Experimental cerebral malaria progresses independently of the Nlrp3 inflammasome

Cerebral malaria is the most severe complication of Plasmodium falciparum infection in humans and the pathogenesis is still unclear. Using the P. berghei ANKA infection model of mice, we investigated a potential involvement of Nlrp3 and the inflammasome in the pathogenesis of cerebral malaria. Nlrp3 mRNA expression was upregulated in brain endothelial cells after exposure to P. berghei ANKA. Although β‐hematin, a synthetic compound of the parasites heme polymer hemozoin, induced the release of IL‐1β in macrophages through Nlrp3, we did not obtain evidence for a role of IL‐1β in vivo. Nlrp3 knock‐out mice displayed a delayed onset of cerebral malaria; however, mice deficient in caspase‐1, the adaptor protein ASC or the IL‐1 receptor succumbed as WT mice. These results indicate that the role of Nlrp3 in experimental cerebral malaria is independent of the inflammasome and the IL‐1 receptor pathway.     

Loss-of-function mutations in caspase recruitment domain-containing protein 14 (CARD14) are associated with a severe variant of atopic dermatitis

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Pathological role of Toll-like receptor signaling in cerebral malaria

Toll-like receptors (TLRs) recognize malaria parasites or their metabolites; however, their physiological roles in malaria infection in vivo are not fully understood. Here, we show that myeloid differentiation primary response gene 88 (MyD88)-dependent TLR signaling mediates brain pathogenesis of severe malaria infection, namely cerebral malaria (CM). A significant number of MyD88-, but not TIR domain containing adaptor-inducing IFN-beta (TRIF)-deficient or wild-type (WT) mice survived CM caused by Plasmodium berghei ANKA (PbA) infection. Although systemic parasitemia was comparable, sequestration of parasite and hemozoin load in the brain blood vessels was significantly lower in MyD88-deficient mice compared with those in TRIF-deficient or WT mice. Moreover, brain-specific pathological changes were associated with MyD88-dependent infiltration of CD8+, CCR5+ T cells and CD11c+ dendritic cells, including CD11c+, NK1.1+ and B220+ cells, and up-regulation of genes such as Granzyme B, Lipocalin 2, Ccl3 and Ccr5. Further studies using mice lacking various TLRs suggest that TLR2 and TLR9, but not TLR4, 5 and 7, were involved in CM. These results strongly suggest that TLR2- and/or TLR9-mediated, MyD88-dependent brain pathogenesis may play a critical role in CM, the lethal complication during PbA infection.     

Murine cerebral malaria development is independent of toll-like receptor signaling

Malaria pigment hemozoin was reported to activate the innate immunity by Toll-like receptor (TLR)-9 engagement. However, the role of TLR activation for the development of cerebral malaria (CM), a lethal complication of malaria infection in humans, is unknown. Using Plasmodium berghei ANKA (PbA) infection in mice as a model of CM, we report here that TLR9-deficient mice are not protected from CM. To exclude the role of other members of the TLR family in PbA recognition, we infected mice deficient for single TLR1, -2, -3, -4, -6, -7, or -9 and their adapter proteins MyD88, TIRAP, and TRIF. In contrast to lymphotoxin alpha-deficient mice, which are resistant to CM, all TLR-deficient mice were as sensitive to fatal CM development as wild-type control mice and developed typical microvascular damage with vascular leak and hemorrhage in the brain and lung, together with comparable parasitemia, thrombocytopenia, neutrophilia, and lymphopenia. In conclusion, the present data do not exclude the possibility that malarial molecular motifs may activate the innate immune system. However, TLR-dependent activation of innate immunity is unlikely to contribute significantly to the proinflammatory response to PbA infection and the development of fatal CM.     

Association between polymorphisms in caspase recruitment domain containing protein 15 and allergy in two German populations

