also involved in the production of Plasmodium-derived extracellular vesicles (EVs), which play an important role in the infection process, either by providing nutrients for parasite growth or by contributing to the immunopathophysiology of the disease. For example, during the hepatic stage, Plasmodium-derived EVs contribute to parasite virulence by modulating the host immune response. EVs help in evading the different autophagy mechanisms deployed by the host for parasite clearance. During cerebral malaria, on the other hand, parasite-derived EVs promote an astrocyte-mediated inflammatory response, through the induction of a non-conventional host autophagy pathway. In this review, we will discuss the cross-talk between Plasmodium-derived microvesicles and autophagy, and how it influences the outcome of infection.

Organotypic endothelial adhesion molecules are key for Trypanosoma brucei tropism and virulence

Trypanosoma brucei is responsible for lethal diseases in humans and cattle in Sub-Saharan Africa. These extracellular parasites extravasate from the blood circulation into several tissues. The importance of the vasculature in tissue tropism is poorly understood. Using intravital imaging and bioluminescence, we observe that gonadal white adipose tissue and pancreas are the two main parasite reservoirs. We show that reservoir establishment happens before vascular permeability is compromised, suggesting that extravasation is an active mechanism. Blocking endothelial surface adhesion molecules (E-selectin, P-selectins, or ICAM2) significantly reduces extravascular parasite density in all organs and delays host lethality. Remarkably, blocking CD36 has a specific effect on adipose tissue tropism that is sufficient to delay lethality, suggesting that establishment of the adipose tissue reservoir is necessary for parasite virulence. This work demonstrates the importance of the vasculature in a T. brucei infection and identifies organ-specific adhesion molecules as key players for tissue tropism.

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Our study investigates the blood vasculature for T. brucei reservoir establishment

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We show the pancreas is a large extravascular reservoir

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We establish that T. brucei tropism is linked to organotypic adhesion molecules

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Interfering with adhesion molecules impacts parasite virulence and host survival

Rodent Malaria Erythrocyte Preference Assessment by an Ex Vivo Tropism Assay

Circulating red blood cells consist of young erythrocytes (early and late reticulocytes) and mature erythrocytes (normocytes). The human malaria parasites, Plasmodium falciparum and P. vivax, have a preference to invade reticulocytes during blood-stage infection. Rodent malaria parasites that also prefer reticulocytes could be useful tools to study human malaria reticulocyte invasion. However, previous tropism studies of rodent malaria are inconsistent from one another, making it difficult to compare cell preference of different parasite species and strains. In vivo measurements of cell tropism are also subjected to many confounding factors. Here we developed an ex vivo tropism assay for rodent malaria with highly purified fractions of murine reticulocytes and normocytes. We measured invasion into the different erythrocyte populations using flow cytometry and evaluated the tropism index of the parasite strains. We found that P. berghei ANKA displayed the strongest reticulocyte preference, followed by P. yoelii 17X1.1, whereas P. chabaudi AS and P. vinckei S67 showed mixed tropism. These preferences are intrinsic and were maintained at different reticulocyte and normocyte availabilities. Our study shed light on the true erythrocyte preference of the parasites and paves the way for future investigations on the receptor-ligand interactions mediating erythrocyte tropism.

Effect of cell geometry in the evaluation of erythrocyte viscoelastic properties

The red blood cell membrane-cytoskeleton is a complex structure mainly responsible for giving the cell rigidity and shape. It also provides the erythrocyte with the ability to pass through narrow capillaries of the vertebrate blood circulatory system. Although the red blood cell viscoelastic properties have been extensively studied, reported experimental data differ by up to three orders of magnitude. This could be attributed to the natural cell variability, to the different techniques employed, and also to the models used for the cell response, which are highly dependent on cell geometry. Here, we use two methodologies based on optical tweezers to investigate the viscoelastic behavior of healthy human red blood cells, one applying small cell deformations (microrheology) and another imposing large deformations (tether extraction). We also establish a defocusing microscopy-based method to characterize the cell geometry and thus the erythrocyte form factor, an essential parameter that allows comparisons among the viscoelastic properties at different conditions. Moreover, for small deformations, a soft glassy rheology model is used to discuss the results, while for large deformations two surface shear moduli and one surface viscosity are determined, together with the surface tension and bending modulus of the erythrocyte membrane lipid component. We also show that F-actin is not detected in tethers, although the erythrocyte membrane has physical properties like those of other adherent cells, known to have tethers containing F-actin inside. Altogether, our results show good agreement with the reported literature and we argue that, to properly compare the viscoelastic properties of red blood cells in different situations, the task of cell geometry characterization must be accomplished. This may be especially important when the influence of agents, like the malaria parasite, induces changes in both the geometry and chemical constituents of the erythrocyte membrane. Together, the new methodologies and procedures used in this study would allow the erythrocyte community to better explore the mechanical behavior of red blood cells and may be useful to characterize erythrocyte viscoelasticity changes in several blood diseases.

Of membranes and malaria: phospholipid asymmetry in Plasmodium falciparum-infected red blood cells

Malaria is a vector-borne parasitic disease with a vast impact on human history, and according to the World Health Organisation, Plasmodium parasites still infect over 200 million people per year. Plasmodium falciparum, the deadliest parasite species, has a remarkable ability to undermine the host immune system and cause life-threatening disease during blood infection. The parasite's host cells, red blood cells (RBCs), generally maintain an asymmetric distribution of phospholipids in the two leaflets of the plasma membrane bilayer. Alterations to this asymmetry, particularly the exposure of phosphatidylserine (PS) in the outer leaflet, can be recognised by phagocytes. Because of the importance of innate immune defence numerous studies have investigated PS exposure in RBCs infected with P. falciparum, but have reached different conclusions. Here we review recent advancements in our understanding of the molecular mechanisms which regulate asymmetry in RBCs, and whether infection with the P. falciparum parasite results in changes to PS exposure. On the balance of evidence, it is likely that membrane asymmetry is disrupted in parasitised RBCs, though some methodological issues need addressing. We discuss the potential causes and consequences of altered asymmetry in parasitised RBCs, particularly for in vivo interactions with the immune system, and the role of host-parasite co-evolution. We also examine the potential asymmetric state of parasite membranes and summarise current knowledge on the parasite proteins, which could regulate asymmetry in these membranes. Finally, we highlight unresolved questions at this time and the need for interdisciplinary approaches to uncover the machinery which enables P. falciparum parasites to hide in mature erythrocytes.

