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W A Siddiqui

Publications and source records attributed to W A Siddiqui.

At least 19 recordsLinked to original sources
PubMed1996

Plasmodium falciparum: gp195 tripeptide repeat-specific monoclonal antibody inhibits parasite growth in vitro.

Seven monoclonal antibodies (mAbs) were produced to the precursor of the merozoite surface antigens (MSA-1 or gp195) using the Plasmodium falciparum Uganda-Palo Alto isolate. Three mAbs (CE2, DB8, and EB2) reacted with epitopes on the 83-kDa N-terminal processing fragment by immunoprecipitation of radiolabeled proteins and in immunoblots of native and recombinant proteins. Three other mAbs (BC9, AG5, and AD9) reacted with epitopes on the 42- and 19-kDa C-terminal processing fragments while one remaining mAb (24A1.7) reacted with only 150- and 110-kDa intermediate processing fragments. Epitopes were mapped to either conserved or dimorphic regions of the expressed protein when parasite isolates with known MSA-1 alleles were examined by indirect immunofluorescence. Moreover, one mAb (CE2), specific for the variable tripeptide repeat region SAQ(SGT)5, was growth inhibitory for P. falciparum in vitro. Growth inhibition by the mAb was concentration dependent and its parasite-neutralizing properties were not enhanced when used in combination with other gp195-specific mAbs. These results may be useful in the elucidation of biological variation of field isolates and in the definition of immunologically relevant epitopes in a gp195-based malaria vaccine.

Amino Acid Sequence↗
PubMed1993

An experimental vaccine cocktail for Plasmodium falciparum malaria.

Surface proteins from several different life-cycle stages of the malaria parasite Plasmodium falciparum were expressed at high levels in the yeast Saccharomyces cerevisiae. Purified proteins, both individually and in cocktails, were used to immunize mice and goats in conjunction with either Freund's adjuvant or a muramyl tripeptide-based adjuvant. Immune responses were measured by enzyme-linked immunosorbent assays and by the ability of antisera to inhibit (1) the invasion of hepatocytes by live sporozoites, (2) in vitro invasion of human erythrocytes by live merozoites, and (3) the development of oocytes in the mosquito vector. These results suggest that cocktails of different stage-specific antigens can provide the components necessary to block the development of the malaria parasite at multiple stages of its life cycle.

Animals↗
PubMed1992

Theileria sergenti proliferates in SCID mice with bovine erythrocyte transfusion.

The unavailability of in vitro or in vivo experimental systems has been the major factor hampering the progress of research studies on Theileria sergenti, causative agent of theileriosis, a major disease of cattle in Japan. We report the first successful propagation of T. sergenti in SCID mice into which uninfected bovine erythrocytes (Bo-RBC) were supplied periodically. The infectivity of T. sergenti proliferated in an SCID mouse was ascertained by successful transfer of infection into another SCID mouse into which uninfected Bo-RBC were supplied periodically.

Animals↗
PubMed1991

Synthetic low-toxicity muramyl dipeptide and monophosphoryl lipid A replace Freund complete adjuvant in inducing growth-inhibitory antibodies to the Plasmodium falciparum major merozoite surface protein, gp195.

The Plasmodium falciparum major merozoite surface protein (gp195) is a protective antigen against lethal malaria. However, increasing evidence indicates that the efficacy of a malaria vaccine will require a strong adjuvant that is safe for human use. We compared the efficacies of two low-toxicity synthetic immunomodulators, B30-MDP (a lipophilic muramyl dipeptide derivative) and LA-15-PH (a synthetic equivalent of monophosphoryl lipid A), with that of Freund complete adjuvant (FCA) in eliciting an antibody response to gp195. Rabbits were immunized with native gp195 and B30-MDP, LA-15-PH, or the two in combination, with liposomes as the vehicle. Aluminum hydroxide and FCA were used as reference adjuvants. Results showed that adjuvant formulations based on B30-MDP alone or in combination with LA-15-PH induced high antibody titers to gp195, as compared with FCA. LA-15-PH alone was less effective. Aluminum hydroxide induced significantly lower antibody titers. The functional activity of the rabbit anti-gp195 antibodies induced by different adjuvants was evaluated in an in vitro parasite growth inhibition assay previously shown to correlate with anti-gp195 immunity in the Aotus monkey model. All rabbits immunized with B30-MDP-LA-15-PH and two of three rabbits immunized with B30-MDP alone produced sera that strongly inhibited parasite growth. The degree of growth inhibition was similar to that with FCA. The antibody titers of the rabbits receiving B30-MDP-LA-15-PH strongly correlated with the degree of in vitro growth inhibition. Our findings provided strong evidence that adjuvant formulations based on synthetic B30-MDP and LA-15-PH can replace FCA as adjuvants in stimulating protective immunity specific for gp195.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1989

Generalized immunological recognition of the major merozoite surface antigen (gp195) of Plasmodium falciparum.

