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

This paper describes the fine structure of the sporogonic development of Plasmodium falciparum in its natural vector Anopheles gambiae (Species A) as seen by scanning and transmission electron microscopy. The parasite was derived from naturally infected volunteers and the vector maintained under natural conditions at the MRC Laboratories, Fajara, The Gambia. Sporogonic development of P. falciparum is similar to that described for other Plasmodium spp. There are however greater similarities between P. falciparum and the avian malaria parasites, than those mammalian (primarily rodent) species described to date--particularly with respect to mitochondrial development, crystalloid morphology and nucleolar organization. Nuclear development is similar to that of the murine malaria parasites, but reconstruction of complete mitotic spindles from serial sections suggest the haploid genome of P. falciparum contains 14 chromosomes compared to eight to ten in the murine plasmodia. Sporoblast formation involves a unique process of cleft formation based on the expansion of the cisternal space of the endoplasmic reticulum. Sporozoite budding is almost exclusively confined to these inner membrane surfaces and results in a characteristic sporozoite distribution in the oocyst. High resolution scanning electron microscopy of free sporozoites provides the first surface view of the micropore of Plasmodium.
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PMID:An ultrastructural study of the sporogonic development of Plasmodium falciparum in Anopheles gambiae. 36 85

Reversal of chloroquine (CQ) resistance by verapamil, a Ca2+ antagonist, has been shown in CQ-resistant human and rodent malaria parasites. Here, we report ultrastructural changes associated with this phenomenon in CQ-resistant Plasmodium chabaudi (AS strain) after infected mice were administered CQ and verapamil. At parasitaemias of 5-7%, CQ at 6 mg/kg caused little morphological effect on CQ-resistant parasites. In contrast, co-administration of CQ and verapamil at 50 mg/kg induced swelling of food vacuoles with clumped pigment at 2.5 h. Morphological changes other than food vacuole enlargement occurred at 21 and 45 h: disappearance of endoplasmic reticulum, formation of myelin structures, focal cytoplasmic vacuolization and coarse clumping of electron-dense material in nuclei. These structural changes appeared to be very similar to those observed in CQ-sensitive P. chabaudi in mice injected with CQ alone or CQ plus verapamil. On the other hand, verapamil at 50 mg/kg alone did not induce any effect on both CQ-sensitive and CQ-resistant P. chabaudi. These results suggest that swelling of the food vacuoles is an initial event associated with reversal of CQ-resistance by verapamil.
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PMID:Ultrastructural changes associated with reversal of chloroquine resistance by verapamil in Plasmodium chabaudi. 174 46

The effects of alpha-dimethylamino-cyclohexoxyl-dimethyl gallium (DCDG), a new antimalarial drug developed in China, on the ultrastructure of murine malaria parasites in vivo was studied in comparison with those of chloroquine (CQ) and artemisinin (Art). All these 3 antimalarials were administered ig to mice at dosages of 1-3, 40-80, and 200-400 mg.kg-1 for DCDG, CQ, and Art respectively, based on a similar intensity of morphological changes in the parasites. Blood samples were collected for electron microscopy from 15 min to 48 h after medication. The results showed that DCDG killed the malaria parasites (both asexual and sexual forms) rapidly. The most prominent changes in DCDG-treated parasites were serious dilation of perinuclear space, endoplasmic reticulum, mitochondrion and some other vesicles or intermembranous spaces. These led to the formation of large autophagic vacuoles containing some membranous materials, which were subsequently extruded. Then the parasite cells became more concentrated, finally pyknotic and died. The mode of action was very different from that of CQ and Art.
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PMID:[Effects of alpha-dimethylamino-cyclohexoxyl-dimethyl gallium on ultrastructure of erythrocytic stage of Plasmodium berghei and P yoelii]. 182 7

Fine structural analysis of the trophic and sexual stages of Plasmodium vivax obtained from naturally infected humans revealed that in general, the structural features as well as certain specialized functions such as haemoglobin ingestion and utilization etc., are similar to those described for other malaria parasites. Young trophozoite is characterised by less condense cytoplasm with scattering of free ribosomes and minimum amount of endoplasmic reticulum. The trophozoite grows by feeding on the host cell cytoplasm with its cytostome. Older trophozoite gets considerably enlarged and its cytoplasm appears coarsely granular due to an increase in endoplasmic reticulum and ribosomal content. The two sexual forms, the macro- and microgametocyte, can be distinguished on the basis of their fine structure. The macrogametocyte has high ribosomal density and more osmiophilic bodies than microgametocyte and possesses a compact dense nucleus with nucleolus-like region whereas the microgametocyte has large diffuse nucleus without nucleolus. Caveola-vesicle complexes and cytoplasmic clefts are observed in all erythrocytes infected with P. vivax and the incidence of these host cell alterations increases as the intraerythrocytic parasite matures.
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PMID:Fine structure of the erythrocytic stages of Plasmodium vivax and the host cell alterations. 220 30

The precursor of major merozoite surface antigens (PMMSA) and its proteolytic products are candidates for an asexual blood stage vaccine. Previous authors have shown that PMMSA epitopes are expressed in the liver or exoerythrocytic (EE) stage of malaria. Using Plasmodium berghei, we show that the molecular weight of the liver stage PMMSA is similar to that of the blood stage and that both EE and blood stage proteins are similarly processed. In the EE stage, it was synthesized toward the end of schizogony and appeared first to localize to the rough endoplasmic reticulum and then, as the cytomeres began to form, to the parasite plasmalemma. The EE and blood stage merozoites expressed similar amounts of this antigen as determined by indirect immunofluorescence.
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PMID:Expression of the precursor of the major merozoite surface antigens during the hepatic stage of malaria. 246 36

