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Biomedical subjects

K M Davern

Publications and source records attributed to K M Davern.

At least 19 recordsLinked to original sources
PubMed2000

Targeted mutagenesis of Plasmodium falciparum erythrocyte membrane protein 3 (PfEMP3) disrupts cytoadherence of malaria-infected red blood cells.

Adhesion of parasite-infected red blood cells to the vascular endothelium is a critical event in the pathogenesis of malaria caused by Plasmodium falciparum. Adherence is mediated by the variant erythrocyte membrane protein 1 (PfEMP1). Another protein, erythrocyte membrane protein-3 (PfEMP3), is deposited under the membrane of the parasite-infected erythrocyte but its function is unknown. Here we show that mutation of PfEMP3 disrupts transfer of PfEMP1 to the outside of the P.FALCIPARUM:-infected cell. Truncation of the C-terminal end of PfEMP3 by transfection prevents distribution of this large (>300 kDa) protein around the membrane but does not disrupt trafficking of the protein from the parasite to the cytoplasmic face of the erythrocyte membrane. The truncated PfEMP3 accumulates in structures that appear to be associated with the erythrocyte membrane. We show that accumulation of mutated PfEMP3 blocks the transfer of PfEMP1 onto the outside of the parasitized cell surface and suggest that these proteins traffic through an erythrocyte membrane-associated compartment that is involved in the transfer of PfEMP1 to the surface of the parasite-infected red blood cell.

Animals↗
PubMed1999

The adhesion of Plasmodium falciparum-infected erythrocytes to chondroitin sulfate A is mediated by P. falciparum erythrocyte membrane protein 1.

Chondroitin sulfate A (CSA) is an important receptor for the sequestration of Plasmodium falciparum in the placenta, but the parasite ligand involved in adhesion has not previously been identified. Here we report the identification of a var gene transcribed in association with binding to CSA and present evidence that the P. falciparum erythrocyte membrane protein 1 product of the gene is the parasite ligand mediating CSA binding. Description of this gene and the implication of P. falciparum erythrocyte membrane protein 1 as the parasite ligand paves the way to a more detailed understanding of the pathogenesis of placental infection and potential therapeutic strategies targeting the interaction.

Animals↗
PubMed1997

The age-specific prevalence of Plasmodium falciparum in migrants to Irian Jaya is not attributable to agglutinating antibody repertoire.

Previous observations have shown that individuals migrating from a malaria free area to a malaria endemic region in North Eastern Irian Jaya quickly acquire anti-parasite immunity, in an age-dependent manner. Sera from migrants and long-term residents in this area were examined for their ability to agglutinate a range of Plasmodium falciparum isolates and to disrupt erythrocyte rosettes. Antibody responses to merozoite surface protein 2 (MSP2) and ring-infected erythrocyte surface antigen (RESA) were also determined. The range of isolates agglutinated by sera from the migrants approached that seen in long-term residents. No difference was found between migrant adults and children in the range of agglutinating antibody, size of agglutinates, nor disruption of rosettes. Anti-MSP2 and anti-RESA antibodies were the only factors examined which showed a correlation with age. We conclude that although antibody to parasite neoantigens expressed on the surface of infected erythrocytes may play a role in the acquisition of immunity, the humoral response to other P. falciparum antigens is more likely to account for the age-dependent prevalence of parasitaemia observed.

Adult↗
PubMed1997

Targeted gene disruption shows that knobs enable malaria-infected red cells to cytoadhere under physiological shear stress.

Knobs at the surface of erythrocytes infected with Plasmodium falciparum have been proposed to be important in adherence of these cells to the vascular endothelium. This structure contains the knob-associated histidine-rich protein (KAHRP) and the adhesion receptor P. falciparum erythrocyte membrane protein 1. We have disrupted the gene encoding KAHRP and show that it is essential for knob formation. Knob-transfectants adhere to CD36 in static assays; when tested under flow conditions that mimic those of postcapillary venules, however, the binding to CD36 was dramatically reduced. These data suggest that knobs on P. falciparum-infected erythrocytes exert an important influence on adherence of parasitized-erythrocytes to microvascular endothelium, an important process in the pathogenesis of P. falciparum infections.

Animals↗
PubMed1993

High level production of hybrid potyvirus-like particles carrying repetitive copies of foreign antigens in Escherichia coli.

