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Biomedical subjects

G F Mitchell

Publications and source records attributed to G F Mitchell.

At least 55 records · Page 3Linked to original sources
PubMed1991

Vaccination against Taenia taeniaeformis infection in rats using a recombinant protein and preliminary analysis of the induced antibody response.

Primary screening of a cDNA expression library of Taenia taeniaeformis oncospheres in lambda gt11 bacteriophage was carried out using rabbit anti-T, taeniaeformis oncosphere serum affinity-purified from oncosphere pellets. From approximately 1.6 x 10(5) plaques, 21 single clones that were positive with the affinity-purified antibodies were isolated. Sibling analysis revealed that 17 clones out of the 21 could be assigned to five different antigen families. Only family 1 was strongly recognized by a serum prepared in a rabbit against a partially purified host-protective oncosphere antigen fraction. The fragments of lambda DNA were inserted into a pGEX plasmid vector that encodes glutathione S-transferase (GST) of Schistosoma japonicum. Clones designated TtO-18, -49.53 (family 1), 46 (family 2), 15 (family 3), 40 (family 4) and 66 (family 5) were established as subclones in pGEX-1 plasmid vectors which produced GST fusion proteins. All GST fusion proteins were soluble and recognized by anti-GST and anti-TtO sera. Three vaccination experiments with these fusion proteins using specific-pathogen-free Wistar rats revealed that all three fusion proteins of family 1 were exclusively effective against T. taeniaeformis oncosphere challenge with approximately 95% and 91% reductions in cystic metacestode and total metacestode recoveries, respectively. Rats vaccinated with fusion proteins of family 1 produced antibodies which reacted with a 21-kDa oncosphere antigen component which appeared to be a major oncosphere stage-specific antigen.

Animals↗
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↗
PubMed1991

Co-evolution of parasites and adaptive immune responses.

The interplay between evolving host populations and evolving parasite populations is dominated by two key genetically based elements, namely the virulence of parasites and the resistance of their hosts. Here, Graham Mitchell gives a personal overview of ideas on the coevolution of parasite-host relationships and the contributions to immunology that are likely to emerge from systematic studies on this relationship.

Adaptation, Biological↗
PubMed1991

Evidence that a 16-kilodalton integral membrane protein antigen from Schistosoma japonicum adult worms is a type A2 phospholipase.

Type A2 phospholipase (PLA2) activity has been observed in integral membrane protein extracts of Schistosoma japonicum. Antiserum raised against bee venom PLA2 recognized a single 16-kDa band in the parasite extracts; it also localized to antigen in the gut lining of fixed adult schistosomes as shown by immunofluorescence techniques. Evidence was obtained that the molecule was expressed at low levels in comparison with other integral membrane proteins and was weakly immunogenic in rabbits. Two oligonucleotide probes were constructed on the basis of highly conserved regions between the nucleotide sequences of rat, bovine, rattlesnake, and bee venom PLA2; these probes were used to isolate S. japonicum genomic DNA phage clones. A 1.8-kb FnuD2 fragment was shown by Southern blot analysis to strongly hybridize with the 5' 32P-labeled PLA2 oligonucleotides in both S. japonicum genomic DNA and DNA from one of the phage clones. The nucleotide and predicted amino acid sequences of this fragment revealed homology with the C terminus of PLA2s from different species.

Amino Acid Sequence↗
PubMed1991

Serological evaluation of the macrofilaricidal effects of diethylcarbamazine treatment in bancroftian filariasis.

