Plasmodium berghei: cerebral malaria in CBA mice is not clearly related to plasma TNF levels or intensity of histopathological changes

From Bench to Bedside: Unraveling Cerebral Malaria and Malarial Retinopathy by Combining Clinical and Pre-Clinical Perspectives

Infection with Plasmodium falciparum carries a significant risk of cerebral malaria (CM). Children are particularly susceptible to human CM (HCM) which manifests as an acute neurovascular encephalopathy leading to high levels of mortality. Occurring in parallel with CM, malarial retinopathy (MR) is readily detected on ophthalmoscopy as one or more of: white-centered retinal hemorrhage, retinal whitening, and vessel discoloration. It leads to several distinct types of blood retinal barrier (BRB) breakdown. The precise molecular mechanisms underpinning CM and MR remain ill-defined, but parasitemia is known to drive progressive neurovascular obstruction and inflammation leading to cerebral and retinal edema and ischemia. Extensive clinical studies in patients with CM have shown that retinal examination is a useful approach for understanding pathology and an indicator for risk of mortality and morbidity. Fully understanding the cellular and molecular mechanisms that underpin CM and MR is important for developing new therapeutic approaches and in this regard the murine model of experimental CM (ECM) has proved to offer considerable value. Much is known about brain pathology in this model although much less is understood about the retina. In this review, we seek to evaluate MR in clinical scenarios and make comparisons with the retina from mice with ECM. Through detailed in vivo and post-mortem studies in the mouse and human retina, this review highlights the links between CM and MR and how this will aid our understanding of the disease progression and pathogenesis.

Intravenous whole blood transfusion results in faster recovery of vascular integrity and increased survival in experimental cerebral malaria

BACKGROUND

Cerebral malaria is a lethal complication of Plasmodium falciparum infections in need of better therapies. Previous work in murine experimental cerebral malaria (ECM) indicated that the combination of artemether plus intraperitoneal whole blood improved vascular integrity and increased survival compared to artemether alone. However, the effects of blood or plasma transfusion administered via the intravenous route have not previously been evaluated in ECM.

OBJECTIVES

To evaluate the effects of intravenous whole blood compared to intravenous plasma on hematological parameters, vascular integrity, and survival in artemether-treated ECM.

METHODS

Mice with late-stage ECM received artemether alone or in combination with whole blood or plasma administered via the jugular vein. The outcome measures were hematocrit and platelets; plasma angiopoietin 1, angiopoietin 2, and haptoglobin; blood-brain barrier permeability; and survival.

FINDINGS

Survival increased from 54% with artemether alone to 90% with the combination of artemether and intravenous whole blood. Intravenous plasma lowered survival to 18%. Intravenous transfusion provided fast and pronounced recoveries of hematocrit, platelets, angiopoietins levels and blood brain barrier integrity.

MAIN CONCLUSIONS

The outcome of artemether-treated ECM was improved by intravenous whole blood but worsened by intravenous plasma. Compared to prior studies of transfusion via the intraperitoneal route, intravenous administration was more efficacious.

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.

Heme on Pulmonary Malaria: Friend or Foe?

Malaria is a hemolytic disease that, in severe cases, can compromise multiple organs. Pulmonary distress is a common symptom observed in severe malaria caused by Plasmodium vivax or Plasmodium falciparum. However, biological components involved in the development of lung malaria are poorly studied. In experimental models of pulmonary malaria, it was observed that parasitized red blood cell-congested pulmonary capillaries are related to intra-alveolar hemorrhages and inflammatory cell infiltration. Thus, it is very likely that hemolysis participates in malaria-induced acute lung injury. During malaria, heme assumes different biochemical structures such as hemin and hemozoin (biocrystallized structure of heme inside Plasmodium sp.). Each heme-derived structure triggers a different biological effect: on the one hand, hemozoin found in lung tissue is responsible for the infiltration of inflammatory cells and consequent tissue injury; on the other hand, heme stimulates heme oxygenase-1 (HO-1) expression and CO production, which protect mice from severe malaria. In this review, we discuss the biological mechanism involved in the dual role of heme response in experimental malaria-induced acute lung injury.

Neutrophils and Malaria

Neutrophils are abundant in the circulation and are one of the immune system's first lines of defense against infection. There has been substantial work carried out investigating the role of neutrophils in malaria and it is clear that during infection neutrophils are activated and are capable of clearing malaria parasites by a number of mechanisms. This review focuses on neutrophil responses to human malarias, summarizing evidence which helps us understand where neutrophils are, what they are doing, how they interact with parasites as well as their potential role in vaccine mediated immunity. We also outline future research priorities for these, the most abundant of leukocytes.

Could Heme Oxygenase-1 Be a New Target for Therapeutic Intervention in Malaria-Associated Acute Lung Injury/Acute Respiratory Distress Syndrome?

