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Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The liver stage of malaria, caused by the genus Plasmodium, is clinically silent, but immunologically significant. Ample evidence exists for an effective CD8(+) T cell response to this stage as well as the involvement of gammadeltaT cells and NK1.1(int) cells in immunized animal models. In contrast, there is little information concerning responses in a naive host. Here we report that several host gene expressions in the liver, spleen, and kidney of BALB/c mice are altered during the liver stage of Plasmodium yoelii infection. Really interesting new gene 3 (Ring3), semaphorin subclass 4 member G, glutamylcysteine synthetase, and p45 NF erythroid 2 were all up-regulated 24 h after infection with P. yoelii. Semaphorin subclass 4 member G expression was elevated in the kidney, whereas Ring3 was elevated in both spleen and kidney. The expression of TNF-alpha (TNF-alpha and IFN-gamma) were down-regulated in all three tissues tested except in infected spleen where IFN-gamma was elevated. P. yoelii-related host gene changes were compared with those in Toxoplasma gondii-infected livers. Ring3 expression increased 5-fold over control values, whereas expression of the other transcripts remained unchanged. TNF-alpha and IFN-gamma expressions were increased in the Toxoplasma-infected livers. The uniform increase of Ring3 expression in both Plasmodium- and Toxoplasma-infected livers suggests an innate immune response against parasitic infections, whereas the other gene expression changes are consistent with Plasmodium parasite-specific responses. Taken together, these changes suggest the immune responses to P. yoelii infection are both parasite and organ specific.
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PMID:Host responses to Plasmodium yoelii hepatic stages: a paradigm in host-parasite interaction. 1116 Feb 43

The extreme rarity of micronucleated reticulocytes (RETs) in the peripheral blood of non-splenectomized humans has precluded facile enumeration of these cells, as well as evaluation of this endpoint as an index of cytogenetic damage. In this report, we describe a high-throughput, single-laser flow cytometric system for scoring the incidence of micronuclei (MN) in newly formed human RETs. The procedure is based on an immunochemical reagent that differentially labels the most immature fraction of RETs from mature erythrocytes based on the expression level of the transferrin receptor (also known as CD71). The resolution of four erythrocyte populations (young RETs and mature erythrocytes, with and without MN) was achieved for human blood cells treated with phycoerythrin-conjugated anti-CD71, RNase, and either SYTOX Green or SYBR Green I nucleic acid dyes. Anti-glycophorin A labeling of erythroid cells (CyChrome conjugate) was also incorporated into the staining procedure to ensure that debris or other potential artifacts did not adversely impact the analyses. Instrument calibration procedures utilizing malaria-infected rodent erythrocytes were also developed, and are described. Using this analytical system, blood samples from 10 healthy non-splenectomized human volunteers were analyzed for micronucleus frequencies with a single-laser flow cytometer. Average micronucleus frequencies in the mature and most immature fraction of RETs were 0.016 and 0.19%, respectively. Blood samples from three healthy splenectomized volunteers were also evaluated. As expected, these samples exhibited higher micronucleus frequencies in the mature subset of erythrocytes (range 0.03-0.18%). The resulting data suggest that MN can be quantified in human erythrocyte populations with a single-laser flow cytometer, and that the frequency of MN cells in the youngest reticulocyte population approaches values expected in the absence of splenic selection against MN-erythrocytes. This high throughput system is potentially important for evaluating the value of the micronucleated reticulocyte endpoint as an index of chromosome breakage and/or chromosome segregational abnormalities in human populations.
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PMID:Enumeration of micronucleated CD71-positive human reticulocytes with a single-laser flow cytometer. 1190 50

