Monocytes, particularly nonclassical ones, lose their opsonic and nonopsonic phagocytosis capacity during pediatric cerebral malaria

IntroductionInnate immunity is crucial to reducing parasite burden and contributing to survival in severe malaria. Monocytes are key actors in the innate response and, like macrophages, are plastic cells whose function and phenotype are regulated by the signals from the microenvironment. In the context of cerebral malaria (CM), monocyte response constitutes an important issue to understand. We previously demonstrated that decreased percentages of nonclassical monocytes were associated with death outcomes in CM children. In the current study, we postulated that monocyte phagocytosis function is impacted by the severity of malaria infection.MethodsTo study this hypothesis, we compared the opsonic and nonopsonic phagocytosis capacity of circulant monocytes from Beninese children with uncomplicated malaria (UM) and CM. For the CM group, samples were obtained at inclusion (D0) and 3 and 30 days after treatment (D3, D30). The phagocytosis capacity of monocytes and their subsets was characterized by flow cytometry and transcriptional profiling by studying genes known for their functional implication in infected-red blood cell (iRBC) elimination or immune escape.ResultsOur results confirm our hypothesis and highlight the higher capacity of nonclassical monocytes to phagocyte iRBC. We also confirm that a low number of nonclassical monocytes is associated with CM outcome when compared to UM, suggesting a mobilization of this subpopulation to the cerebral inflammatory site. Finally, our results suggest the implication of the inhibitory receptors LILRB1, LILRB2, and Tim3 in phagocytosis control.DiscussionTaken together, these data provide a better understanding of the interplay between monocytes and malaria infection in the pathogenicity of CM

Identification of immune factors involved in neuroinflammation and its resolution, in cerebral malaria context : Role of the monocyte responses