Malaria is a serious disease and was responsible for 429,000 deaths in 2015. Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is one of the main clinical complications of severe malaria; it is characterized by a high mortality rate and can even occur after antimalarial treatment when parasitemia is not detected. Rodent models of ALI/ARDS show similar clinical signs as in humans when the rodents are infected with murine Plasmodium. In these models, it was shown that the induction of the enzyme heme oxygenase 1 (HO-1) is protective against severe malaria complications, including cerebral malaria and ALI/ARDS. Increased lung endothelial permeability and upregulation of VEGF and other pro-inflammatory cytokines were found to be associated with malaria-associated ALI/ARDS (MA-ALI/ARDS), and both were reduced after HO-1 induction. Additionally, mice were protected against MA-ALI/ARDS after treatment with carbon monoxide- releasing molecules or with carbon monoxide, which is also released by the HO-1 activity. However, high HO-1 levels in inflammatory cells were associated with the respiratory burst of neutrophils and with an intensification of inflammation during episodes of severe malaria in humans. Here, we review the main aspects of HO-1 in malaria and ALI/ARDS, presenting the dual role of HO-1 and possibilities for therapeutic intervention by modulating this important enzyme.

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.

Young Sprague Dawley rats infected by Plasmodium berghei: A relevant experimental model to study cerebral malaria

Cerebral malaria (CM) is the most severe manifestation of human malaria yet is still poorly understood. Mouse models have been developed to address the subject. However, their relevance to mimic human pathogenesis is largely debated. Here we study an alternative cerebral malaria model with an experimental Plasmodium berghei Keyberg 173 (K173) infection in Sprague Dawley rats. As in Human, not all infected subjects showed cerebral malaria, with 45% of the rats exhibiting Experimental Cerebral Malaria (ECM) symptoms while the majority (55%) of the remaining rats developed severe anemia and hyperparasitemia (NoECM). These results allow, within the same population, a comparison of the noxious effects of the infection between ECM and severe malaria without ECM. Among the ECM rats, 77.8% died between day 5 and day 12 post-infection, while the remaining rats were spontaneously cured of neurological signs within 24-48 hours. The clinical ECM signs observed were paresis quickly evolving to limb paralysis, global paralysis associated with respiratory distress, and coma. The red blood cell (RBC) count remained normal but a drastic decrease of platelet count and an increase of white blood cell numbers were noted. ECM rats also showed a decrease of glucose and total CO2 levels and an increase of creatinine levels compared to control rats or rats with no ECM. Assessment of the blood-brain barrier revealed loss of integrity, and interestingly histopathological analysis highlighted cyto-adherence and sequestration of infected RBCs in brain vessels from ECM rats only. Overall, this ECM rat model showed numerous clinical and histopathological features similar to Human CM and appears to be a promising model to achieve further understanding the CM pathophysiology in Humans and to evaluate the activity of specific antimalarial drugs in avoiding/limiting cerebral damages from malaria.

The antimicrobial molecule trappin-2/elafin has anti-parasitic properties and is protective in vivo in a murine model of cerebral malaria

According to the WHO, and despite reduction in mortality rates, there were an estimated 438 000 malaria deaths in 2015. Therefore new antimalarials capable of limiting organ damage are still required. We show that systemic and lung adenovirus (Ad)-mediated over-expression of trappin-2 (T-2) an antibacterial molecule with anti-inflammatory activity, increased mice survival following infection with the cerebral malaria-inducing Plasmodium berghei ANKA (PbANKA) strain. Systemically, T-2 reduced PbANKA sequestration in spleen, lung, liver and brain, associated with a decrease in pro-inflammatory cytokines (eg TNF-α in spleen and lung) and an increase in IL-10 production in the lung. Similarly, local lung instillation of Ad-T-2 resulted in a reduced organ parasite sequestration and a shift towards an anti-inflammatory/repair response, potentially implicating monocytes in the protective phenotype. Relatedly, we demonstrated in vitro that human monocytes incubated with Plasmodium falciparum-infected red blood cells (Pf-iRBCs) and IgGs from hyper-immune African human sera produced T-2 and that the latter colocalized with merozoites and inhibited Pf multiplication. This array of data argues for the first time for the potential therapeutic usefulness of this host defense peptide in human malaria patients, with the aim to limit acute lung injury and respiratory distress syndrom often observed during malaria episodes.

Probucol-Induced α-Tocopherol Deficiency Protects Mice against Malaria Infection

The emergence of malaria pathogens having resistance against antimalarials implies the necessity for the development of new drugs. Recently, we have demonstrated a resistance against malaria infection of α-tocopherol transfer protein knockout mice showing undetectable plasma levels of α-tocopherol, a lipid-soluble antioxidant. However, dietary restriction induced α-tocopherol deficiency is difficult to be applied as a clinical antimalarial therapy. Here, we report on a new strategy to potentially treat malaria by using probucol, a drug that can reduce the plasma α-tocopherol concentration. Probucol pre-treatment for 2 weeks and treatment throughout the infection rescued from death of mice infected with Plasmodium yoelii XL-17 or P. berghei ANKA. In addition, survival was extended when the treatment started immediately after parasite inoculation. The ratio of lipid peroxidation products to parent lipids increased in plasma after 2 weeks treatment of probucol. This indicates that the protective effect of probucol might be mediated by the oxidative stressful environment induced by α-tocopherol deficiency. Probucol in combination with dihydroartemisin suppressed the proliferation of P. yoelii XL-17. These results indicated that probucol might be a candidate for a drug against malaria infection by inducing α-tocopherol deficiency without dietary α-tocopherol restriction.