Toxicity studies were performed with a chemically defined mixture of 25 groundwater contaminants, using dose levels considered to have environmental relevance. The mixture contained 19 organic compounds and six metals (shown below); the selection of these compounds was based primarily on the frequency of their occurrence in United States Environmental Protection Agency surveys of groundwater contamination in the vicinity of hazardous waste disposal sites. This report focuses primarily on 26-week drinking water toxicity studies with male and female F344/N rats and B6C3F(1) mice. The endpoints evaluated included histopathology, clinical pathology, neurobehavioral studies, and reproductive toxicity. Additional studies using this same chemical mixture are briefly reviewed in this report and include an evaluation of spermatogenesis in B6C3F(1) mice exposed to the chemical mixture for 13 weeks, a continuous breeding study with Sprague-Dawley rats and CD-1(R) Swiss mice, studies of myelotoxicity in B6C3F(1) mice exposed to the chemical mixture for up to 31.5 weeks, studies of immunosuppression in B6C3F(1) mice exposed for up to 13 weeks, in vitro mutagenicity assays in Salmonella typhimurium and Escherichia coli, and measures of genetic damage in bone marrow and peripheral blood of F344/N rats and B6C3F(1) mice in 2-week drinking water studies. In a 26-week drinking water study in which rats were administered the chemical mixture at composite contaminant concentrations of 0, 11, 38, 113, or 378 ppm, no deaths occurred and the body weight gain of high-dose males was slightly less than that of the controls. Water consumption decreased with dose and was 24% to 28% less than that of the controls at the highest concentration. Changes in organ weights occurred primarily in high-dose rats and included increased absolute and relative liver and kidney weights in females, increased relative kidney weight in males, and decreased absolute and relative thymus weights in males and females. Hematologic assessments indicated that rats receiving 378 ppm developed a microcytic anemia consistent with that accompanying iron depletion. Multiple foci of inflammation occurred in the liver of exposed rats. In high-dose females, these liver lesions were especially prominent and included bile duct and oval cell hyperplasia. Inflammation also occurred in the mesenteric lymph nodes, the adrenal gland, and the spleen. The amount of hemosiderin in the spleens of rats receiving the higher concentrations of the chemical mixture was less than normal. Components of a chemical mixture of 25 groundwater contaminants include acetone, aroclor 1260, arsenic, benzene, cadmium, carbon tetrachloride, chlorobenzene, chloroform, chromium, 1,1-dichloroethane, 1,2-dichloroethane, 1,1-dichloroethylene, 1,2-trans-dichloroethylene, di(2-ethylhexyl) phthalate, ethylbenzene, lead, mercury, methylene chloride, nickel, phenol, tetrachloroethylene, toluene, 1,1,1-trichloroethane, trichloroethylene, xylenes. In a 26-week study in which mice were exposed to the chemical mixture at concentrations of 0, 11, 38, 113, and 378 ppm in drinking water, there were no clear adverse effects noted in survival, weight gain, clinical pathology parameters, or histopathologic evaluations. Water consumption decreased with increasing dose, and water consumption by high-dose mice was approximately 40% less than that by the controls. In neurobehavioral assessments, no clear treatment-related effects were observed in measures of forelimb and hindlimb grip strength, hindlimb footsplay, motor activity, response to a thermal stimulus, or startle response in rats or mice evaluated at 6-week intervals throughout the 26- week drinking water studies. There were no effects on sperm morphology or motility or on estrous cycle length in rats or mice receiving the chemical mixture during the 26-week studies. Sperm concentration was decreased in F(1) CD-1(R) Swiss mice during continuous breeding studies, although there were no clear adverse effects on the fertility of Sprague-Dawley rats or CD-1(R) Swiss mice in th CD-1® Swiss mice in these studies. Pup weight, the number of live males, and the number of male pups per litter were slightly decreased in dosed rats in the continuous breeding study in rats; the number of live female mouse pups in litters born of the F(0) and F(1) generations was decreased in the 378 ppm group. The significance of these observations, if any, is not known. F(1) mice receiving 378 ppm had increased incidences of hepatic inflammation compared to the controls. In female B6C3F(1) mice that received the chemical mixture in drinking water at concentrations as high as 756 ppm for 2 weeks or 378 ppm for 13 weeks, assessments of immune function showed suppression of hematopoietic stem cells and antigen-induced antibody-forming cells. This was manifested by impaired resistance to challenge with a nonlethal strain of mouse malaria, Plasmodium yoelii. Additional evidence of an adverse effect on hematopoietic stem cells was demonstrated by decreases in the in vitro colony-forming ability of granulocyte-macrophage progenitor cells and erythroid precursor cells isolated from female mice that had received the chemical mixture at a concentration of 378 or 756 ppm in 31.5 week studies. Potential genotoxic effects of the chemical mixture to the bone marrow of F344/N rats and B6C3F(1) mice were assessed in 2-week drinking water studies with concentrations as high as 756 ppm. Small increases in sister chromatid exchanges and micronucleated polychromatic erythrocytes occurred in the bone marrow of dosed male mice, and micronucleated polychromatic erythrocytes were also increased in dosed female mice. The chemical mixture did not induce mutations in Salmonella typhimurium strains TA98 and TA100 and did not induce DNA damage in Escherichia coli with or without metabolic activation. In summary, rats receiving drinking water containing a mixture of 25 common groundwater contaminants at levels of potential environmental relevance developed inflammatory lesions in the liver, spleen, lymph nodes, and adrenal gland, as well as evidence of an iron deficiency anemia. The inflammatory lesions could not be predicted based on the known toxic effects of the individual components of the chemical mixture. Mice exposed to similar concentrations of the chemical mixture did not show adverse effects in a standard toxicity study but developed deficits in bone marrow function, evidence of genetic damage, hepatic inflammation, and immunosuppression in other studies that generally included exposures to higher concentrations or exposures of longer duration. A no-observed-adverse-effect level for histologic injury (granulomatous inflammation of the liver) was 11 ppm in rats; however, no clear evidence for histologic injury was seen in mice exposed to concentrations of the chemical mixture as high as 378 ppm in a standard 26-week study. NOTE: These studies were supported in part by funds from the Comprehensive Environmental Response, Compensation, and Liability Act trust fund (Superfund) by an interagency agreement with the Agency for Toxic Substances and Disease Registry, U.S. Public Health Service.
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PMID:NTP technical report on the toxicity studies of a Chemical Mixture of 25 Groundwater Contaminants Administered in Drinking Water to F344/N Rats and B6C3F(1) Mice. 1220 89

