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

The presence of a signal sequence preceding the gene encoding a target antigen in a DNA vaccine should facilitate secretion of the in vivo translated antigen. The immune responses elicited upon injection with such a vector could differ from those induced by the same vector lacking a signal sequence. In the present study, the humoral responses elicited in mice immunized with two plasmids, either containing or lacking the human tissue plasminogen activator signal sequence, were compared. Both plasmids encode the chimeric antigen ZZN4, containing a malaria antigen Pf332-derived sequence (N4) linked to a bacterial fusion partner (ZZ). In vitro transfection of COS cells with each plasmid and treatment of the transfectants with brefeldin A confirmed that secretion of ZZN4 via the endoplasmic reticulum and Golgi pathway only occurred in cells transfected with the signal peptide-encoding plasmid. Repeated intramuscular injections of mice with either of the plasmids elicited comparable antibody responses to ZZN4 with regard to kinetics, specific IgG levels and persistence. These results indicate that in vivo transfection of muscle cells by either of these two plasmids generated comparable levels of antigen available for B-cell recognition and for uptake by antigen-presenting cells, despite the differential intracellular targeting of the encoded antigen. The relevance of these findings for the design of DNA vaccine vectors is discussed.
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PMID:Comparative study of DNA-based immunization vectors: effect of secretion signals on the antibody responses in mice. 927 Nov 70

DNA vaccine plasmids were constructed that encoded four pre-erythrocytic antigens from the human malaria parasite Plasmodium falciparum: circumsporozoite protein (PfCSP); sporozoite surface protein 2 (PfSSP2); carboxyl terminus of liver stage antigen 1 (PfLSA-1 c-term); and, exported protein 1 (PfExp-1). Antigen expression was evaluated in vitro by immunoblot analysis of tissue culture cells following transient transfection with each plasmid. Clearly detectable levels of expression depended upon, or were markedly enhanced by, fusion of the antigen encoding sequences in-frame with the initiation complex and peptide leader sequence of human tissue plasminogen activator protein. Mice injected with these plasmids produced antigen specific antibody and cytotoxic T lymphocyte responses. However, the magnitudes of the responses were not always predicted by the in vitro expression assay. The results of this study provided the basis for further testing of these plasmids in primates and the formulation of multi-component pre-erythrocytic DNA vaccines for efficacy testing in human volunteers.
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PMID:In vitro expression and in vivo immunogenicity of Plasmodium falciparum pre-erythrocytic stage DNA vaccines. 985 39

The gene for a 45 kDa merozoite surface protein (MSA-2) of the human malaria parasite Plasmodium falciparum was PCR amplified and cloned into eukaryotic expression vectors VR1012 and pcDNA3 to yield plasmids P1 and P2, respectively. The coding sequences for two N-terminal fragments of the 185 kDa merozoite surface protein (MSA-1) gene were similarly PCR amplified and cloned into vectors VR1020 and VR1012 to yield plasmids P3 and P4, respectively. The MSA-1 signal peptide sequence, present in P4, was replaced with the human tissue plasminogen activator signal sequence in P3. The four plasmids expressed the cloned genes under the control of the cytomegalovirus promoter and carried 3' bovine growth hormone termination/poly A signals. P1, P3 and P4 also contained the cytomegalovirus intron A enhancer sequence. MSA-1 expression was more readily detected than MSA-2 in Cos cells transfected with P3/P4 and P1/P2 respectively. The MSA-2 gene was also cloned into the phagemid pBluescript IISK+ with and without a 3' poly A tail composed of 35 A residues. MSA-2 was synthesised in HeLa cells infected with a recombinant vaccinia virus carrying T7 RNA polymerase when MSA-2 recombinant pBluescript was transfected into the cells. Inoculation with P1 intramuscularly or intradermally and with P2 intradermally into rabbits led to the production of antibodies to MSA-2 detectable by immunofluorescence and Western blotting. Antibodies were also produced against MSA-1 after intramuscular/intradermal inoculation with P3 and P4. Inoculation of rabbits with MSA-2 mRNA yielded better antibody titres when a poly A tail was present. Antibody levels were maintained for > 9 weeks after the final immunisation. However the immune sera failed to inhibit in vitro parasite growth.
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PMID:Mammalian cell expression of malaria merozoite surface proteins and experimental DNA and RNA immunisation. 998 40