Adipose tissue parasite sequestration drives leptin production in mice and correlates with human cerebral malaria

Circulating levels of the adipokine leptin are linked to neuropathology in experimental cerebral malaria (ECM), but its source and regulation mechanism remain unknown. Here, we show that sequestration of infected red blood cells (iRBCs) in white adipose tissue (WAT) microvasculature increased local vascular permeability and leptin production. Mice infected with parasite strains that fail to sequester in WAT displayed reduced leptin production and protection from ECM. WAT sequestration and leptin induction were lost in CD36KO mice; however, ECM susceptibility revealed sexual dimorphism. Adipocyte leptin was regulated by the mechanistic target of rapamycin complex 1 (mTORC1) and blocked by rapamycin. In humans, although Plasmodium falciparum infection did not increase circulating leptin levels, iRBC sequestration, tissue leptin production, and mTORC1 activity were positively correlated with CM in pediatric postmortem WAT. These data identify WAT sequestration as a trigger for leptin production with potential implications for pathogenesis of malaria infection, prognosis, and treatment.

Teratogen update: Malaria in pregnancy and the use of antimalarial drugs in the first trimester

Malaria is a particular problem in pregnancy because of enhanced sensitivity, the possibility of placental malaria, and adverse effects on pregnancy outcome. Artemisinin-containing combination therapies (ACTs) are the most effective antimalarials known. WHO recommends 7-day quinine therapy for uncomplicated Plasmodium falciparum malaria in the first trimester despite the superior tolerability and efficacy of 3-day ACT regimens because artemisinins caused embryolethality and/or cardiovascular malformations at relatively low doses in rats, rabbits, and monkeys. The developmental toxicity of artesunate, artemether, and DHA were similar in rats but artesunate was embryotoxic at lower doses in rabbits (5 mg/kg/day) than artemether (no effect level = 25 mg/kg/day). In clinical studies in Africa, treatment with artemether-lumefantrine in the first trimester was observed to be highly efficacious and the miscarriage rate (≤3.1%) was similar to no antimalarial treatment (2.6%). When data from the first-trimester use of largely artesunate-based therapies in Thailand were pooled together, there was no difference in miscarriage rate compared to quinine. However, individually, artesunate-mefloquine was associated with a higher miscarriage rate (15/71 = 21%) compared to other artemisinin-based therapies including 7-day artesunate + clindamycin (2/50 = 4%) and quinine (92/842 = 11%). Thus, appropriate statistical comparisons of individual ACT groups are needed prior to assuming that they all have the same risk for developmental toxicity. Current limitations in the assessment of the safety of ACTs in the first trimester are a lack of exposures early in gestation (gestational weeks 6-7), limited postnatal evaluation for cardiovascular malformations, and the pooling of all ACTs for the assessment of risk.

Quantitative diffuse optical spectroscopy for noninvasive measurements of the malaria pigment hemozoin

Hemozoin (Hz) is a crystal by-product of hemoglobin consumption by malaria parasites. There are currently no in vivo deep tissue sensing methods that can quantify Hz presence noninvasively, which would be advantageous for malaria research and treatment. In this work, we describe the broadband near-infrared optical characterization of synthetic Hz in static and dynamic tissue-simulating phantoms. Using hybrid frequency domain and continuous-wave near-infrared spectroscopy, we quantified the broadband optical absorption and scattering spectra of Hz and identified the presence of Hz at a minimum tissue-equivalent concentration of 0.014 µg/mL in static lipid emulsion phantoms simulating human adipose. We then constructed a whole blood-containing tissue-simulating phantom and demonstrated the detection of Hz at physiologically-relevant tissue oxygen saturations ranging from 70-90%. Our results suggest that quantitative diffuse optical spectroscopy may be useful for detecting deep tissue Hz in vivo.

The skeletal muscles of mice infected with Plasmodium berghei and Plasmodium chabaudi reveal a crosstalk between lipid mediators and gene expression

Background

Malaria is one of the most prevalent infectious disease in the world with 3.2 billion humans at risk. Malaria causes splenomegaly and damage in other organs including skeletal muscles. Skeletal muscles comprise nearly 50% of the human body and are largely responsible for the regulation and modulation of overall metabolism. It is essential to understand how malaria damages muscles in order to develop effective preventive measures and/or treatments. Using a pre-clinical animal model, the potential molecular mechanisms of Plasmodium infection affecting skeletal muscles of mice were investigated.

Methods

Mouse Signal Transduction Pathway Finder PCR Array was used to monitor gene expression changes of 10 essential signalling pathways in skeletal muscles from mice infected with Plasmodium berghei and Plasmodium chabaudi. Then, a new targeted-lipidomic approach using liquid chromatography with tandem mass spectrometry (LC–MS/MS) to profile 158 lipid signalling mediators (LMs), mostly eicosanoids derived from arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), was applied. Finally, 16 key LMs directly associated with inflammation, oxidative stress, and tissue healing in skeletal muscles, were quantified.

Results

The results showed that the expression of key genes altered by Plasmodium infection is associated with inflammation, oxidative stress, and atrophy. In support to gene profiling results, lipidomics revealed higher concentrations of LMs in skeletal muscles directly related to inflammatory responses, while on the levels of LMs crucial in resolving inflammation and tissue repair reduced significantly.

Conclusion

The results provide new insights into the molecular mechanisms of malaria-induced muscle damage and revealed a potential mechanism modulating inflammation in malarial muscles. These pre-clinical studies should help with future clinical studies in humans aimed at monitoring of disease progression and development of specific interventions for the prevention and mitigation of long-term chronic effects on skeletal muscle function.