Imaging Plasmodium immunobiology in the liver, brain, and lung

Plasmodium falciparum malaria is responsible for the deaths of over half a million African children annually. Until a decade ago, dynamic analysis of the malaria parasite was limited to in vitro systems with the typical limitations associated with 2D monocultures or entirely artificial surfaces. Due to extremely low parasite densities, the liver was considered a black box in terms of Plasmodium sporozoite invasion, liver stage development, and merozoite release into the blood. Further, nothing was known about the behavior of blood stage parasites in organs such as the brain where clinical signs manifest and the ensuing immune response of the host that may ultimately result in a fatal outcome. The advent of fluorescent parasites, advances in imaging technology, and availability of an ever-increasing number of cellular and molecular probes have helped illuminate many steps along the pathogenetic cascade of this deadly tropical parasite.

Improvement of the efficacy of dihydroartemisinin with atorvastatin in an experimental cerebral malaria murine model

Background

The medical care of malaria is a clinical emergency because it may develop into severe malaria, which has a high risk of complications and death. One of the major complications of Plasmodium falciparum infections is cerebral malaria (CM), which is responsible for at least 175,000 deaths worldwide each year and has long-term neurological sequelae. Moreover, treatment for CM is only partially effective. Statins are now known to have anti-inflammatory action, to attenuate sepsis and to have neuroprotective effects. In vitro, atorvastatin (AVA) has an anti-malarial activity and has improved the activity of quinine (QN), mefloquine (MQ), and dihydroartemisinin (DHA).

Objectives

This study had two objectives. First, the ability of AVA to enhance DHA efficacy by improving the survival rate for CM and also decreasing signs of CM was evaluated in a murine model of experimental cerebral malaria (ECM), which was designed in C57BL6/N mice. Second, the inflammatory biomarkers were assessed at D6 and D10 in mice treated by DHA and in untreated mice in which clinical signs of CM appear rapidly and death occurs before D12. Both experiments were designed with seven days of treatment with 40 mg/kg AVA combined with five days of 3 mg/kg DHA administered intraperitoneally.

Results

AVA in combination with DHA in a therapeutic scheme leads to a significant delay in mouse death, and it has an effect on the onset of CM symptoms and on the level of parasitaemia. Evaluation of the biomarkers highlights the significant difference between treated and control mice for five cytokines and chemokines (Eotaxin-CCL11, IL-13, LIX-CXCL5, MIP1b-CCL4 and MIP2) that are known to have a role in chemotaxis.

Conclusions

The combination of DHA and AVA seems to be effective as a therapeutic scheme for improving mouse survival but less effective for cytokine modulation, which is associated with protection against CM. These results call for clinical trials of AVA as an adjuvant with anti-malarial therapy, especially with artemisinin-based combination therapy, in CM treatment or prevention.

S-nitrosoglutathione prevents experimental cerebral malaria

Administration of the exogenous nitric oxide (NO) donor dipropylenetriamine-NONOate (DPTA-NO) to mice during Plasmodium berghei ANKA (PbA) infection largely prevents development of experimental cerebral malaria (ECM). However, a high dose (1 mg/mouse twice a day) is necessary and causes potent side effects such as marked hypotension. In the present study we evaluated whether an alternative, physiologically relevant NO donor, S-nitrosoglutathione (GSNO), was able to prevent ECM at lower doses with minimal side effects. Prophylactic treatment with high (3.5 mg), intermediate (0.35 mg) or low (0.035 mg) doses of GSNO decreased incidence of ECM in PbA-infected mice, decreasing also edema, leukocyte accumulation and hemorrhage incidence in the brain. The high dose inhibited parasite growth and also induced transient hypotension. Low and intermediate doses had no or only mild effects on parasitemia, blood pressure, and heart rate compared to saline-treated mice. PbA infection decreased brain total and reduced (GSH) glutathione levels. Brain levels of oxidized (GSSG) glutathione and the GSH/GSSG ratio were positively correlated with temperature and motor behavior. Low and intermediate doses of GSNO failed to restore the depleted brain total glutathione and GSH levels, suggesting that ECM prevention by GSNO was probably related to other effects such as inhibition of inflammation and vascular protection. These results indicate that ECM is associated with depletion of the brain glutathione pool and that GSNO is able to prevent ECM development in a wide range of doses, decreasing brain inflammation and inducing milder cardiovascular side effects.

Atorvastatin treatment is effective when used in combination with mefloquine in an experimental cerebral malaria murine model

BACKGROUND

One of the major complications of Plasmodium falciparum infection is cerebral malaria (CM), which causes one million deaths worldwide each year, results in long-term neurological sequelae and the treatment for which is only partially effective. Statins are recognized to have an immunomodulatory action, attenuate sepsis and have a neuroprotective effect. Atorvastatin (AVA) has shown in vitro anti-malarial activity and has improved the activity of mefloquine (MQ) and quinine.

