Hemozoin-inducible proinflammatory events in vivo: potential role in malaria infection

Hemozoin-induced IFN-γ production mediates innate immune protection against sporozoite infection

Hemozoin is a crystal synthesized by Plasmodium parasites during hemoglobin digestion in the erythrocytic stage. The hemozoin released when the parasites egress from the red blood cell, which is complexed with parasite DNA, is cleared from the circulation by circulating and tissue-resident monocytes and macrophages, respectively. Recently, we reported that intravenous administration of purified hemozoin complexed with Plasmodium berghei DNA (HzPbDNA) resulted in an innate immune response that blocked liver stage development of sporozoites that was dose-dependent and time-limited. Here, we further characterize the organismal, cellular, and molecular events associated with this protective innate response in the liver and report that a large proportion of the IV administered HzPbDNA localized to F4/80+ cells in the liver and that the rapid and strong protection against liver-stage development waned quickly such that by 1 week post-HzPbDNA treatment animals were fully susceptible to infection. RNAseq of the liver after IV administration of HzPbDNA demonstrated that the rapid and robust induction of genes associated with the acute phase response, innate immune activation, cellular recruitment, and IFN-γ signaling observed at day 1 was largely absent at day 7. RNAseq analysis implicated NK cells as the major cellular source of IFN-γ. In vivo cell depletion and IFN-γ neutralization experiments supported the hypothesis that tissue-resident macrophages and NK cells are major contributors to the protective response and the NK cell-derived IFN-γ is key to induction of the mechanisms that block sporozoite development in the liver. These findings advance our understanding of the innate immune responses that prevent liver stage malaria infection.

Circadian Control of the Response of Macrophages to Plasmodium Spp.-Infected Red Blood Cells

Malaria is a serious vector-borne disease characterized by periodic episodes of high fever and strong immune responses that are coordinated with the daily synchronized parasite replication cycle inside RBCs. As immune cells harbor an autonomous circadian clock that controls various aspects of the immune response, we sought to determine whether the intensity of the immune response to Plasmodium spp., the parasite causing malaria, depends on time of infection. To do this, we developed a culture model in which mouse bone marrow-derived macrophages are stimulated with RBCs infected with Plasmodium berghei ANKA (iRBCs). Lysed iRBCs, but not intact iRBCs or uninfected RBCs, triggered an inflammatory immune response in bone marrow-derived macrophages. By stimulating at four different circadian time points (16, 22, 28, or 34 h postsynchronization of the cells' clock), 24-h rhythms in reactive oxygen species and cytokines/chemokines were found. Furthermore, the analysis of the macrophage proteome and phosphoproteome revealed global changes in response to iRBCs that varied according to circadian time. This included many proteins and signaling pathways known to be involved in the response to Plasmodium infection. In summary, our findings show that the circadian clock within macrophages determines the magnitude of the inflammatory response upon stimulation with ruptured iRBCs, along with changes of the cell proteome and phosphoproteome.

S100A9: The Unusual Suspect Connecting Viral Infection and Inflammation

The study of S100A9 in viral infections has seen increased interest since the COVID-19 pandemic. S100A8/A9 levels were found to be correlated with the severity of COVID-19 disease, cytokine storm, and changes in myeloid cell subsets. These data led to the hypothesis that S100A8/A9 proteins might play an active role in COVID-19 pathogenesis. This review explores the structures and functions of S100A8/9 and the current knowledge on the involvement of S100A8/A9 and its constituents in viral infections. The potential roles of S100A9 in SARS-CoV-2 infections are also discussed.

Epigenetic and transcriptional regulation of cytokine production by Plasmodium falciparum-exposed monocytes

Plasmodium falciparum infection causes the most severe form of malaria, where excessive production of proinflammatory cytokines can drive the pathogenesis of the disease. Monocytes play key roles in host defense against malaria through cytokine production and phagocytosis; however, they are also implicated in pathogenesis through excessive proinflammatory cytokine production. Understanding the underlying molecular mechanisms that contribute to inflammatory cytokine production in P. falciparum-exposed monocytes is key towards developing better treatments. Here, we provide molecular evidence that histone 3 lysine 4 (H3K4) methylation is key for inflammatory cytokine production in P. falciparum-exposed monocytes. In an established in vitro system that mimics blood stage infection, elevated proinflammatory TNF and IL-6 cytokine production is correlated with increased mono- and tri-methylated H3K4 levels. Significantly, we demonstrate through utilizing a pharmacological inhibitor of H3K4 methylation that TNF and IL-6 expression can be suppressed in P. falciparum-exposed monocytes. This elucidated epigenetic regulatory mechanism, controlling inflammatory cytokine production, potentially provides new therapeutic options for future malaria treatment.

Thermoneutrality and severe malaria: investigating the effect of warmer environmental temperatures on the inflammatory response and disease progression

Introduction

Most studies using murine disease models are conducted at housing temperatures (20 - 22°C) that are sub-optimal (ST) for mice, eliciting changes in metabolism and response to disease. Experiments performed at a thermoneutral temperature (TT; 28 - 31°C) have revealed an altered immune response to pathogens and experimental treatments in murine disease model that have implications for their translation to clinical research. How such conditions affect the inflammatory response to infection with Plasmodium berghei ANKA (PbA) and disease progression is unknown. We hypothesized that changes in environmental temperature modulate immune cells and modify host response to malaria disease. To test this hypothesis, we conducted experiments to determine: (1) the inflammatory response to malarial agents injection in a peritonitis model and (2) disease progression in PbA-infected mice at TT compared to ST.

Methods

In one study, acclimatized mice were injected intraperitoneally with native hemozoin (nHZ) or Leishmania at TT (28 - 31°C) or ST, and immune cells, cytokine, and extracellular vesicle (EV) profiles were determined from the peritoneal cavity (PEC) fluid. In another study, PbA-infected mice were monitored until end-point (i.e. experimental malaria score ≥4).

Results

We found that Leishmania injection resulted in decreased cell recruitment and higher phagocytosis of nHZ in mice housed at TT. We found 398 upregulated and 293 downregulated proinflammatory genes in mice injected with nHZ, at both temperatures. We report the presence of host-derived EVs never reported before in a murine parasitic murine model at both temperatures. We observed metabolic changes in mice housed at TT, but these did not result to noticeable changes in disease progression compared to ST.

Discussion

To our knowledge, these experiments are the first to investigate the effect of thermoneutrality on a malaria murine model. We found important metabolic difference in mice housed at TT. Our results offer insights on how thermoneutrality might impact a severe malaria murine model and directions for more targeted investigations.

The ability of Interleukin-10 to negate haemozoin-related pro-inflammatory effects has the potential to restore impaired macrophage function associated with malaria infection

BACKGROUND

Although pro-inflammatory cytokines are involved in the clearance of Plasmodium falciparum during the early stages of the infection, increased levels of these cytokines have been implicated in the pathogenesis of severe malaria. Amongst various parasite-derived inducers of inflammation, the malarial pigment haemozoin (Hz), which accumulates in monocytes, macrophages and other immune cells during infection, has been shown to significantly contribute to dysregulation of the normal inflammatory cascades.

METHODS

The direct effect of Hz-loading on cytokine production by monocytes and the indirect effect of Hz on cytokine production by myeloid cells was investigated during acute malaria and convalescence using archived plasma samples from studies investigating P. falciparum malaria pathogenesis in Malawian subjects. Further, the possible inhibitory effect of IL-10 on Hz-loaded cells was examined, and the proportion of cytokine-producing T-cells and monocytes during acute malaria and in convalescence was characterized.

RESULTS

Hz contributed towards an increase in the production of inflammatory cytokines, such as Interferon Gamma (IFN-γ), Tumor Necrosis Factor (TNF) and Interleukin 2 (IL-2) by various cells. In contrast, the cytokine IL-10 was observed to have a dose-dependent suppressive effect on the production of TNF among other cytokines. Cerebral malaria (CM) was characterized by impaired monocyte functions, which normalized in convalescence. CM was also characterized by reduced levels of IFN-γ-producing T cell subsets, and reduced expression of immune recognition receptors HLA-DR and CD 86, which also normalized in convalescence. However, CM and other clinical malaria groups were characterized by significantly higher plasma levels of pro-inflammatory cytokines than healthy controls, implicating anti-inflammatory cytokines in balancing the immune response.

CONCLUSIONS

Acute CM was characterized by elevated plasma levels of pro-inflammatory cytokines and chemokines but lower proportions of cytokine-producing T-cells and monocytes that normalize during convalescence. IL-10 is also shown to have the potential to indirectly prevent excessive inflammation. Cytokine production dysregulated by the accumulation of Hz appears to impair the balance of the immune response to malaria and exacerbates pathology.