Inappropriately low reticulocytosis may exacerbate malarial anemia, but the under-lying mechanism is not clear. In this study, naive and infected mice were treated with recombinant murine erythropoietin (EPO), and the upstream events of erythropoiesis affected by blood-stage Plasmodium chabaudi AS were investigated. Malaria infection, with or without EPO treatment, led to a suboptimal increase in TER119(+) erythroblasts compared with EPO-treated naive mice. Furthermore, a lower percentage of TER119(+) erythroblasts in infected mice were undergoing terminal differentiation to become mature hemoglobin-producing erythroblasts. The impaired maturation of erythroblasts during infection was associated with a shift in the transferrin receptor (CD71) expression from the TER119(+) population to B220(+) population. Moreover, the suboptimal increase in TER119(+) erythroblasts during infection coincided with a blunted proliferative response by splenocytes to EPO stimulation in vitro, although a high frequency of these splenocytes expressed EPO receptor (EPOR). Taken together, these data suggest that during malaria, EPO-induced proliferation of early EPOR-positive erythroid progenitors is suppressed, which may lead to a suboptimal generation of TER119(+) erythroblasts. The shift in CD71 expression may result in impaired terminal maturation of these erythroblasts. Thus, inadequate reticulocytosis during malaria is associated with suppressed proliferation, differentiation, and maturation of erythroid precursors.
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PMID:Inappropriately low reticulocytosis in severe malarial anemia correlates with suppression in the development of late erythroid precursors. 1473 26