The antibody response to the Plasmodium falciparum major merozoite surface antigen (gp195) of congenic mouse strains differing in H-2 haplotype has been examined. All seven strains of mice were capable of producing gp195-specific antibodies. Generalized immune recognition of gp195 by mice of diverse H-2 haplotypes distinguished gp195 from the P. falciparum circumsporozoite protein and the 230-kDa and 48/45-kDa gamete surface antigens. However, the H-2 genetic locus appeared to influence the specificity of gp195-specific antibodies. Immunoblot patterns of mouse sera with parasite antigens revealed a complex pattern of reactivity with terminal and intermediate processing fragments of gp195. The majority of immunoblot bands observed were similar for all of the mouse strains; however, there were several strains that additionally recognized a few unique fragments or displayed more intense reactivities with specific processing fragments. These results suggest that while individuals of diverse major histocompatibility complex makeup are capable of recognizing the gp195 antigen, the recognition of specific gp195 B-cell and T-cell epitopes may be under control of the major histocompatibility complex.

Animals↗
PubMed1988

Plasmodium falciparum: gene structure and hydropathy profile of the major merozoite surface antigen (gp195) of the Uganda-Palo Alto isolate.

The gene encoding the 195,000-Da major merozoite surface antigen (gp195) of the FUP (Uganda-Palo Alto) isolate of Plasmodium falciparum, a strain widely used for monkey vaccination experiments, has been cloned and sequenced. The translated amino acid sequence of the FUP gp195 protein is closely related to the sequences of corresponding proteins of the CAMP (Malaysia) and MAD-20 (Papua New Guinea) isolates and more distantly related to those of the Wellcome (West Africa) and K1 (Thailand) isolates, supporting the proposed allelic dimorphism of gp195 within the parasite population. The prevalence of dimorphic sequences within the gp195 protein suggests that many gp195 epitopes would be group-specific. Despite the extensive differences in amino acid sequence between gp195 proteins of these two groups, the hydropathy profiles of proteins representative of both groups are very similar. The conservation of overall secondary structure shown by the hydropathy profile comparison indicates that gp195 proteins of the various P. falciparum isolates are functionally equivalent. This information on the primary structure of the FUP gp195 protein will enable us to evaluate the possible roles of conserved, group-specific and variable epitopes in immunity to the blood stage of the malaria parasite.

Amino Acid Sequence↗
PubMed1988

Characterization of a Plasmodium falciparum polypeptide associated with membrane vesicles in the infected erythrocytes.

A Plasmodium falciparum polypeptide (46 kDa) associated with the infected erythrocytes of all asexual stages as well as immature gametocytes was identified by the monoclonal antibody (Mab) 30B8.3. The expression of this protein was not dependent upon the knobby phenotype and was detected in parasites grown either in human or Aotus erythrocytes. The antigen was heatstable, did not label with [14C]glucosamine, and was not sensitive to periodate oxidation. Immunofluorescent staining patterns of Mab 30B8.3 on in vitro cultured parasites varied from punctate (rings and trophozoites) to patchy (trophozoites and schizonts) fluorescence. The Mab 30B8.3 antigen was not detected on the infected erythrocyte surface by conventional wet-mount IFA procedure. However, when parasites were cultured in the presence of Mab 30B8.3, the epitope was detected by the monoclonal antibodies present in the culture medium. Differential extraction of the polypeptide from infected erythrocytes and immune electron microscopy of cryosectioned parasites localized the 30B8.3 epitope primarily on membranes of Maurer's clefts within the infected erythrocyte's cytosol. This 46 kDa polypeptide is unique because it seemed to be an integral membrane protein of the Maurer's clefts/vesicles and it was not secreted into the culture medium nor deposited on the infected erythrocyte membrane. Previous studies indicate that several parasite proteins, excreted extracellularly or deposited on infected erythrocyte membrane, are found to be associated with Maurer's cleft membranes and vesicles. The 46 kDa polypeptide described in this study may play an important role in the transport of the parasite antigens.

Animals↗
PubMed1987

Merozoite surface coat precursor protein completely protects Aotus monkeys against Plasmodium falciparum malaria.

Groups of Aotus (owl) monkeys were immunized with either the Plasmodium falciparum merozoite surface-coat precursor protein and its processing fragments or a complex of high molecular mass rhoptry proteins and challenged with a lethal infection of the homologous P. falciparum Uganda Palo Alto (FUP) strain. No patent parasitemia could be detected on thick blood films of monkeys immunized with the merozoite surface antigens; however, only one of three monkeys immunized with the rhoptry proteins was partially protected, while two required drug therapy. The experiment clearly demonstrates that the merozoite surface-coat precursor protein can completely protect Aotus monkeys against a lethal infection of the human malaria parasite.

Animals↗
PubMed1987

Ultrastructural localization of protective and nonprotective Plasmodium falciparum proteins using serum samples from vaccinated Aotus monkeys.