Droplet Digital PCR for the Detection of Plasmodium falciparum DNA in Whole Blood and Serum: A Comparative Analysis with Other Molecular Methods

Background: The estimation of Plasmodium falciparum parasitaemia can vary according to the method used. Recently, droplet digital PCR (ddPCR) has been proposed as a promising approach in the molecular quantitation of Plasmodium, but its ability to predict the actual parasitaemia on clinical samples has not been largely investigated. Moreover, the possibility of applying the ddPCR-sensitive method to serum samples has never been explored. Methods: We used, for the first time, ddPCR on both blood and serum to detect the DNA of P. falciparum in 52 paired samples from 26 patients. ddPCR was compared with loop-mediated isothermal amplification (LAMP) and rtPCR. The correlation between the ddPCR results, microscopy, and clinical parameters was examined. Results: ddPCR and microscopy were found to be strongly correlated (ρ(26) = 0.83111, p < 0.0001) in blood. Samples deviating from the correlation were partially explained by clinical parameters. In serum samples, ddPCR revealed the best performance in detecting P. falciparum DNA, with 77% positive samples among malaria subjects. Conclusion: Absolute quantitation by ddPCR can be a flexible technique for Plasmodium detection, with potential application in the diagnosis of malaria. In particular, ddPCR is a powerful approach for Plasmodium DNA analysis on serum when blood samples are unavailable.

Detection of Protein Aggregation in Live Plasmodium Parasites

The rapid evolution of resistance in the malaria parasite to every single drug developed against it calls for the urgent identification of new molecular targets. Using a stain specific for the detection of intracellular amyloid deposits in live cells, we have detected the presence of abundant protein aggregates in Plasmodium falciparum blood stages and female gametes cultured in vitro, in the blood stages of mice infected by Plasmodium yoelii, and in the mosquito stages of the murine malaria species Plasmodium berghei Aggregated proteins could not be detected in early rings, the parasite form that starts the intraerythrocytic cycle. A proteomics approach was used to pinpoint actual aggregating polypeptides in functional P. falciparum blood stages, which resulted in the identification of 369 proteins, with roles particularly enriched in nuclear import-related processes. Five aggregation-prone short peptides selected from this protein pool exhibited different aggregation propensity according to Thioflavin-T fluorescence measurements, and were observed to form amorphous aggregates and amyloid fibrils in transmission electron microscope images. The results presented suggest that generalized protein aggregation might have a functional role in malaria parasites. Future antimalarial strategies based on the upsetting of the pathogen's proteostasis and therefore affecting multiple gene products could represent the entry to new therapeutic approaches.

Influenza infection rewires energy metabolism and induces browning features in adipose cells and tissues

Like all obligate intracellular pathogens, influenza A virus (IAV) reprograms host cell's glucose and lipid metabolism to promote its own replication. However, the impact of influenza infection on white adipose tissue (WAT), a key tissue in the control of systemic energy homeostasis, has not been yet characterized. Here, we show that influenza infection induces alterations in whole-body glucose metabolism that persist long after the virus has been cleared. We report depot-specific changes in the WAT of IAV-infected mice, notably characterized by the appearance of thermogenic brown-like adipocytes within the subcutaneous fat depot. Importantly, viral RNA- and viral antigen-harboring cells are detected in the WAT of infected mice. Using in vitro approaches, we find that IAV infection enhances the expression of brown-adipogenesis-related genes in preadipocytes. Overall, our findings shed light on the role that the white adipose tissue, which lies at the crossroads of nutrition, metabolism and immunity, may play in influenza infection.

Tissue tropism in parasitic diseases

Parasitic diseases, such as sleeping sickness, Chagas disease and malaria, remain a major cause of morbidity and mortality worldwide, but particularly in tropical, developing countries. Controlling these diseases requires a better understanding of host-parasite interactions, including a deep appreciation of parasite distribution in the host. The preferred accumulation of parasites in some tissues of the host has been known for many years, but recent technical advances have allowed a more systematic analysis and quantifications of such tissue tropisms. The functional consequences of tissue tropism remain poorly studied, although it has been associated with important aspects of disease, including transmission enhancement, treatment failure, relapse and clinical outcome. Here, we discuss current knowledge of tissue tropism in Trypanosoma infections in mammals, describe potential mechanisms of tissue entry, comparatively discuss relevant findings from other parasitology fields where tissue tropism has been extensively investigated, and reflect on new questions raised by recent discoveries and their potential impact on clinical treatment and disease control strategies.

Haemosporidioses in wild Eurasian blackbirds (Turdus merula) and song thrushes (T. philomelos): an in situ hybridization study with emphasis on exo-erythrocytic parasite burden

Background

Passerine birds are frequently infected with diverse haemosporidian parasites. While infections are traditionally considered benign in wild birds, recent studies demonstrated mortalities of passerine species due to exo-erythrocytic development of the parasites, which can damage organs in affected hosts. However, exo-erythrocytic development remains insufficiently investigated for most haemosporidian species and thus little is known about the virulence of tissue stages in wild passerine birds. The aim of the present study was to investigate natural haemosporidian infections in deceased Eurasian blackbirds (Turdus merula) and song thrushes (Turdus philomelos) and to determine parasite burden and associated histological effects.

Methods

For molecular analysis, blood and tissue samples from 306 thrushes were screened for Plasmodium, Haemoproteus and Leucocytozoon parasites by nested PCR. For the detection of parasite stages in organ samples, tissue sections were subjected to chromogenic in situ hybridization (CISH) using genus- and species-specific probes targeting the rRNAs of parasites. Exo-erythrocytic parasite burden was semi-quantitatively assessed and histological lesions were evaluated in haematoxylin–eosin-stained sections.

Results

By PCR, 179 of 277 Eurasian blackbirds and 15 of 29 song thrushes were positive for haemosporidians. Parasites of all three genera were detected, with Plasmodium matutinum LINN1 and Plasmodium vaughani SYAT05 showing the highest prevalence. CISH revealed significant differences in exo-erythrocytic parasite burden between lineages in Eurasian blackbirds, with P. matutinum LINN1 frequently causing high exo-erythrocytic parasite burdens in various organs that were associated with histological alterations. Song thrushes infected with P. matutinum LINN1 and birds infected with other haemosporidian lineages showed mostly low exo-erythrocytic parasite burdens. Two Eurasian blackbirds infected with Leucocytozoon sp. TUMER01 showed megalomeronts in various organs that were associated with inflammatory reactions and necroses.