En 2020, le paludisme reste un problème majeur de santé publique. Malgré des avancées scientifiques capitales, il est encore responsable de plus de 400 000 décès chaque année, principalement chez les enfants en Afrique Sub-saharienne. Le neuropaludisme est l'une des formes les plus sévères du paludisme. Sa physiopathologie est complexe, impliquant l'adhésion des érythrocytes infectés par Plasmodium falciparum à l'endothélium vasculaire dans le cerveau. Ce mécanisme conduit à une obstruction du flux sanguin, une inflammation locale, une altération de la barrière hémato-encéphalique et à un éventail de réponses cellulaires visant à résoudre le processus de neuroinflammation. Parmi ces cellules, les monocytes/macrophages jouent un rôle clé de par leur capacité à s'adapter à leur microenvironnement en fonction des différents signaux qu'ils perçoivent, modulant ainsi les balances pro/anti-inflammatoire et pro/antioxydante, essentielles à la résolution du neuropaludisme. Les monocytes sont composés de trois sous-populations dont le rôle dans la physiopathologie du neuropaludisme a été peu étudié et reste à éclaircir. Pour compléter ces connaissances, une approche combinant modèle murin et études chez des patients béninois a été menée. Une première étude a été conduite chez des enfants béninois présentant un paludisme simple, une anémie sévère palustre, ou un neuropaludisme dans le but de déterminer si les paramètres monocytaires constituent des facteurs de sévérité et/ou de risque de décès au cours d'un paludisme grave. Les pourcentages et phénotypes des sous-populations monocytaires obtenus chez les trois groupes d'enfants lors de leur admission dans les centres de santé (J0) ont été comparés. Les résultats ont permis de mettre en lumière l'implication des monocytes non classiques dans la protection vis-à-vis des formes sévères de paludisme et de confirmer l'importance du récepteur CD36 des monocytes comme facteur protecteur de sévérité et de survenue de décès. Pour aller plus loin, un travail a ensuite été mené sur un modèle murin de neuropaludisme mis en place pour se rapprocher des conditions réelles, à savoir un traitement tardif, et débouchant sur une résolution de l'infection. Des souris C57BL/6 ont été infectées par P. berghei ANKA (J0) et traitées tardivement à la chloroquine. La cinétique d'évolution des sous-populations monocytaires a été suivie en termes de pourcentage et d'expression protéique et génique, à la fois dans le sang, la rate et le cerveau, jusqu'à la résolution de l'infection (J12). Les résultats suggèrent une implication des monocytes classiques et intermédiaires dans la neuroinflammation, au contraire des monocytes non classiques. A J12 était observé un nouvel afflux de monocytes intermédiaires vers le cerveau, suggérant également un rôle de cette sous-population dans la résolution tardive de la neuroinflammation. Les analyses protéique et génique ont mis en évidence une implication favorable de Nrf2, CD36, HO-1, CMH-II, COX-2 et de la 12/15-LOX dans la résolution de l'infection. Une deuxième étude a ensuite été menée chez des enfants béninois, avec un plus grand nombre de patients et un suivi à J3 et J30. Deux groupes de sujets ont été inclus, présentant un paludisme simple (n = 94) ou un neuropaludisme (n = 65). Dans l'ensemble, les résultats indiquent que les monocytes non classiques et intermédiaires étaient respectivement impliqués dans l'amélioration clinique et la survie des patients. L'expression de CD14, CD16, CD36 et HLA-DR était un facteur protecteur vis-à-vis du neuropaludisme. De manière intéressante, nos résultats montrent également une association entre une réponse pro-oxydante moins active, la sévérité du paludisme, et la survenue de décès. L'ensemble de ces résultats apporte un nouvel éclairage sur l'implication des monocytes/macrophages au cours du neuropaludisme.In 2020, malaria remains a major public health problem. Despite major scientific advances, it is still responsible for more than 400,000 deaths each year, mainly among children in Sub-Saharan Africa. Cerebral malaria is one of the most severe forms of malaria. Its physiopathology is complex, involving adhesion of Plasmodium falciparum-infected erythrocytes to the vascular endothelium in the brain. This mechanism leads to obstruction of blood flow, local inflammation, alteration of the blood-brain barrier and a range of cellular responses aiming to resolve the neuroinflammation process. Among these cells, monocytes/macrophages play a key role due to their ability to adapt to their microenvironment according to the different signals they perceive, thus modulating the pro/anti-inflammatory and pro/antioxidant balances that are essential to the resolution of cerebral malaria. Monocytes are composed of three subpopulations whose role in the physiopathology of cerebral malaria has been little studied and remains to be clarified. To complete this knowledge, an approach combining a mouse model and studies in Beninese patients was conducted. A first study was conducted in Beninese children with uncomplicated malaria, severe malarial anaemia, or cerebral malaria, in order to determine whether monocytic parameters are factors of severity and/or risk of death during severe malaria. The percentages and phenotypes of monocyte subpopulations obtained in the three groups of children on admission to the health centres (D0) were compared. The results highlighted the involvement of the non-classical monocytes in the protection against severe forms of malaria and confirmed the importance of the monocyte CD36 receptor as a protective factor for severity and death. To go further, we carried out experiments on a mouse model of cerebral malaria set up to mimic real-life conditions, i.e. late treatment leading to a resolution of the infection. C57BL/6 mice were infected with P. berghei ANKA (D0) and treated late with chloroquine. The kinetics of the monocyte subpopulations were monitored in terms of percentage and protein and gene expression in both blood, spleen and brain until resolution of infection (D12). The results suggest an involvement of classical and intermediate monocytes in neuroinflammation, unlike non-classical monocytes. At D12 a new influx of intermediate monocytes to the brain was observed, also suggesting a role of this subpopulation in the late resolution of neuroinflammation.Protein and gene analyses showed a favourable involvement of Nrf2, CD36, HO-1, CMHII, COX-2 and 12/15-LOX in the resolution of the infection. A second study was then conducted in Beninese children, with a larger number of patients and follow-up at D3 and D21. Two groups of subjects were included, with either uncomplicated malaria (n = 94) or cerebral malaria (n = 65). Overall, the results indicate that non-classical and intermediate monocytes were respectively involved in clinical improvement and patient survival. The expression of CD14, CD16, CD36 and HLA-DR was a protective factor against cerebral malaria. Interestingly, our results also show an association between a less active pro-oxidant response, malaria severity, and the occurrence of death. All these results shed new light on the involvement of monocytes/macrophages in cerebral malaria