BACKGROUND: Early exposure to microbial matter such as LPS may influence the development of asthma and allergies by activation of innate immunity pathways as indicated by studies in farming environments. Recently, polymorphisms in caspase recruitment domain containing protein 15 (CARD15), an intracellular LPS receptor protein, have been associated with Crohn's disease. Because these polymorphisms lead to changes in LPS recognition, they may affect the development of asthma and allergies. OBJECTIVE: We genotyped a large population of German schoolchildren (N = 1872) from East and West Germany for 3 functional relevant CARD15 polymorphisms for their role in the development of asthma and allergy. METHODS: By use of parental questionnaires, skin prick testing, pulmonary function tests, bronchial challenge tests, and measurements of serum IgE levels, children were phenotyped for the presence of atopic diseases. Genotyping was performed with PCR-based restriction enzyme assays. To assess associations between atopic phenotypes and genotypes standard statistical procedures were applied. RESULTS: Children with the polymorphic allele C2722 had a more than 3-fold risk to develop allergic rhinitis (P <.001) and an almost 2-fold risk for atopic dermatitis (P <.05). Furthermore, the T2104 allele was associated with an almost 2-fold risk for allergic rhinitis (P <.05). When a C insertion at position 3020 was present, the risk of atopy increased by 50% (P <.05) and serum IgE levels were elevated (P <.01). CONCLUSION: The shared genetic background between Crohn's disease and atopy may indicate that an impaired recognition of microbial exposures results in an insufficient downregulation of excessive immune responses, giving rise to either T(H)2 dominated allergies or T(H)1 related Crohn's disease.     

TIR domain-containing adaptors define the specificity of TLR signaling

The concept that Toll-like receptors (TLRs) recognize specific molecular patterns in various pathogens has been established. In signal transduction via TLRs, MyD88, which harbors a Toll/IL-1 receptor (TIR)-domain and a death domain, has been shown to link between TLRs and MyD88-dependent downstream events leading to proinflammatory cytokine production and splenocyte proliferation. However, recent studies using MyD88-deficient mice have revealed that some TLRs possess a MyD88-independent pathway, which is represented by interferon (IFN)-beta production induced by LPS stimulation. This indicates that additional signaling molecules other than MyD88 exist in the TLR signaling pathway. Indeed, two additional TIR domain-containing adaptors, TIRAP/Mal and TRIF, have recently been identified. Both define the specific biological responses of each TLR.     

锌转运蛋白9在实验性脑疟小鼠脑内的表达改变

目的 探讨锌离子转运蛋白9在实验性脑疟小鼠大脑皮层和海马中的表达改变。方法 6周龄C57BL/6小鼠随机分为2组,对照组给予正常饮食,感染组（PbA组）经腹腔注射1×10 6个伯氏疟原虫（P.bergheiANKA）寄生的红细胞,采用吉姆萨染色检测红细胞感染率,并监测小鼠生存率;采用Western blot和免疫组织化学染色检测ZnT9在大脑皮层和海马中的表达改变;激光共聚焦扫描显微镜检测ZnT9在小鼠大脑中的共定位表达。结果 PbA感染组在感染后5-7天逐渐出现脑疟症状,外周血红细胞内有大量感染的疟原虫存在。ZnT9主要定位于神经元中,ZnT9在实验性脑疟小鼠大脑皮层和海马中表达降低。结论 ZnT9在实验性脑疟小鼠神经元细胞中表达降低,可能参与调控锌离子在神经元内稳态的维持。     

Fgf signaling induces posterior neuroectoderm independently of Bmp signaling inhibition.

Whereas according to the neural default model, neural specification is induced by extracellular inhibitors of bone morphogenetic proteins (Bmps), the role of fibroblast growth factors (Fgfs) during neural induction is heavily debated. Here, we show that, in zebrafish embryos, Bmps and Fgfs play differential roles during the induction and patterning of the anterior vs. the posterior neuroectoderm. Induction of anterior neuroectoderm, giving rise to fore- and midbrain, is accomplished by Bmp inhibition, with Fgfs playing a moderate posteriorizing/patterning role, possibly by blocking Bmp signaling at the level of Smad proteins. In contrast, in the posterior-most neuroectoderm, which is located in marginal regions of the early gastrula embryo to give rise to spinal cord and hindbrain, Fgfs play a neural-inducing rather than a neural-patterning role. This Fgf-dependent posterior neural induction takes place during late blastula and early gastrula stages, after mesoderm has been induced and cannot be blocked by Bmps or the Bmp target gene and downstream effector Delta Np63 alpha, indicating that here, Fgfs act independently of Bmp signaling inhibition.     

Induction of experimental cerebral malaria is independent of TLR2/4/9

The contribution of the Toll-like receptor (TLR) cascade to the pathogenesis of cerebral malaria (CM) is controversially discussed. TLR2 and TLR9 were reported to be involved in the induction of CM in a study while recently TLR signaling was shown to be dispensable for the development of CM. Using Plasmodium berghei ANKA (PbA) infection of mice as a model of CM, we demonstrate here that the induction of CM is independent of TLR2, 4 and 9. Using triple TLR2/4/9-deficient mice, we exclude synergistic effects between the single TLRs that have been previously implicated with malaria pathology. In conclusion, this study shows that the activation of the innate immune response and the development of CM is not dependent on the engagement of TLR2/4/9.     