Conclusion

This study suggests that P. matutinum LINN1, a common lineage among native thrushes, regularly causes high exo-erythrocytic parasite burdens in Eurasian blackbirds, which may result in disease and mortalities, indicating its high pathogenic potential. The findings further illustrate that the same parasite lineage may show different levels of virulence in related bird species which should be considered when assessing the pathogenicity of haemosporidian parasite species. Finally, the study provides evidence of virulent Leucocytozoon sp. TUMER01 infections in two Eurasian blackbirds caused by megalomeront formation.

ZBTB7B (ThPOK) Is Required for Pathogenesis of Cerebral Malaria and Protection against Pulmonary Tuberculosis

We used a genome-wide screen in N-ethyl-N-nitrosourea (ENU)-mutagenized mice to identify genes in which recessive loss-of-function mutations protect against pathological neuroinflammation. We identified an R367Q mutation in the ZBTB7B (ThPOK) protein in which homozygosity causes protection against experimental cerebral malaria (ECM) caused by infection with Plasmodium berghei ANKA. Zbtb7b^R367Q homozygous mice show a defect in the lymphoid compartment expressed as severe reduction in the number of single-positive CD4 T cells in the thymus and in the periphery, reduced brain infiltration of proinflammatory leukocytes in P. berghei ANKA-infected mice, and reduced production of proinflammatory cytokines by primary T cells ex vivo and in vivo Dampening of proinflammatory immune responses in Zbtb7b^R367Q mice is concomitant to increased susceptibility to infection with avirulent (Mycobacterium bovis BCG) and virulent (Mycobacterium tuberculosis H37Rv) mycobacteria. The R367Q mutation maps to the first DNA-binding zinc finger domain of ThPOK and causes loss of base contact by R367 in the major groove of the DNA, which is predicted to impair DNA binding. Global immunoprecipitation of ThPOK-containing chromatin complexes coupled to DNA sequencing (ChIP-seq) identified transcriptional networks and candidate genes likely to play key roles in CD4⁺ CD8⁺ T cell development and in the expression of lineage-specific functions of these cells. This study highlights ThPOK as a global regulator of immune function in which alterations may affect normal responses to infectious and inflammatory stimuli.

Specific Biological Features of Adipose Tissue, and Their Impact on HIV Persistence

Although white AT can contribute to anti-infectious immune responses, it can also be targeted and perturbed by pathogens. The AT's immune involvement is primarily due to strong pro-inflammatory responses (with both local and paracrine effects), and the large number of fat-resident macrophages. Adipocytes also exert direct antimicrobial responses. In recent years, it has been found that memory T cells accumulate in AT, where they provide efficient secondary responses against viral pathogens. These observations have prompted researchers to re-evaluate the links between obesity and susceptibility to infections. In contrast, AT serves as a reservoir for several persistence pathogens, such as human adenovirus Ad-36, Trypanosoma gondii, Mycobacterium tuberculosis, influenza A virus, and cytomegalovirus (CMV). The presence and persistence of bacterial DNA in AT has led to the concept of a tissue-specific microbiota. The unexpected coexistence of immune cells and pathogens within the specific AT environment is intriguing, and its impact on anti-infectious immune responses requires further evaluation. AT has been recently identified as a site of HIV persistence. In the context of HIV infection, AT is targeted by both the virus and the antiretroviral drugs. AT's intrinsic metabolic features, large overall mass, and wide distribution make it a major tissue reservoir, and one that may contribute to the pathophysiology of chronic HIV infections. Here, we review the immune, metabolic, viral, and pharmacological aspects that contribute to HIV persistence in AT. We also evaluate the respective impacts of both intrinsic and HIV-induced factors on AT's involvement as a viral reservoir. Lastly, we examine the potential consequences of HIV persistence on the metabolic and immune activities of AT.

Plasmodium Infection Induces Dyslipidemia and a Hepatic Lipogenic State in the Host through the Inhibition of the AMPK-ACC Pathway

Malaria is a major parasitic disease of humans and is a health public problem that affects more than 100 countries. In 2017, it caused nearly half a million deaths out of 219 million infections. Malaria is caused by the protozoan parasites of the genus Plasmodium and is transmitted by female mosquitoes of the genus Anopheles. Once in the bloodstream, Plasmodium merozoites invade erythrocytes and proliferate until the cells lyses and release new parasites that invade other erythrocytes. Remarkably, they can manipulate the vertebrate host's lipid metabolism pathways, since they cannot synthesize lipid classes that are essential for their development and replication. In this study, we show that mice infected with Plasmodium chabaudi present a completely different plasma profile from control mice, with marked hyperproteinemia, hypertriglyceridemia, hypoglycemia, and hypocholesterolemia. In addition, white adipose and hepatic tissue and analyses from infected animals revealed the accumulation of triacylglycerol in both tissues and free fatty acids and free cholesterol in the liver. Hepatic mRNA and protein expression of key enzymes and transcription factors involved in lipid metabolism were also altered by P. chabaudi infection, leading to a lipogenic state. The enzyme 5' AMP-activated protein kinase (AMPK), a master regulator of cell energetic metabolism, was also modulated by the parasite, which reduced AMPK phosphorylation levels upon infection. Pretreatment with metformin for 21 days followed by infection with P. chabaudi was effective in preventing infection of mice and also lowered the hepatic accumulation of lipids while activating AMPK. Together, these results provide new and important information on the specific molecular mechanisms induced by the malaria parasite to regulate hepatic lipid metabolism in order to facilitate its development, proliferation, and lifespan in its vertebrate host.