Identification des facteurs immunitaires impliqués dans la neuroinflammation et sa résolution, dans un contexte de paludisme cérébral : rôle des réponses monocytaires

In 2020, malaria remains a major public health problem. Despite major scientific advances, it is still responsible for more than 400,000 deaths each year, mainly among children in Sub-Saharan Africa. Cerebral malaria is one of the most severe forms of malaria. Its physiopathology is complex, involving adhesion of Plasmodium falciparum-infected erythrocytes to the vascular endothelium in the brain. This mechanism leads to obstruction of blood flow, local inflammation, alteration of the blood-brain barrier and a range of cellular responses aiming to resolve the neuroinflammation process. Among these cells, monocytes/macrophages play a key role due to their ability to adapt to their microenvironment according to the different signals they perceive, thus modulating the pro/anti-inflammatory and pro/antioxidant balances that are essential to the resolution of cerebral malaria. Monocytes are composed of three subpopulations whose role in the physiopathology of cerebral malaria has been little studied and remains to be clarified. To complete this knowledge, an approach combining a mouse model and studies in Beninese patients was conducted. A first study was conducted in Beninese children with uncomplicated malaria, severe malarial anaemia, or cerebral malaria, in order to determine whether monocytic parameters are factors of severity and/or risk of death during severe malaria. The percentages and phenotypes of monocyte subpopulations obtained in the three groups of children on admission to the health centres (D0) were compared. The results highlighted the involvement of the non-classical monocytes in the protection against severe forms of malaria and confirmed the importance of the monocyte CD36 receptor as a protective factor for severity and death. To go further, we carried out experiments on a mouse model of cerebral malaria set up to mimic real-life conditions, i.e. late treatment leading to a resolution of the infection. C57BL/6 mice were infected with P. berghei ANKA (D0) and treated late with chloroquine. The kinetics of the monocyte subpopulations were monitored in terms of percentage and protein and gene expression in both blood, spleen and brain until resolution of infection (D12). The results suggest an involvement of classical and intermediate monocytes in neuroinflammation, unlike non-classical monocytes. At D12 a new influx of intermediate monocytes to the brain was observed, also suggesting a role of this subpopulation in the late resolution of neuroinflammation.Protein and gene analyses showed a favourable involvement of Nrf2, CD36, HO-1, CMHII, COX-2 and 12/15-LOX in the resolution of the infection. A second study was then conducted in Beninese children, with a larger number of patients and follow-up at D3 and D21. Two groups of subjects were included, with either uncomplicated malaria (n = 94) or cerebral malaria (n = 65). Overall, the results indicate that non-classical and intermediate monocytes were respectively involved in clinical improvement and patient survival. The expression of CD14, CD16, CD36 and HLA-DR was a protective factor against cerebral malaria. Interestingly, our results also show an association between a less active pro-oxidant response, malaria severity, and the occurrence of death. All these results shed new light on the involvement of monocytes/macrophages in cerebral malaria.En 2020, le paludisme reste un problème majeur de santé publique. Malgré des avancées scientifiques capitales, il est encore responsable de plus de 400 000 décès chaque année, principalement chez les enfants en Afrique Sub-saharienne. Le neuropaludisme est l'une des formes les plus sévères du paludisme. Sa physiopathologie est complexe, impliquant l'adhésion des érythrocytes infectés par Plasmodium falciparum à l'endothélium vasculaire dans le cerveau. Ce mécanisme conduit à une obstruction du flux sanguin, une inflammation locale, une altération de la barrière hémato-encéphalique et à un éventail de réponses cellulaires visant à résoudre le processus de neuroinflammation. Parmi ces cellules, les monocytes/macrophages jouent un rôle clé de par leur capacité à s'adapter à leur microenvironnement en fonction des différents signaux qu'ils perçoivent, modulant ainsi les balances pro/anti-inflammatoire et pro/antioxydante, essentielles à la résolution du neuropaludisme. Les monocytes sont composés de trois sous-populations dont le rôle dans la physiopathologie du neuropaludisme a été peu étudié et reste à éclaircir. Pour compléter ces connaissances, une approche combinant modèle murin et études chez des patients béninois a été menée. Une première étude a été conduite chez des enfants béninois présentant un paludisme simple, une anémie sévère palustre, ou un neuropaludisme dans le but de déterminer si les paramètres monocytaires constituent des facteurs de sévérité et/ou de risque de décès au cours d'un paludisme grave. Les pourcentages et phénotypes des sous-populations monocytaires obtenus chez les trois groupes d'enfants lors de leur admission dans les centres de santé (J0) ont été comparés. Les résultats ont permis de mettre en lumière l'implication des monocytes non classiques dans la protection vis-à-vis des formes sévères de paludisme et de confirmer l'importance du récepteur CD36 des monocytes comme facteur protecteur de sévérité et de survenue de décès. Pour aller plus loin, un travail a ensuite été mené sur un modèle murin de neuropaludisme mis en place pour se rapprocher des conditions réelles, à savoir un traitement tardif, et débouchant sur une résolution de l'infection. Des souris C57BL/6 ont été infectées par P. berghei ANKA (J0) et traitées tardivement à la chloroquine. La cinétique d'évolution des sous-populations monocytaires a été suivie en termes de pourcentage et d'expression protéique et génique, à la fois dans le sang, la rate et le cerveau, jusqu'à la résolution de l'infection (J12). Les résultats suggèrent une implication des monocytes classiques et intermédiaires dans la neuroinflammation, au contraire des monocytes non classiques. A J12 était observé un nouvel afflux de monocytes intermédiaires vers le cerveau, suggérant également un rôle de cette sous-population dans la résolution tardive de la neuroinflammation. Les analyses protéique et génique ont mis en évidence une implication favorable de Nrf2, CD36, HO-1, CMH-II, COX-2 et de la 12/15-LOX dans la résolution de l'infection. Une deuxième étude a ensuite été menée chez des enfants béninois, avec un plus grand nombre de patients et un suivi à J3 et J30. Deux groupes de sujets ont été inclus, présentant un paludisme simple (n = 94) ou un neuropaludisme (n = 65). Dans l'ensemble, les résultats indiquent que les monocytes non classiques et intermédiaires étaient respectivement impliqués dans l'amélioration clinique et la survie des patients. L'expression de CD14, CD16, CD36 et HLA-DR était un facteur protecteur vis-à-vis du neuropaludisme. De manière intéressante, nos résultats montrent également une association entre une réponse pro-oxydante moins active, la sévérité du paludisme, et la survenue de décès. L'ensemble de ces résultats apporte un nouvel éclairage sur l'implication des monocytes/macrophages au cours du neuropaludisme