Postembedding immunoelectron microscopy, using pooled serum samples from a recent vaccination experiment involving Aotus monkeys, was used to localize immune targets in Plasmodium falciparum-infected erythrocytes and free merozoites. Serum samples from Aotus monkeys, protected completely by immunization with the P. falciparum merozoite surface coat precursor protein, identified immune targets on the surface of free and intracellular merozoites as well as the cytoplasm, plasma membrane, and parasitophorous vacuole membrane of immature schizonts. Serum samples from unprotected monkeys, which had been immunized with a complex of 143-kDa, 132-kDa, and 102-kDa polypeptides reacted specifically with the rhoptries of immature schizonts and mature merozoites.

Animals↗
PubMed1986

Induction of protective immunity to monoclonal-antibody-defined Plasmodium falciparum antigens requires strong adjuvant in Aotus monkeys.

Monoclonal antibodies to the major Plasmodium falciparum merozoite surface coat and rhoptry antigens were produced. A combination of the affinity-purified polypeptides with Freund complete adjuvant which was given three times completely protected an Aotus lemurinus azure (karotype VI) monkey against homologous challenge; however, immunization with the same polypeptides with a muramyl dipeptide derivative [MDP-Lys(L18)] did not protect a second Aotus monkey, even though comparable high antibody titers were induced.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1984

Plasmodium falciparum: comparative analysis of antigens from continuous in vitro cultured and in vivo derived malarial parasites.

A comparison of metabolically labeled proteins from continuous in vitro and in vivo derived Plasmodium falciparum revealed both similarities and differences. Metabolic labeling of synchronized cultures showed that the uptake of label increased as the parasites matured from the ring to the schizont stage in both cultures. Also, in both continuous in vitro and in vivo derived cultures, prominent high-molecular-weight proteins were synthesized during the late developmental stages. However, the continuous in vitro cultured parasites incorporated twice as much of the label at each stage as did the in vivo derived parasites. Immunoprecipitation with serum samples from vaccinated Aotus trivirgatus griseimembra monkeys revealed major differences involving protein antigens that migrated in the molecular weight regions of b (Mr = 152,000), c (Mr = 143,000), j (Mr = 82,700), and n (Mr = 57,400). These antigens were more readily detected in the continuous in vitro cultured schizonts than in the in vivo derived schizonts.

Animals↗
PubMed1984

Use of human plasma for continuous in vitro cultivation of Plasmodium falciparum.

Plasma from units of human blood collected in CPDA-1 preservative were compared with human serum in cultures of Plasmodium falciparum. No significant differences in parasite growth and multiplication were seen between cultures containing serum or plasma. The wider availability of plasma makes it an attractive alternative to serum, especially in large scale cultures.

Animals↗
PubMed1984

Plasmodium falciparum: protein antigens identified by analysis of serum samples from vaccinated Aotus monkeys.

Serum samples from Aotus trivirgatus subsp. griseimembra monkeys obtained at different stages of a vaccination experiment were analyzed for total antibody titer to Plasmodium falciparum and were used for identifying protective antigens of the human malaria parasite. Total malarial antibody titers were higher in serum samples from protected monkeys (vaccinated with antigen in an adjuvant) than in those from unprotected monkeys (vaccinated with either antigen or adjuvant only). Parasite proteins were labeled with [3H]isoleucine, solubilized with nonionic detergent, and reacted with immune Aotus sera. Immunoprecipitates obtained were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. Thirteen protein antigen bands in the molecular weight range 73,000 to 180,000 were resolved. Serum samples obtained from protected Aotus monkeys reacted more intensely with these proteins than samples from unprotected monkeys did. Evidence is presented that the protective antigen is not a single, normally nonimmunogenic, protein that is recognized only in protected monkeys. Rather, the present data indicate that a heightened immune response to multiple proteins correlated with in vivo protection to P. falciparum in Aotus monkeys. This finding may have a significant bearing on strategies for the development of a human P. falciparum vaccine.

Animals↗
PubMed1984

Plasmodium falciparum merozoite vaccine in Aotus monkeys. An evaluation of the tolerableness of three types of adjuvants.

Eight Aotus trivirgatus monkeys were included in a comparative study of adverse reactions caused by 3 types of malarial vaccine. The antigen consisted of late schizonts and merozoites combined with each of 3 adjuvants, a lipoidal amine CP-20,961, a muramyl dipeptide derivative [B30]-MDP, or Freund's complete adjuvant (FCA); 3 monkeys received CP-20,961 and 3 [B30]-MDP, whereas the FCA vaccine was given to 2 animals. All the vaccine combinations caused some adverse reactions, but their nature and intensity varied. Oedema, petechiae and/or ecchymosis, induration, and formation of fluctuating masses at the injection site were the local reactions observed, but except for the FCA group, all reactions disappeared without notable sequelae. Fever was the commonest general reaction, being mildest in the [B30]-MDP group. A transient increase (about 50%) in leukocyte count and a decrease (15-20%) in red blood cell count were observed in all animals, regardless of the type of adjuvant or whether it was a primary or booster injection in question. However, because the vaccine using [B30]-MDP evoked the mildest reactions, this may be the one most promising for future human studies if its protective efficacy is proven.

Acetylmuramyl-Alanyl-Isoglutamine↗