Erythropoiesis and Malaria, a Multifaceted Interplay

One of the major pathophysiologies of malaria is the development of anemia. Although hemolysis and splenic clearance are well described as causes of malarial anemia, abnormal erythropoiesis has been observed in malaria patients and may contribute significantly to anemia. The interaction between inadequate erythropoiesis and Plasmodium parasite infection, which partly occurs in the bone marrow, has been poorly investigated to date. However, recent findings may provide new insights. This review outlines clinical and experimental studies describing different aspects of ineffective erythropoiesis and dyserythropoiesis observed in malaria patients and in animal or in vitro models. We also highlight the various human and parasite factors leading to erythropoiesis disorders and discuss the impact that Plasmodium parasites may have on the suppression of erythropoiesis.

Macrophage migration inhibitory factor contributes to immunopathogenesis during Plasmodium yoelii 17XL infection

Macrophage migration inhibitory factor (MIF) is a cytokine recognized regulator of the inflammatory immune response associated with several immune cells that produce inflammatory cytokines such as IL-1β, IL-6, IL-12, IL-18, and TNF-α. This study aimed to understand the effect of MIF on the immune response and pathogenesis during Plasmodium infection. Wild-type (Wt) and MIF knockout (Mif ^-/-) mice were intravenously infected with 1×10³ Plasmodium yoelii (Py) 17XL-parasitized red blood cells. Our data showed that Py17XL-infected Wt mice died 11 days postinfection, while Mif ^-/- mice showed reduced parasitemia and an increase in their survival at day 11 up to 58%, importantly they succumb up to day 21 postinfection. The increased survival rate in Mif ^-/- mice was associated with less severe cachexia and anemia as a result of a mixed Th1/Th2 cytokine profile, high levels of IL-12, IL-17/IL-4, and IL-10 in serum; and high levels of IL-4 and IL-10, and low levels of IFN-γ in spleen cells compared to Py17XL infected Wt mice. Moreover, macrophages (Mφs) from Mif ^-/- mice exhibited higher concentrations of IL-10 and IL-12 and reduced levels of TNF-α and nitric oxide (NO) compared to Py17XL-infected Wt mice. These results demonstrate that MIF has an important role in regulating the immune response associated with host pathogenesis and lethality, which is relevant to consider in preventing/reducing complications in Plasmodium infections.

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.

Hemozoin: a Complex Molecule with Complex Activities

Purpose of Review

Malaria is a disease caused by parasites that reside in host red blood cells and use hemoglobin as a nutrient source. Heme released by hemoglobin catabolism is modified by the parasite to produce hemozoin (HZ), which has toxic effects on the host. Experimentation aiming to elucidate how HZ contributes to malaria pathogenesis has utilized different preparations of this molecule, complicating interpretation and comparison of findings. We examine natural synthesis and isolation of HZ and highlight studies that have used multiple preparations, including synthetic forms, in a comparative fashion.

Recent Findings

Recent work utilizing sophisticated imaging and detection techniques reveals important molecular characteristics of HZ synthesis and biochemistry. Other recent studies further refine understanding of contributions of HZ to malaria pathogenesis yet highlight the continuing need to characterize HZ preparations and contextualize experimental conditions in the in vivo infection milieu.

Summary

This review highlights the necessity of collectively determining what is physiologically relevant HZ. Characterization of isolated natural HZ and use of multiple preparations in each study are recommended with application of in vivo studies whenever possible. Adoption of such practices is expected to improve reproducibility of results and elucidate the myriad of ways that HZ participates in malaria pathogenesis.

Protective Effect of an Anti-HMGB-1 Neutralizing Antibody on Hemozoin-Induced Alveolar Epithelial Cell in a Model of Malaria Associated ALI/ARDS

Background:

We aimed to determine whether neutralizing high mobility group box-1 (HMGB-1) prevents the release of HMGB-1 and proinflammatory cytokines on hemozoin (Hz)-induced alveolar epithelial cell in a model of malaria associated ALI/ARDS.

Methods:

This study was conducted in the Department of Tropical Pathology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand in 2020. Human pulmonary alveolar epithelial cells (HPAEpiCs) were exposed to medium alone or 20 μM Hz for 24 h and incubated with different concentrations (1, 5, and 10 μg/ml) of anti-HMGB-1 monoclonal antibody (mAb) for various times (0, 4, 12, 24, and 48 h). The levels of HMGB-1, TNF-α and IFN-γ in the supernatants were measured by ELISA. The mRNA expression of RAGE, TLR-2 and TLR-4 were analyzed by real-time PCR.

Results:

The HPAEpiCs treated with 10 μg/ml anti-HMGB-1 mAb showed a significant reduction in HMGB-1 release into the supernatant compared with those treated with 1 and 5 μg/ml anti-HMGB-1 mAb. The levels of TNF-α and IFN-γ were significantly decreased in the supernatant of HPAEpiCs treated with 1, 5, and 10 μg/ml anti-HMGB-1 mAb for 4, 12, 24, and 48 h compared with those stimulated with Hz alone. The mRNA expression levels of RAGE, TLR-2, and TLR-4 were significantly decreased after 24 h of anti-HMGB-1 antibody treatment at all concentrations.

Conclusion:

An anti-HMGB-1 antibody could be an effective agent for inhibiting the release of HMGB-1, TNF-α and IFN-γ. Furthermore, a neutralizing anti-HMGB-1 antibody could be applicable for the treatment of malaria-associated ALI/ARDS.

Zanthoxylum zanthoxyloides inhibits lipopolysaccharide- and synthetic hemozoin-induced neuroinflammation in BV-2 microglia: roles of NF-κB transcription factor and NLRP3 inflammasome activation

OBJECTIVES

The effects of a root extract of Zanthoxylum zanthoxyloides on neuroinflammation in BV-2 microglia stimulated with LPS and hemozoin were investigated.

METHODS

ELISA, enzyme immunoassay and Griess assay were used to evaluate levels of cytokines, PGE2 and NO in culture supernatants, respectively. Microglia-mediated neurotoxicity was evaluated using a BV-2 microglia-HT-22 neuron transwell co-culture.

KEY FINDINGS

Treatment with Z. zanthoxyloides caused reduced elevated levels of TNFα, IL-6, IL-1β, NO and PGE2, while increasing the levels of IL-10. In addition, there were reduced levels of iNOS and COX-2 proteins. This was accompanied by a prevention of microglia-mediated damage to HT-22 mouse hippocampal neurons. Z. zanthoxyloides reduced elevated levels of phospho-IκB and phospho-p65, while preventing degradation of IκB protein and DNA binding of p65. Further mechanistic studies revealed that Z. zanthoxyloides reduced the levels of pro-IL-1β and IL-1β in hemozoin-activated BV-2 microglia. This was accompanied by a reduction in caspase-1 activity and NLRP3 protein expression. Bioassay-guided fractionation resulted in the isolation of skimmianine as an anti-inflammatory compound in Z. zanthoxyloides.

CONCLUSION

This is the first report showing the inhibition of neuroinflammation in LPS- and hemozoin-activated BV-2 microglia by the root extract of Z. zanthoxyloides by targeting the activation of both NF-κB and NLRP3 inflammasome.

Hemozoin in Malarial Complications: More Questions Than Answers

Plasmodium parasites contain various virulence factors that modulate the host immune response. Malarial pigment, or hemozoin (Hz), is an undegradable crystalline product of the hemoglobin degradation pathway in the parasite and possesses immunomodulatory properties. An association has been found between Hz accumulation and severe malaria, suggesting that the effects of Hz on the host immune response may contribute to the development of malarial complications. Although the immunomodulatory roles of Hz have been widely investigated, many conflicting data exist, likely due to the variability between experimental set-ups and technical limitations of Hz generation and isolation methods. Here, we critically assess the potential immunomodulatory effects of Hz, its role in malarial complications, and its potential effects after parasite clearance.

Plasmodium infection inhibits tumor angiogenesis through effects on tumor-associated macrophages in a murine implanted hepatoma model

Background

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death in China. The lack of an effective treatment for this disease results in a high recurrence rate in patients who undergo radical tumor resection, and the 5-year survival rate of these patients remains low. Our previous studies demonstrated that Plasmodium infection provides a potent antitumor effect by inducing innate and adaptive immunity in a murine Lewis lung carcinoma (LLC) model.

Methods

This study aimed to investigate the inhibitory effect of Plasmodium infection on hepatocellular carcinoma in mice, and various techniques for gene expression analysis were used to identify possible signal regulation mechanisms.