Kinetics of monocyte subpopulations during experimental cerebral malaria and its resolution in a model of late chloroquine treatment

International audienceCerebral malaria (CM) is one of the most severe forms of malaria and is a neuropathology that can lead to death. Monocytes have been shown to accumulate in the brain microvasculature at the onset of neurological symptoms during CM. Monocytes have a remarkable ability to adapt their function to their microenvironment from pro-inflammatory to resolving activities. This study aimed to describe the behavior of monocyte subpopulations during infection and its resolution. C57BL/6 mice were infected with the Plasmodium berghei ANKA strain and treated or not with chloroquine (CQ) on the first day of the onset of neurological symptoms (day 6) for 4 days and followed until day 12 to mimic neuroinflammation and its resolution during experimental CM. Ly6C monocyte subpopulations were identified by flow cytometry of cells from the spleen, peripheral blood, and brain and then quantified and characterized at different time points. In the brain, the Ly6C int and Ly6C low monocytes were associated with neuroinflammation, while Ly6C hi and Ly6C int were mobilized from the peripheral blood to the brain for resolution. During neuroinflammation, CD36 and CD163 were both involved via splenic monocytes, whereas our results suggest that the low CD36 expression in the brain during the neuroinflammation phase was due to degradation. The resolution phase was characterized by increased expressions of CD36 and CD163 in blood Ly6C low monocytes, a higher expression of CD36 in the microglia, and restored high expression levels of CD163 in Ly6C hi monocytes localized in the brain. Thus, our results suggest that increasing the expressions of CD36 and CD163 specifically in the brain during the neuroinflammatory phase contributes to its resolution