Sticking for a Cause: The Falciparum Malaria Parasites Cytoadherence Paradigm

After a successful invasion, malaria parasite Plasmodium falciparum extensively remodels the infected erythrocyte cellular architecture, conferring cytoadhesive properties to the infected erythrocytes. Cytoadherence plays a central role in the parasite's immune-escape mechanism, at the same time contributing to the pathogenesis of severe falciparum malaria. In this review, we discuss the cytoadhesive interactions between P. falciparum infected erythrocytes and various host cell types, and how these events are linked to malaria pathogenesis. We also highlight the limitations faced by studies attempting to correlate diversity in parasite ligands and host receptors with the development of severe malaria.

Contribution of Murine Models to the Study of Malaria During Pregnancy

Annually, many pregnancies occur in areas of Plasmodium spp. transmission, particularly in underdeveloped countries with widespread poverty. Estimations have suggested that several million women are at risk of developing malaria during pregnancy. In particular cases, systemic infection caused by Plasmodium spp. may extend to the placenta, dysregulating local homeostasis and promoting the onset of placental malaria; these processes are often associated with increased maternal and fetal mortality, intrauterine growth restriction, preterm delivery, and reduced birth weight. The endeavor to understand and characterize the mechanisms underlying disease onset and placental pathology face several ethical and logistical obstacles due to explicit difficulties in assessing human gestation and biological material. Consequently, the advent of murine experimental models for the study of malaria during pregnancy has substantially contributed to our understanding of this complex pathology. Herein, we summarize research conducted during recent decades using murine models of malaria during pregnancy and highlight the most relevant findings, as well as discuss similarities to humans and the translational capacity of achieved results.

HIV Persistence in Adipose Tissue Reservoirs

PURPOSE OF REVIEW

The purpose of this review is to examine the evidence describing adipose tissue as a reservoir for HIV-1 and how this often expansive anatomic compartment contributes to HIV persistence.

RECENT FINDINGS

Memory CD4 T cells and macrophages, the major host cells for HIV, accumulate in adipose tissue during HIV/SIV infection of humans and rhesus macaques. Whereas HIV and SIV proviral DNA is detectable in CD4 T cells of multiple fat depots in virtually all infected humans and monkeys examined, viral RNA is less frequently detected, and infected macrophages may be less prevalent in adipose tissue. However, based on viral outgrowth assays, adipose-resident CD4 T cells are latently infected with virus that is replication-competent and infectious. Additionally, adipocytes interact with CD4 T cells and macrophages to promote immune cell activation and inflammation which may be supportive for HIV persistence. Antiviral effector cells, such as CD8 T cells and NK/NKT cells, are abundant in adipose tissue during HIV/SIV infection and typically exceed CD4 T cells, whereas B cells are largely absent from adipose tissue of humans and monkeys. Additionally, CD8 T cells in adipose tissue of HIV patients are activated and have a late differentiated phenotype, with unique TCR clonotypes of less diversity relative to blood CD8 T cells. With respect to the distribution of antiretroviral drugs in adipose tissue, data is limited, but there may be class-specific penetration of fat depots. The trafficking of infected immune cells within adipose tissues is a common event during HIV/SIV infection of humans and monkeys, but the virus may be mostly transcriptionally dormant. Viral replication may occur less in adipose tissue compared to other major reservoirs, such as lymphoid tissue, but replication competence and infectiousness of adipose latent virus are comparable to other tissues. Due to the ubiquitous nature of adipose tissue, inflammatory interactions among adipocytes and CD4 T cells and macrophages, and selective distribution of antiretroviral drugs, the sequestration of infected immune cells within fat depots likely represents a major challenge for cure efforts.

Genesis of placental sequestration in malaria and possible targets for drugs for placental malaria

Malaria during pregnancy results in intrauterine growth restriction, fetal anemia, and infant mortality. Women are more susceptible to malaria during pregnancy due to malaria‐induced inflammation and the sequestration of infected red blood cells in the placenta, which bind to the chondroitin sulfate portion of syndecan‐1 on the syncytiotrophoblast and in the intervillous space. Syndecan‐1 is a dimeric proteoglycan with an extracellular ectodomain that is cleaved from the transmembrane domain (referred to as “shedding”) by matrix metalloproteinases (MMPs), likely the secreted MMP‐9. The ectodomain includes four binding sites for chondroitin sulfate, which are proximal to the transmembrane domain, and six distal binding sites primarily for heparan sulfate. This “shedding” of syndecan‐1 is inhibited by the presence of the heparan sulfate chains, which can be removed by heparanase. The intervillous space contains fibrin strands and syndecan‐1 ectodomains free of heparan sulfate. The following is proposed as the sequence of events that leads to and is primarily responsible for sequestration in the intervillous space of the placenta. Inflammation associated with malaria triggers increased heparanase activity that degrades the heparan sulfate on the membrane‐bound syndecan‐1. Inflammation also upregulates MMP‐9 and the removal of heparan sulfate gives MMP‐9 access to cleave syndecan‐1, thereby releasing dimeric syndecan‐1 ectodomains with at least four chondroitin sulfate chains attached. These multivalent ectodomains bind infected RBCs together leading to their aggregation and entrapment in intervillous fibrin. This mechanism suggests possible new targets for anti‐placental malaria drugs such as the inhibition of MMP‐9. Doxycycline is an antimalarial drug which inhibits MMP‐9.

Intravital microscopy: Imaging host-parasite interactions in the brain

Intravital fluorescence microscopy (IVM) is a powerful technique for imaging multiple organs, including the brain of living mice and rats. It enables the direct visualisation of cells in situ providing a real-life view of biological processes that in vitro systems cannot. In addition, to the technological advances in microscopy over the last decade, there have been supporting innovations in data storage and analytical packages that enable the visualisation and analysis of large data sets. Here, we review the advantages and limitations of techniques predominantly used for brain IVM, including thinned skull windows, open skull cortical windows, and a miniaturised optical system based on microendoscopic probes that can be inserted into deep tissues. Further, we explore the relevance of these techniques for the field of parasitology. Several protozoan infections are associated with neurological symptoms including Plasmodium spp., Toxoplasma spp., and Trypanosoma spp. IVM has led to crucial findings on these parasite species, which are discussed in detail in this review.