METHODS

The efficiency of 40 mg/kg intraperitoneal AVA, alone or in association with MQ, was assessed in an experimental Plasmodium berghei ANKA rodent parasite model of CM and performed according to different therapeutic schemes. The effects on experimental CM were assessed through the evaluation of brain histopathological changes and neuronal apoptosis by TUNEL staining.

RESULTS

AVA alone in the therapeutic scheme show no effect on survival, but the prophylactic scheme employing AVA associated with MQ, rather than MQ alone, led to a significant delay in mouse death and had an effect on the onset of CM symptoms and on the level of parasitaemia. Histopathological findings show a correlation between brain lesions and CM onset. A neuronal anti-apoptotic effect of AVA in the AVA + MQ combination was not shown.

CONCLUSIONS

The combination of AVA and MQ therapy led to a significant delay in mouse mortality. There were differences in the incidence, time to cerebral malaria and the level of parasitaemia when the drug combination was administered to mice. When used in combination with MQ, AVA had a relevant effect on the in vivo growth inhibition and clinical outcome of P. berghei ANKA-infected mice.

Exogenous nitric oxide decreases brain vascular inflammation, leakage and venular resistance during Plasmodium berghei ANKA infection in mice

BACKGROUND

Cerebral malaria (CM) is a lethal complication of Plasmodium falciparum infections. In the Plasmodium berghei ANKA (PbA) murine model, CM is associated with marked brain inflammation, increased expression of endothelial cell adhesion molecules and leukocyte and platelet accumulation in brain vessels, causing vascular occlusion and decreased blood flow, damaging the endothelium and leading to blood-brain barrier breakdown, leakage and hemorrhages. Exogenous nitric oxide (NO) administration largely prevents the syndrome. Here we evaluated whether the mechanism of action of NO in preventing murine CM is related to its anti-inflammatory properties and to protection of the endothelium.

METHODS

C57Bl/6 mice infected with PbA were treated twice a day with saline or dipropylenetriamineNONOate (DPTA-NO). Endothelial cell adhesion molecule (ICAM-1, VCAM, E- and P-selectin) expression in brain tissue on day 6 of infection was assessed in both groups by western blot. For intravital microscopy studies, DPTA-NO-treated and saline-treated mice with a previously implanted closed cranial window were injected with albumin-FITC, anti-CD45-TxR and anti-CD41-FITC antibodies on day 6 of infection for quantification of albumin leakage, leukocyte and platelet adherence in pial vessels.

RESULTS

PbA-infected mice treated with the NO-donor DPTA-NO showed decreased expression of ICAM-1 and P-selectin, but not VCAM-1, in the brain, compared to saline-treated mice. DPTA-NO treatment also decreased the number of adherent leukocytes and platelets in pial vessels, particularly in venules 30-50 μm in diameter, decreased inflammatory vascular resistance and prevented the occurrence of arteriolar and venular albumin leakage observed in saline-treated PbA-infected mice, as assessed by intravital microscopy.

CONCLUSIONS

These results indicate that the protective effect of exogenous NO on murine CM is associated with decreased brain vascular expression of inflammatory markers resulting in attenuated endothelial junction damage and facilitating blood flow.

Algorithms to predict cerebral malaria in murine models using the SHIRPA protocol

Background

Plasmodium berghei ANKA infection in C57Bl/6 mice induces cerebral malaria (CM), which reproduces, to a large extent, the pathological features of human CM. However, experimental CM incidence is variable (50-100%) and the period of incidence may present a range as wide as 6-12 days post-infection. The poor predictability of which and when infected mice will develop CM can make it difficult to determine the causal relationship of early pathological changes and outcome. With the purpose of contributing to solving these problems, algorithms for CM prediction were built.

Methods

Seventy-eight P. berghei-infected mice were daily evaluated using the primary SHIRPA protocol. Mice were classified as CM+ or CM- according to development of neurological signs on days 6-12 post-infection. Logistic regression was used to build predictive models for CM based on the results of SHIRPA tests and parasitaemia.

Results

The overall CM incidence was 54% occurring on days 6-10. Some algorithms had a very good performance in predicting CM, with the area under the receiver operator characteristic (_auROC) curve ≥ 80% and positive predictive values (PV+) ≥ 95, and correctly predicted time of death due to CM between 24 and 72 hours before development of the neurological syndrome (_auROC = 77-93%; PV+ = 100% using high cut off values). Inclusion of parasitaemia data slightly improved algorithm performance.

Conclusion

These algorithms work with data from a simple, inexpensive, reproducible and fast protocol. Most importantly, they can predict CM development very early, estimate time of death, and might be a valuable tool for research using CM murine models.