Monocytes, particularly nonclassical ones, lose their opsonic and nonopsonic phagocytosis capacity during pediatric cerebral malaria

International audienceIntroduction Innate immunity is crucial to reducing parasite burden and contributing to survival in severe malaria. Monocytes are key actors in the innate response and, like macrophages, are plastic cells whose function and phenotype are regulated by the signals from the microenvironment. In the context of cerebral malaria (CM), monocyte response constitutes an important issue to understand. We previously demonstrated that decreased percentages of nonclassical monocytes were associated with death outcomes in CM children. In the current study, we postulated that monocyte phagocytosis function is impacted by the severity of malaria infection. Methods To study this hypothesis, we compared the opsonic and nonopsonic phagocytosis capacity of circulant monocytes from Beninese children with uncomplicated malaria (UM) and CM. For the CM group, samples were obtained at inclusion (D0) and 3 and 30 days after treatment (D3, D30). The phagocytosis capacity of monocytes and their subsets was characterized by flow cytometry and transcriptional profiling by studying genes known for their functional implication in infected-red blood cell (iRBC) elimination or immune escape. Results Our results confirm our hypothesis and highlight the higher capacity of nonclassical monocytes to phagocyte iRBC. We also confirm that a low number of nonclassical monocytes is associated with CM outcome when compared to UM, suggesting a mobilization of this subpopulation to the cerebral inflammatory site. Finally, our results suggest the implication of the inhibitory receptors LILRB1, LILRB2, and Tim3 in phagocytosis control. Discussion Taken together, these data provide a better understanding of the interplay between monocytes and malaria infection in the pathogenicity of CM

Changes in monocyte subsets are associated with clinical outcomes in severe malarial anaemia and cerebral malaria

Monocytes are plastic heterogeneous immune cells involved in host-parasite interactions critical for malaria pathogenesis. Human monocytes have been subdivided into three populations based on surface expression of CD14 and CD16.We hypothesised that proportions and phenotypes of circulating monocyte subsets can be markers of severity or fatality in children with malaria. To address this question, we compared monocytes sampled in children with uncomplicated malaria, severe malarial anaemia, or cerebral malaria. Flow cytometry was used to distinguish and phenotype monocyte subsets through CD14, CD16, CD36 and TLR2 expression. Data were first analysed by univariate analysis to evaluate their link to severity and death. Second, multinomial logistic regression was used to measure the specific effect of monocyte proportions and phenotypes on severity and death, after adjustments for other variables unrelated to monocytes. Multivariate analysis demonstrated that decreased percentages of non-classical monocytes were associated with death, suggesting that this monocyte subset has a role in resolving malaria. Using univariate analysis, we also showed that the role of non-classical monocytes involves a mostly anti-inflammatory profile and the expression of CD16. Further studies are needed to decipher the functions of this sub-population during severe malaria episodes, and understand the underlying mechanisms

Terminalia albida treatment improves survival in experimental cerebral malaria through reactive oxygen species scavenging and anti-inflammatory properties