Development of a label-free Raman imaging technique for differentiation of malaria parasite infected from non-infected tissue

During malarial infection, the host uses the spleen to clear the malaria parasites, however, the parasites have evolved the ability to bind to endothelial receptors in blood vessels of tissues to avoid removal, known as sequestration, and this is largely responsible for the symptoms and severity of infection. So a technique which could non-invasively diagnose tissue burden could be utilised as an aid for localised malaria diagnosis within tissue. Raman spectroscopy is a label-free imaging technique and can provide unique and chemically specific Raman 'fingerprint' spectrum of biological samples such as tissue. Within this study, Raman imaging was used to observe the changes to the molecular composition of mice spleen tissue under malarial infection, compared with non-infected samples. From analysis of the Raman imaging data, both tissue types showed very similar spectral profiles, which highlighted that their biochemical compositions were closely linked. Principal component analysis showed very clear separation of the two sample groups, with an associated increase in concentration of heme-based Raman vibrations within the infected dataset. This was indicative of the presence of hemozoin, the malaria pigment, being detected within the infected spleen. Separation also showed that as the hemozoin content within the tissue increased, there was a corresponding change to hemoglobin and some lipid/nucleic acid vibrations. These results demonstrate that Raman spectroscopy can be used to easily discriminate the subtle changes in tissue burden upon malarial infection.

Comparative effects of parenteral antimalarials in Swiss albino mice after chronic exposure to Plasmodium berghei

Mice are considered to be a similar model to humans in the pathogenesis of malaria. This study evaluates the effect of parenteral antimalarials on the spleen and liver of Swiss albino mice after chronic exposure to Plasmodium berghei. After chronic exposure to P.  berghei NK65 strain, the level of parasitemia was assessed. The mice were treated for 3 days using chloroquine (5 mg/kg), quinine (10 mg/kg), and artemether (2 mg/kg). The effect of chronic exposure and the pattern of recovery were evaluated. There was significant decrease in total body weight after chronic exposure to P. berghei (P < 0.05). An increase in total weight recovery was seen after day 15 of treatment with the antimalarials; this was more pronounced with artemether. A significant increase in liver and spleen weights due to P. berghei infection was seen. There was a recovery pattern due to decrease in liver and spleen weights following antimalarial administration, which was greatest with artemether (P < 0.05). Significant changes were more in parasitized, quinine and artemether groups (P < 0.05). There was a significant decrease in total spleen protein due to chloroquine but a decrease due to quinine and artemether (P < 0.05). No significant changes in liver and spleen albumin were observed after treatment. The highest parasite clearance was observed with artemether, followed by quinine. Five mice died after chronic exposure in all the groups prior to treatment. There was significant enlargement and discoloration of spleen and liver after chronic exposure. This study showed that artemether aided recovery of the liver and spleen better than quinine and chloroquine in albino mice after chronic exposure to P. berghei. This suggests there is potential for improvement in antimalarial therapy.

Elimination of intravascular thrombi prevents early mortality and reduces gliosis in hyper-inflammatory experimental cerebral malaria

BACKGROUND

Cerebral malaria (CM) is the most lethal outcome of Plasmodium infection. There are clear correlations between expression of inflammatory cytokines, severe coagulopathies, and mortality in human CM. However, the mechanisms intertwining the coagulation and inflammation pathways, and their roles in CM, are only beginning to be understood. In mice with T cells deficient in the regulatory cytokine IL-10 (IL-10 KO), infection with Plasmodium chabaudi leads to a hyper-inflammatory response and lethal outcome that can be prevented by anti-TNF treatment. However, inflammatory T cells are adherent within the vasculature and not present in the brain parenchyma, suggesting a novel form of cerebral inflammation. We have previously documented behavioral dysfunction and microglial activation in infected IL-10 KO animals suggestive of neurological involvement driven by inflammation. In order to understand the relationship of intravascular inflammation to parenchymal dysfunction, we studied the congestion of vessels with leukocytes and fibrin(ogen) and the relationship of glial cell activation to congested vessels in the brains of P. chabaudi-infected IL-10 KO mice.

METHODS

Using immunofluorescence microscopy, we describe severe thrombotic congestion in these animals. We stained for immune cell surface markers (CD45, CD11b, CD4), fibrin(ogen), microglia (Iba-1), and astrocytes (GFAP) in the brain at the peak of behavioral symptoms. Finally, we investigated the roles of inflammatory cytokine tumor necrosis factor (TNF) and coagulation on the pathology observed using neutralizing antibodies and low-molecular weight heparin to inhibit both inflammation and coagulation, respectively.

RESULTS

Many blood vessels in the brain were congested with thrombi containing adherent leukocytes, including CD4 T cells and monocytes. Despite containment of the pathogen and leukocytes within the vasculature, activated microglia and astrocytes were prevalent in the parenchyma, particularly clustered near vessels with thrombi. Neutralization of TNF, or the coagulation cascade, significantly reduced both thrombus formation and gliosis in P. chabaudi-infected IL-10 KO mice.

CONCLUSIONS

These findings support the contribution of cytokines, coagulation, and leukocytes within the brain vasculature to neuropathology in malaria infection. Strikingly, localization of inflammatory leukocytes within intravascular clots suggests a mechanism for interaction between the two cascades by which cytokines drive local inflammation without considerable cellular infiltration into the brain parenchyma.

Endoparasites of Small Mammals in Edo State, Nigeria: Public Health Implications

Some small mammals occur as household pests and harbour a number of parasites that could be of public health importance. This study profiled the helminth and protozoan parasites in trapped small mammals within and around human dwelling places (houses) located across 4 major towns (Auchi, Benin, Ekpoma, and Uromi) and environs in Edo state, Nigeria. Six genera (Apodemus sp., Crocidura sp., Mastomys natalensis, Mus musculus, Rattus sp., and Sorex sp.) were identified from 502 trapped small mammals. Overall, M. musculus (71.9%) and Rattus rattus (20.1%) were the most frequently trapped. In total, on examination of blood, gastrointestinal contents, and brain tissues, 12 helminth taxa (Angiostrongylus sp., Aspicularis sp., Capillaria sp., Gongylonema sp., Heterakis spumosa, Hymenolepis diminuta, Hymenolepis nana, Mastophorus muris, Moniliformis moniliformis, Nippostrongylus brasiliensis, Strongyloides sp., Trichosomoides sp., and Trichuris sp.), and 6 protozoan parasites (Babesia sp., Trypanosoma lewisi, Plasmodium sp., Eimeria sp., Isospora sp., and Toxoplasma gondii) were isolated. Most prevalent helminths with relatively heavy mean intensity were Strongyloides sp. and Heterakis spumosa, while Plasmodium, Eimeria, and Isospora were the most prevalent protozoan parasites. Generally, intrinsic factors like sex and age had marginal influence on the rate and burden of infection in M. musculus and R. rattus. Although the infection rate and prevalence of zoonotic parasites were low, they were largely recovered in rodents from Ekpoma. This study elucidates the public health implication of the presence of zoonotic parasites in these small mammals.