Results

We found that Plasmodium infection efficiently inhibited tumor progression and prolonged survival in tumor-bearing mice, which served as a murine implanted hepatoma model. The inhibition of tumor progression by Plasmodium infection was related to suppression of tumor angiogenesis within the tumor tissue and decreased infiltration of tumor-associated macrophages (TAMs). Further study demonstrated that matrix metalloprotease 9 (MMP-9) produced by TAMs contributed to tumor angiogenesis in the tumor tissue and that the parasite-induced reduction in MMP-9 expression in TAMs resulted in the suppression of tumor angiogenesis. A mechanistic study revealed that the Plasmodium-derived hemozoin (HZ) that accumulated in TAMs inhibited IGF-1 signaling through the PI3-K and MAPK signaling pathways and thereby decreased the expression of MMP-9 in TAMs.

Conclusions

Our study suggests that this novel approach of inhibiting tumor angiogenesis by Plasmodium infection is of high importance for the development of new therapies for cancer patients.

Blood-cerebrospinal fluid barrier: another site disrupted during experimental cerebral malaria caused by Plasmodium berghei ANKA

Cerebral malaria is one of the most severe pathologies of malaria; it induces neuro-cognitive sequelae and has a high mortality rate. Although many factors involved in the development of cerebral malaria have been discovered, its pathogenic mechanisms are still not completely understood. Most studies on cerebral malaria have focused on the blood-brain barrier, despite the importance of the blood-cerebrospinal fluid barrier, which protects the brain from peripheral inflammation. Consequently, the pathological role of the blood-cerebrospinal fluid barrier in cerebral malaria is currently unknown. To examine the status of the blood-cerebrospinal fluid barrier in cerebral malaria and malaria without this pathology (non-cerebral malaria), we developed a new method for evaluating the permeabilization of the blood-cerebrospinal fluid barrier during cerebral malaria in mice, using Evans blue dye and a software-assisted image analysis. Using C57BL/6J (B6) mice infected with Plasmodium berghei ANKA strain as an experimental cerebral malaria model and B6 mice infected with P. berghei NK65 strain or Plasmodium yoelii as non-cerebral malaria models, we revealed that the permeability of the blood-cerebrospinal fluid barrier increased during experimental cerebral malaria but not during non-cerebral malaria. We observed haemorrhaging in the cerebral ventricles and hemozoin-like structures in the choroid plexus, which is a key component of the blood-cerebrospinal fluid barrier, in cerebral malaria mice. Taken together, this evidence indicates that the blood-cerebrospinal fluid barrier is disrupted in experimental cerebral malaria, whereas it remains intact in non-cerebral malaria. We also found that P. berghei ANKA parasites and CD8⁺ T cells are involved in the blood-cerebrospinal fluid barrier disruption in experimental cerebral malaria. An understanding of the mechanisms underlying cerebral malaria might help in the development of effective strategies to prevent and manage cerebral malaria in humans.

Acute Plasmodium berghei Mouse Infection Elicits Perturbed Erythropoiesis With Features That Overlap With Anemia of Chronic Disease

Severe malaria anemia is one of the most common causes of morbidity and mortality arising from infection with Plasmodium falciparum. The pathogenesis of malarial anemia is complex, involving both parasite and host factors. As mouse models of malaria also develop anemia, they can provide a useful resource to study the impact of Plasmodium infections and the resulting host innate immune response on erythropoiesis. In this study, we have characterized the bone marrow and splenic responses of the erythroid as well as other hematopoietic lineages after an acute infection of Balb/c mice with Plasmodium berghei. Such characterization of the hematopoietic changes is critical to underpin future studies, using knockout mice and transgenic parasites, to tease out the interplay between host genes and parasite modulators implicated in susceptibility to malaria anemia. P. berghei infection led to a clear perturbation of steady-state erythropoiesis, with the most profound defects in polychromatic and orthochromatic erythroblasts as well as erythroid colony- and burst-forming units (CFU-E and BFU-E), resulting in an inability to compensate for anemia. The perturbation in erythropoiesis was not attributable to parasites infecting erythroblasts and affecting differentiation, nor to insufficient erythropoietin (EPO) production or impaired activation of the Signal transducer and activator of transcription 5 (STAT5) downstream of the EPO receptor, indicating EPO-signaling remained functional in anemia. Instead, the results point to acute anemia in P. berghei-infected mice arising from increased myeloid cell production in order to clear the infection, and the concomitant release of pro-inflammatory cytokines and chemokines from myeloid cells that inhibit erythroid development, in a manner that resembles the pathophysiology of anemia of chronic disease.

The immunology of Plasmodium vivax malaria

Plasmodium vivax infection, the predominant cause of malaria in Asia and Latin America, affects ~14 million individuals annually, with considerable adverse effects on wellbeing and socioeconomic development. A clinical hallmark of Plasmodium infection, the paroxysm, is driven by pyrogenic cytokines produced during the immune response. Here, we review studies on the role of specific immune cell types, cognate innate immune receptors, and inflammatory cytokines on parasite control and disease symptoms. This review also summarizes studies on recurrent infections in individuals living in endemic regions as well as asymptomatic infections, a serious barrier to eliminating this disease. We propose potential mechanisms behind these repeated and subclinical infections, such as poor induction of immunological memory cells and inefficient T effector cells. We address the role of antibody-mediated resistance to P. vivax infection and discuss current progress in vaccine development. Finally, we review immunoregulatory mechanisms, such as inhibitory receptors, T regulatory cells, and the anti-inflammatory cytokine, IL-10, that antagonizes both innate and acquired immune responses, interfering with the development of protective immunity and parasite clearance. These studies provide new insights for the clinical management of symptomatic as well as asymptomatic individuals and the development of an efficacious vaccine for vivax malaria.

Induction of Neuroinflammation and Neurotoxicity by Synthetic Hemozoin

Hemozoin produced by Plasmodium falciparum during malaria infection has been linked to the neurological dysfunction in cerebral malaria. In this study, we determined whether a synthetic form of hemozoin (sHZ) produces neuroinflammation and neurotoxicity in cellular models. Incubation of BV-2 microglia with sHZ (200 and 400 µg/ml) induced significant elevation in the levels of TNFα, IL-6, IL-1β, NO/iNOS, phospho-p65, accompanied by an increase in DNA binding of NF-κB. Treatment of BV-2 microglia with sHZ increased protein levels of NLRP3 with accompanying increase in caspase-1 activity. In the presence of NF-κB inhibitor BAY11-7082 (10 µM), there was attenuation of sHZ-induced release of pro-inflammatory cytokines, NO/iNOS. In addition, increase in caspase-1/NLRP3 inflammasome activation was blocked by BAY11-7082. Pre-treatment with BAY11-7082 also reduced both phosphorylation and DNA binding of the p65 sub-unit. The NLRP3 inhibitor CRID3 (100 µM) did not prevent sHZ-induced release of TNFα and IL-6. However, production of IL-1β, NO/iNOS as well as caspase-1/NLRP3 activity was significantly reduced in the presence of CRID3. Incubation of differentiated neural progenitor (ReNcell VM) cells with sHZ resulted in a reduction in cell viability, accompanied by significant generation of cellular ROS and increased activity of caspase-6, while sHZ-induced neurotoxicity was prevented by N-acetylcysteine and Z-VEID-FMK. Taken together, this study shows that the synthetic form of hemozoin induces neuroinflammation through the activation of NF-κB and NLRP3 inflammasome. It is also proposed that sHZ induces ROS- and caspase-6-mediated neurotoxicity. These results have thrown more light on the actions of malarial hemozoin in the neurobiology of cerebral malaria.

The malaria toxin hemozoin induces apoptosis in human neurons and astrocytes: Potential role in the pathogenesis of cerebral malaria

Malaria, caused by an intracellular protozoan parasite of the genus Plasmodium, is one of the most important infectious diseases worldwide. In 2017, a total of 219 millions cases were reported with 435,000 deaths related to malaria. A major complication of malaria infection is cerebral malaria (CM), characterized by enhanced blood-brain barrier permeability, leukocyte infiltration and/or activation, and neuronal dropout resulting in coma and death in significant numbers of individuals, especially children. Despite the high incidence and mortality, the pathogenesis of cerebral malaria is not well characterized. Hemozoin (HMZ) or "malaria pigment," a by-product of intraerythrocytic parasite-mediated hemoglobin catabolism, is released into the bloodstream after lysis of the host infected erythrocyte. The effects of HMZ on brain cells has not been studied due to the contamination/adhesion/aggregation of the HMZ with host and toxic parasitic factors. We now demonstrate that extracellular purified HMZ is taken up by human neurons and astrocytes, resulting in cellular dysfunction and toxicity. These findings contribute to a better understanding of the neuropathogenesis of CM and provide evidence that HMZ accumulation in the bloodstream could result in CNS compromise. Thus, alternative approaches to reducing circulating HMZ could serve as a potential treatment.

