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Biomedical subjects

L F Yuan

Publications and source records attributed to L F Yuan.

At least 19 recordsLinked to original sources
PubMed1997

Development of two monoclonal antibodies against Plasmodium falciparum sporozoite surface protein 2 and mapping of B-cell epitopes.

The Plasmodium yoelii sporozoite surface protein 2 (PySSP2) is the target of protective cellular immunity. Cytotoxic T cells specific for the Plasmodium falciparum analog PfSSP2, also known as thrombospondin-related anonymous protein (TRAP), are induced in human volunteers immunized with irradiated sporozoites. PfSSP2 is an important candidate antigen for a multicomponent malaria vaccine. We generated and characterized three monoclonal antibodies (MAbs) specific for PfSSP2/TRAP. The MAbs PfSSP2.1 (immunoglobulin G1 [IgG1]), PfSSP2.2 (IgG2a), and PfSSP2.3 (IgM) were species specific and identified three distinct B-cell epitopes containing sequences DRYI, CHPSDGKC, and TRPHGR, respectively. PfSSP2.1 partially inhibited P. falciparum liver-stage parasite development in human hepatocyte cultures (42 and 86% in two experiments at 100 microg/ml). Mice immunized with vaccinia virus expressing full-length PfSSP2 protein produced antibodies to (DRYIPYSP)3, and humans living in malaria-endemic areas (Indonesia and Kenya), who have lifelong exposure and partial clinical immunity to malaria, had antibodies to both (DRYIPYSP)3 and (CHPSDGKCN)2. Mice immunized with multiple antigen peptides MAP4 (DRYIPYSP)3P2P30 and MAP4 (CHPSDGKCN)3P2P30 in TiterMax developed antibodies to sporozoites that partially inhibited sporozoite invasion of human hepatoma cells (39 to 71% at a serum dilution of 1:50 in three different experiments). The modest inhibitory activities of the MAbs and the polyclonal antibodies to PfSSP2/TRAP epitopes do not suggest that a single-component vaccine designed to induce antibodies against PfSSP2/TRAP will be protective. Nonetheless, the MAbs directed against PfSSP2, and the peptides recognized by these MAbs, will be essential reagents in the development of PfSSP2/TRAP as a component of a multivalent P. falciparum human malaria vaccine.

Amino Acid Sequence↗
PubMed1992

Identification of three novel missense PKU mutations among Chinese.

Three novel missense mutations have been identified in the phenylalanine hydroxylase (PAH) genes of Chinese individuals afflicted with various degrees of phenylketonuria (PKU). A T-to-C transition was observed in exon 5 of the gene, resulting in the substitution of Phe161 by Ser161. Two substitutions, G-to-T and T-to-G, were observed in exon 7, resulting in the substitution of Gly247 by Val247 and Leu255 by Val255, respectively. Expression analysis demonstrated that these mutant proteins produced between 0 and 15% of normal PAH enzyme activity. Population screening of a Chinese sample population indicates that these mutations are quite rare, together accounting for only about 4% of all PKU alleles among the Chinese. The P161S and G247V mutations were each present on a single PAH RFLP haplotype 4 chromosome in patients form Northern China, while the L255V mutation was present on chromosomes of both haplotypes 18 and 21 in patients from Southern China. These results suggest that the remaining 30% of uncharacterized PKU alleles in the Chinese population may bear a large number of relatively rare PAH mutations.

Alleles↗
PubMed1992

Identification of three novel PKU mutations among Chinese: evidence for recombination or recurrent mutation at the PAH locus.

Three novel mutations have been identified in the phenylalanine hydroxylase (PAH) genes of Chinese classical phenylketonuria (PKU) patients. Two of these substitutions (W326X and Y356X) result in the generation of a premature stop codon, while the third (IVS-7nt2) alters an invariant dinucleotide splicing signal. These mutations together account for about 10% of all PKU alleles in the Chinese population. The W326X mutation is associated with PAH RFLP haplotype 4, the most common haplotype in Orientals, while the IVS-7nt2 mutation occurs once on a haplotype 7 chromosome. The Y356X mutation is associated with multiple haplotypes, possibly due to crossover, gene conversion, or recurrent mutation.

Asian People↗
PubMed1992

Low immunogenicity of a Plasmodium vivax circumsporozoite protein epitope bound by a protective monoclonal antibody.