Tissue-specific immunopathology during malaria infection

Systemic inflammation mediated by Plasmodium parasites is central to malaria disease and its complications. Plasmodium parasites reside in erythrocytes and can theoretically reach all host tissues via the circulation. However, actual interactions between parasitized erythrocytes and host tissues, along with the consequent damage and pathological changes, are limited locally to specific tissue sites. Such tissue specificity of the parasite can alter the outcome of malaria disease, determining whether acute or chronic complications occur. Here, we give an overview of the recent progress that has been made in understanding tissue-specific immunopathology during Plasmodium infection. As knowledge on tissue-specific host-parasite interactions accumulates, better treatment modalities and targets may emerge for intervention in malaria disease.

Chemopreventive and remediation effect of Adansonia digitata L. Baobab (Bombacaceae) stem bark extracts in mouse model malaria

ETHNOPHARMACOLOGICAL RELEVANCE

Adansonia digitata L. Baobab (Bombacaceae) solvent extracts have been reported to possess medicinal properties and are currently been used traditionally for the treatment of malaria and several other diseases and infection; however few reports exist in literature that provides supportive scientific evidence in favour of its medicinal use.

AIM OF THE STUDY

This study investigated the efficacy of Adansonia digitata stem bark extract in offering protection against experimental malaria and also examined its remediation effect when administered after established infection.

MATERIALS AND METHODS

Weanling albino mice were used in the study. The mice were transfected intraperitonially with an inoculums size of 1× 10⁷ of chloroquine susceptible strain of plasmodium berghei infected erythrocytes. Mechanisms of action of the extract were investigated by measuring the degree of tissue peroxidation and tissue antioxidant status. Severity of malaria was determined by measuring the serum C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-α), and serum and tissue Alkaline phosphatase (ALP) activity.

RESULTS

There was a significant increase in serum CRP, TNF-α concentrations and serum and tissue ALP activity in the control mice following Plasmodium berghei infection. All the treatment had effect on the growth of Plasmodium berghei parasites in mice. The extracts showed a significant dose dependent increase packed cell volume (PCV), percentage chemosupression/clearance and a significant decrease in percentage parasitemia at the two doses when administered after established infection. Methanolic extract (MEAD) at 400mg/kg exhibited the highest chemosupressive activity. The extract significantly reduced the degree of tissue peroxidation, increased the level of reduced glutathione (GSH), catalase and superoxide dismutase activity. Administration of the extract after established infection reduced serum CRP and TNF-α concentrations and serum and tissue ALP activity.

CONCLUSION

Our study suggests that Adansonia digitata protects against Plasmodium berghei induced-malaria, and that administration of the extract after established infection reduced malaria progression.

Targeting the master regulator mTOR: a new approach to prevent the neurological of consequences of parasitic infections?

A systematic analysis of 240 causes of death in 2013 revealed that parasitic diseases were responsible for more than one million deaths. The vast majority of these fatalities resulted from protozoan infections presenting with neurological sequelae. In the absence of a vaccine, development of effective therapies is essential to improving global public health. In 2015, an intriguing strategy to prevent cerebral malaria was proposed by Gordon et al. 2015 mBio, 6:e00625. Their study suggested that inhibition of the mammalian target of rapamycin prevented experimental cerebral malaria by blocking the damage to the blood brain barrier and stopping the accumulation of parasitized red blood cells and T cells in the brain. Here, we hypothesize that the same therapeutic strategy could be adopted for other protozoan infections with a brain tropism, to prevent cerebral parasitosis by limiting pathogen replication and preventing immune mediated destruction of brain tissue.

Mycobacterium tuberculosis infection modulates adipose tissue biology

Mycobacterium tuberculosis (Mtb) primarily resides in the lung but can also persist in extrapulmonary sites. Macrophages are considered the prime cellular habitat in all tissues. Here we demonstrate that Mtb resides inside adipocytes of fat tissue where it expresses stress-related genes. Moreover, perigonadal fat of Mtb-infected mice disseminated the infection when transferred to uninfected animals. Adipose tissue harbors leukocytes in addition to adipocytes and other cell types and we observed that Mtb infection induces changes in adipose tissue biology depending on stage of infection. Mice infected via aerosol showed infiltration of inducible nitric oxide synthase (iNOS) or arginase 1 (Arg1)-negative F4/80⁺ cells, despite recruitment of CD3⁺, CD4⁺ and CD8⁺ T cells. Gene expression analysis of adipose tissue of aerosol Mtb-infected mice provided evidence for upregulated expression of genes associated with T cells and NK cells at 28 days post-infection. Strikingly, IFN-γ-producing NK cells and Mtb-specific CD8⁺ T cells were identified in perigonadal fat, specifically CD8⁺CD44^-CD69⁺ and CD8⁺CD44^-CD103⁺ subpopulations. Gene expression analysis of these cells revealed that they expressed IFN-γ and the lectin-like receptor Klrg1 and down-regulated CD27 and CD62L, consistent with an effector phenotype of Mtb-specific CD8⁺ T cells. Sorted NK cells expressed higher abundance of Klrg1 upon infection, as well. Our results reveal the ability of Mtb to persist in adipose tissue in a stressed state, and that NK cells and Mtb-specific CD8⁺ T cells infiltrate infected adipose tissue where they produce IFN-γ and assume an effector phenotype. We conclude that adipose tissue is a potential niche for Mtb and that due to infection CD8⁺ T cells and NK cells are attracted to this tissue.