Synthesis in E. coli of native coat protein of Johnsongrass mosaic virus, and hybrid protein molecules containing foreign antigens, resulted in the intracellular formation of potyvirus-like particles (PVLPs). The foreign antigens used were an octapeptide epitope from Plasmodium falciparum and a decapeptide hormone (luteinizing hormone releasing hormone) at the N- or at both N- and C-terminal regions of the coat protein molecule, and a full length protein antigen (Sj26-glutathione S-transferase of 26 kD from Schistosoma japonicum) replacing the N-terminal 62 amino acids of the coat protein. Electron microscopy of ultrathin sections of E. coli revealed that PVLPs resulting from coat protein molecules containing peptide fusions appeared in vast arrays of parallel strands within the cytoplasm sometimes extending the length of the cell and at times the cells were strung together, with "threads" of PVLPs appearing to connect individual bacterial cells. PVLPs resulting from the fusion of the 26 kD antigen Sj26 to coat protein were shorter and wider. The physical form of the high molecular weight PVLPs enabled purification by simple size exclusion column chromatography. The Sj26-PVLPs administered to mice without adjuvant elicited antibody responses comparable to monomeric Sj26 administered with Freund's Complete Adjuvant.

Animals↗
PubMed1992

Adherence of infected erythrocytes to venular endothelium selects for antigenic variants of Plasmodium falciparum.

Erythrocytes (E) infected with asexual forms of malaria parasites exhibit surface antigenic variation. In Plasmodium falciparum infections, the variant Ag is the P. falciparum E membrane protein 1 (PfEMP1). This molecule may also mediate the adherence of infected E to host venular endothelium. We show here that parasite lines selected for increased adherence to endothelial cells have undergone antigenic variation. Three adherent lines selected from the same P. falciparum clone reacted with the same agglutinating antiserum that failed to agglutinate the parental clone. Immunoprecipitation experiments with the agglutinating anti-serum demonstrated that the selected lines expressed cross-reactive forms of PfEMP1 that were of higher m.w. and antigenically distinct from PfEMP1 of the parental clone. When one of the adherent lines was cloned in the absence of selection, a range of variant antigenic types emerged with differing cytoadherence phenotypes. These findings show that selection for cytoadherence in vitro favors the emergence of antigenic variants of P. falciparum and suggest that the requirement for cytoadherence in vivo may restrict the range of antigenic variants of P. falciparum in natural infections.

Animals↗
PubMed1991

Serologic reactivities of the 23-kDa integral membrane proteins of schistosomes.

The 23-kDa integral membrane proteins of Schistosoma mansoni and Schistosoma japonicum (Sm23 and Sj23) are Ag of some interest in terms of both antiparasite vaccination and immunodiagnosis. We have raised an antiserum against a recombinant fusion protein expressing the extracellular hydrophyllic domain of Sm23 (Sm23HD-pGEX) and used this serum, as well as other antibody reagents reacting with Sm/Sj23, in immunochemical analyses. The immunogenicity and antigenicity of Sm23HD-pGEX, and the surprising lack of cross-reactivity between Sm23 and Sj23 support the hypothesis that Sm/Sj23 are host-like molecules with a very limited number of B cell epitopes that are likely to reside in the extracellular hydrophilic domain. We also present evidence that, unlike the highly immunogenic Sj23, Sm23 is not immunogenic in chronically infected mice. Moreover, we confirm a surface location for Sj23 in adult worms, in S. japonicum.

Animals↗
PubMed1991

Further characterisation of the Schistosoma japonicum protein Sj23, a target antigen of an immunodiagnostic monoclonal antibody.

Sj23, the 23-kDa target antigen in Schistosoma japonicum adult worms of the hybridoma monoclonal antibody (mAb) I-134, has been identified and cloned from cDNA libraries, mAb I-134 has been successfully used in immunodiagnostic assays to detect S. japonicum infection in Philippine patients. Sequence analysis has shown that Sj23 is the homologue, with 84% amino acid identity, of Sm23, a 23-kDa molecule from S. mansoni worms previously described from our laboratory. The domain structures of Sj23 and Sm23 are strikingly similar to the human membrane proteins ME491, CD37, CD53 and TAPA-1, which may suggest a functional role for the schistosome molecules in cellular proliferation.

Amino Acid Sequence↗
PubMed1991

The functional and immunological significance of some schistosome surface molecules.

The molecules discussed in this review include some of the leading vaccine candidates in schistosomiasis: the glutathione S-transferases, triose-phosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase and the 23 and 25 kDa surface integral membrane proteins. Mark Wright, Kathy Davem and Graham Mitchell highlight the possible biological roles and immunological relevance of these molecules.

