The hidden pathologies of malaria
Abstract
Individuals from malaria-endemic regions often acquire partial immunity after multiple repeated infections throughout their lives. This partial immunity ...prevents them from developing severe complications and they often remain asymptomatic with a persistent, low parasite density in the blood, and therefore the necessity for treatment is neglected. These patients with chronic, asymptomatic malaria serve as a reservoir for Plasmodium parasite transmission, becoming a major obstacle for eradication efforts. The constant exposure to malaria infection may have benefits in the short term by conferring protection from acute, severe malaria; however, it may cause substantially more harm in the long term. Rather than the parasite burden itself, the complications induced by the dysregulated immune responses and the tissue damage done by the parasites and their products can cause chronic and irreversible suffering. Furthermore, the complete clearance of parasites in the body may not lead to complete recovery from the disease as complications can still persist. The fact that there are chronic pathologies caused by malaria that mostly remain obscure and have the potential to cause a serious burden has recently been gaining attention. Here, we present and discuss the evidence of unforeseen pathologies and the risks associated with malaria.
•Chloroquine/hydroxychloroquine is an old anti-malarial drug belongs to 4-aminoquinolines.•Chloroquine has additional anti-virus, anti-bacteria, anti-protozoan, anti-autoimmunity and anti-cancer ...effects.•Mechanism of action of chloroquine in malaria and other diseases is not understood well.•Chloroquine directly targets Plasmodium hemoglobin degradation pathway.•In addition, chloroquine may directly target host’s autophagy, innate and adaptive immunity in malaria.
Due to the rapid onset and spread of the COVID-19 pandemic, the treatment of COVID-19 patients by hydroxychloroquine alone or in combination with other drugs has captured a great deal of attention and triggered considerable debate. Historically, the worldwide use of quinoline based-drugs has led to a spectacular reduction in death from malaria. Unfortunately, scientists have been forced to seek alternative drugs to treat malaria due to the emergence of chloroquine-resistant parasites in the 1960s. The repurposing of hydroxychloroquine against viral infections, various types of cancer and autoimmune diseases has been ongoing for more than 70 years, with no clear understanding of its mechanism of action (MOA). Here, we closely examine the MOA of this old but influential drug in and beyond malaria. Better insights into how chloroquine targets the host’s cellular and immune responses may help to develop applications against to new pathogens and diseases, and perhaps even restore the clinical utility of chloroquine against malaria.
Aluminum-based adjuvants (aluminum salts or alum) are widely used in human vaccination, although their mechanisms of action are poorly understood. Here we report that, in mice, alum causes cell death ...and the subsequent release of host cell DNA, which acts as a potent endogenous immunostimulatory signal mediating alum adjuvant activity. Furthermore, we propose that host DNA signaling differentially regulates IgE and IgG1 production after alum-adjuvanted immunization. We suggest that, on the one hand, host DNA induces primary B cell responses, including IgG1 production, through interferon response factor 3 (Irf3)-independent mechanisms. On the other hand, we suggest that host DNA also stimulates 'canonical' T helper type 2 (T(H)2) responses, associated with IgE isotype switching and peripheral effector responses, through Irf3-dependent mechanisms. The finding that host DNA released from dying cells acts as a damage-associated molecular pattern that mediates alum adjuvant activity may increase our understanding of the mechanisms of action of current vaccines and help in the design of new adjuvants.
The complexity of the immune system mirrors its manifold mechanisms of host-microbe interactions. A relatively simplified view was posited after the identification of host innate immune receptors ...that their distinct mechanisms of sensing "microbial signatures" create unique molecular switches to trigger the immune system. Recently, more sophisticated and cooperative strategies for these receptors have been revealed during receptor-ligand interactions, trafficking, and intra- and intercellular signaling, in order to deal with a diverse range of microbes. Continued mapping of the complex networks of host-microbe interactions may improve our understanding of self/non-self discrimination in immunity and its intervention.
Abstract
Cerebral malaria (CM) is a life-threatening complication of the malaria disease caused by Plasmodium falciparum infection and is responsible for the death of half a million people annually. ...The molecular pathogenesis underlying CM in humans is not completely understood, although sequestration of infected erythrocytes in cerebral microvessels is thought to play a major role. In contrast, experimental cerebral malaria (ECM) models in mice have been thought to be distinct from human CM, and are mainly caused by inflammatory mediators. Here, to understand the spatial distribution and the potential sequestration of parasites in the whole-brain microvessels during a mouse model of ECM, we utilized the new tissue-clearing method CUBIC (Clear, Unobstructed, Brain/Body Imaging Cocktails and Computational analysis) with light-sheet fluorescent microscopy (LSFM), and reconstructed images in three dimensions (3D). We demonstrated significantly greater accumulation of Plasmodium berghei ANKA (PbANKA) parasites in the olfactory bulb (OB) of mice, compared with the other parts of the brain, including the cerebral cortex, cerebellum and brainstem. Furthermore, we show that PbANKA parasites preferentially accumulate in the brainstem when the OB is surgically removed. This study therefore not only highlights a successful application of CUBIC tissue-clearing technology to visualize the whole brain and its microvessels during ECM, but it also shows CUBIC’s future potential for visualizing pathological events in the whole ECM brain at the cellular level, an achievement that would greatly advance our understanding of human cerebral malaria.