Erythropoietin is a growth factor for endothelial cells as well as for erythroid cells. In contrast to their proliferative response to physiological levels of erythropoietin, endothelial cells may respond to decreased levels by triggering a process called neocytolysis. Neocytolysis is the selective destruction of the youngest circulating red cells, which may be prompted by endothelial cells communicating with macrophages to stimulate phagocytosis of this unusual cell subset. We speculate that this is due to decreased production by endothelial cells of the macrophage-deactivating transforming growth factor-beta. The resulting proinflammatory phenotype may include macrophage production of thrombospondin, which forms bridges between adhesion molecules selectively expressed on young red cells (CD36) and the CD36/alphavbeta3 complex on macrophages that triggers phagocytosis. Alternatively, inflammatory mediators secreted by endothelial cells and macrophages during erythropoietin withdrawal may signal young red cells to expose phosphatidylserine, which would mark them for elimination via the normal pathway for aged red cell destruction. Neocytolysis has been demonstrated in returning astronauts and in polycythemic individuals at high altitude on descent to sea level. It contributes to the anemia of renal disease, is triggered by the rapidly falling levels of erythropoietin seen after intravenous administration, and may be the normal mechanism for reduction of red cell mass in newborns. It may play a role in chronic diseases including malaria and sickle cell anemia. New erythropoietin products and methods of administration avoid the intermittent rapid decreases associated with the stimulus for neocytolysis, but study of this phenomenon may yield further improvements in drug design.
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PMID:Erythropoietin withdrawal leads to the destruction of young red cells at the endothelial-macrophage interface. 1475 97

The recombinant congenic mouse strains AcB55 and AcB61 are extremely resistant to malaria (Plasmodium chabaudi AS) despite the presence of susceptibility alleles at the known Char1/Char2 resistance loci. Resistance in AcB55 and AcB61 is controlled by a locus on chromosome 3 (Char4) shown to be allelic with or tightly linked to a loss-of-function mutation in pyruvate kinase (Pklr). AcB55 and AcB61 show important splenomegaly prior to infection caused by the expansion of the red pulp, and display histological signs of extramedullary erythropoiesis in the liver. Examination of splenic cell populations by flow cytometry demonstrates elevated numbers of TER119-positive erythroid precursor cells (>30% of total spleen cells), while RNA expression studies show elevated expression of erythrocyte-specific transcripts such as globin, transferrin receptor, and Nramp2/Slc11a2 in the spleen of both strains. Hematological profiling in both strains is consistent with the presence of anemia as evidenced by low total erythrocyte counts, decreased hemoglobin, as well as abnormally high numbers of circulating reticulocytes (15-20%). These results strongly suggest that the mutant Pklr allele (Pklr(269A)) of AcB55/61 strains causes hemolytic anemia compensated by constitutive erythropoiesis, which in turn protects the mice against P. chabaudi infection. The possible molecular basis of the Pklr protective effect is discussed and is under current investigation in these two strains.
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PMID:Phenotypic expression of pyruvate kinase deficiency and protection against malaria in a mouse model. 1502 38

It has been proposed that the basis of severe malarial anaemia, a major cause of morbidity and mortality in endemic areas, is multifactorial. Inappropriately low reticulocytosis is observed in malaria patients suggesting that insufficient erythropoiesis is a major factor. Clinical studies provide conflicting data concerning the production of adequate levels of erythropoietin (EPO) during malaria. Plasmodium chabaudi AS causes non-lethal infection in resistant C57BL/6 mice, and lethal infection in susceptible A/J mice. In P. chabaudi AS infected C57BL/6 and A/J mice, which experience varying degrees of severity of anaemia, kidney EPO production is appropriate to the severity of anaemia and is regulated by haematocrit level. Neutralisation of endogenous EPO during infection leads to lethal anaemia while timely administration of exogenous EPO rescues mice although reticulocytosis is suppressed in proportion to the parasitemia level. Characterisation of alterations in splenic erythroid compartments in naive and P. chabaudi AS infected A/J mice revealed that infection, with or without EPO treatment, leads to sub-optimal increases in TER119+ erythroblasts compared to EPO-treated naive mice. A lower percentage of TER119+ erythroblasts in infected mice undergo terminal differentiation to become mature haemoglobin-producing cells. Furthermore, there is a shift in transferrin receptor (CD71) expression from TER119+ cells to a non-erythroid population. Deficiencies in the number and maturation of TER119+ erythroblasts during infection coincide with blunted proliferation to EPO stimulation in vitro by splenocytes, although a high frequency express EPO receptor (EPOR). Together, these data suggest that during malaria, EPO-induced proliferation of early EPOR+ erythroid progenitors is suppressed, leading to sub-optimal generation of TER119+ erythroblasts. Moreover, a shift in CD71 expression may result in impaired terminal maturation of erythroblasts. Thus, suppressed proliferation, differentiation, and maturation of erythroid precursors in association with inadequate reticulocytosis may be the basis of insufficient erythropoiesis during malaria.
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PMID:Malarial anaemia: mechanisms and implications of insufficient erythropoiesis during blood-stage malaria. 1558 27