Journal Article↗
PubMed1990

Schistosoma japonicum: monoclonal antibodies to the Mr 26,000 schistosome glutathione S-transferase (Sj26) in an assay for circulating antigen in infected individuals.

Two monoclonal antibodies have been produced that bind to separate epitopes on the Mr 26,000 glutathione S-transferase (GST) of Schistosoma japonicum worms (Sj26). Both antibodies have been used in an enzyme immunoassay (EIA) with sera from infected individuals from the Philippines. Relatively high signals were obtained with sera from some, but not all, individuals who are positive for fecal eggs. Evidence was obtained that the material detected by the monoclonal antibodies was present in minute amounts and in some sera was bound in a complex with phosphorylcholine-containing molecules. It could not be absorbed by reaction with glutathione-agarose columns. There was no detectable immunoglobulin in the complex. The possibility exists that the complexes are composed of schistosome GST, or fragments, and damaged tegumental lipids shed as a result of surface immune attack. However, the presence of the native Sj26 molecule has not been proven. More detailed longitudinal studies in endemic areas are required to determine whether the assay can be used as an indicator of acquired resistance ("concomitant immunity") and whether it will be useful in the search for immunological correlates of this resistance in humans.

Adolescent↗
PubMed1990

Comparison of the cloned genes of the 26- and 28-kilodalton glutathione S-transferases of Schistosoma japonicum and Schistosoma mansoni.

Both Schistosoma japonicum and S. mansoni contain 28- and 26-kDa glutathione S-transferases (GSTs). Despite their immunological cross-reactivity using rabbit antisera, the S. japonicum 28-kDa GST (Sj28) is weakly immunogenic relative to the S. mansoni protein (Sm28) in mouse immunization experiments using GSTs purified from adult worms. The difference in immunogenicity is also observed during schistosome infection in mice. Using surface-labeled living S. japonicum worms, evidence was obtained for a surface location of Sj28 comparable to that reported for the S. mansoni molecule. The nucleotide and deduced amino acid sequences of cDNA clones corresponding to Sj28 and Sm28 were compared. Despite obvious homology (77% identity), differences were found in regions known to contain T epitopes in the S. mansoni protein which may be an explanation for the striking differences in immunogenicity in regard to antibody production in mice. The 26-kDa GSTs of these two parasites (Sj26 and Sm26) are also closely related on the basis of nucleotide and deduced amino acid sequences, there being 82% identity in the putative coding regions. When the amino acid sequences of Sj28 and Sm28 were compared with those of Sj26 and Sm26, the overall sequence identity was approximately 20%. However, a relatively conserved region was identified in otherwise structurally different molecules which may participate in common properties of these enzymes.

Amino Acid Sequence↗
PubMed1990

Studies on the sex ratio of worms in schistosome infections.

Sex ratios of adult schistosomes in mice are almost invariably different from 1.0 and are biased towards males. The bias applies to wild rats infected with Schistosoma japonicum and trapped in an endemic area of the Philippines (male:female ratio = 1.7). It also applies to cercariae of snails collected in such areas and assessed by infection of laboratory mice using cercariae from individual snails (male:female ratio may approach 6.0). Experiments were designed to determine if duration of infection in the mammalian host was a factor that influenced the sex ratio of miracidia used for infecting snails and subsequently mice. BALB/c and C57BL/6 mice were infected with 100 cercariae of S. mansoni, and liver eggs harvested at early and late time points for infection of snails and production of cercariae. Two phenomena were demonstrated: firstly, a more pronounced male bias when eggs were harvested late compared with early in infection; secondly, a reduced apparent hatchability of eggs in BALB/c compared with C57BL/6 livers. The possibility is raised by the data that female miracidia within eggs of chronically infected individuals may be more prone to immune damage than male miracidia with important epidemiological consequences.

Animals↗
PubMed1990

Attempts to induce resistance in mice to Schistosoma japonicum and Schistosoma mansoni by exposure to crude schistosome antigens plus cloned glutathione-S-transferases.

