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Biomedical subjects

A Saul

Publications and source records attributed to A Saul.

At least 145 records · Page 8Linked to original sources
PubMed1990

Characterization of a Plasmodium falciparum epitope recognized by a monoclonal antibody with broad isolate and species specificity.

Monoclonal antibody (MAb) 7H8 raised against Plasmodium yoelii reacted with a series of proteins from P. falciparum that range in molecular weight from 46 to 194 kDa. By immunofluorescence assay, this MAb reacted with all isolates of P. falciparum tested. MAb 7H8 was used to screen a genomic expression library of asexual blood stage antigens of P. falciparum, Malayan Camp K+ and 7 independent clones were identified. These 7 clones were sequenced and the epitope recognized by MAb 7H8 in the recombinant protein of one of these clones was mapped. This epitope contained Lys Tyr Pro as core amino acids. However, similar sequences were not found in the other clones, indicating that this MAb binds to a structural epitope formed by different amino acids. The variable composition of the epitope may account for the number of P. falciparum malarial proteins recognized by MAb 7H8.

Amino Acid Sequence↗
PubMed1989

The use of maleimidocaproyloxysuccinimide to prepare malarial peptide carrier immunogens. Immunogenicity of the linking region.

Malarial peptides synthesized with an added N terminal cysteine were conjugated to purified diphtheria toxoid (DT) protein using the bifunctional reagent maleimidocaproyloxysuccinimide (MCS). The molar ratio of peptide to carrier was determined by subtractive sulphydryl titration and confirmed by sodium dodecyl sulphate (SDS) electrophoresis. For enzyme-linked immunoabsorbent (ELISA) analysis of sera from animals immunized with the DT conjugates, peptides were conjugated to bovine serum albumin (BSA) using MCS as well as a glutaraldehyde based coupling procedure. Western blotting analysis shows that both DT and BSA adducts were recognized by monoclonal antibodies (Mabs) directed against the peptide epitopes in the native sequences. Animals immunized with the DT-peptide conjugates produced antibodies to the coupling reagent (MCS) as well as diphtheria toxoid and peptide specific antibodies. This MCS specificity could be largely abolished by pre-incubation of sera with a soluble MCS homologue, a thiosuccinimidocaproylamide (TSC).

Amino Acid Sequence↗
PubMed1989

Immune response to a synthetic peptide corresponding to an epitope of a parasitophorous vacuole membrane antigen from Plasmodium falciparum.

The parasitophorous vacuole membrane antigen QF 116 from Plasmodium falciparum contains a defined epitope, DNNLVSGP, proximal to the carboxyl-terminus which binds to the inhibitory monoclonal antibody 8E7/55. A synthetic peptide containing this epitope was constructed and coupled to diphtheria toxoid as carrier. Mice and rabbits were inoculated with this conjugate using CFA, SAF-1, or aluminum phosphate as adjuvants. The peptide conjugate was highly immunogenic in both animal species, giving rise to polyclonal antibodies with a similar epitope specificity as the original mAb. Antibody titers were dependent on the route of immunization. Rabbit antibodies produced in sufficient quantity for biologic assays inhibited parasite growth in vitro. This synthetic peptide thus shows promise as an immunogen for use in synthetic vaccine design.

Amino Acid Sequence↗
PubMed1989

A protective monoclonal antibody recognizes a linear epitope in the precursor to the major merozoite antigens of Plasmodium chabaudi adami.

The monoclonal antibody 5C10/66 was shown to afford strong protection in mice against fulminating Plasmodium chabaudi adami infection. This was remarkable, as immunity to this organism is regarded to be mainly T-cell mediated. This antibody identified a 250-kDa molecule in schizonts and an 83-kDa fragment in merozoites. A cDNA clone selected by 5C10/66 was the homologue of the Plasmodium falciparum precursor to the major merozoite surface antigen (PMMSA). Comparison with the P. falciparum sequence showed that the P. chabaudi adami clone encoded the middle portion of the gene and that it can also be divided into variable and conserved blocks. Screening of a set of all possible octamer peptides predicted by the cDNA clone revealed that the core epitope of 5C10/66 was Glu-Thr-Thr-Glu-Thr. This region resides in a variable block of PMMSA.

