Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The role of antigen specific CD8+ T-lymphocytes in mediating protection against sporozoite-induced malaria has been well established in murine models. In humans, indirect evidence has accumulated suggesting a similar protective role for antigen-specific CD8+ T-lymphocytes. Nevertheless, the low frequency of circulating specific cells together with the lack of sensitive methods to quantify them has hampered the direct assessment of their function. Using a combination of short-term cell culture and IFN-gamma ELISPOT, we studied CD8+ T-lymphocyte responses to a panel of HLA-A*0201 binding peptides. In addition to confirming the response to already described epitopes, we also identified five new CD8+ T-lymphocyte epitopes. These epitopes are presented in pre-erythrocytic stages gene products of Plasmodium falciparum 7G8 strain and correspond to the following protein segments: circumsporozoite (CS) 64-72, 104-113, 299-308 and 403-411; liver stage antigen (LSA-1) repeat region; sporozoite surface protein 2 or thrombospondin related anonymous protein (SSP2/TRAP) 78-88 and 504-513. Four of these peptides are conserved amongst all published sequences of P. falciparum strains. We conclude that the modified IFN-gamma ELISPOT assay is a sensitive technique to monitor antigen-specific CD8+ T-lymphocyte responses in human malaria which may help in the improvement and assessment of the efficacy of malaria subunit vaccines.
 ...
PMID:HLA-A*0201 restricted CD8+ T-lymphocyte responses to malaria: identification of new Plasmodium falciparum epitopes by IFN-gamma ELISPOT. 1101 76

It is anticipated that the sequencing of Plasmodium falciparum genome will soon be completed. Rodent models of malaria infection and stable transformation systems provide powerful means of using this information to study gene function in vivo. To date, gene targeting has only been developed for one rodent malaria species, Plasmodium berghei. Another rodent species, Plasmodium yoelii, however, is favored to study the mechanisms of protective immunity to the pre-erythrocytic stages of infection and vaccine development. In addition, it offers the opportunity to investigate unique aspects of pathogenesis of blood stage infection. Here, we report on the stable transfection and gene targeting of P. yoelii. Purified late blood stage schizonts were used as targets for electroporation with a plasmid that contains a pyrimethamine-resistant form of the P. berghei dihydrofolate reductase-thymidylate synthase (Pbdhfr-ts) fused to green fluorescent protein (gfp) gene. After drug selection, fluorescent parasites contained intact, non-rearranged plasmids that remain stable under drug-pressure. In addition, we used another dhfr-ts/gfp based plasmid to disrupt the P. yoelii trap (thrombospondin-related anonymous protein) locus by site-specific integration. The phenotype of P. yoelii TRAP knockout was identical to that previously reported for the P. berghei TRAP knockout. In the absence of TRAP, the erythrocytic cycle, gametocyte and oocyst development of the mutant parasites were indistinguishable from wild type (WT). Although the sporozoites appeared morphologically normal, they failed to glide and to invade the salivary glands of mosquitoes.
 ...
PMID:Gene targeting in the rodent malaria parasite Plasmodium yoelii. 1129 81

We have established an amplified fragment length polymorphism (AFLP) protocol for identifying anonymous polymorphic loci of the malarial parasite, Plasmodium falciparum. The method consists of the following steps (i) digestion and ligation in one reaction; (ii) selective fluorescence forward primers labelled; (iii) PCR products resolved in polyacrylamide gels using the ABIPRISM 377 XL DNA sequencer and, (iv) the use of Genescan software to size the fragments. This standardized protocol distinguished between 2 standard reference clones of P. falciparum from West African and Southeast Asian and 2 Central African isolates from patients with clinical malaria. The AFLP protocol resulted in evenly distributed and reproducible band patterns for amplified fragments ranking from 163 to 489 bp long +/-0.5 S.D. The primer Tru ACA labelled with the phosphoramidite 6-carboxifluorescein (FAM-blue) was easy to interpret, with a maximum of 53 bands per clone and of 81 per isolate (mixed falciparum populations) whereas the primer Tru AG labelled with the hexachlorinated analogue (HEX-green) showed a less clear pattern of bands and reproducibility than Tru ACA.
 ...
PMID:Amplified fragment length polymorphism (AFLP) protocol for genotyping the malarial parasite Plasmodium falciparum. 1167 64