Caspase 9及其相关分子基因表达水平改变对同型半胱氨酸内皮凋亡的影响

目的 了解caspase 3信号传导通路中上游分子Bcl 2、细胞色素c（cytochrome-c）、caspase 9在同型半胱氨酸作用下的人脐静脉血管内皮细胞内的mRNA及蛋白表达水平的改变，揭示线粒体参与信号传导链在caspase 3所介导的内皮细胞凋亡过程中的作用。方法 培养人脐静脉内皮细胞，用不同浓度同型半胱氨酸作用于细胞后，用逆转录-聚合酶链反应及Western印迹分别检测各分子基因及蛋白表达水平的改变。结果 Bcl 2、cytochrome-c和caspase 9在同型半胱氨酸作用下mRNA及蛋白表达水平下降，并且随同型半胱氨酸浓度的升高而降低。结论 Bcl 2可能参与了同型半胱氨酸促进细胞凋亡的信号传导途径。Caspase 3没有通过上游分子apoptosome和caspase 9途径活化。这些研究结果提示，同型半胱氨酸诱导细胞凋亡并不是通过以线粒体凋亡通路为主的信号传导通路。     

A novel Sushi domain-containing protein of Plasmodium falciparum

Using bioinformatics analyses of the completed malaria genome sequence, we have identified a novel protein with a potential role in erythrocyte invasion. The protein (PFD0295c, ) has a predicted signal sequence and transmembrane domain and a sequence near the C-terminus of the protein shows significant similarity with Sushi domains. These domains, which exist in a wide variety of complement and adhesion proteins, have previously been shown to be involved in protein-protein and protein-ligand interactions. Orthologous genes have also been identified in the genomes of several other Plasmodium species, suggesting a conserved function for this protein in Plasmodium. Our results show that this protein is located in apical organelles and we have therefore designated the protein apical Sushi protein (ASP). We show that the expression of ASP is tightly regulated in the intraerythrocytic stages of the parasite and that it undergoes post-translational proteolytic processing. Based on our observations of timing of expression, location and proteolytic processing, we propose a role for ASP in erythrocyte invasion.     

Selective induction of Kunitz-type protease inhibitor domain-containing amyloid precursor protein mRNA after persistent focal ischemia in rat cerebral cortex

An induction of amyloid precursor protein (APP) mRNA was examined in a middle cerebral artery occlusion model of rats using Northern blot analyses. The level of tubulin mRNA was measured as an internal standard. With persistent focal ischemia, APP mRNA species which contain a Kunitz-type protease inhibitor (KPI) domain were induced in the rat cerebral cortex from 1 to 21 days after the insult with a maximum at 4 days, while total amounts of APP mRNA did not change. No change was observed in the level of tubulin mRNA. These results suggest a selective role of APP species which contain the KPI domain in focal cerebral ischemia.     

Potential serological biomarkers of cerebral malaria

Biomarkers have been used to diagnose and prognosticate the progress and outcome of many chronic diseases such as neoplastic and non communicable diseases. However, only recently did the field of malaria research move in the direction of actively identifying biomarkers that can accurately discriminate the severe forms of malaria. Malaria continues to be a deadly disease, killing close to a million people (mostly children) every year. One life-threatening complication of malaria is cerebral malaria (CM). Studies carried out in Africa have demonstrated that even with the best treatment, as high as 15-30% of CM patients die and about 10-24% of CM survivors suffer short-or long-term neurological impairment. The transition from mild malaria to CM can be sudden and requires immediate intervention. Currently, there is no biological test available to confirm the diagnosis of CM and its complications. It is hoped that development of biomarkers to identify CM patients and potential risk for adverse outcomes would greatly enhance better intervention and clinical management to improve the outcomes. We review here what is currently known regarding biomarkers for CM outcomes. A Pub Med literature search was performed using the following search terms: "malaria," "cerebral malaria," "biomarkers," "mortality" and "neurological sequelae." This search revealed a paucity of usable biomarkers for CM management. We propose three main areas in which researchers can attempt to identify CM biomarkers: 1) early biomarkers, 2) diagnostic biomarkers and 3) prognostic biomarkers.     

Role of immune complexes in cerebral malaria

To investigate the involvement of immune complexes in the pathogenesis of cerebral malaria, a comparative study between Plasmodium berghei infected Swiss albino mice and BALB/c mice was conducted. Rise in parasitemia was found to be same with differences in manifestation of disease and mortality, level of immune complexes and histopathology. Increased parasitized red cells with swelling of endothelial cells in the brain capillaries along with increased levels of circulating immune complexes were observed in the BALB/c mice.     