Molecular basis of reduced LAIR1 expression in childhood severe malarial anaemia: Implications for leukocyte inhibitory signalling

BACKGROUND

Leukocyte-associated immunoglobulin like receptor-1 (LAIR1) is a transmembrane inhibitory receptor that influences susceptibility to a myriad of inflammatory diseases. Our recent investigations of severe malarial anaemia (SMA) pathogenesis in Kenyan children discovered that novel LAIR1 genetic variants which were associated with decreased LAIR1 transcripts enhanced the longitudinal risk of SMA and all-cause mortality.

METHODS

To characterize the molecular mechanism(s) responsible for altered LAIR1 signalling in severe malaria, we determined LAIR1 transcripts and protein, sLAIR1, sLAIR2, and complement component 1q (C1q) in children with malarial anaemia, followed by a series of in vitro experiments investigating the LAIR1 signalling cascade.

FINDINGS

Kenyan children with SMA had elevated circulating levels of soluble LAIR1 (sLAIR1) relative to non-SMA (1.69-fold P < .0001). The LAIR1 antagonist, sLAIR2, was also elevated in the circulation of children with SMA (1.59 fold-change, P < .0001). There was a positive correlation between sLAIR1 and sLAIR2 (ρ = 0.741, P < .0001). Conversely, circulating levels of complement component 1q (C1q), a LAIR1 natural ligand, were lower in SMA (-1.21-fold P = .048). These in vivo findings suggest that reduced membrane-bound LAIR1 expression in SMA is associated with elevated production of sLAIR1, sLAIR2 (antagonist), and limited C1q (agonist) availability. Since reduced LAIR1 transcripts in SMA were associated with increased acquisition of haemozoin (PfHz) by monocytes (P = .028), we explored the relationship between acquisition of intraleukocytic PfHz, LAIR1 expression, and subsequent impacts on leukocyte signalling in cultured PBMCs from malaria-naïve donors stimulated with physiological concentrations of PfHz (10 μg/mL). Phagocytosis of PfHz reduced LAIR1 transcript and protein expression in a time-dependent manner (P < .050), and inhibited LAIR1 signalling through decreased phosphorylation of LAIR1 (P < .0001) and SH2-domain containing phosphatase-1 (SHP-1) (P < .001). This process was associated with NF-κB activation (P < .0001) and enhanced production of IL-6, IL-1β, and TNF-α (all P < .0001).

INTERPRETATION

Collectively, these findings demonstrate that SMA is characterized by reduced LAIR1 transmembrane expression, reduced C1q, and enhanced production of sLAIR1 and sLAIR2, molecular events which can promote enhanced production of cytokines that contribute to the pathogenesis of SMA. These investigations are important for discovering immune checkpoints that could be future targets of immunotherapy to improve disease outcomes.

Malaria infection promotes a selective expression of kinin receptors in murine liver

BACKGROUND

Malaria represents a worldwide medical emergency affecting mainly poor areas. Plasmodium parasites during blood stages can release kinins to the extracellular space after internalization of host kininogen inside erythrocytes and these released peptides could represent an important mechanism in liver pathophysiology by activation of calcium signaling pathway in endothelial cells of vertebrate host. Receptors (B1 and B2) activated by kinins peptides are important elements for the control of haemodynamics in liver and its physiology. The aim of this study was to identify changes in the liver host responses (i.e. kinin receptors expression and localization) and the effect of ACE inhibition during malaria infection using a murine model.

METHODS

Balb/C mice infected by Plasmodium chabaudi were treated with captopril, an angiotensin I-converting enzyme (ACE) inhibitor, used alone or in association with the anti-malarial chloroquine in order to study the effect of ACE inhibition on mice survival and the activation of liver responses involving B1R and B2R signaling pathways. The kinin receptors (B1R and B2R) expression and localization was analysed in liver by western blotting and immunolocalization in different conditions.

RESULTS

It was verified that captopril treatment caused host death during the peak of malaria infection (parasitaemia about 45%). B1R expression was stimulated in endothelial cells of sinusoids and other blood vessels of mice liver infected by P. chabaudi. At the same time, it was also demonstrated that B1R knockout mice infected presented a significant reduction of survival. However, the infection did not alter the B2R levels and localization in liver blood vessels.

CONCLUSIONS

Thus, it was observed through in vivo studies that the vasodilation induced by plasma ACE inhibition increases mice mortality during P. chabaudi infection. Besides, it was also seen that the anti-malarial chloroquine causes changes in B1R expression in liver, even after days of parasite clearance. The differential expression of B1R and B2R in liver during malaria infection may have an important role in the disease pathophysiology and represents an issue for clinical treatments.

Monocyte phagocytosis of malaria β-haematin in the presence of artemisinin, amodiaquine, chloroquine, doxycycline, primaquine, pyrimethamine and quinine

The intraerythrocytic malaria parasite digests haemoglobin to provide amino acids for metabolism and releases toxic haem that is sequestered into haemozoin, a non-toxic, insoluble, crystalline pigment. Following erythrocyte rupture, haemozoin is released into circulation and phagocytosed by monocytes. Phagocytosed haemozoin and antimalarial drugs have both been reported to modulate monocyte functions. This study determined the effects of therapeutic concentrations of seven antimalarial drugs; amodiaquine, artemisinin, chloroquine, doxycycline, primaquine, pyrimethamine and quinine, on the phagocytosis of β-haematin (synthetic haemozoin) by two monocytic cell lines, J774A.1 and U937, and human peripheral blood mononuclear cells. A novel spectrophotometric method based on the absorbance (O.D 400 nm) of alkali/SDS treated monocytes containing β-haematin was developed to complement counting phagocytosis with microscopy. The method has potential use for the large scale screening of monocyte phagocytic activity. Artemisinin, quinine, primaquine and pyrimethamine activated β-haematin phagocytosis by 12% or more, whereas amodiaquine, chloroquine and doxycyline inhibited β-haematin phagocytosis. In contrast, antimalarial drugs had minimal inhibitory effects on the phagocytosis of latex beads with only quinine resulting in more than 20% inhibition. Antimalarial drugs appear to alter monocyte phagocytic activity which has implications for the treatment, pathogenicity and adjunct therapies for malaria.

Systematic Overview of Solid Particles and Their Host Responses

Crystalline/particulate substances trigger a plethora of signaling events in host cells. The most prominent consequence is the inflammatory reactions that underlie crystal arthropathies, such as gout and pseudogout. However, their impact on our health was underestimated. Recent work on the role of cholesterol crystal in the development of atherosclerosis and the harm of environmental particulates has set up new frontiers in our defense against their detrimental effects. On the other hand, in the last 100 years, crystalline/particulate substances have been used with increasing frequencies in our daily lives as a part of new industrial manufacturing and engineering. Importantly, they have become a tool in modern medicine, used as vaccine adjuvants and drug delivery vehicles. Their biological effects are also being dissected in great detail, particularly with regard to their inflammatory signaling pathways. Solid structure interaction with host cells is far from being uniform, with outcomes dependent on cell types and chemical/physical properties of the particles involved. In this review, we offer a systematic and broad outlook of this landscape and a sage analysis of the complex nature of this topic.

Plasmodium parasite as an effective hepatocellular carcinoma antigen glypican-3 delivery vector

We have previously demonstrated that malaria parasite infection has an anti-tumor effect in a mouse model. This research aimed to investigate the possibility of using Plasmodium parasite as a novel vaccine vector for hepatocellular carcinoma (HCC) immunotherapy. We constructed a Plasmodium yoelii 17XNL strain (P.y) expressing murine glypican-3 (GPC3) protein (P.y-GPC3), and examined its therapeutic potency in a murine Hepa1-6-induced hepatoma model that highly expressed GPC3 protein. The prerequisites for invoking a CD8+ T cell response were assessed after P.y-based immunization, which included obviously increased concentrations of T helper cell type 1 (Th1)-associated cytokines, such as IL-2, IFN-γ and TNF-α, in serum and preferential expansion of the CD8α+ dendritic cell (DC) subset with higher expression of CD80 and CD86 molecules. Compared with uninfected and wild-type P.y-infected mice, a significant GPC3-specific cytotoxic T lymphocyte (CTL) response was detected in P.y-GPC3 vaccinated mice. Furthermore, P.y-GPC3-based vaccination dramatically inhibited Hepa1-6-induced tumor growth in the implanted HCC and prolonged the survival of tumor-bearing mice. We concluded that a Plasmodium-based vector is highly efficient in inducing tumor antigen-specific T cell-mediated immunity and protection against tumor cells. More broadly, this strategy supported our hypothesis that Plasmodium parasites, as novel therapeutic antigen vectors, may be applicable to tumor immunotherapy for patients with HCC.