Malaria is transmitted through the bite of an infected mosquito, which introduces Plasmodium sporozoites into the mammalian host. Sporozoites rapidly reach the liver of the host where they are sequestered, a process probably mediated by circumsporozoite (CS) protein. Once in the liver, sporozoites migrate through several hepatocytes by breaching their plasma membranes before infecting a final hepatocyte with formation of a vacuole around the sporozoite, where development occurs into blood stage parasites. We propose that migration through several host cells activates sporozoites for ultimate productive invasion. This migration triggers sporozoite exocytosis, which is necessary for hepatocyte invasion, probably because it provides molecules, such as thrombospondin-related anonymous protein (TRAP), likely required for sporozoite invasion with the formation of a vacuole. How sporozoites migrate from the skin to the liver and invade hepatocytes remains unclear. Understanding this initial stage of malaria is crucial for the development of new approaches against the disease.
 ...
PMID:Invasion of mammalian host cells by Plasmodium sporozoites. 1183 79

Several polymerase chain reaction (PCR)-based methods have recently been developed for diagnosing malarial infections in both birds and reptiles, but a critical evaluation of their sensitivity in experimentally-infected hosts has not been done. This study compares the sensitivity of several PCR-based methods for diagnosing avian malaria (Plasmodium relictum) in captive Hawaiian honeycreepers using microscopy and a recently developed immunoblotting technique. Sequential blood samples were collected over periods of up to 4.4 yr after experimental infection and rechallenge to determine both the duration and detectability of chronic infections. Two new nested PCR approaches for detecting circulating parasites based on P. relictum 18S rRNA genes and the thrombospondin-related anonymous protein (TRAP) gene are described. The blood smear and the PCR tests were less sensitive than serological methods for detecting chronic malarial infections. Individually, none of the diagnostic methods was 100% accurate in detecting subpatent infections, although serological methods were significantly more sensitive (97%) than either nested PCR (61-84%) or microscopy (27%). Circulating parasites in chronically infected birds either disappear completely from circulation or to drop to intensities below detectability by nested PCR. Thus, the use of PCR as a sole means of detection of circulating parasites may significantly underestimate true prevalence.
 ...
PMID:PCR diagnostics underestimate the prevalence of avian malaria (Plasmodium relictum) in experimentally-infected passerines. 1205 56

Plasmodium sporozoites are transmitted through the bite of infected mosquitoes and first invade the liver of the mammalian host, as an obligatory step of the life cycle of the malaria parasite. Within hepatocytes, Plasmodium sporozoites reside in a membrane-bound vacuole, where they differentiate into exoerythrocytic forms and merozoites that subsequently infect erythrocytes and cause the malaria disease. Plasmodium sporozoite targeting to the liver is mediated by the specific binding of major sporozoite surface proteins, the circumsporozoite protein and the thrombospondin-related anonymous protein, to glycosaminoglycans on the hepatocyte surface. Still, the molecular mechanisms underlying sporozoite entry and differentiation within hepatocytes are largely unknown. Here we show that the tetraspanin CD81, a putative receptor for hepatitis C virus, is required on hepatocytes for human Plasmodium falciparum and rodent Plasmodium yoelii sporozoite infectivity. P. yoelii sporozoites fail to infect CD81-deficient mouse hepatocytes, in vivo and in vitro, and antibodies against mouse and human CD81 inhibit in vitro the hepatic development of P. yoelii and P. falciparum, respectively. We further demonstrate that the requirement for CD81 is linked to sporozoite entry into hepatocytes by formation of a parasitophorous vacuole, which is essential for parasite differentiation into exoerythrocytic forms.
 ...
PMID:Hepatocyte CD81 is required for Plasmodium falciparum and Plasmodium yoelii sporozoite infectivity. 1248 5

The invasion of host cells by the malaria parasite Plasmodium falciparum requires specific protein-protein interactions between parasite and host receptors and an intracellular translocation machinery to power the process. The transmembrane erythrocyte binding protein-175 (EBA-175) and thrombospondin-related anonymous protein (TRAP) play central roles in this process. EBA-175 binds to glycophorin A on human erythrocytes during the invasion process, linking the parasite to the surface of the host cell. In this report, we show that the cytoplasmic domain of EBA-175 encodes crucial information for its role in merozoite invasion, and that trafficking of this protein is independent of this domain. Further, we show that the cytoplasmic domain of TRAP, a protein that is not expressed in merozoites but is essential for invasion of liver cells by the sporozoite stage, can substitute for the cytoplasmic domain of EBA-175. These results show that the parasite uses the same components of its cellular machinery for invasion regardless of the host cell type and invasive form.
 ...
PMID:The cytoplasmic domain of the Plasmodium falciparum ligand EBA-175 is essential for invasion but not protein trafficking. 1287 79