A new method to visualize cerebral malaria
Particulates such as silica crystal (silica) and aluminum salts (alum) activate the inflammasome and induce the secretion of proinflammatory cytokines in macrophages. These particulates also induce ...the production of immunoglobulin E via a T helper 2 (Th2) cell-associated mechanism. However, the mechanism involved in the induction of type 2 immunity has not been elucidated. Here, we showed that silica and alum induced lipopolysaccharide-primed macrophages to produce the lipid mediator prostaglandin E
2 (PGE
2) and interleukin-1β (IL-1β). Macrophages deficient in the inflammasome components caspase 1, NALP3, and ASC revealed that PGE
2 production was independent of the NALP3 inflammasome. PGE
2 expression was markedly reduced in PGE synthase-deficient (
Ptges
−/−) macrophages, and
Ptges
−/−mice displayed reduced antigen-specific serum IgE concentrations after immunization with alum or silica. Our results indicate that silica and alum regulate the production of PGE
2 and that the induction of PGE
2 by particulates controls the immune response in vivo.
► Silica and alum induced Mϕs to produce PGE
2 ► The inflammasome was not involved in silica- and alum-induced PGE
2 production ► Silica- and alum-induced PGE
2 regulate IgE production in vivo ► Lysosomal damage triggered PGE
2 production via the activation of Syk and p38
Particulates and crystals stimulate the immune system to induce inflammatory responses. Several nanometer- to micrometer-sized particulates, such as particle matter 2.5 (PM2.5), diesel particles, and ...sand dust, induce pulmonary inflammation and allergic asthma. Conversely, nanometer- to micrometer-sized crystal, sphere, and hydrogel forms of aluminum salts (referred to as "alum") have been used as vaccine adjuvants to enhance antibody responses in animals and humans. Although most of these particulates induce type-2 immune responses in vivo, the molecular and immunological mechanisms of action as a vaccine adjuvant are poorly understood. In this review, recent advances in particulate adjuvant research from the standpoint of innate immune responses are discussed.
CpG DNA, a ligand for Toll-like receptor 9 (TLR9), has been one of the most promising immunotherapeutic agents. Although there are several types of potent humanized CpG oligodeoxynucleotide (ODN), ...developing “all-in-one” CpG ODNs activating both B cells and plasmacytoid dendritic cells forming a stable nanoparticle without aggregation has not been successful. In this study, we generated a novel nanoparticulate K CpG ODN (K3) wrapped by the nonagonistic Dectin-1 ligand schizophyllan (SPG), K3-SPG. In sharp contrast to K3 alone, K3-SPG stimulates human peripheral blood mononuclear cells to produce a large amount of both type I and type II IFN, targeting the same endosome where IFN-inducing D CpG ODN resides without losing its K-type activity. K3-SPG thus became a potent adjuvant for induction of both humoral and cellular immune responses, particularly CTL induction, to coadministered protein antigens without conjugation. Such potent adjuvant activity of K3-SPG is attributed to its nature of being a nanoparticle rather than targeting Dectin-1 by SPG, accumulating and activating antigen-bearing macrophages and dendritic cells in the draining lymph node. K3-SPG acting as an influenza vaccine adjuvant was demonstrated in vivo in both murine and nonhuman primate models. Taken together, K3-SPG may be useful for immunotherapeutic applications that require type I and type II IFN as well as CTL induction.
Heparin induces NET formation via a novel pathway
Abstract
Heparin is used extensively as an anticoagulant in a broad range of diseases and procedures; however, its biological effects are not limited ...to coagulation and remain incompletely understood. Heparin usage can lead to the life-threatening complication known as heparin-induced thrombocytopenia (HIT), caused by the development of antibodies against heparin/PF4 complexes. Here, we demonstrate the ability of heparin to induce neutrophil extracellular traps (NETs). NETs occurred with cell lysis and death, but live neutrophils releasing extracellular DNA strands, known as vital NETs, also occurred abundantly. Formation of NETs was time and dose dependent, and required reactive oxygen species and neutrophil elastase. Other compounds related to heparin such as low molecular weight heparin, fondaparinux and heparan sulfate either failed to induce NETs, or did so to a much lesser extent. Our findings suggest the ability of heparin to directly induce NET formation should be considered in the context of heparin treatment and HIT pathogenesis.
The innate immune system recognizes influenza A virus via TLR 7 or retinoic acid-inducible gene I in a cell-type specific manner in vitro, however, physiological function(s) of the MyD88- or ...interferon-beta promoter stimulator 1 (IPS-1)-dependent signaling pathways in antiviral responses in vivo remain unclear. In this study, we show that although either MyD88- or IPS-1-signaling pathway was sufficient to control initial antiviral responses to intranasal influenza A virus infection, mice lacking both pathways failed to show antiviral responses, resulting in increased viral load in the lung. By contrast, induction of B cells or CD4 T cells specific to the dominant hemagglutinin or nuclear protein Ags respectively, was strictly dependent on MyD88 signaling, but not IPS-1 signaling, whereas induction of nuclear protein Ag-specific CD8 T cells was not impaired in the absence of either MyD88 or IPS-1. Moreover, vaccination of TLR7- and MyD88-deficient mice with inactivated virus failed to confer protection against a lethal live virus challenge. These results strongly suggest that either the MyD88 or IPS-1 signaling pathway is sufficient for initial antiviral responses, whereas the protective adaptive immune responses to influenza A virus are governed by the TLR7-MyD88 pathway.
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