Search PubMed⌕ Search

Biomedical subjects

A J Simpson

Publications and source records attributed to A J Simpson.

At least 145 records · Page 8Linked to original sources
PubMed1992

Tegumental proteins of Schistosoma mansoni: complex biomolecules and potent antigens.

The passive transfer of monoclonal antibodies, direct vaccination and in vitro assays have all shown that antigens associated with the tegumental membranes of Schistosoma mansoni are capable of mediating protective immune responses against the parasite in animal models. Furthermore, the principal antigens are highly antigenic during natural infection in man and stimulate strong humoral and cellular responses although, at present, their role in mediating protective immune responses in man remains equivocal. This presentation will review the current state of knowledge of the structure and expression of the major antigenic tegumental proteins of the schistosome and will attempt to relate the relevance of their structural features to possible function both in terms of protective immunity and the parasite's ability to survive within the definitive host. A focus will be the recent advances that have been made in the identification of means of anchoring of the antigenic proteins to the tegumental membrane. In addition, the implications of the structural complexity of the tegumental proteins in terms of their possible utility in vaccination and diagnosis will be considered.

Animals↗
PubMed1991

Human IgE, IgG4 and resistance to reinfection with Schistosoma haematobium.

A well recognized feature of the immune response to parasitic helminth infections, including schistosomiasis, is the production of large amounts of specific and nonspecific IgE1,2. Immunological pathways involving IgE can lead to damage to the developing schistosomulum and it has been suggested that responses involving IgE could have evolved as protection against helminth infections. There has been no epidemiological evidence to support this idea and the only significant IgE responses known in man are those involved in the pathogenesis of allergic disease. Here we measure serological response during reinfection with S. haematobium and demonstrate that IgE antibodies in man can be beneficial. Our results support the hypothesis that the slow build-up of IgE to high levels and the early production of IgG4 antibodies, which may block IgE pathways are responsible for delaying the development of protective immunity to S. haematobium.

Adolescent↗
PubMed1991

Sm25, a major schistosome tegumental glycoprotein, is dependent on palmitic acid for membrane attachment.

Sm25, a major antigen in the surface tegument of the parasitic helminth Schistosoma mansoni, is a 25 kDa N-glycosylated glycoprotein which co-purifies with isolated surface membranes and behaves as an integral membrane protein in Triton X-114 (TX-114). The deduced amino acid sequence of Sm25 shows a short C-terminal hydrophobic domain between residues 163 and 180, containing six uncharged polar amino acids and followed by a Lys181-Ser192 dipeptide. We were interested in whether or not this marginal C-terminal amphiphilic domain is responsible for the association of Sm25 with the membrane or whether a post-translational modification such as the addition of glycosyl phosphatidyl inositol (GPI) represents the membrane anchor for this molecule. We find that treatment with phosphatidyl inositol-specific phospholipase C, which cleaves many GPI anchors, does not reveal Cross Reacting Determinant (CRD) on Sm25, nor affect the association of this protein with membranes, providing no support for the addition of GPI. However, Sm25 is palmitoylated via a thioester bond to the single Cys residue, at position 168, which lies within the C-terminal hydrophobic domain. Removal of palmitate by reduction results in a marked decrease in the hydrophobicity of Sm25, as demonstrated by its partitioning into the aqueous rather than detergent phase of TX-114 and its quantitative release from membrane preparations. The hydrophobicity of several membrane proteins in addition to Sm25 is also decreased by reduction, raising the possibility that fatty acylation by thioester linkage is an important mechanism used by schistosomes to stabilize protein-membrane interactions.

Amino Acid Sequence↗
PubMed1991

Sequence of a small subunit rRNA gene of Schistosoma mansoni and its use in phylogenetic analysis.

The complete sequence of a small ribosomal RNA gene of Schistosoma mansoni contained within plasmids pSM389 and pSM889 is presented. It was found to be 1992 bp in length, larger than that of most eukaryotes. Extra nucleotides occur in regions known to be variable (V4 and V7). The predicted secondary structure of the nucleotides 660-853 revealed additional helices which have been designated E21-1A and E21-1B. The other region to differ from higher eukaryotes lies between nucleotides 1457 and 1569. Secondary structure prediction demonstrated that a single extended helix may be formed from this part of the schistosome small subunit rRNA sequence. Nucleotides that could be unambiguously aligned with those of 12 other eukaryotes were used to estimate phylogenetic relationships. The consensus tree obtained by Maximum Parsimony analysis showed the schistosome as a sister taxon to the flatworm Dugesia tigrina.

Amino Acid Sequence↗
PubMed1991

Structure of Sm25, an antigenic integral membrane glycoprotein of adult Schistosoma mansoni.