Several attempts have been made to induce resistance in mice to Schistosoma japonicum (Philippines) or Schistosoma mansoni by exposure to living male and/or female adult worms, their antigens or irradiated cercariae. No resistance was demonstrated in the following cases: re-exposure of mice to cercariae following praziquantel (PZQ) treatment of existing infection; re-exposure of mice following cyclosporin A (CsA) treatment at the time of first cercarial exposure; subcutaneous or intraperitoneal deposition of living male or female worms; repeated intranasal administration of crude worm homogenates plus Bordetella pertussis vaccine (BPV) as adjuvant. Homologous 60Co-irradiated cercariae were very effective at inducing resistance to infection with S. mansoni but not to infection with S. japonicum (Philippines) in a limited series of experiments. A regime of infection, immunization with homologous Escherichia coli-derived glutathione-S-transferases (GST), then PZQ treatment followed by homologous re-exposure did not result in significant resistance in either the S. mansoni or the S. japonicum (Philippines) systems. Mice given irradiated cercariae plus GST were not more resistant to subsequent S. mansoni infection than mice given irradiated cercariae alone. The results generally confirm and extend those reported by others with the conclusion that resistance to schistosomes in mice is difficult to achieve by exposure to adult worm antigens alone. Moreover, additional immunization with the GST available to date as cloned gene products, and injected in Freund's complete adjuvant, does not influence the outcome of exposure to crude worm antigens including any additive effects of protective irradiated cercariae.

Adjuvants, Immunologic↗
PubMed1989

Monoclonal antibodies reacting with Schistosoma japonicum eggs and their target epitopes.

Ten monoclonal antibodies (McAbs) raised to Schistosoma japonicum eggs could be assigned using several serological and immunochemical techniques to 3 groups. The McAbs, termed A, B and C-McAbs, apparently recognize carbohydrate epitopes that can be located on the same antigen molecule. The antibodies, generally of IgM isotype, are idiotypically related. They are distinct from another IgM McAb (Group D-McAb) the carbohydrate target epitope of which can also be associated with the epitopes of A, B and C-McAbs. The McAbs produce large vacuolated bleb reactions in the circumoval precipitin test (COPT) and target epitopes have different representations in various life cycle stages such as immature and mature eggs, male and female worms (including S. mansoni). Antigens affinity purified on columns containing A, B, C and D-McAbs stimulate proliferation of T cells from egg-sensitized mice and elicit DTH reactions in such mice. This raises the possibility that the target antigens of these carbohydrate-reactive monoclonal antibodies are immunopathologic and involved in egg-induced granuloma formation.

Animals↗
PubMed1988

Expression of an enzymatically active parasite molecule in Escherichia coli: Schistosoma japonicum glutathione S-transferase.

The NH2-terminal amino acid sequence of the Mr 26 000 glutathione S-transferase (EC 2.5.1.18) of Schistosoma japonicum (Sj26) has been deduced by RNA and protein sequence analysis. Using this information, a bacterial plasmid has been constructed that directs the synthesis of the entire Sj26 molecule in Escherichia coli. Recombinant Sj26 exhibits glutathione S-transferase activity and can be readily purified from bacteria in a one-step procedure under non-denaturing conditions. The availability of recombinant Sj26 in essentially unlimited quantities will aid its assessment as a candidate vaccine molecule in schistosomiasis and could eventually lead to the rational design of a drug targetted on schistosome glutathione S-transferases.

Amino Acid Sequence↗
PubMed1988

Sensitization against the parasite antigen Sj26 is not sufficient for consistent expression of resistance to Schistosoma japonicum in mice.

Mice immunized with purified antigen preparations produced in Escherichia coli and containing the glutathione S-transferase (GST) isoenzyme of Schistosoma japonicum (Sj26) can be partially resistant to infection with this parasite. Maximum resistance was approximately 50% and no protection was obtained in BALB/c mice, known low responders to Sj26. Although only Freund's complete adjuvant has been used, the data obtained indicate that satisfactory levels of resistance to S. japonicum will not be attained by vaccination with Sj26 alone. Other antigens, including the additional GST isoenzyme of S. japonicum Sj28, will probably be required to establish whether Sj26 will be an important component of a defined multivalent vaccine against schistosomiasis japonica.

Animals↗
PubMed1988

Immunoblotting analysis of the major integral membrane protein antigens of Schistosoma japonicum.

Triton X-114 has been employed to isolate integral membrane proteins from Schistosoma japonicum and Schistosoma mansoni adult worms. Suitable marker molecules and antisera directed or raised against schistosome proteins partitioned by Triton X-114 extraction indicated that the phase separation and purification of integral membrane proteins had been successful and this fraction was free of contamination with aqueous (soluble) or secretory antigens. Two dimensional immunoblots further exemplified differences between antigens in the integral membrane protein extract and those of the aqueous fraction. Seven S. japonicum integral membrane proteins have been identified on immunoblots by serum from a hyperimmune and an infected rabbit and by sera from Philippine patients with a history of schistosomiasis japonica. Integral membrane proteins of S. mansoni and S. japonicum had surprisingly little conformity in the molecular weights and electrophoretic mobilities between the two species.

Alkaline Phosphatase↗