Amino Acid Sequence↗
PubMed1989

Cross-reactivity of antibody against an epitope of the Plasmodium falciparum second merozoite surface antigen.

Monoclonal antibodies directed against the 51 kD merozoite surface antigen of Plasmodium falciparum also bind to other antigens within the infected cell. The sizes of these cross-reacting antigens have been characterized. Immunofluorescence due to the reaction of one of the monoclonal antibodies with these cross-reacting antigens was localized in the intra-erythrocytic parasite and in granules in the infected red cell cytoplasm. This immunofluorescence could be distinguished from the merozoite surface antigen in parasite lines with a variant serotype of the merozoite surface antigen which fails to react with the monoclonal antibodies. It was found that the in-vitro growth inhibition caused by the presence of one of the monoclonal antibodies, 8G10/48, was dependent on the expression of the corresponding serotype of merozoite surface antigen, a finding consistent with the inhibitory effect of this antibody being primarily directed against the merozoite surface antigen and not the cross-reacting antigens. Analysis of the frequency at which epitopes occur suggests that such cross-reacting proteins will be commonly seen in malaria, without the need to postulate a selective advantage for such cross-reacting specificities.

Animals↗
PubMed1988

Two approximately 300 kilodalton Plasmodium falciparum proteins at the surface membrane of infected erythrocytes.

Two very large Plasmodium falciparum proteins are identified as constituents of the infected erythrocyte membrane. Sera were obtained from Aotus monkeys that had been repeatedly infected with asexual P. falciparum from one of four strains. The capacity of these sera to block in vitro cytoadherence of infected erythrocytes and agglutinate intact infected cells was determined. The sera were also used to immunoprecipitate protein antigens from detergent extracts of 125I-surface labeled or biosynthetically radiolabeled infected erythrocytes. For each serum/antigen combination, precipitation of only one protein correlated with the ability of the serum to interfere with cytoadherence and agglutinate infected cells. This malarial protein, denoted Pf EMP 1 (P. falciparum-erythrocyte-membrane-protein 1) bore strain-specific epitope(s) on the cell surface and displayed size heterogeneity (Mr approximately 220,000-350,000). Pf EMP 1 was strongly labeled by cell-surface radioiodination but was a quantitatively very minor malarial protein. Pf EMP 1 was distinguished by its size, surface accessibility and antigenic properties from a more predominant malarial protein in the same size range (Pf EMP 2) that is under the infected erythrocyte membrane at knobs. Monoclonal antibodies and rabbit antisera raised against Pf EMP 2 were used to show that this size heterogeneous antigen was indistinguishable from the previously described MESA (mature parasite infected erythrocyte surface antigen), identified by precipitation with rabbit antisera raised against the MESA hexapeptide repeats. Antibodies raised against Pf EMP 2/MESA did not precipitate Pf EMP 1. We conclude that Pf EMP 1 is either directly responsible for the cytoadherence phenomenon, or is very closely associated with another as yet unidentified functional molecule. Pf EMP 2/MESA must have a structural property/function that is important under the host cell membrane.

Animals↗
PubMed1988

Codon usage in Plasmodium falciparum.

The codon frequencies used in 7874 codons from 17 sequences of Plasmodium falciparum have been examined. The frequency distribution is markedly biased. A and C occur with similar frequency in all positions but G is predominantly in the first base and T is predominantly in the last position. This information can be used to predict the coding strand and reading frame of P. falciparum genes.

Animals↗
PubMed1988

A portion of the Pf155/RESA antigen of Plasmodium falciparum is accessible on the surface of infected erythrocytes.