Immunization with the outer membrane proteins OmpK17 and OmpK36 elicits protection against Klebsiella pneumoniae in the murine infection model

Klebsiella pneumoniae is a Gram-negative bacterium that is increasingly reported as a serious nosocomial and community-acquired pathogen. In the current study, two K. pneumoniae antigens, OmpK17 and OmpK36, as well as their fusion protein cognate F36/17 were investigated as potential vaccine candidates in a murine infection model. Three immunoadjuvants, namely the Gram-positive Enhancer Matrix (GEM) adjuvant, synthetic hemozoin (Hz) adjuvant and incomplete Freund's adjuvant (IFA) were evaluated. Genes of OmpK17 and OmpK36 antigens as well as their fusion protein were cloned in Escherichia coli for recombinant expression. Mice were immunized thrice with the individual recombinant purified antigens adjuvanted with one of the three adjuvants. Two weeks after the last booster, animals were challenged with a lethal dose of K. pneumoniae and immune protection parameters were assessed. Animals immunized with GEM- or Hz-adjuvanted K. pneumoniae antigens did not show significant protection upon bacterial challenge. Animals immunized with subcutaneous IFA-adjuvanted antigens showed the best results with survival percentages of 50, 60 and 50% for groups immunized with OmpK17, OmpK36 and F36/17, respectively. Serum IgG1, rather than IgG2a, antibodies were the most prevalent following vaccination indicating bias towards T helper type 2 (Th2) immune response. Opsonophagocytic assays demonstrated significant percentage killing in case of animals immunized with IFA-adjuvanted antigens. Overall, OmpK17 and OmpK36 are promising vaccine antigens which are worthy of further optimization of the immunization conditions, particularly the used immunoadjuvants, in order to achieve full protection against K. pneumoniae.

Featured Article: Immunomodulatory effect of hemozoin on pneumocyte apoptosis via CARD9 pathway, a possibly retarding pulmonary resolution

Plasmodium falciparum, the most virulent malaria parasite species, causes severe symptoms especially acute lung injury (ALI), of which characterized by alveolar epithelium and endothelium destruction and accelerated to blood-gas-barrier breakdown. Parasitized erythrocytes, endothelial cells, monocytes, and cytokines are all involved in this mechanism, but hemozoin (HZ), the parasitic waste from heme detoxification, also mainly contributes. In addition, it is not clear why type II pneumocyte proliferation, alveolar restorative stage, is rare in malaria-associated ALI. To address this, in vitro culture of A549 cells with Plasmodium HZ or with interleukin (IL)-1β triggered by HZ and monocytes (HZ-IL-1β) was conducted to determine their alveolar apoptotic effect using ethidium bromide/acridine orange staining, annexin-V-FITC/propidium iodide staining, and electron mircroscopic study. Caspase recruitment domain-containing protein 9 ( CARD9), the apoptotic regulator gene, and IL-1β were quantified by reverse-transcriptase PCR. Junctional cellular defects were characterized by immunohistochemical staining of E-cadherin. The results revealed that cellular apoptosis and CARD9 expression levels were extremely high 24 h after induction by HZ-IL-1β when compared to the HZ- and non-treated groups. E-cadherin was markedly down-regulated by HZ-IL-1β and HZ treatments. CARD9 expression was positively correlated with IL-1β expression and the number of apoptotic cells. Interestingly, the localization of HZ in the vesicular surfactant of apoptotic pneumocyte was also identified and submitted to be a cause of alveolar resolution abnormality. Thus, HZ triggers monocytes to produce IL-1β and induces pneumocyte type II apoptosis through CARD9 pathway in association with down-regulated E-cadherin, which probably impairs alveolar resolution in malaria-associated ALI. Impact statement The present work shows the physical and immunomodulatory properties of hemozoin on the induction of pneumocyte apoptosis in relation to IL-1β production through the CARD9 pathway. This occurrence may be a possible pathway for the retardation of lung resolution leading to blood-gas-barrier breakdown. Our findings lead to the understanding of the host-parasite relationship focusing on the dysfunction in ALI induced by HZ, a possible pathway of the recovering lung epithelial retardation in malaria-associated ARDS.

Parasitic and fungal infections

Parasitic infections of the central nervous system (CNS) comprise a plethora of infectious agents leading to a multitude of different disease courses and thus diagnostic and therapeutic challenges. The prevalence of different pathogens is basically dependent on geographic and ethnic backgrounds, its infectious route frequently involving a third party, such as flies or domestic animals. The present review focuses on cerebral malaria due to Plasmodium falciparum infection, and Toxoplasma gondii encephalitis. Fungi produce a large variety of inflammatory conditions of the CNS with a variegated spectrum of signs and symptoms, which may involve the meninges and the brain parenchyma, where they produce cerebritis or abscesses and granulomatous lesions, respectively. Fungal CNS lesions are increasingly prevalent and diagnostically relevant due to increasing numbers of human immunodeficiency virus-positive patients, increasing numbers of patients reaching old age suffering from malignant tumors or decreased immunity, and finally the increasing use of established and new immunosuppressive treatments, which increase the susceptibility of patients to develop invasive mycoses. Fungi appear with characteristic morphotypes comprising hyphae, yeasts, and pseudohyphae. The mode by which fungi penetrate into the CNS, and the host/immune requirements are incompletely understood and remain a challenge for research.

RANTES levels as a determinant of falciparum malaria severity or recovery

The study explored the role of differential RANTES concentrations, its receptor CCR5 expression and resulting immunomodulation in the pathogenesis and/or recovery from falciparum malaria. The study population included cases of uncomplicated malaria (UC-M, N=128, enrolled on follow-up basis), severe malaria (SM, N=25), and healthy controls (N=112). Serum RANTES and TNF-α levels were evaluated by ELISA. Monocyte levels and activation profile were studied by flow cytometry. Differential mRNA expression profile was studied by real-time PCR. Blood parasite count was evaluated by registered pathologists. RANTES concentration was significantly downregulated in SM cases compared to UC-M (P=.046) and controls (P<.001). Expression of monocyte marker mCD14, activation markers CCR5 and CD40, and downstream effector cytokine TNF-α was significantly higher in malaria cases compared to controls, in SM cases compared to UC-M. TNF-α expression correlated positively with CD40 and CCR5 expressions. Follow-up-based analysis showed that RANTES concentrations increased on recovery compared to baseline in UC-M cases (P=.106) and inversely correlated with malaria parasite load, mCD14, CCR5 and CD40, and TNF-α expressions. These findings suggest an important association of RANTES concentrations in Plasmodium falciparum malaria disease pathogenesis, as well as recovery, mediated through differential modulation and regulated activation of monocytes and cytokine TNF-α.

Schistosoma hemozoin and its possible roles

More than 95years ago Schistosoma pigment had been deemed as a degradation product of haemoglobin. Until the 1950s, scientists initiated to pay attention to understand the hematophagous habit of schistosomes, and to study the degradation of haemoglobin as well as the formation of hemozoin inside the gut of the worms. For a long time, the formation of hemozoin in both Plasmodium and in Schistosoma was considered to be the major route of heme detoxification, and hemozoin served a role in waste disposal. At the beginning of this century, the chemical structure of Schistosoma pigment was confirmed to be identical to that of malarial pigment (hemozoin) and its synthetic analogue, β-hematin. Since then, studies on Schistosoma hemozoin have been investigated by some workers and the results showed that Schistosoma hemozoin may play important roles in pathogenicity, immune modulation, iron supply for egg formation, and interaction with some anti-schistosomal drugs. In this review, we briefly review and discuss the hematophagous habit of schistosomes, degradation of haemoglobin, formation of hemozoin in the worm gut, and possible roles of hemozoin.