The repeat region of the Plasmodium vivax circumsporozoite (CS) protein contains 20 copies of the nine-amino acid sequence DRA A/D GQPAG. A monoclonal antibody that passively protects monkeys against sporozoite challenge recognizes a four-amino acid linear sequence AGDR included within this nonamer, but when monkeys were immunized with a vaccine, NS1(81)V20, which contains 20 copies of the nonamer, they failed to produce antibodies to AGDR. To determine if natural exposure to sporozoites induces antibodies to AGDR, we tested sera from 176 individuals from a malaria-endemic area in Flores, Indonesia. Seventy-one percent of the adults had antibodies to the P. vivax repeat region; only 18% had detectable antibodies to AGDR. None of the subjects had antibodies to the P. vivax variant repeat ANGAGNQPG. We next tested sera from six human volunteers immunized with NS1(81)V20 and found that the vaccine, despite inducing antibodies against the nonamer, as it did in the monkeys, did not induce antibodies against AGDR. To further test our ability to raise anti-AGDR antibodies using synthetic peptides, we immunized Aotus monkeys and BALB/c mice with AGDR. Sera from the mice reacted strongly with both AGDR and a recombinant protein containing the 20 copies of the nonamer. Sera from the monkeys reacted only minimally with a protein (VIVAX-1) that contains monomeric AGDR within its sequence. Sera from the mice also bound air-dried P. vivax sporozoites, while sera from the monkeys did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Founder effect of a prevalent phenylketonuria mutation in the Oriental population.

A missense mutation has been identified in the human phenylalanine hydroxylase [PAH; phenylalanine 4-monooxygenase; L-phenylalanine, tetrahydrobiopterin:oxygen oxidoreductase (4-hydroxylating), EC 1.14.16.1] gene in a Chinese patient with classic phenylketonuria (PKU). A G-to-C transition at the second base of codon 413 in exon 12 of the gene results in the substitution of Pro413 for Arg413 in the mutant protein. This mutation (R413P) results in negligible enzymatic activity when expressed in heterologous mammalian cells and is compatible with a classic PKU phenotype in the patient. Population genetic studies reveal that this mutation is tightly linked to restriction fragment length polymorphism haplotype 4, which is the predominant haplotype of the PAH locus in the Oriental population. It accounts for 13.8% of northern Chinese and 27% of Japanese PKU alleles, but it is rare in southern Chinese (2.2%) and is absent in the Caucasian population. The data demonstrate unambiguously that the mutation occurred after racial divergence of Orientals and Caucasians and suggest that the allele has spread throughout the Orient by a founder effect. Previous protein polymorphism studies in eastern Asia have led to the hypothesis that "northern Mongoloids" represented a founding population in Asia. Our results are compatible with this hypothesis in that the PKU mutation might have occurred in northern Mongoloids and subsequently spread to the Chinese and Japanese populations.

Asian People↗
PubMed1991

Monoclonal, but not polyclonal, antibodies protect against Plasmodium yoelii sporozoites.

One of the primary strategies for malaria vaccine development has been to design subunit vaccines that induce protective levels of antibodies against the circumsporozoite (CS) protein of malaria sporozoites. In the Plasmodium yoelii mouse model system such vaccines have been uniformly unsuccessful in protecting against sporozoite-induced malaria. To demonstrate that antibodies to P. yoelii CS protein could provide protection we established a passive transfer model. Passive transfer of Navy yoelii sporozoite 1 (NYS1), an IgG3 mAb against the P. yoelii CS protein, protected 100% of mice against challenge with 5000 P. yoelii sporozoites. Binding of NYS1 to sporozoites was inhibited by incubation with (QGPGAP)2, a synthetic peptide derived from the repeat region of the P. yoelii CS protein, indicating that the epitope on sporozoites recognized by this mAb was included within this peptide. The levels of antibodies to (QGPGAP)2 by ELISA, and to sporozoites by indirect fluorescent antibody test and CS precipitation reaction were similar in sera from mice that received NYS1 in passive transfer and were protected against challenge with 5000 sporozoites, and from mice that had been immunized with subunit vaccines containing (QGPGAP)2 but were not protected against challenge with 40-200 sporozoites. To determine if antibody avidity, not absolute concentration could explain the striking differences in protection, we established a thiocyanate elution assay. The results suggest that NYS1, the protective mAb, has a lower avidity for (QGPGAP)2 and for sporozoites than do the vaccine-induced antibodies. Although the results of the conventional antibody assays did not correlate with protection, sera from the protected animals inhibited sporozoite development in mouse hepatocyte cultures significantly more than did the sera from the unprotected, subunit vaccine-immunized animals, correlating with protection. The data clearly demonstrate that antibodies to the CS protein can protect against intense sporozoite infection. Improved understanding of the differences between protective mAb and nonprotective polyclonal antibodies will be important in the further development of malaria vaccines.

Animals↗
PubMed1991

Missense mutations prevalent in Orientals with phenylketonuria: molecular characterization and clinical implications.

Two missense mutations in the phenylalanine hydroxylase (PAH) genes of Orientals with phenylketonuria (PKU) have been identified. A G-to-A transition in exon 7 of the gene results in the substitution of Gln243 for Arg243 (R243Q) and accounts for 18% of all PKU chromosomes among Chinese. An A-to-G transition in exon 6 of the gene results in the substitution of Cys204 for Tyr204 (Y204C) and identifies about 13 and 5% of all PKU chromosomes in the Chinese and Japanese populations, respectively. The R243Q construct produced less than 10% of normal PAH activity in in vitro expression analysis in a eukaryotic cell system, and patients homozygous for this substitution exhibit a severe clinical phenotype. These results are consistent with previous findings in this expression system. The Y204C construct, however, produced near normal levels of PAH enzyme activity and immunoreactivity in this in vitro expression system. Because this substitution is present only on PKU chromosomes, it is a valuable marker for identifying the corresponding mutant allele for carrier screening of PKU. With the characterization of these two substitutions, about 60% of PKU alleles in China can now be identified. The continuing search for additional PKU mutations will permit effective carrier screening and prenatal gene diagnosis of PKU in East Asia.