An investigation of antigens accessible to lactoperoxidase-catalysed cell surface iodination on intact Plasmodium falciparum-infected red blood cells (RBC) has identified a 125I-labelled antigen with an apparent size of about 155 kD. This labelled protein was specifically immunoprecipitated by the following antibodies: a rabbit antiserum and a mouse monoclonal antibody raised against a synthetic peptide comprising the 3',8-mer repeat EENVEHDA of the Pf155/RESA protein; a rabbit antiserum raised against a synthetic octapeptide comprising two copies of the 3',4-mer repeat EENV of the Pf155/RESA protein; and rabbit antisera against another synthetic peptide C(MYSNNNVED)2. The last antibody shows a strong reaction in asexual blood stage parasites with the Pf155/RESA antigen. While this antigen has been described previously as a submembrane component of the outer membrane of infected RBC, this report shows that at least part of its is accessible to the surface of both ring and late trophozoite-infected erythrocytes.

Amino Acid Sequence↗
PubMed1987

Human T clones reactive to the sexual stages of Plasmodium falciparum malaria. High frequency of gamete-reactive T cells in peripheral blood from nonexposed donors.

Malarial gametocytes, which are taken up by mosquitoes during a blood meal, develop in the gut of the mosquito into gametes. Gametes and gametocytes contain the target antigens of transmission-blocking immunity. Here, we show that the peripheral blood of nonexposed donors contains Plasmodium falciparum gamete-reactive T cells at frequencies ranging from 1/300 to 1/4000. Studies on long-term clones demonstrated that these cells often recognized antigens shared between gametes and asexual stage parasites or even between heterologous gametes, although it has been possible to derive a P. falciparum gamete-specific T clone. The T clones examined were T3+, T4+, T8-, and either HLA-DR- or HLA-DQ-restricted. They responded to gametes by both proliferation and the secretion of gamma-interferon. The gamete-specific clone and other asexual cross-reactive clones examined could be stimulated in vitro by a preparation of mature gametocytes within RBC, but not by RBC alone, suggesting that gametocytes are immunogenic or can become immunogenic for T cells in vivo. The significance of these observations to mosquito transmission of malaria and development and application of a gamete vaccine are discussed.

Adult↗
PubMed1985

A specific S-antigen of Plasmodium falciparum is expressed in a proportion of primary isolates in Brazil, Thailand and Papua New Guinea.

The expression by Plasmodium falciparum of a specific S-antigen has been examined in primary isolates in different regions of the world using a monoclonal antibody that recognizes an epitope within a known repeated amino acid sequence. The epitope was expressed by a small proportion of primary isolates in each of Brazil, Thailand and Papua New Guinea, demonstrating that this S-antigen gene is widespread. The data are consistent with the possibility that the occurrence of P. falciparum strains expressing a particular S-antigen is periodic, related to the duration of immunity against that antigen in a given human population.

Adult↗
PubMed1985

Invasion of erythrocytes in vitro by Plasmodium falciparum can be inhibited by monoclonal antibody directed against an S antigen.

A monoclonal antibody has been produced which binds to the heat stable S antigen present in the FCQ-27/PNG isolate of Plasmodium falciparum. This monoclonal antibody also inhibits the invasion in vitro of erythrocytes by malarial merozoites thus demonstrating that the S antigens of Plasmodium falciparum may be a target of protective immune responses.

Antibodies, Monoclonal↗
PubMed1985

Two apparently nonrepeated epitopes on gametes of Plasmodium falciparum are targets of transmission-blocking antibodies.

One-site and two-site immunoradiometric assays have been developed against an antigen on gametocytes of Plasmodium falciparum, using monoclonal antibodies (Mabs) which block transmission of the parasites to mosquitoes. Three such Mabs have been studied, each of which immunoprecipitates a complex of three gamete surface proteins of apparent Mr 260,000, 59,000, and 53,000 from Triton X-100 extracts of the parasites. The assays showed that the Mabs recognized one or the other of two distinct, nonrepeated epitopes on the target antigen(s). In the one-site assay certain combinations of two Mabs interacted at appropriate concentrations to enhance binding of the Mabs to the antigen. The same combinations of Mabs synergize to suppress infectivity of gametocytes to mosquitoes.

Animals↗