Tissue-Resident CD169(+) Macrophages Form a Crucial Front Line against Plasmodium Infection

Tissue macrophages exhibit diverse functions, ranging from the maintenance of tissue homeostasis, including clearance of senescent erythrocytes and cell debris, to modulation of inflammation and immunity. Their contribution to the control of blood-stage malaria remains unclear. Here, we show that in the absence of tissue-resident CD169(+) macrophages, Plasmodium berghei ANKA (PbA) infection results in significantly increased parasite sequestration, leading to vascular occlusion and leakage and augmented tissue deposition of the malarial pigment hemozoin. This leads to widespread tissue damage culminating in multiple organ inflammation. Thus, the capacity of CD169(+) macrophages to contain the parasite burden and its sequestration into different tissues and to limit infection-induced inflammation is crucial to mitigating Plasmodium infection and pathogenesis.

Understanding malarial toxins

Recognized since antiquity, malaria is one of the most infamous and widespread infectious diseases in humans and, although the death rate during the last century has been diminishing, it still accounts for more than a half million deaths annually. It is caused by the Plasmodium parasite and typical symptoms include fever, shivering, headache, diaphoresis and nausea, all resulting from an excessive inflammatory response induced by malarial toxins released into the victim's bloodstream. These toxins are hemozoin and glycosylphosphatidylinositols. The former is the final product of the parasite's detoxification of haeme, a by-product of haemoglobin catabolism, while the latter anchor proteins to the Plasmodium cell surface or occur as free molecules. Currently, only two groups of antimalarial toxin drugs exist on the market, quinolines and artemisinins. As we describe, they both target biosynthesis of hemozoin. Other substances, currently in various phases of clinical trials, are directed towards biosynthesis of glycosylphosphatidylinositol, formation of hemozoin, or attenuation of the inflammatory response of the patient. Among the innovative approaches to alleviating the effects of malarial toxins, is the development of antimalarial toxin vaccines. In this review the most important lessons learned from the use of treatments directed against the action of malarial toxins in antimalarial therapy are emphasized and the most relevant and promising directions for future research in obtaining novel antimalarial agents acting on malarial toxins are discussed.

Erythropoiesis in Malaria Infections and Factors Modifying the Erythropoietic Response

Anemia is the primary clinical manifestation of malarial infections and is responsible for the substantial rate of morbidity. The pathophysiology discussed till now catalogued several causes for malarial anemia among which ineffective erythropoiesis being remarkable one occurs silently in the bone marrow. A systematic literature search was performed and summarized information on erythropoietic response upon malaria infection and the factors responsible for the same. This review summarizes the clinical and experimental studies on patients, mouse models, and in vitro cell cultures reporting erythropoietic changes upon malaria infection as well as factors accountable for the same. Inadequate erythropoietic response during malaria infection may be the collective effect of various mediators generated by host immune response as well as parasite metabolites. The interplay between various modulators causing the pathophysiology needs to be explored further. Globin gene expression profiling upon malaria infection should also be looked into as abnormal production of globin chains could be a possible contributor to ineffective erythropoiesis.

Type I Interferon Transcriptional Signature in Neutrophils and Low-Density Granulocytes Are Associated with Tissue Damage in Malaria

Neutrophils are the most abundant leukocyte population in the bloodstream, the primary compartment of Plasmodium sp. infection. However, the role of these polymorphonuclear cells in mediating either the resistance or the pathogenesis of malaria is poorly understood. We report that circulating neutrophils from malaria patients are highly activated, as indicated by a strong type I interferon transcriptional signature, increased expression of surface activation markers, enhanced release of reactive oxygen species and myeloperoxidase, and a high frequency of low-density granulocytes. The activation of neutrophils was associated with increased levels of serum alanine and aspartate aminotransferases, indicating liver damage. In a rodent malaria model, we observed intense recruitment of neutrophils to liver sinusoids. Neutrophil migration and IL-1β and chemokine expression as well as liver damage were all dependent on type I interferon signaling. The data suggest that type I interferon signaling has a central role in neutrophil activation and malaria pathogenesis.

PKC/ROS-Mediated NLRP3 Inflammasome Activation Is Attenuated by Leishmania Zinc-Metalloprotease during Infection

Parasites of the Leishmania genus infect and survive within macrophages by inhibiting several microbicidal molecules, such as nitric oxide and pro-inflammatory cytokines. In this context, various species of Leishmania have been reported to inhibit or reduce the production of IL-1β both in vitro and in vivo. However, the mechanism whereby Leishmania parasites are able to affect IL-1β production and secretion by macrophages is still not fully understood. Dependent on the stimulus at hand, the maturation of IL-1β is facilitated by different inflammasome complexes. The NLRP3 inflammasome has been shown to be of pivotal importance in the detection of danger molecules such as inorganic crystals like asbestos, silica and malarial hemozoin, (HZ) as well as infectious agents. In the present work, we investigated whether Leishmania parasites modulate NLRP3 inflammasome activation. Using PMA-differentiated THP-1 cells, we demonstrate that Leishmania infection effectively inhibits macrophage IL-1β production upon stimulation. In this context, the expression and activity of the metalloprotease GP63 - a critical virulence factor expressed by all infectious Leishmania species - is a prerequisite for a Leishmania-mediated reduction of IL-1β secretion. Accordingly, L. mexicana, purified GP63 and GP63-containing exosomes, caused the inhibition of macrophage IL-1β production. Leishmania-dependent suppression of IL-1β secretion is accompanied by an inhibition of reactive oxygen species (ROS) production that has previously been shown to be associated with NLRP3 inflammasome activation. The observed loss of ROS production was due to an impaired PKC-mediated protein phosphorylation. Furthermore, ROS-independent inflammasome activation was inhibited, possibly due to an observed GP63-dependent cleavage of inflammasome and inflammasome-related proteins. Collectively for the first time, we herein provide evidence that the protozoan parasite Leishmania, through its surface metalloprotease GP63, can significantly inhibit NLRP3 inflammasome function and IL-1β production.

Leishmania parasites are the causative agent of leishmaniasis, a wide spread disease in tropical and subtropical areas. The microorganisms have been shown to be well-adapted to their hosts and are able to enter their target cells where they replicate themselves. To ensure these processes, Leishmania disrupts a multitude of cellular signals and protective mechanisms, which overall attenuates immune responses against the parasites. A key factor for inflammatory processes, also during infections, is IL-1β. As previous studies suggested a dysregulation of IL-1β levels after infection with Leishmania parasites, we herein investigated the underlying mechanisms. Our work reveals that Leishmania suppressing IL-1β production through its virulence factor GP63. Furthermore, our data suggests that the parasites can dampen the maturation of IL-1β after different stimuli. In this regard we established a role for the suppression of the kinase PKC and the generation of reactive oxygen species, as well as the cleavage of cellular proteins that are important for IL-1β-generation. Thus, we here present a novel aspect for how Leishmania parasites can counteract host protective mechanisms.

Hemozoin induces hepatic inflammation in mice and is differentially associated with liver pathology depending on the Plasmodium strain

Malaria is a global disease that clinically affects more than two hundred million people annually. Despite the availability of effective antimalarials, mortality rates associated with severe complications are high. Hepatopathy is frequently observed in patients with severe malarial disease and its pathogenesis is poorly understood. Previously, we observed high amounts of hemozoin or malaria pigment in livers from infected mice. In this study, we investigated whether hemozoin is associated with liver injury in different mouse malaria models. C57BL/6J mice infected with the rodent parasites Plasmodium berghei ANKA, P. berghei NK65 or P. chabaudi AS had elevated serum liver enzymes without severe histological changes in the liver, in line with the observations in most patients. Furthermore, liver enzymes were significantly higher in serum of P. chabaudi AS-infected mice compared to mice infected with the P. berghei parasite strains and a strong positive correlation was found between hepatic hemozoin levels, hepatocyte damage and inflammation in the liver with P. chabaudi AS. The observed liver injury was only marginally influenced by the genetic background of the host, since similar serum liver enzyme levels were measured in infected C57BL/6J and BALB/c mice. Intravenous injection of P. falciparum-derived hemozoin in malaria-free C57BL/6J mice induced inflammatory gene transcription in the liver, suggesting that hemozoin may be involved in the pathogenesis of malaria hepatopathy by inducing inflammation.

Plasmodium and mononuclear phagocytes

Plasmodium, the causative agent of malaria, initially multiplies inside liver cells and then in successive cycles inside erythrocytes, causing the symptoms of the disease. In this review, we discuss interactions between the extracellular and intracellular forms of the Plasmodium parasite and innate immune cells in the mammalian host, with a special emphasis on mononuclear phagocytes. We overview here what is known about the innate immune cells that interact with parasites, mechanisms used by the parasite to evade them, and the protective or detrimental contribution of these interactions on parasite progression through its life cycle and pathology in the host.