Alleles↗
PubMed1990

Active and passive immunization against Plasmodium yoelii sporozoites.

Three subunit vaccines based on the major repeat, (QGPGAP)n, and flanking regions of the Plasmodium yoelii circumsporozoite protein were designed, produced, and tested. All were immunogenic, but none gave consistent protection against a 40-200 sporozoite challenge. To demonstrate that antibodies to P. yoelii CS protein could provide protection we established a passive transfer model. Passive transfer of NYS1, an IgG3 MAb against the P. yoelii CS protein, protected 100% of mice against challenge with 5000 P. yoelii sporozoites. Binding of NYS1 to sporozoites was inhibited by incubation with (QGPGAP)2, indicating that the epitope on sporozoites recognized by this MAb was included within this peptide. The levels of antibodies to (QGPGAP)2 by ELISA, and to sporozoites by IFAT and CS precipitation reaction were similar in sera from mice that received NYS1 in passive transfer and were protected against challenge with 5000 sporozoites, and from mice that had been immunized with subunit vaccines containing QGPGAP but were not protected against challenge with 40-200 sporozoites. To determine if antibody avidity, not the absolute concentration, could explain the striking differences in protection, we established a thiocyanate elution assay. The results suggest that NYS1, the protective MAb, has a lower avidity for (QGPGAP)2 and for sporozoites than do the vaccine-induced antibodies. The data clearly demonstrate that antibodies to the CS protein can protect against intense sporozoite infection. Improved understanding of the differences between protective MAbs and non-protective polyclonal antibodies will be important in the further development of malaria vaccines.

Animals↗
PubMed1989

Analysis of 4628 cases in the genetic counselling clinic of PUMC Hospital.

An analysis of 4628 cases in the genetic counseling clinic of PUMC Hospital is reported. Althogether 966 cases (20.87%) were diagnosed as having genetic diseases, among whom were 436 cases (45.13%) with chromosome aberrations, 161 (16.67%) with inherited metabolic diseases, 111 (11.49%) with constitutional bone diseases, 103 (10.66%) with various kinds of genetic neuromuscular diseases, 109 (11.28%) with different dysmorphic syndromes, and 46 (4.76%) with different kinds of genetic dermatoses and oculopathies. 973 cases (21.02%) were suspected to suffer from some form of genetic disease, but this could not be proved due to a lack of specific diagnostic methods. 2689 cases (58.10%) were found to be unaffected by inherited diseases. Some of the experiences gained and the key role of genetic counselling in family planning are briefly discussed.

Adolescent↗
PubMed1988

The use of dextran as a blocking agent on nitrocellulose membrane in the analysis of sporozoite antigens of Plasmodium vivax.

Dextran (molecular weight, 71,200) has been found to block the unbound sites of the nitrocellulose membrane, to which antigens have been electroblotted from acrylamide gel, for use in assaying monoclonal antibodies. The use of polysaccharide as a blocking agent allows the antigens on the nitrocellulose membrane to be digested with pronase and subsequently reacted with monoclonal antibodies. Sporozoite antigens of Plasmodium vivax, after being digested with pronase, completely lost their antigenicity to bind to the sporozoite-specific monoclonal antibodies, thus suggesting that they are proteins or protein conjugates in nature. The method described here for qualitative determination of protein antigens requires as little as 2000 sporozoites for each assay.

Animals↗
PubMed1987

Characterization of Plasmodium yoelii monoclonal antibodies directed against stage-specific sporozoite antigens.

A battery of monoclonal antibodies against Plasmodium yoelii sporozoites was produced. Five of these (NYS1 through NYS5) were selected for characterization. All five were positive in the indirect immunofluorescent antibody test with P. yoelii sporozoites; however, each showed a different immunofluorescence pattern. Although NYS1 (immunoglobulin G3 [IgG3]), NYS2 (IgG3), and NYS3 (IgM) were positive in the circumsporozoite precipitation test, only NYS1 and NYS2 were able to neutralize sporozoite infectivity in mice. NYS4 (IgM) and NYS5 (IgG1) were not positive in the precipitation test and did not protect mice from sporozoite infection. All except NYS4 were species as well as stage specific. NYS4 cross-reacted with sporozoites of P. berghei. Electrophoretic immunoblotting analysis showed that these monoclonal antibodies detected sporozoite antigens of various molecular weights. Inhibition enzyme-linked immunosorbent assays indicated that each recognized a different antigenic epitope. The differences in their immunochemical and biological reactivity make them useful for screening a variety of P. yoelii antigens in recombinant DNA libraries. These antigens will be used in an animal model system for vaccine development.

Animals↗