In the eye of experimental cerebral malaria

Cerebral malaria is the most severe complication of Plasmodium falciparum infection, accounting for 1 million deaths per year. We characterized the murine disease using in vivo magnetic resonance imaging (MRI) at 4.7 T, proving that ischemic edema is responsible for fatality. The aim of the present study was to identify early markers of experimental cerebral malaria using very high field conventional MRI (11.75 T). CBA/J mice infected with Plasmodium berghei ANKA were observed at an early stage of the disease, before the onset of detectable brain swelling and at the most acute stage of cerebral malaria. Herein, we report the first detection of damage to the optic and trigeminal nerves on T(2)-weighted MRI. The trigeminal nerves appeared hypointense, with significantly reduced diameter and cross-sectional area. The optic nerves were hypointense and often not visible. In addition, the internerve distance between the optic nerves was significantly and progressively reduced between the early and severest stages. Cranial nerve injury was the earliest anatomic hallmark of the disease, visible before brain edema became detectable. Thus, cranial nerve damage may manifest in neurologic signs, which may assist in the early recognition of cerebral malaria.     

Apical location of a novel EGF-like domain-containing protein of Plasmodium falciparum

Using bioinformatics analyses of the unfinished malaria genome sequence, we have identified a novel protein of Plasmodium falciparum that contains two epidermal growth factor (EGF)-like domains near the C-terminus of the protein. The sequence contains a single open reading frame of 1572bp with the potential to encode a protein of 524 residues containing hydrophobic regions at the extreme N- and C-termini which appear to represent signal peptide and glycosylphosphatidylinositol (GPI)-attachment sites, respectively. RT-PCR analysis has confirmed that the novel gene is transcribed in asexual stages of P. falciparum. Antibodies to the EGF-like domains of the novel protein are highly specific and do not cross-react with the EGF-like domains of MSP1, MSP4, MSP5 or MSP8 expressed as GST fusion proteins. Antisera to the C-terminal fragments react with two bands of 80 and 36kDa in P. falciparum parasite lysates whereas antisera to the most N-terminal fusion protein only recognises the 80kDa band, suggesting that the novel protein may undergo processing in a similar way to MSP1 and MSP8, but with fewer cleavage events. Immunoblot analysis of stage-specific parasite samples reveals that the protein is present in trophozoites, schizonts and in isolated merozoites. The protein partitions in the detergent-enriched phase after Triton X-114 fractionation and is localised to the surfaces of trophozoites, schizonts and free merozoites in an apical distribution. Based on the accepted nomenclature in the field we now designate this protein MSP10. We have shown that the MSP10 fusion proteins are in a conformation that can be recognised by human immune sera and that there is very limited sequence diversity in an approximately lkb region of MSP10, encompassing the two EGF-like domains. A sequence similar to MSP10 can be identified in the available P. yoelii genomic sequence, offering the possibility of ascertaining whether this novel protein can induce host protective responses in an in vivo model.     

Effects of monocyte chemoattractant protein 1 on blood-borne cell recruitment after transient focal cerebral ischemia in mice

Monocyte chemoattractant protein 1 (MCP-1) plays an important role in inflammatory reactions following cerebral ischemia. It is known that MCP-1 overexpression leads to increased infarct volume and elevated hematogenous cell recruitment, while MCP-1-deficient mice develop smaller infarcts. It was supposed that MCP-1 dependent macrophage recruitment might be the underlying mechanism of ischemic brain damage but a precise distinction of local microglia and invading macrophages was not performed. In this study we investigated the differential role of MCP-1 on inflammatory cells in MCP-1-deficient mice, using green fluorescent protein (GFP) transgenic bone marrow chimeras. After 30-min of focal cerebral ischemia microglia was rapidly activated and was not different between MCP-1-deficient mice and wild type controls. Activated microglia outnumbered GFP-positive macrophages over the study period. Furthermore, macrophage infiltration was significantly reduced at day 7 in MCP-1-deficient animals (31.2±20.1 cells/mm²) compared to MCP-1 wild type mice (131.5±66.7 cells/mm², P<0.001). Neutrophils were also significantly reduced in MCP-1-deficient mice (62% on day 4% and 87% on day 7; P<0.001). This is the first investigation in cerebral ischemia showing that MCP-1 is necessary for recruiting blood-borne cells to the injury site whereas it does not affect the microglia activation and migration. However, the remarkable predominance of activated microglia and the additional attenuation of invading macrophages suggest that different mechanisms than macrophage recruitment are responsible for the MCP-1-mediated neuroprotective effects after experimental stroke.