Malaria is a global problem, and there is a critical need for further understanding of the disease process. When malarial parasites invade and develop within the bloodstream, they stimulate a profound host response whose main clinical sign is fever. To explore this response, we measured host gene expression in whole blood from Kenyan children hospitalized with either acute malaria or other febrile illnesses. Genomewide analysis of expression identified 2 principal gene-expression profiles related to neutrophil and erythroid activity. In addition to these general acute responses, a third gene-expression profile was associated with host parasitemia; mediators of erythrophagocytosis and cellular stress were notable components of this response. The delineation of subjects on the basis of patterns of gene expression provides a molecular perspective of the host response to malaria and further functional insight into the underlying processes of pathogenesis.
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PMID:Genomewide analysis of the host response to malaria in Kenyan children. 1583 86

The destruction of erythrocytes and defects in erythropoiesis are among the most frequently observed causes of morbidity in severe Plasmodium falciparum malaria. The molecular mechanisms involved remain unclear, despite extensive investigation. We show here, for the first time, that tagging with the parasite rhoptry protein ring surface protein 2 (RSP2) is not restricted to the surfaces of normal erythrocytes, as previously reported, but that it extends to erythroid precursor cells in the bone marrow of anemic malaria patients. Monoclonal mouse antibodies and human sera from patients with severe anemia, reacting with RSP2-tagged erythrocytes, induced cell destruction by phagocytosis and complement activation in vitro. Our observations reveal a new parasite mechanism implicated in the destruction of normal erythrocytes and probably dyserythropoiesis in malaria patients. These data suggest that the tagging of host cells with RSP2 may trigger anemia in falciparum malaria.
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PMID:Plasmodium falciparum rhoptry protein RSP2 triggers destruction of the erythroid lineage. 1604 31

The mechanism of anemia in severe falciparum malaria is still not completely understood. The purpose of this study was to determine whether apoptosis in the erythroid lineage causes anemia in falciparum malaria. Bone marrow aspirated from 8 severe falciparum malaria patients, 3 normal volunteers and 5 retrospective normal bone marrow smears were investigated. By light microscopic study, 5 of 8 hyperparasitemic patients had hypocellular bone marrows and erythroid hypoplasia, whereas the other 3 patients had normal cellularity. The mean myeloid : erythroid ratio of these 5 patients was significantly (p < or = 0.05) higher than normal. Apoptosis of bone marrow nucleated cells (BMNC) could be determined from the exposure of phosphatidylserine (PS) on the cell membrane but not DNA fragmentation (180-250 bp) or ultrastructural morphology. The percentages of apoptotic BMNC and apoptotic erythroid cells in bone marrow from each patient and controls varied from low to high, and were not associated with parasitemia. This study suggests that destruction of erythroid lineage, particularly through apoptosis regulation, cannot solely account for anemia in falciparum malaria.
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PMID:Hematopoietic features and apoptosis in the bone marrow of severe Plasmodium falciparum-infected patients: preliminary study. 1612 15


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