Sm25 is the principal antigen recognised by antibodies from mice protectively vaccinated with isolated tegumental membranes of adult Schistosoma mansoni. The full-length amino acid sequence of this protein has been deduced from the sequence of two cDNAs, one isolated by screening a cDNA library and the other, including the 5' end of the gene, amplified directly from adult worm RNA using the polymerase chain reaction. The predicted sequence represents a nascent polypeptide of Mr 21,500. Following cleavage of a predicted signal sequence, the Mr of the resulting polypeptide is 17,600. The polypeptide contains 2 potential sites for N-linked glycosylation and a hydrophobic domain at the C-terminus that could facilitate membrane association. Analysis of the mature gene product confirmed that Sm25 is an N-glycosylated integral membrane protein and that the Mr of the deglycosylated polypeptide is between 15,000 and 20,000.

Amino Acid Sequence↗
PubMed1991

Molecular cloning and characterisation of the 22-kilodalton adult Schistosoma mansoni antigen recognised by antibodies from mice protectively vaccinated with isolated tegumental surface membranes.

A cDNA clone from an adult Schistosoma mansoni lambda gt11 expression library (A12) encoding an antigenic polypeptide of 22 kDa is described. A12 is 797 bp long and has one open reading frame encoding a protein of 190 amino acids which does not contain a signal sequence or membrane anchor motif and has no homologies with any sequences on the currently available data bases. Its product (sm22.6) is recognised by antibodies from mice protectively vaccinated with purified adult S. mansoni tegumental membranes and by serum from S. mansoni-infected Brazilians. It is present in all post-snail life cycle stages except the egg, is not sex-specific, and is found in 9 species of Schistosoma, but not in a range of other helminths. Data are presented which suggest that sm22.6 is a soluble, peripheral membrane protein.

Amidohydrolases↗
PubMed1991

Distribution of plasminogen activator inhibitor (PAI-1) in tissues.

Extracts of human tissue were analysed for plasminogen activator inhibitor (PAI-1) antigen and activity. PAI-1 was localised in tissues by an immunochemical method, using monoclonal antibodies. PAI-1 occurred throughout the body; its concentration and activity differed considerably from organ to organ. Extracts of liver and spleen had the greatest abundance of PAI-1, but the activity of the inhibitor was much higher in liver than in spleen: the liver may be a source of plasma PAI-1. Immunochemical staining for PAI-1 was observed in endothelium, platelets and their precursor cells, the megakaryocytes, and locations central to the process of haemostasis. PAI-1 also occurred in neutrophil polymorphs and macrophages, cells important in inflammatory and immune processes, but not in lymphocytes. Other cell types, in particular, vascular smooth muscle cells and mesangial cells, also stained positively for PAI-1 and such cells seem to represent an important reservoir of PAI-1.

Autopsy↗
PubMed1990

Schistosome surface antigens: developmental expression and immunological function.

It has long been held as axiomatic that antigens exposed on the surfaces of parasitic organisms are primary targets of protective immune responses. It is becoming apparent that not all protective schistosome antigens are surface antigens and that not all surface antigens are necessarily targets of protective immunity. Andy Simpson suggests that one of the factors that determines the immunological function of surface antigens may be developmental expression.

Journal Article↗
PubMed1990

Epitopes expressed on very low Mr Schistosoma mansoni adult tegumental antigens conform to a general pattern of life-cycle cross-reactivity.

The relationship between antigens associated with the surface of newly transformed schistosomula of Schistosoma mansoni and the tegumental surface membrane of adult S. mansoni worms has been further explored. Immunoprecipitation of detergent-solubilized 125I-tegumental surface membrane antigens of adult S. mansoni with antibodies from mice vaccinated with highly irradiated S. mansoni cercariae revealed major antigens of Mr 32, 20, 15 and 8K. The Mr 32 and 20K antigens have been previously demonstrated to be antigenically and electrophoretically identical to major antigens on the schistosomulum surface. The Mr 15 and 8K antigens, on the other hand, have not been identified by the immunoprecipitation of 125I-schistosomulum surface antigens, although a distinct schistosomulum surface antigen of Mr 15K is precipitated by antibodies from mice vaccinated with highly irradiated cercariae. Nevertheless, it was shown that antibodies to the Mr 15 and 8K antigens were specifically absorbed from vaccinated mouse serum by intact, live schistosomula, demonstrating that the Mr 15 and 8K antigens are exposed on or released from the schistosomulum surface. In contrast, absorption of the antiserum with eggs failed to remove antibody against any of the four tegumental membrane antigens examined. The Mr 15 and 8K antigens were shown to be recognized via polypeptide epitopes and not periodate-sensitive carbohydrate epitopes, further emphasizing the similarity of these to the well-characterized Mr 32 and 20K tegumental surface membrane antigens. A general relationship between schistosomulum surface, adult tegumental membrane and egg antigens was demonstrated by ELISA, using antibodies raised against the three antigenic fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

The platelet and plasma pools of plasminogen activator inhibitor (PAI-1) vary independently in disease.