Murine cerebral malaria is associated with a vasospasm-like microcirculatory dysfunction, and survival upon rescue treatment is markedly increased by nimodipine

Brain hemodynamics in cerebral malaria (CM) is poorly understood, with apparently conflicting data showing microcirculatory hypoperfusion and normal or even increased blood flow in large arteries. Using intravital microscopy to assess the pial microvasculature through a closed cranial window in the murine model of CM by Plasmodium berghei ANKA, we show that murine CM is associated with marked decreases (mean: 60%) of pial arteriolar blood flow attributable to vasoconstriction and decreased blood velocity. Leukocyte sequestration further decreased perfusion by narrowing luminal diameters in the affected vessels and blocking capillaries. Remarkably, vascular collapse at various degrees was observed in 44% of mice with CM, which also presented more severe vasoconstriction. Coadministration of artemether and nimodipine, a calcium channel blocker used to treat postsubarachnoid hemorrhage vasospasm, to mice presenting CM markedly increased survival compared with artemether plus vehicle only. Administration of nimodipine induced vasodilation and increased pial blood flow. We conclude that vasoconstriction and vascular collapse play a role in murine CM pathogenesis and nimodipine holds potential as adjunctive therapy for CM.

Characterization of cerebral malaria in the outbred Swiss Webster mouse infected by Plasmodium berghei ANKA

Plasmodium berghei ANKA (PbA) infection in susceptible inbred mouse strains is the most commonly used experimental model to study pathogenesis of cerebral malaria (CM). Indeed, many concepts on mechanisms related to this complication have arisen from works using this model. Although inbred strains present several advantages and are indicated for most studies, the use of outbred models can show unique usefulness in a number of approaches such as fine post-quantitative trait loci mapping and discovery of genes relevant to CM susceptibility or resistance, as well as pharmacological and vaccine studies. Here we describe the features of PbA infection and CM incidence, and characterize the associated multiorgan pathology in the outbred Swiss Webster mouse. This model showed a sizeable (62.7%) and reproducible incidence of CM demonstrated by clinical signs and histopathological changes in brain (microhaemorrhages, oedema and vessel plugging by mononuclear cells). Major pathological changes were also observed in lungs, liver, thymus and spleen, analogous to those observed in inbred strains. Parasitaemia levels were associated with the risk of CM development, the risk being significantly higher in mice showing higher values of parasitaemia on days 6-7 of infection. This outbred CM model is then suitable for genetic, vaccine and drug studies targeting this malaria complication.

Glatiramer acetate reduces the risk for experimental cerebral malaria: a pilot study

Background

Cerebral malaria (CM) is associated with high mortality and morbidity caused by a high rate of transient or persistent neurological sequelae. Studies on immunomodulatory and neuroprotective drugs as ancillary treatment in murine CM indicate promising potential. The current study was conducted to evaluate the efficacy of glatiramer acetate (GA), an immunomodulatory drug approved for the treatment of relapsing remitting multiple sclerosis, in preventing the death of C57Bl/6J mice infected with Plasmodium berghei ANKA.

Methods and Results

GA treatment led to a statistically significant lower risk for developing CM (57.7% versus 84.6%) in treated animals. The drug had no effect on the course of parasitaemia. The mechanism of action seems to be an immunomodulatory effect since lower IFN-gamma levels were observed in treated animals in the early course of the disease (day 4 post-infection) which also led to a lower number of brain sequestered leukocytes in treated animals. No direct neuro-protective effect such as an inhibition of apoptosis or reduction of micro-bleedings in the brain was found.

Conclusion

These findings support the important role of the host immune response in the pathophysiology of murine CM and might lead to the development of new adjunctive treatment strategies.

Parasite burden and CD36-mediated sequestration are determinants of acute lung injury in an experimental malaria model

Although acute lung injury (ALI) is a common complication of severe malaria, little is known about the underlying molecular basis of lung dysfunction. Animal models have provided powerful insights into the pathogenesis of severe malaria syndromes such as cerebral malaria (CM); however, no model of malaria-induced lung injury has been definitively established. This study used bronchoalveolar lavage (BAL), histopathology and gene expression analysis to examine the development of ALI in mice infected with Plasmodium berghei ANKA (PbA). BAL fluid of PbA-infected C57BL/6 mice revealed a significant increase in IgM and total protein prior to the development of CM, indicating disruption of the alveolar–capillary membrane barrier—the physiological hallmark of ALI. In contrast to sepsis-induced ALI, BAL fluid cell counts remained constant with no infiltration of neutrophils. Histopathology showed septal inflammation without cellular transmigration into the alveolar spaces. Microarray analysis of lung tissue from PbA-infected mice identified a significant up-regulation of expressed genes associated with the gene ontology categories of defense and immune response. Severity of malaria-induced ALI varied in a panel of inbred mouse strains, and development of ALI correlated with peripheral parasite burden but not CM susceptibility. Cd36^−/− mice, which have decreased parasite lung sequestration, were relatively protected from ALI. In summary, parasite burden and CD36-mediated sequestration in the lung are primary determinants of ALI in experimental murine malaria. Furthermore, differential susceptibility of mouse strains to malaria-induced ALI and CM suggests that distinct genetic determinants may regulate susceptibility to these two important causes of malaria-associated morbidity and mortality.