Malarial pigment hemozoin impairs chemotactic motility and transendothelial migration of monocytes via 4-hydroxynonenal

Natural hemozoin, nHZ, is avidly phagocytosed in vivo and in vitro by human monocytes. The persistence of the undigested β-hematin core of nHZ in the phagocyte lysosome for long periods of time modifies several cellular immune functions. Here we show that nHZ phagocytosis by human primary monocytes severely impaired their chemotactic motility toward MCP-1, TNF, and FMLP, by approximately 80% each, and their diapedesis across a confluent human umbilical vein endothelial cell layer toward MCP-1 by 45±5%. No inhibition was observed with latex-fed or unfed monocytes. Microscopic inspection revealed polarization defects in nHZ-fed monocytes due to irregular actin polymerization. Phagocytosed nHZ catalyzes the peroxidation of polyunsaturated fatty acids and generation of the highly reactive derivative 4-hydroxynonenal (4-HNE). Similar to nHZ phagocytosis, the exposure of monocytes to in vivo-compatible 4-HNE concentrations inhibited cell motility in both the presence and the absence of chemotactic stimuli, suggesting severe impairment of cytoskeleton dynamics. Consequently, 4-HNE conjugates with the cytoskeleton proteins β-actin and coronin-1A were immunochemically identified in nHZ-fed monocytes and mass spectrometrically localized in domains of protein-protein interactions involved in cytoskeleton reorganization and cell motility. The molecular and functional modifications of actin and coronin by nHZ/4-HNE may also explain impaired phagocytosis, another motility-dependent process previously described in nHZ-fed monocytes. Further studies will show whether impaired monocyte motility may contribute to the immunodepression and the frequent occurrence of secondary infections observed in malaria patients.

Malarial pigment hemozoin and the innate inflammatory response

Malaria is a deadly infectious disease caused by the intraerythrocytic protozoan parasite Plasmodium. The four species of Plasmodium known to affect humans all produce an inorganic crystal called hemozoin (HZ) during the heme detoxification process. HZ is released from the food vacuole into circulation during erythrocyte lysis, while the released parasites further infect additional naive red blood cells. Once in circulation, HZ is rapidly taken up by circulating monocytes and tissue macrophages, inducing the production of pro-inflammatory mediators, such as interleukin-1β (IL-1β). Over the last few years, it has been reported that HZ, similar to uric acid crystals, asbestos, and silica, is able to trigger IL-1β production via the activation of the NOD-like receptor containing pyrin domain 3 (NLRP3) inflammasome complex. Additionally, recent findings have shown that host factors, such as fibrinogen, have the ability to adhere to free HZ and modify its capacity to activate host immune cells. Although much has been discovered regarding NLRP3 inflammasome induction, the mechanism through which this intracellular multimolecular complex is activated remains unclear. In the present review, the most recent discoveries regarding the capacity of HZ to trigger this innate immune complex as well as the impact of HZ on several other inflammatory signaling pathways will be discussed.

Immunopathological effects of malaria pigment or hemozoin and other crystals

Blood-stage malaria parasites produce insoluble hemozoin (Hz) crystals that are released in the blood circulation upon schizont rupture. In general, endogenous crystal formation or inhalation of crystalline materials is often associated with pathology. As the immune system responds differently to crystalline particles than to soluble molecules, in this review, the properties, immunological recognition, and pathogenic responses of Hz are discussed, and compared with two other major pathogenic crystals, monosodium urate (MSU) and asbestos. Because of the size and shape of MSU crystals and asbestos fibers, phagolysosomal formation is inefficient and often results in leakage of lysosomal content in the cell cytoplasm and/or in the extracellular environment with subsequent cell damage and cell death. Phagolysosomal formation after Hz ingestion is normal, but Hz remains stored inside these cells for months or even longer without any detectable degradation. Nonetheless, the different types of crystals are recognized by similar immune receptors, involving Toll-like receptors, the inflammasome, antibodies, and/or complement factors, and through similar signaling cascades, they activate both proinflammatory and anti-inflammatory immune responses that contribute to inflammation-associated pathology.

The association of IL-8-251T/A polymorphism with complicated malaria in Karbi Anglong district of Assam

Amongst host genetic factors, cytokine gene polymorphism can be anticipated to be an important factor as qualitative, quantitative and time of secretion play an important role in disease outcome. We have investigated association of cytokine promoter SNPs with risk of Plasmodium falciparum malaria and disease severity in a case control study in malaria endemic Karbi Anglong district of Assam, India. Frequency of IL-8-251T/A (p=0.03 and p=0.01) and TGF-β1-509C/T (p=0.02 and p=0.03) was higher in malaria in comparison to control participants and non-malarial fever controls. Interestingly, a higher frequency of mutant allele of IL-10-819T/C was observed in non-malarial fever controls compared to malaria thus suggesting its role as a distinguishing marker of the two disease groups. Higher IL-8 expression and increased frequency of IL-8-251T/A in complicated malaria (p=0.002) was reported indicating its role in susceptibility to complicated malaria. In conclusion, our study suggests the role of mutant genotype of IL-8-251T/A as a marker of complicated malaria in our population. Surprisingly, decreased expression of TGF-β1 in uncomplicated malaria even in presence of high expressing mutant genotype was observed and needs to be investigated in context of the pool of activated cells producing the cytokine.

Hemoglobinopathies: slicing the Gordian knot of Plasmodium falciparum malaria pathogenesis

Plasmodium falciparum malaria kills over 500,000 children every year and has been a scourge of humans for millennia. Owing to the co-evolution of humans and P. falciparum parasites, the human genome is imprinted with polymorphisms that not only confer innate resistance to falciparum malaria, but also cause hemoglobinopathies. These genetic traits—including hemoglobin S (HbS), hemoglobin C (HbC), and α-thalassemia—are the most common monogenic human disorders and can confer remarkable degrees of protection from severe, life-threatening falciparum malaria in African children: the risk is reduced 70% by homozygous HbC and 90% by heterozygous HbS (sickle-cell trait). Importantly, this protection is principally present for severe disease and largely absent for P. falciparum infection, suggesting that these hemoglobinopathies specifically neutralize the parasite's in vivo mechanisms of pathogenesis. These hemoglobin variants thus represent a “natural experiment” to identify the cellular and molecular mechanisms by which P. falciparum produces clinical morbidity, which remain partially obscured due to the complexity of interactions between this parasite and its human host. Multiple lines of evidence support a restriction of parasite growth by various hemoglobinopathies, and recent data suggest this phenomenon may result from host microRNA interference with parasite metabolism. Multiple hemoglobinopathies mitigate the pathogenic potential of parasites by interfering with the export of P. falciparum erythrocyte membrane protein 1 (PfEMP1) to the surface of the host red blood cell. Few studies have investigated their effects upon the activation of the innate and adaptive immune systems, although recent murine studies suggest a role for heme oxygenase-1 in protection. Ultimately, the identification of mechanisms of protection and pathogenesis can inform future therapeutics and preventive measures. Hemoglobinopathies slice the “Gordian knot” of host and parasite interactions to confer malaria protection, and offer a translational model to identify the most critical mechanisms of P. falciparum pathogenesis.

Chickens treated with a nitric oxide inhibitor became more resistant to Plasmodium gallinaceum infection due to reduced anemia, thrombocytopenia and inflammation

Malaria is a serious infectious disease caused by parasites of the Plasmodium genus that affect different vertebrate hosts. Severe malaria leads to host death and involves different pathophysiological phenomena such as anemia, thrombocytopenia and inflammation. Nitric oxide (NO) is an important effector molecule in this disease, but little is known about its role in avian malaria models. Plasmodium gallinaceum-infected chickens were treated with aminoguanidine (AG), an inhibitor of inducible nitric oxide synthase, to observe the role of NO in the pathogenesis of this avian model. AG increased the survival of chickens, but also induced higher parasitemia. Treated chickens demonstrated reduced anemia and thrombocytopenia. Moreover, erythrocytes at different stages of maturation, heterophils, monocytes and thrombocytes were infected by Plasmodium gallinaceum and animals presented a generalized leucopenia. Activated leukocytes and thrombocytes with elongated double nuclei were observed in chickens with higher parasitemia; however, eosinophils were not involved in the infection. AG reduced levels of hemozoin in the spleen and liver, indicating lower inflammation. Taken together, the results suggest that AG reduced anemia, thrombocytopenia and inflammation, explaining the greater survival rate of the treated chickens.