Intrahepatocytic transformation in vivo of the rodent malaria sporozoite of Plasmodium berghei, into the young trophic exoerythrocytic tissue stage was studied by immunofluorescence, light- and electron microscopy. The first 20 h of intracellular life were involved entirely in dedifferentiation with limited proliferation of organelles. From about 20 h onwards nuclear division commenced, rough endoplasmic reticulum became markedly expanded, and mitochondria increased in numbers. However, remains of the sporozoite pellicle (i.e., inner membranes and subpellicular microtubules) persisted for at least 28 h, which correlates with the persisting reaction of young exoerythrocytic forms with antisporozoite antibodies. In general, the basic mechanism of transformation resembles that of the ookinete into oocyst and that of the merozoite into erythrocytic trophozoite.
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PMID:Transformation of sporozoites of Plasmodium berghei into exoerythrocytic forms in the liver of its mammalian host. 389 6

Liposomes have been proposed as vehicles for vaccines against parasitic and viral illnesses. Experimental vaccines against malaria, HIV, hepatitis A, and influenza virus have been shown to be safe and highly immunogenic in several human trials. Analysis of the intracellular trafficking patterns of liposomal antigen reveals that after being phagocytosed by macrophages, liposomal antigen readily escapes from endosomes into the cytoplasm of the macrophages. It is proposed that liposomal peptide antigen can enter either the Golgi apparatus or the endoplasmic reticulum and thereby interact with MHC class II or class I molecules. The intracellular cytoplasmic trafficking patterns of liposomal antigens raise the possibility that liposomes may have utility in human vaccines for induction of either humoral immunity or cytotoxic T lymphocytes.
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PMID:Liposomal vaccines: clinical status and immunological presentation for humoral and cellular immunity. 762 48

We report here the nucleotide sequence of hsp90 (heat shock protein 90) of Plasmodium falciparum. Computer analysis of the deduced protein sequence revealed an unusually large region of charged amino acids when compared to hsp90 from other species. This region shows striking homology to the calcium binding domain of calreticulin, the major calcium binding protein of endoplasmic reticulum. Phylogenetic tree analysis indicates that P. falciparum hsp90 is more closely related to hsp90 from plants than to hsp90 from vertebrates or other parasites. The malaria hsp90 is an ATP binding protein encoded by a single gene constitutively expressed in both asexual (trophozoite) and sexual (gametocyte) stage parasites. The hsp90 protein is homologous to a previously identified 90-kDa antigen strongly recognised by both sera from vaccinated monkeys and monoclonal antibody XIV/7.
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PMID:Molecular characterization of the heat shock protein 90 gene of the human malaria parasite Plasmodium falciparum. 783 76

The ERD2 gene product in mammalian cells and yeast is a receptor required for protein retention in the endoplasmic reticulum (ER); immunolocalization studies indicate that the protein is concentrated in the cis Golgi. We have identified a homologue of ERD2 in the malaria parasite, Plasmodium falciparum (PfERD2). The deduced protein sequence is 42% identical to mammalian and yeast homologues and bears striking homology in its proposed tertiary structure. PfERD2 is tightly confined to a single focus of staining in the perinuclear region as seen by indirect immunofluorescence. This is redistributed by brefeldin A (BFA) to a diffuse pattern similar to that of parasite BiP, a marker for the ER; removal of the drug results in recovery of the single focus, consistent with the localization of PfERD2 to the parasite Golgi and its participation in a retrograde transport pathway to the ER. Sphingomyelin synthesis is a second resident activity of the cis Golgi whose organization is sensitive to BFA in mammalian cells. Within the parasite it again localizes to a perinuclear region but does not reorganize upon BFA treatment. The results strongly suggest that these two activities are in distinct compartments of the Golgi in the malaria parasite.
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PMID:Identification and localization of ERD2 in the malaria parasite Plasmodium falciparum: separation from sites of sphingomyelin synthesis and implications for organization of the Golgi. 822 85

A Ca(2+)-ATPase gene was cloned from the genomic libraries of Plasmodium falciparum. From the deduced amino acid sequence of the gene, a 139 kDa protein with a total of 1228 amino acids was predicted. Sequence of a partial cDNA clone of the gene identified two introns near the 3'-end at the regions identical to the regions assumed for the Ca(2+)-ATPase gene of P. yoelii, a rodent malaria species. As compared with a variety of Ca(2+)-ATPases, the P. falciparum Ca(2+)-ATPase had the highest amino acid sequence homology (78%) to the P. yoelii Ca(2+)-ATPase, moderate homology (45-50%) to vertebrate sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases (SERCAs), and lowest homology (20%) to a plasma membrane Ca(2+)-ATPase. The P. falciparum protein conserved sequences and residues that are important for the function and/or structure of the organellar type Ca(2+)-ATPase, such as high affinity Ca(2+)-binding sites, fluorescein isothiocyanate (FITC)-binding regions, and the phosphorylation site, but the protein did not contain calmodulin-binding regions that occur in the plasma membrane type Ca(2+)-ATPase. Thus we concluded the cloned gene was the organellar type Ca(2+)-ATPase of P. falciparum. In a region between the phosphorylation site and FITC-binding region, the P. falciparum protein was about 200 residues longer than the rabbit SERCA and lacked a sequence that binds to phospholamban, a protein that regulates the activity of the rabbit SERCA.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cloning of a Ca(2+)-ATPase gene of Plasmodium falciparum and comparison with vertebrate Ca(2+)-ATPases. 831 97


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