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) can occur in adult malaria infections with a case fatality rate of 70%–100%. ALI and ARDS are characterized by protein-rich fluid in the lungs, with reduced gas exchange, and in malaria, often accompany high parasite levels and severe or cerebral disease. In this work we have examined lung physiology, pathology and genomics in mouse malaria—Plasmodium berghei ANKA—to show that mice develop malaria-induced ALI. Infected mice have proteinaceous fluid in their lungs, have a migration of inflammatory cells from the blood into the lung walls, and express immune response–related genes. We also found that severity of ALI depended on high parasite levels, both overall and specifically in the lung tissue, but was not consistent with whether the mice developed cerebral malaria. ALI due to Plasmodium berghei ANKA infection models prominent characteristics of human malaria-associated ALI, and we have better defined this model of malaria ALI so it may be used to further explore disease mechanisms and eventual treatment.

Similar cytokine responses and degrees of anemia in patients with Plasmodium falciparum and Plasmodium vivax infections in the Brazilian Amazon region

The mechanisms of malarial anemia induction are poorly understood, but cytokines and autoantibodies are considered to play important roles. This work aimed at evaluating the degree of anemia and the plasmatic profile of the cytokines tumor necrosis factor alpha (TNF-alpha), gamma interferon (IFN-gamma), interleukin-12 (IL-12), migration inhibitory factor (MIF), and IL-10 and the monocyte chemotactic protein-1 (MCP-1) chemokine, as well as evaluating the presence of antibodies directed to components of the normal erythrocyte membrane and to cardiolipin in individuals with malaria from the Brazilian Amazon. No difference was observed in the frequency of anemia between patients infected by Plasmodium vivax and those infected by Plasmodium falciparum, and there was no relationship between the levels of parasitemia and the manifestations of anemia in P. vivax and P. falciparum patients. Significant increases in the concentrations of TNF-alpha, IFN-gamma, MIF, and MCP-1 were observed in patients with P. falciparum and P. vivax malaria, whereas the concentrations of IL-10 was increased only in patients with P. vivax infection. Higher concentrations of IL-12 and IL-10 were observed in the P. falciparum anemic patients, while for TNF-alpha this profile was observed in the nonanemic ones. P. vivax-infected and P. falciparum-infected patients with positive immunoglobulin M (IgM) or IgM and IgG responses, respectively, against blood-stage forms of the parasites had significantly lower hemoglobin levels than did those with negative responses. There was no correlation between the presence of anti-erythrocyte and anti-cardiolipin antibodies and the presence or intensity of the anemia. Our data suggest that in areas of low endemicity and unstable transmission of malaria, P. vivax and P. falciparum infections present similar characteristics in terms of the induction of anemia and cytokine responses.

Intravascular infiltrates and organ-specific inflammation in malaria pathogenesis

Malaria infects 5-10% of humanity and causes around two million deaths annually, mostly in children. The disease is of significant interest to immunologists, as acquired host immunity can limit the clinical impact of infection and partially reduces parasite replication; however, immunological reactions also contribute significantly to pathogenesis and fatalities. This review addresses the view that immunopathology in severe malaria arises predominantly from intravascular lesions resulting from a pathogen-initiated cascade of activated immune effector and regulatory cells infiltrating the vascular beds of diverse target organs, including bone marrow, spleen, brain, placenta and lungs. The main feature distinguishing these processes from classical cellular inflammation is the absence of extravasation, resulting from the intravascular location of the pathogen. Clinical and epidemiological observations combined with experimental infections in animal models suggest that parasite 'molecular patterns' or toxins cause cytokine and chemokine enhancement of infiltrates, composed of macrophages, neutrophils, natural killer (NK) cells, invariant natural killer T (iNKT) cells, gamma/delta T cells and both CD4(+) and CD8(+) effector T cells, leading to local vascular and organ derangement. Diverse pattern recognition and NK receptors crucially regulate these responding cell populations. Thus, innate immune mechanisms lie at the heart of this massive global public health problem.

Germinal center architecture disturbance during Plasmodium berghei ANKA infection in CBA mice

Background

Immune responses to malaria blood stage infection are in general defective, with the need for long-term exposure to the parasite to achieve immunity, and with the development of immunopathology states such as cerebral malaria in many cases. One of the potential reasons for the difficulty in developing protective immunity is the poor development of memory responses. In this paper, the potential association of cellular reactivity in lymphoid organs (spleen, lymph nodes and Peyer's patches) with immunity and pathology was evaluated during Plasmodium berghei ANKA infection in CBA mice.

Methods

CBA mice were infected with 1 × 10⁶ P. berghei ANKA-parasitized erythrocytes and killed on days 3, 6–8 and 10 of infection. The spleen, lymph nodes and Peyer's patches were collected, fixed in Carson's formalin, cut in 5 μm sections, mounted in glass slides, stained with Lennert's Giemsa and haematoxylin-eosin and analysed with bright-field microscopy.

Results

Early (day 3) strong activation of T cells in secondary lymphoid organs was observed and, on days 6–8 of infection, there was overwhelming activation of B cells, with loss of conventional germinal center architecture, intense centroblast activation, proliferation and apoptosis but little differentiation to centrocytes. In the spleen, the marginal zone disappeared and the limits between the disorganized germinal center and the red pulp were blurred. Intense plasmacytogenesis was observed in the T cell zone.

Conclusion

The observed alterations, especially the germinal center architecture disturbance (GCAD) with poor centrocyte differentiation, suggest that B cell responses during P. berghei ANKA infection in mice are defective, with potential impact on B cell memory responses.