In 2015, tuberculosis (TB) affected 10.4 million individuals causing 1.8 million deaths per year. Yet, a much larger group– 2 billion people–harbors latent TB infection (LTBI) without clinical symptoms, but at lifelong risk of reactivation. The physiological niches of Mycobacterium tuberculosis (Mtb) persistence remain incompletely defined and both pulmonary and extrapulmonary sites have been proposed. Adipose tissue constitutes 15–25% of total body mass and is an active production site for hormones and inflammatory mediators. The increasing prevalence of obesity, has led to greater incidence of type 2 diabetes. These patients suffer from three times higher risk of developing TB, pointing to a potential link between adipose tissue and TB pathogenesis. In individuals with LTBI, Mtb survives in a stressed, non-replicating state with low metabolic activity and resting macrophages serve as preferred habitat and become effectors after appropriate stimulation. Here we demonstrate that Mtb can infect and persist within adipocytes where it upregulates stress-related genes. In vivo, relative proportions of leukocyte subsets infiltrating adipose tissue varied under different conditions of infection. During natural aerosol Mtb infection, distinct leukocyte subsets, including mononuclear phagocytes, Mtb-specific CD8⁺ T cells and NK cells infiltrated adipose tissue and became activated. Thus, our study shows that adipose tissue is not only a potential reservoir for this pathogen but also undergoes significant alteration during TB infection.

Pathogenesis of Plasmodium berghei ANKA infection in the gerbil (Meriones unguiculatus) as an experimental model for severe malaria

Background: As the quest to eradicate malaria continues, there remains a need to gain further understanding of the disease, particularly with regard to pathogenesis. This is facilitated, apart from in vitro and clinical studies, mainly via in vivo mouse model studies. However, there are few studies that have used gerbils (Meriones unguiculatus) as animal models. Thus, this study is aimed at characterizing the effects of Plasmodium berghei ANKA (PbA) infection in gerbils, as well as the underlying pathogenesis. Methods: Gerbils, 5-7 weeks old were infected by PbA via intraperitoneal injection of 1 × 10⁶ (0.2 mL) infected red blood cells. Parasitemia, weight gain/loss, hemoglobin concentration, red blood cell count and body temperature changes in both control and infected groups were monitored over a duration of 13 days. RNA was extracted from the brain, spleen and whole blood to assess the immune response to PbA infection. Organs including the brain, spleen, heart, liver, kidneys and lungs were removed aseptically for histopathology. Results: Gerbils were susceptible to PbA infection, showing significant decreases in the hemoglobin concentration, RBC counts, body weights and body temperature, over the course of the infection. There were no neurological signs observed. Both pro-inflammatory (IFNγ and TNF) and anti-inflammatory (IL-10) cytokines were significantly elevated. Splenomegaly and hepatomegaly were also observed. PbA parasitized RBCs were observed in the organs, using routine light microscopy and in situ hybridization. Conclusion: Gerbils may serve as a good model for severe malaria to further understand its pathogenesis.

Deletion of the rodent malaria ortholog for falcipain-1 highlights differences between hepatic and blood stage merozoites

Proteases have been implicated in a variety of developmental processes during the malaria parasite lifecycle. In particular, invasion and egress of the parasite from the infected hepatocyte and erythrocyte, critically depend on protease activity. Although falcipain-1 was the first cysteine protease to be characterized in P. falciparum, its role in the lifecycle of the parasite has been the subject of some controversy. While an inhibitor of falcipain-1 blocked erythrocyte invasion by merozoites, two independent studies showed that falcipain-1 disruption did not affect growth of blood stage parasites. To shed light on the role of this protease over the entire Plasmodium lifecycle, we disrupted berghepain-1, its ortholog in the rodent parasite P. berghei. We found that this mutant parasite displays a pronounced delay in blood stage infection after inoculation of sporozoites. Experiments designed to pinpoint the defect of berghepain-1 knockout parasites found that it was not due to alterations in gliding motility, hepatocyte invasion or liver stage development and that injection of berghepain-1 knockout merosomes replicated the phenotype of delayed blood stage growth after sporozoite inoculation. We identified an additional role for berghepain-1 in preparing blood stage merozoites for infection of erythrocytes and observed that berghepain-1 knockout parasites exhibit a reticulocyte restriction, suggesting that berghepain-1 activity broadens the erythrocyte repertoire of the parasite. The lack of berghepain-1 expression resulted in a greater reduction in erythrocyte infectivity in hepatocyte-derived merozoites than it did in erythrocyte-derived merozoites. These observations indicate a role for berghepain-1 in processing ligands important for merozoite infectivity and provide evidence supporting the notion that hepatic and erythrocytic merozoites, though structurally similar, are not identical.

Malaria affects hundreds of millions of people and is the cause of hundreds of thousands of deaths each year. Infection begins with the inoculation of sporozoites into the skin during the bite of an infected mosquito. Sporozoites subsequently travel to the liver, where they invade and replicate in hepatocytes, eventually releasing the stage of the parasite that is infectious for red blood cells, termed merozoites. Hepatic merozoites initiate blood stage infection, the stage that is responsible for the clinical symptoms of malaria. The blood stage of the parasite grows through repeated rounds of invasion, development and egress of blood stage merozoites, which then continue the cycle. Proteases are among the enzymes that are essential for parasite survival and their functions range from invasion of red blood cells, to the breakdown of red cell hemoglobin, to the release of parasites from red cells. As the function of the cysteine protease falcipain-1 in the lifecycle of the human malaria parasite Plasmodium falciparum remains poorly understood, we decided to study berghepain-1, the orthologue of the rodent malaria parasite P. berghei by generating a berghepain-1 deletion parasite. Using this mutant, we demonstrate that berghepain-1 has a critical role in both hepatic and erythrocytic merozoite infectivity. Little is known about differences between these two types of merozoites and our data leads us to conclude that these merozoites are not identical.