Plasmodium vivax is the second most common agent of human malaria. Although infection is rarely fatal, it nonetheless imposes a significant burden of illness in endemic areas. A successful vaccine against P. vivax will likely need to induce immune responses against both pre-erythrocytic and erythrocytic stage forms of the parasite. Accordingly, we constructed eight nucleic acid vaccines based on four antigens, the circumsporozoite protein (PvCSP) and sporozoite surface protein 2 (PvSSP2) from the pre-erythrocytic stage, and apical membrane antigen 1 (PvAMA1) and merozoite surface protein 1 (PvMSP1) from the erythrocytic stage. The constructs induced high levels of specific antibody in mice regardless of whether the antigen was expressed in native form or fused to a human tissue plasminogen activator leader peptide. High titer antibodies induced against PvCSP did not react with the protective AGDR epitope within the sequence of this antigen. These results support the immunogenicity of these four vaccine candidate antigens when delivered as nucleic acid vaccines.
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PMID:Construction and immunogenicity of DNA vaccine plasmids encoding four Plasmodium vivax candidate vaccine antigens. 1046 50

Plasmodium falciparum merozoite surface protein 4 (MSP4) is being developed as a component of a subunit vaccine against asexual stages of malaria. Three DNA constructs were produced that induced expression of MSP4 either in the cytoplasm of transfected cells or secreted from cells under the control of the human tissue plasminogen activator (TPA) signal or the native P. falciparum MSP4 signal. Only the construct containing the TPA signal induced detectable antibodies in mice, although gene expression was demonstrated in all constructs and MSP4 was shown to be secreted using either signal by in vitro transient transfection of COS cells. Two recombinant MSP4 proteins that encoded the same sequence as the plasmid DNA were produced in E. coli (EcMSP4-His) and S. cerevisiae (yMSP4-His) and used to raise antibodies in mice. Comparison of the antibodies elicited by these various antigen formulations showed differences in titer, isotype and epitope recognition. The titer of antibodies induced by DNA vaccination was lower than that induced by yMSP4-His, which in turn was lower than that induced by EcMSP4-His. The isotype profiles of the antibodies were also different, the plasmid DNA induced predominantly IgG(2a) responses whereas the two proteins induced predominantly IgG(1) responses. The antibodies induced by DNA and yMSP4-His recognized predominantly the C-terminal epidermal growth factor (EGF)-like domain of the protein, whereas EcMSP4-His induced antibodies recognizing all domains of the protein equally. The antibodies induced by DNA vaccination were directed almost extensively to conformational epitopes so that reactivity with native MSP4 was abolished after disulfide bonds in the protein were disrupted. Antibodies induced by recombinant proteins recognized linear epitopes as well and reactivity to native MSP4 was preserved after reduction and alkylation of parasite proteins.
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PMID:Differences in epitope recognition, isotype and titer of antisera to Plasmodium falciparum merozoite surface protein 4 raised by different modes of DNA or protein immunization. 1111 4

Transmission-blocking vaccines target the sexual stages of the malaria parasite and prevent further development within the mosquito vector halting the transmission of the parasite. Zygote/ookinetes are potential targets of antibodies inhibiting oocyst development in the mosquito midgut and rendering mosquitoes non-infectious. DNA vaccine constructs were developed expressing Pvs25 and Pvs28 (Plasmodium vivax zygote/ookinete surface proteins) fused at the amino terminus with tissue plasminogen activator signal peptide. Antibodies produced in mice after immunization with three doses recognized respective antigens in the parasites and in an ELISA, and these antibodies when tested in membrane feeding assay were potent blockers of P. vivax transmission. Co-immunization with Pvs25 and Pvs28 DNA vaccine constructs did not affect the antigen specific antibody responses against individual antigens, and the antibodies remained effective in blocking parasite transmission demonstrating 91-99% reduction in oocyst number in the mosquito midgut. Several combinations of homologous and heterologous antigen-delivery prime boost strategy were also evaluated and the results suggested that antibody titers and transmission-blocking activities by the three prime-boost strategies (DNA prime/DNA boost, DNA prime/protein boost, and protein prime/protein boost) were comparable with slightly better immunogenicity of heterologous antigen-delivery prime/boost as compared to DNA/DNA alone. These results demonstrate potent immunogenicity of DNA vaccines encoding Pvs25 and Pvs28 and warrant further evaluation in non-human primates.
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PMID:Potent immunogenicity of DNA vaccines encoding Plasmodium vivax transmission-blocking vaccine candidates Pvs25 and Pvs28-evaluation of homologous and heterologous antigen-delivery prime-boost strategy. 1529 75