Plasmodium berghei ANKA infection induces thymocyte apoptosis and thymocyte depletion in CBA mice

Immune responses to malaria infections are characterized by strong T and B cell activation, which, in addition of potentially causing immunopathology, are of poor efficacy against the infection. It is possible that the thymus is involved in the origin of immunopathological reactions and a target during malaria infections. This work was developed in an attempt to further clarify these points. We studied the sequential changes in the thymus of CBA mice infected with Plasmodium berghei ANKA, a model in which 60-90% of the infected animals develop cerebral malaria. During the acute phase of infection, different degrees of thymocyte apoptosis were recorded. (1) starry-sky pattern of diffuse apoptosis with maintenance of cortical-medullary structure; (2) intense apoptosis with cortical atrophy, with absence of large cells; (3) severe cortical thymocyte depletion, resulting in cortical-medullary inversion. In the latter, only residual clusters of small thymocytes were observed within the framework of epithelial cells. The intensity of thymus alterations could not be associated with the degree of parasitemia, the expression of clinical signs of cerebral malaria or intensity of brain lesions. The implications of these events for malaria immunity and pathology are discussed.

Scanning electron microscopy of the neuropathology of murine cerebral malaria

Background

The mechanisms leading to death and functional impairments due to cerebral malaria (CM) are yet not fully understood. Most of the knowledge about the pathomechanisms of CM originates from studies in animal models. Though extensive histopathological studies of the murine brain during CM are existing, alterations have not been visualized by scanning electron microscopy (SEM) so far. The present study investigates the neuropathological features of murine CM by applying SEM.

Methods

C57BL/6J mice were infected with Plasmodium berghei ANKA blood stages. When typical symptoms of CM developed perfused brains were processed for SEM or light microscopy, respectively.

Results

Ultrastructural hallmarks were disruption of vessel walls, parenchymal haemorrhage, leukocyte sequestration to the endothelium, and diapedesis of macrophages and lymphocytes into the Virchow-Robin space. Villous appearance of observed lymphocytes were indicative of activated state. Cerebral oedema was evidenced by enlargement of perivascular spaces.

Conclusion

The results of the present study corroborate the current understanding of CM pathophysiology, further support the prominent role of the local immune system in the neuropathology of CM and might expose new perspectives for further interventional studies.

Behavioural and histopathological alterations in mice with cerebral malaria

Different features of sensorimotor function and behaviour were studied in murine cerebral malaria (CM) and malaria without cerebral involvement (non-CM) applying the primary screen of the SHIRPA protocol. Histopathological analysis of distinct brain regions was performed and the relative size of haemorrhages and plugging of blood cells to brain vasculature was analysed. Animals suffering from CM develop a wide range of behavioural and functional alterations in the progressive course of the disease with a statistically significant impairment in all functional categories assessed 36 h prior to death when compared with control animals. Early functional indicators of cerebral phenotype are impairments in reflex and sensory system and in neuropsychiatric state. Deterioration in function is paralleled by the degree of histopathological changes with a statistically significant correlation between the SHIRPA score of CM animals and the mean size of brain haemorrhage. Furthermore, image analysis yielded that the relative area of the brain lesions was significantly larger in the forebrain and brainstem compared with the other regions of interest. Our results indicate that assessment of sensory and motor tasks by the SHIRPA primary screen is appropriate for the early in vivo discrimination of cerebral involvement in experimental murine malaria. Our findings also suggest a correlation between the degree of functional impairment and the size of the brain lesions as indicated by parenchymal haemorrhage. Applying the SHIRPA protocol in the functional characterization of animals suffering from CM might prove useful in the preclinical assessment of new antimalarial and potential neuroprotective therapies.

Estradiol, but not dehydroepiandrosterone, decreases parasitemia and increases the incidence of cerebral malaria and the mortality in plasmodium berghei ANKA-infected CBA mice

OBJECTIVE

The effect of castration and subsequent replacement of dehydroepiandrosterone (DHEA) or estradiol on parasitemia, mortality and incidence of cerebral malaria (CM) was evaluated in CBA mice infected with Plasmodium berghei ANKA.

METHODS

Female mice were castrated, and groups of 12-15 animals received daily injections of DHEA, estradiol or saline. Four days after the start of treatment, mice were inoculated with 1 x 10(6)P. berghei ANKA-parasitized erythrocytes. DHEA treatment was continued during the 5 days after infection, and estradiol was administered during the follow-up. Parasitemia was evaluated daily in Giemsa-stained blood smears. Signs of CM were determined by the manifestation of coma, limb paralysis and/or convulsions. Plasma TNF-alpha levels were evaluated by sandwich ELISA. Nitric oxide synthase (NOS) activity in the brain of moribund mice was measured by the method of Bredt and Snyder.

RESULTS

In non-castrated infected mice, the incidence of CM was 50%, and plasma TNF-alpha increased and brain NOS activity decreased compared to non-infected controls. Castration had no major effect on the parameters analyzed (parasitemia, mortality, CM incidence, TNF-alpha levels or NOS activity). Estradiol replacement caused a decrease in parasitemia but resulted in higher CM incidence and faster mortality, with an increase in NOS activity.