International audienceBackground: The development of Plasmodium resistance to the last effective anti-malarial drugs necessitates the urgent development of new anti-malarial therapeutic strategies. To this end, plants are an important source of new molecules. The objective of this study was to evaluate the anti-malarial effects of Terminalia albida, a plant used in Guinean traditional medicine, as well as its anti-inflammatory and antioxidant properties, which may be useful intreating cases of severe malaria.Methods: In vitro antiplasmodial activity was evaluated on a chloroquine-resistant strain of Plasmodium falciparum (K-1). In vivo efficacy of the plant extract was measured in the experimental cerebral malaria model based on Plasmodium berghei (strain ANKA) infection. Mice brains were harvested on Day 7–8 post-infection, and T cells recruitment to the brain, expression levels of pro- and anti-inflammatory markers were measured by flow cytometry, RT-qPCR and ELISA. Non-malarial in vitro models of inflammation and oxidative response were used to confirm Terminalia albida effects. Constituents of Terminalia albida extract were characterized by ultra‐high performance liquid chromatography coupled with high resolution mass spectrometry. Top ranked compounds were putatively identified using plant databases and in silico fragmentation patterns.Results: In vitro antiplasmodial activity of Terminalia albida was confirmed with an IC50 of 1.5 μg/mL. In vivo, Terminalia albida treatment greatly increased survival rates in P. berghei-infected mice. Treated mice were all alive until Day 12, and the survival rate was 50% on Day 20. Terminalia albida treatment also significantly decreased parasitaemia by 100% on Day 4 and 89% on Day 7 post-infection. In vivo anti-malarial activity was related to anti-inflammatory properties, as Terminalia albida treatment decreased T lymphocyte recruitment and expression of pro-inflammatory markers in brains of treated mice. These properties were confirmed in vitro in the non-malarial model. In vitro, Terminalia albida also demonstrated a remarkable dosedependent neutralization activity of reactive oxygen species. Twelve compounds were putatively identified in Terminalia albida stem bark. Among them, several molecules already identified may be responsible for the different biological activities observed, especially tannins and triterpenoids

From genomic to LC-MS/MS evidence: Analysis of PfEMP1 in Benin malaria cases

International audienceBackground PfEMP1 is the major protein from parasitic origin involved in the pathophysiology of severe malaria, and PfEMP1 domain subtypes are associated with the infection outcome. In addition, PfEMP1 variability is endless and current publicly available protein repositories do not reflect the high diversity of the sequences of PfEMP1 proteins. The identification of PfEMP1 protein sequences expressed with samples remains challenging. The aim of our study is to identify the different PfEMP1 proteins variants expressed within patient samples, and therefore identify PfEMP1 proteins domains expressed by patients presenting uncomplicated malaria or severe malaria in malaria endemic setting in Cotonou, Benin. Methods We performed a multi-omic approach to decipher PfEMP1 expression at the patient's level in different clinical settings. Using a combination of whole genome sequencing approach and RNA sequencing, we were able to identify new PfEMP1 sequences and created a new custom protein database. This database was used for protein identification in mass spectrometry analysis. Results The differential expression analysis of RNAsequencing data shows an increased expression of the var domains transcripts DBL alpha 1.7, DBL alpha 1.1, DBL alpha 2 and DBL beta 12 in samples from patients suffering from Cerebral Malaria compared to Uncomplicated Malaria. Our approach allowed us to attribute PfEMP1 sequences to each sample and identify new peptides associated to PfEMP1 proteins in mass spectrometry. Conclusion We highlighted the diversity of the PfEMP1 sequences from field sample compared to reference sequences repositories and confirmed the validity of our approach. These findings should contribute to further vaccine development strategies based on PfEMP1 proteins

Identification of Plasmodium falciparum and host factors associated with cerebral malaria: description of the protocol for a prospective, case-control study in Benin (NeuroCM)

International audienceIn 2016, an estimated 216 million cases and 445 000 deaths of malaria occurred worldwide, in 91 countries. In Benin, malaria causes 26.8% of consultation and hospitalisation motif in the general population and 20.9% in children under 5 years old.The goal of the NeuroCM project is to identify the causative factors of neuroinflammation in the context of cerebral malaria. There are currently very few systematic data from West Africa on the aetiologies and management of non-malarial non-traumatic coma in small children, and NeuroCM will help to fill this gap. We postulate that an accurate understanding of molecular and cellular mechanisms involved in neuroinflammation may help to define efficient strategies to prevent and manage cerebral malaria.Ethics approval for the NeuroCM study has been obtained from Comité National d'Ethique pour la Recherche en santé of Benin (n°67/MS/DC/SGM/DRFMT/CNERS/SA; 10/17/2017). NeuroCM study has also been approved by Comité consultatif de déontologie et d'éthique of Institut de Recherche pour le Développement (IRD; 10/24/2017). The study results will be disseminated through the direct consultations with the WHO's Multilateral Initiative on Malaria (TDR-MIM) and Roll Back Malaria programme, through scientific meetings and peer-reviewed publications in scientific or medical journals, and through guidelines and booklets