The relative importance and behaviour of plasma and platelet plasminogen activator inhibitor (PAI-1) in disease has not hitherto been examined. In this study the concentration of PAI-1 in the plasma and platelets of patients with a variety of disorders was examined using a specific ELISA and a functional assay. Mean plasma PAI-1 was elevated in groups of patients with diabetes mellitus, hypertension, alcoholic cirrhosis, angina and myocardial infarction. Plasma PAI-1 was raised in the post-operative phase and the PAI-1 released after surgery was not derived from platelets. In all groups PAI-1 in the platelet pool reflected the platelet count, except in type II diabetes mellitus and chronic renal failure, where a reduced quantity of PAI-1 antigen per platelet was found. In severe chronic renal failure, abnormal platelets and diminished platelet PAI-1 may contribute to the haemorrhagic tendency sometimes seen in this disorder. Plasma PAI-1 represents a larger proportion of total circulating PAI-1 in disease than it does in healthy individuals; PAI-1 per platelet is abnormal only in a minority of disorders. Plasma and platelet pools of PAI-1 vary independently in disease and both merit consideration in evaluating the importance, if any, of PAI-1 in thrombosis or haemorrhage.

Blood Platelets↗
PubMed1990

A method for measuring neuroretinal rim area.

A practical method for measuring the neuroretinal rim area (NRA) of the optic nervehead is described. Sequential stereo photographs are taken on 35 mm colour transparencies using a Zeiss fundus camera with Allen stereoseparator. While examining a stereo pair with a pocket viewer the disc and cup margins are traced against the stereo image with a Rotring pen (0.1 mm tip) on a clear transparency overlying one of the photographs. This tracing is digitised and analysed by an 'edge detection' algorithm which measures the area between the traced lines, i.e. NRA. The intraobserver intraphotograph coefficient of variation (standard deviation/mean) was calculated for measurements of disc area, cup area and NRA made on 10 stereo photographs of discs with various topographies. Coefficients for NRA ranged from 3.2% to 3.9% for discs with easily discernible cup margins and from 1.6% to 7.2% for discs with less obvious cups.

Glaucoma↗
PubMed1989

Predicted structure of a major Schistosoma mansoni eggshell protein.

The complete sequence for a major Schistosome mansoni eggshell protein gene has been determined from a genomic DNA fragment. The use of an open reading frame encoding a glycine-rich polypeptide was confirmed by in vitro translation of schistosome mRNA in the presence of [3H]glycine and comparison with the amino acid composition of purified, schistosome eggshells. Apart from the extraordinary abundance of glycine and tyrosine which are evenly distributed throughout the polypeptide chain, the most striking features of the deduced amino acid sequence are the presence of five well-conserved tandem repeats of 16-18 residues in the N-terminal region and the asymmetrical distribution of charged residues. Acidic residues (Asp) are confined to the N-terminal region, while basic residues (Lys, His), with the exception of a single histidine, are found in the C-terminal region. A model structure composed of short anti-parallel beta-strands is proposed, in which glycines and residues with small side chains lie within the strands and tyrosines and cysteines are arranged at the bends, where they would be available for cross-linking. Four such strands form one of the tandem repeats which are predicted in turn to form a stack of five closely packed beta-sheets, each of three strands and linked by the more variable fourth strand. The C-terminal region may form a similar but less compact structure. The ordered structure demonstrated by birefringence studies of the schistosome eggshell [Kusel, J. (1970) Parasitology 60, 79-88] could be formed by packing of the polypeptides such that the N-terminal domain contributes counter ions or cross-links to the C-terminal domain of adjacent molecules.

Amino Acid Sequence↗
PubMed1989

A cDNA clone encoding part of the major 25,000-dalton surface membrane antigen of adult Schistosoma mansoni.

Immunoscreening of an adult Schistosoma mansoni cDNA expression library, using antibodies raised against purified adult worm tegumental surface membranes, identified a recombinant clone containing a 141-bp insert. Antibodies raised against the recombinant antigen bound specifically to the tegument of adult worms and immunoprecipitated the major 25,000-dalton surface membrane antigen as well as a 22,000-dalton nascent polypeptide generated by cell-free translation of adult S. mansoni mRNA. The mature 25,000-dalton antigen was found to be precipitated by antibodies from infected mice, rats and humans.

Amino Acid Sequence↗