CONCLUSIONS

Estradiol modulated the immune response of P. berghei ANKA-infected CBA mice, decreasing parasitemia and increasing NOS activity, and impacted negatively on survival and CM incidence, showing that neuroimmunoendocrine interactions are important in the physiopathogenesis of malaria infections.

Thalidomide influences the function of macrophages and increases the survival of Plasmodium berghei-infected CBA mice

Malaria remains a major cause of morbidity and mortality in vast areas of the world, mainly due to the severe forms of Plasmodium falciparum infection. The exacerbated immune response, with increased production of TNF and reactive nitrogen and oxygen intermediates, plays a role in the complex pathogenesis of the disease. It is recognised that thalidomide decreases TNF production and may modulate several functions of the immune system. This work evaluated the influence of thalidomide on macrophage functions, and its ability to protect against severe disease. Plasmodium berghei ANKA-infected mice were (n=11) or were not (n=10) intra-gastric treated with thalidomide (150 mg/kg per day), and two other control groups not infected with the parasite were (n=8) or were not (n=10) treated with the drug, and macrophage production of hydrogen peroxide and nitric oxide, and phagocytosis were assessed on the eighth day post-infection. Thalidomide increased the survival time of infected mice, in parallel with a 26.5% increase of the mean of macrophage phagocytic index, and augmented in 13% the mean of the production of hydrogen peroxide and in 45% the mean of nitric oxide production by macrophages related to the non-treated P. berghei-infected mice. Our data indicate that thalidomide improves the outcome of P. berghei ANKA-infected CBA mice and suggest that this drug could represent a new alternative to be associated to antimalarial drugs to decrease the morbidity and mortality of severe malaria in non-pregnant individuals.

Review Article: Blood-brain barrier in falciparum malaria*

Plasmodium falciparum malaria is the most important parasitic disease infecting the central nervous system of humans worldwide. The pathogenesis of the neurological complications of falciparum malaria remains unclear. In particular, how do asexual parasites confined to the vascular space of the brain cause neuronal impairment? The evidence for a breakdown in the blood-brain barrier (BBB) is conflicting. In some animal models of malaria, there is evidence of breakdown of the BBB, but the data from humans suggests the BBB is mildly impaired only, with few morphological changes. Whether these changes in the BBB are sufficient to account for the neurological complications remains to be determined.

Role of the tumor necrosis factor receptor 2 (TNFR2) in cerebral malaria in mice

Infection of susceptible mice with Plasmodium berghei Anka leads to a syndrome of severe or cerebral malaria. Tumor necrosis factor (TNF) contributes to this syndrome, apparently by acting on its receptor 2 (TNFR2) because TNFR1-/- are susceptible, whereas TNFR2-/- mice are resistant. In this work, we confirmed the essential role of the TNFR2 in cerebral malaria because 6 to 8 days after Plasmodium berghei Anka infection, hypothermia, coma, and death were observed in +/+ or TNFR1-/-, but never in TNFR2-/-, mice. TNF production, evaluated by the serum levels or the mRNA levels in the brain, spleen or lung, was similar in +/+, TNFR1-/-, or TNFR2-/- mice. Macrophage or parasitized red blood cell sequestration in brain or lung was similar in TNFR1-/- and TNFR2-/- mice. Accordingly, up-regulation of CD54 or CD40 in brain or lung was also similar in TNFR1-/- or TNFR2-/- mice. Platelet loss, manifested by thrombocytopenia and the presence of microparticles in plasma, was similar in TNFR1-/- or TNFR2-/- mice. Breakdown of the blood-brain barrier, detected by the diffusion of tracers, was attenuated in both TNFR1-/- and TNFR2-/-, compared with +/+, mice. Endothelial cells from brain capillaries, examined by transmission electron microscopy, were similar in infected TNFR1-/- or TNFR2-/- mice, whereas the basement membrane was enlarged in TNFR1-/- mice. Hypothermic mice were also hyperglycemic, and this was evident in +/+ and TNFR1-/-, but not in TNFR2-/-, mice. In addition, infected +/+ and TNFR1-/- mice became insulin resistant, while in contrast TNFR2-/- became extremely insulin sensitive. This study supports the possibility that coma and death are mediated not by cell sequestration or breakdown of vascular permeability, similar in TNFR1-/- or TNFR2-/- mice, but by metabolic disturbances selectively mediated by the TNFR2.

Association of a determinant on mouse chromosome 18 with experimental severe Plasmodium berghei malaria

Experimental severe malaria (ESM; also known as experimental cerebral malaria) is an acute lethal syndrome caused by infection with Plasmodium berghei ANKA and associated with coma and other neurological manifestations in mice. Various inbred strains of mice exhibit differences in susceptibility to the development of ESM. For example, C57BL/6 mice are highly susceptible and DBA/2 mice are relatively resistant. We report here the results of a genomewide scan for host genomic regions that control resistance to ESM in DBA/2 mice using an F(2) intercross population of susceptible and resistant strains. A region of mid-chromosome 18 was found to be a major determinant of resistance to ESM.