Chronic exposure to Plasmodium falciparum is associated with phenotypic evidence of B and T cell exhaustion

Naturally acquired immunity to malaria develops slowly, requiring several years of repeated exposure to be effective. The cellular and molecular factors underlying this observation are only partially understood. Recent studies suggest that chronic Plasmodium falciparum exposure may induce functional exhaustion of lymphocytes, potentially impeding optimal control of infection. However, it remains unclear whether the "atypical" memory B cells (MBCs) and "exhausted" CD4 T cells described in humans exposed to endemic malaria are driven by P. falciparum per se or by other factors commonly associated with malaria, such as coinfections and malnutrition. To address this critical question we took advantage of a "natural" experiment near Kilifi, Kenya, and compared profiles of B and T cells of children living in a rural community where P. falciparum transmission is ongoing to the profiles of age-matched children living under similar conditions in a nearby community where P. falciparum transmission ceased 5 y prior to this study. We found that continuous exposure to P. falciparum drives the expansion of atypical MBCs. Persistent P. falciparum exposure was associated with an increased frequency of CD4 T cells expressing phenotypic markers of exhaustion, both programmed cell death-1 (PD-1) alone and PD-1 in combination with lymphocyte-activation gene-3 (LAG-3). This expansion of PD-1-expressing and PD-1/LAG-3-coexpressing CD4 T cells was largely confined to CD45RA(+) CD4 T cells. The percentage of CD45RA(+)CD27(+) CD4 T cells coexpressing PD-1 and LAG-3 was inversely correlated with frequencies of activated and classical MBCs. Taken together, these results suggest that P. falciparum infection per se drives the expansion of atypical MBCs and phenotypically exhausted CD4 T cells, which has been reported in other endemic areas.

Schistosoma mansoni hemozoin modulates alternative activation of macrophages via specific suppression of Retnla expression and secretion

The trematode Schistosoma mansoni is one of the etiological agents of schistosomiasis, a key neglected tropical disease responsible for an estimated annual loss of 70 million disability-adjusted life years. Hematophagy represents the primary nutrient acquisition pathway of this parasite, but digestion of hemoglobin also liberates toxic heme. Schistosomes detoxify heme via crystallization into hemozoin, which is subsequently regurgitated into the host's circulation. Here we demonstrate that during experimental schistosomiasis, hemozoin accumulating in the mouse liver is taken up by phagocytes at a time coincident with the development of the egg-induced T-helper 2 (Th2) granulomatous immune response. Furthermore, the uptake of hemozoin also coincides with the hepatic expression of markers of alternative macrophage activation. Alternatively activated macrophages are a key effector cell population associated with protection against schistosomiasis, making hemozoin well placed to play an important immunomodulatory role in this disease. To systematically explore this hypothesis, S. mansoni hemozoin was purified and added to in vitro bone marrow-derived macrophage cultures concurrently exposed to cytokines chosen to reflect the shifting state of macrophage activation in vivo. Macrophages undergoing interleukin-4 (IL-4)-induced alternative activation in the presence of hemozoin developed a phenotype specifically lacking in Retnla, a characteristic alternatively activated macrophage product associated with regulation of Th2 inflammatory responses. As such, in addition to its important detoxification role during hematophagy, we propose that schistosome hemozoin also provides a potent immunomodulatory function in the coevolved network of host-parasite relationships during schistosomiasis.

Neutrophil paralysis in Plasmodium vivax malaria

Background

The activation of innate immune responses by Plasmodium vivax results in activation of effector cells and an excessive production of pro-inflammatory cytokines that may culminate in deleterious effects. Here, we examined the activation and function of neutrophils during acute episodes of malaria.

Materials and Methods

Blood samples were collected from P. vivax-infected patients at admission (day 0) and 30–45 days after treatment with chloroquine and primaquine. Expression of activation markers and cytokine levels produced by highly purified monocytes and neutrophils were measured by the Cytometric Bead Assay. Phagocytic activity, superoxide production, chemotaxis and the presence of G protein-coupled receptor (GRK2) were also evaluated in neutrophils from malaria patients.

Principal Findings

Both monocytes and neutrophils from P. vivax-infected patients were highly activated. While monocytes were found to be the main source of cytokines in response to TLR ligands, neutrophils showed enhanced phagocytic activity and superoxide production. Interestingly, neutrophils from the malaria patients expressed high levels of GRK2, low levels of CXCR2, and displayed impaired chemotaxis towards IL-8 (CXCL8).

Conclusion

Activated neutrophils from malaria patients are a poor source of pro-inflammatory cytokines and display reduced chemotactic activity, suggesting a possible mechanism for an enhanced susceptibility to secondary bacterial infection during malaria.

Plasmodium vivax is responsible for approximately 60–80% of the malaria cases in the world, and contributes to significant social and economic instability in the developing countries of Latin America and Asia. The pathogenesis of P. vivax malaria is a consequence of host derived inflammatory mediators. Hence, a better understanding of the mechanisms involved in induction of systemic inflammation during P. vivax malaria is critical for the clinical management and prevention of severe disease. The innate immune receptors recognize Plasmodium sp. and initiate a broad spectrum of host defense mechanisms that mediate resistance to infection. However, the innate immune response is the classic “two-edged sword”, and clinical malaria is associated with high levels of circulating pro-inflammatory cytokines. Our findings show that both monocytes and neutrophils are highly activated during malaria. Monocytes produced high levels of IL-1β, IL-6 and TNF-α during acute malaria. On the other hand, neutrophils were a poor source of cytokines, but displayed an enhanced phagocytic activity and superoxide production. Unexpectedly, we noticed an impaired chemotaxis of neutrophils towards an IL-8 (CXCL8) gradient. We proposed that neutrophil paralysis is in part responsible for the enhanced susceptibility to bacterial infection observed in malaria patients.

Impact of intravascular hemolysis in malaria on liver dysfunction: involvement of hepatic free heme overload, NF-κB activation, and neutrophil infiltration

We have investigated the impact of persistent intravascular hemolysis on liver dysfunction using the mouse malaria model. Intravascular hemolysis showed a positive correlation with liver damage along with the increased accumulation of free heme and reactive oxidants in liver. Hepatocytes overinduced heme oxygenase-1 (HO-1) to catabolize free heme in building up defense against this pro-oxidant milieu. However, in a condition of persistent free heme overload in malaria, the overactivity of HO-1 resulted in continuous transient generation of free iron to favor production of reactive oxidants as evident from 2',7'-dichlorofluorescein fluorescence studies. Electrophoretic mobility shift assay documented the activation of NF-κB, which in turn up-regulated intercellular adhesion molecule 1 as evident from chromatin immunoprecipitation studies. NF-κB activation also induced vascular cell adhesion molecule 1, keratinocyte chemoattractant, and macrophage inflammatory protein 2, which favored neutrophil extravasation and adhesion in liver. The infiltration of neutrophils correlated positively with the severity of hemolysis, and neutrophil depletion significantly prevented liver damage. The data further documented the elevation of serum TNFα in infected mice, and the treatment of anti-TNFα antibodies also significantly prevented neutrophil infiltration and liver injury. Deferoxamine, which chelates iron, interacts with free heme and bears antioxidant properties that prevented oxidative stress, NF-κB activation, neutrophil infiltration, hepatocyte apoptosis, and liver damage. Furthermore, the administration of N-acetylcysteine also prevented NF-κB activation, neutrophil infiltration, hepatocyte apoptosis, and liver damage. Thus, hepatic free heme accumulation, TNFα release, oxidative stress, and NF-κB activation established a link to favor neutrophil infiltration in inducing liver damage during hemolytic conditions in malaria.

Effects of Extracts from Paederia scandens (LOUR.) MERRILL (Rubiaceae) on MSU Crystal-Induced Rats Gouty Arthritis

The effects of extract of Paederia scandens (LOUR.) MERRILL (Rubiaceae) (EPS), a Chinese traditional herbal medicine, on inflammatory and immune responses and their mechanisms in MSU crystals-induced (GA) rats were studied. GA rats were established. Ankle joint volume of rats was measured by volume meter; the level of TNF-α and IL-1β was determined by radioimmunoassay. mRNA expressions of TNF-α and IL-1β in synovial tissue of GA rats were analyzed by RT-PCR, and the expression of NF-κB was detected by immunohistochemistry. The administration of EPS (2.25, 4.5 g/kg, ig 9 days) inhibited the inflammatory response in GA rats. The mRNA expressions of TNF-α and IL-1β were also significantly suppressed in synovial tissue. In addition, EPS (2.25, 4.5 g/kg, ig 9 days) inhibited the expression of TNF-α and IL-1β and the biological activity of NF-κB. These results suggested that EPS possesses antiinflammatory effects by modulating pro-inflammatory mediators' production in synovial tissue and inactivating NF-κB pathway transmembrane signal transduction which plays a crucial role in the pathogenesis of this disease.