An Mr 200,000 phosphorylcholine-containing antigen (PC-Ag) of predominantly adult worm origin was found in the sera of humans infected with Wuchereria bancrofti. This paper describes results of a longitudinal study of changes in levels of PC-Ag in response to diethylcarbamazine (DEC) therapy as measured by two-site immunoradiometric assay (IRMA) and Western blotting. One hundred thirty-two residents of a bancroftian filariasis-endemic area of Papua New Guinea (PNG) were treated with a 72 mg/kg dose of DEC. A macrofilaricidal effect was seen with this dose of DEC as 34% of the treated subjects had localized side effects and long-term decreases in microfilariae (mf) counts were observed 12 months after treatment. The PC-Ag levels were reduced to 72%, 52%, and 51% of pretreatment values at 21 days and at six and 12 months after treatment. These decreases, observed by IRMA, were specifically associated with loss of the Mr 200,000 PC-Ag detected by immunoadsorption and Western blotting. From drug treatment data, the maximum half-life of PC-Ag in circulation was calculated to be 50 days, assuming a first-order decay process. This maximum half-life indicates that persistent antigenemia observed in the majority of treated subjects could only result from the survival of adult worms. In the absence of methods to directly demonstrate W. bancrofti adult worms, detection of serum PC-Ag levels provides a sensitive indirect measure of the dynamics of adult worm populations. This serological measurement may be useful in optimizing the macrofilaricidal and therapeutic effects of DEC and in assessing the macrofilaricidal action of new antifilarial drugs and immunological interventions.

Adolescent↗
PubMed1990

Glutathione S-transferase. Novel vaccine against Fasciola hepatica infection in sheep.

The potential of GST as a vaccine candidate against liver fluke infection in ruminants was studied by vaccinating sheep (n = 9) with GST purified from adult worms of Fasciola hepatica and challenging with 500 F. hepatica metacercariae. The immunization induced a high antibody response to GST in contrast to the poor or undetectable response to this Ag observed in naturally infected sheep. Throughout the trial, the progress of the fluke infection was monitored by measuring RBC hemoglobin levels, the extent of liver damage and the fecal egg output in the sheep. This analysis indicated that a subpopulation (n = 4) of the GST vaccinated animals exhibited no anemia, reduced liver damage and a lower mean fecal egg count relative to the infected control group suggesting a lower fluke burden in these animals. Worm burdens in the livers of the GST vaccine group (107 +/- 22) were 57% lower than in the infected control group (250 +/- 25). The subpopulation of the GST vaccine group demonstrated a 78% reduction in mean worm burdens relative to the control group. These results show that GST of adult F. hepatica is a novel Ag that can significantly protect sheep against liver fluke infection. The results suggest that the immune response to GST is directed to the juvenile worm reducing the number of worms that can establish in the liver of the vaccinated animals.

Animals↗
PubMed1990

An immunogenic Mr 23,000 integral membrane protein of Schistosoma mansoni worms that closely resembles a human tumor-associated antigen.

A Mr 23,000 Ag of the human trematode parasite, Schistosoma mansoni, has been identified by immunoscreening an adult worm cDNA library with antibody affinity purified on the Mr 23,000 to 25,000 integral membrane protein fraction of the parasite. This Ag is immunogenic in infected humans as well as in rabbits exposed to S. mansoni. The protein sequence of the Ag as deduced from cloned DNA sequences is 218 amino acids long and contains four putative transmembrane regions. Of particular significance, the Ag is strikingly similar, with respect to both amino acid sequence (36% identity) and putative domain structure to ME491, a human stage-specific melanoma-associated Ag.

Amino Acid Sequence↗
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

Purification of a putative lipoprotein receptor from Schistosoma japonicum adult worms.

A 43-kDa putative lipoprotein receptor from Schistosoma japonicum adult worms (Sj43) has been purified by reverse-phase high-performance liquid chromatography (HPLC) using a Waters Delta-pak C4 300 A 15 mu 3.9 mm x 300 mm column. A linear acetonitrile gradient from 10-95%, spanning 40 min and at a flow rate of 0.9 ml min-1 was employed for the elution of bound material. Sj43 had a retention time of approximately 13 min on the column, whereas other main components from the parasite extract had a much longer retention time. Sj43 purified as a doublet which could be cleaved with Staphylococcus aureus V8 protease but was unaffected by treatment with a mixture of endoglycosidase F and glycopeptidase F. Human low-density lipoprotein exhibited typical saturation kinetics on the HPLC-purified Sj43 with a calculated stoichiometry of 2 mol LDL mol-1 of the putative receptor. No evidence of high-density lipoprotein (HDL3) saturation was observed on purified Sj43, this being of some interest since it parallels observations made with mammalian HDL3-binding proteins.

Animals↗
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↗