Vaccine development research is an important component of malaria control strategies. Thrombospondin related anonymous protein (TRAP) and the circumsporozoite (CS) protein are two antigens of sporozoite surface. Immune response to these two antigens may contribute to the development of anti-sporozoite vaccine. Recent studies suggest that antibodies anti-TRAP may partially block sporozoites penetration in hepatocyte, and thereby reducing malaria morbidity. We carried out a study to assess the seroprevalence of anti-TRAP and anti-CS antibodies and to identify a possible role of these antibodies on malaria morbidity in children 1-9 years old living in a rural hyperendemic village. We performed 5 cross sectional surveys and a longitudinal follow up in 1993 and 1994. During each cross sectional study, children were examined for fever and splenomegaly; all febrile children received thick film examination, and serologic analysis was performed in one third of these, randomly selected. The results show that the seroprevalence of anti-TRAP and anti-CS varied with age and season (p < 0.05). Association between the prevalence of anti-TRAP and splenomegaly was observed during two cross sectional surveys (June and October 1993). The presence of anti-TRAP antibody was associated with Plasmodium falciparum infection at the beginning of the transmission season (June 1993 and July 1994). A negative association between the level of anti-TRAP title and parasitemia was observed (March and October 1994). These findings suggest no clear evidence of the protective role of anti-TRAP antibodies in uncomplicated malaria, possibly due to the limited persistence of these antibodies under natural situations.
 ...
PMID:[Epidemiology of malaria in a village of Sudanese savannah in Mali (Bancoumana). Anti-TRAP and anti-CS humoral immunity response]. 1471 43

TRAP (thrombospondin-related anonymous protein) is a sporozoite surface protein that plays a central role in hepatocyte invasion. We have developed procedures for recombinant production of the entire ECD (extracellular domain) and A domain of TRAP using bacterial- and baculovirus-expression systems respectively. The ECD and A domain were purified to homogeneity and migrated on gel-filtration columns as non-aggregated, monomeric proteins. These adhesive modules bound to HepG2 cells in a dose-dependent and bivalent cation-independent manner. The binding of ECD and the A domain to HepG2 cells was inhibited poorly by an excess of sulphatide analogues, suggesting the presence of as yet unidentified receptors for the A domain on hepatocytes. Using surface-plasmon-resonance-based sensor technology (Biacore), we demonstrate that TRAP ECD has higher affinity for heparin (K(D)=40 nM) compared with the A domain (K(D)=79 nM). We also present a three-dimensional structure of the A domain based on the crystal structure of the homologous von Willebrand factor A1 domain. The TRAP A domain shows two spatially distinct ligand-binding surfaces. One surface on the A domain contains the MIDAS (metal-ion-dependent adhesion site) motif, where point mutations of Thr131 and Asp162 correlate with impairment of cell infectivity by sporozoites. The other surface contains a putative heparin-binding site and consists of a basic residue cluster. Our studies suggest that TRAP interacts with multiple receptors during the hepatocyte invasion process. Our results also pave the way for inclusion of these high-quality recombinant TRAP domains in subunit-based vaccines against malaria.
 ...
PMID:Structural and functional dissection of the adhesive domains of Plasmodium falciparum thrombospondin-related anonymous protein (TRAP). 1474 Oct 48

Invasive sporozoite and merozoite stages of malaria parasites that infect mammals enter and subsequently reside in hepatocytes and red blood cells respectively. Each invasive stage may exhibit unique adaptations that allow it to interact with and survive in its distinct host cell environment, and these adaptations are likely to be controlled by differential gene expression. We used suppression subtractive hybridization (SSH) of Plasmodium yoelii salivary gland sporozoites versus merozoites to identify stage-specific pre-erythrocytic transcripts. Sequencing of the SSH library and matching the cDNA sequences to the P. yoelii genome yielded 25 redundantly tagged genes including the only two previously characterized sporozoite-specific genes encoding the circumsporozoite protein (CSP) and thrombospondin-related anonymous protein (TRAP). Twelve novel genes encode predicted proteins with signal peptides, indicating that they enter the secretory pathway of the sporozoite. We show that one novel protein bearing a thrombospondin type 1 repeat (TSR) exhibits an expression pattern that suggests localization in the sporozoite secretory rhoptry organelles. In addition, we identified a group of four genes encoding putative low-molecular-mass proteins. Two proteins in this group exhibit an expression pattern similar to TRAP, and thus possibly localize in the sporozoite secretory micronemes. Proteins encoded by the differentially expressed genes identified here probably mediate specific interactions of the sporozoite with the mosquito vector salivary glands or the mammalian host hepatocyte and are not used during merozoite-red blood cell interactions.
 ...
PMID:Differential transcriptome profiling identifies Plasmodium genes encoding pre-erythrocytic stage-specific proteins. 1498 20


<< Previous 1 2 3 4 5 6 7 Next >>