The ultimate malaria vaccine will require the delivery of multiple antigens from different stages of the complex malaria life cycle. In order to efficiently deliver multiple antigens with use of DNA vaccine technology, new antigen delivery systems must be assessed. This study utilized a bicistronic vector construct, containing an internal ribosome entry site, expressing a combination of malarial candidate antigens: merozoite surface protein 4/5 (MSP4/5) (fused to a monocyte chemotactic protein 3 chemoattractant sequence) and apical membrane antigen 1 (AMA-1) (fused to a tissue plasminogen activator secretion signal). Transfection of COS 7 cells with bicistronic plasmids resulted in production and secretion of both AMA-1 and MSP4/5 in vitro. Vaccination of BALB/c mice via intraepidermal gene gun and intramuscular routes against AMA-1 and MSP4/5 resulted in antibody production and significant in vitro proliferation of splenocytes stimulated by both AMA-1 and MSP4/5. Survival of BALB/c mice vaccinated with bicistronic constructs after lethal Plasmodium chabaudi adami DS erythrocytic-stage challenge was variable, although significant increases in survival and reductions in peak parasitemia were observed in several challenge trials when the vaccine was delivered by the intramuscular route. This study using a murine model demonstrates that the delivery of malarial antigens via bicistronic vectors is feasible. Further experimentation with bicistronic delivery systems is required for the optimization and refinement of DNA vaccines to effectively prime protective immune responses against malaria.
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PMID:A bicistronic DNA vaccine containing apical membrane antigen 1 and merozoite surface protein 4/5 can prime humoral and cellular immune responses and partially protect mice against virulent Plasmodium chabaudi adami DS malaria. 1538 53

Blood coagulation activation is frequently found in patients with malaria. Clinically apparent bleeding or disseminated intravascular coagulation (DIC) is associated with very severe disease and a high mortality. Protein C, protein S, and antithrombin levels were found to be low in P. falciparum, but were normal in P. vivax infection. Plasma levels of plasminogen activator inhibitor-1 were high in cases of P. falciparum infection whereas tissue plasminogen activator levels were low. Elevated plasma levels of von Willebrand factor (vWF) and vWF propeptide, thrombomodulin, endothelial microparticles have been reported in P. falciparum-infected patients. It has been demonstrated that severe P. falciparum infection is associated with acute endothelial cell (EC) activation, abnormal circulating ultralarge vWF multimers, and a significant reduction in plasma ADAMTS13 function. These changes may result in intravascular platelet aggregation, thrombocytopenia, and microvascular disease. It has also been shown that P. falciparum-parasitized red blood cells (pRBCs) induce tissue factor (TF) expression in microvascular ECs in vitro. Recently, loss of endothelial protein C receptor (EPCR) localized to sites of cytoadherent pRBCs in cerebral malaria has been demonstrated. Severe malaria is associated with parasite binding to EPCR. The cornerstone of the treatment of coagulopathy in malaria is the use of effective anti-malarial agents. DIC with spontaneous systemic bleeding should be treated with screened blood products. Study in Thailand has shown that for patients who presented with parasitemia >30% and severe systemic complications such as acute renal failure and ARDS, survival was superior in the group who received exchange transfusion. The use of heparin is generally restricted to patients with DIC and extensive deposition of fibrin, as occurs with purpura fulminans or acral ischemia. Antiplatelet agents interfere with the protective effect of platelets against malaria and should be avoided.
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PMID:Coagulopathy in malaria. 2409 98

Malaria is a disease caused by Plasmodium parasites and remains one of the most prevalent and persistent maladies, affecting hundreds of millions of people. In the present work, we evaluated the capability of Plasmodium falciparum proteases to hydrolyze the multifunctional protein plasminogen, which is implicated in angiogenesis and coagulation processes by the generation of angiostatin and plasmin, respectively. Using fluorescence microscopy, we visualized the internalization of FITC-labeled plasminogen in erythrocytes infected by P. falciparum and showed that the parasites are able to hydrolyze the protein. The cleavage of plasminogen by the P. falciparum proteases was also observed by SDS-PAGE, followed by immunoblotting with anti-angiostatin antibody. N-terminal sequencing of the main generated fragments indicated that they are comprised in the five plasminogen kringle domains, suggesting as being angiostatin-like peptides. This assumption was reinforced by the demonstration that the products of plasminogen processing mimic angiostatin functions, including the capability to inhibit angiogenesis and to stimulate calcium response in endothelial cells in vitro. However, no plasmin activity was detected after plasminogen hydrolysis by P. falciparum. Nonetheless, exogenous tissue plasminogen activator (tPA) activated plasmin in infected erythrocytes, suggesting that the uptake of plasminogen by P. falciparum may be modulated by the vertebrate host. Taken together, the data presented here provide evidence for the processing of host plasminogen by malaria parasites to generate active fragments that may modulate host physiology events during malaria infection.
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PMID:Plasmodium falciparum proteases hydrolyze plasminogen, generating angiostatin-like fragments. 2450 44