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Biomedical subjects

A J Simpson

Publications and source records attributed to A J Simpson.

At least 163 records · Page 9Linked to original sources
PubMed1989

A DNA probe from Schistosoma mansoni allows rapid determination of the sex of larval parasites.

A DNA clone representing a 0.4 kb degenerative repeat has been isolated. The DNA sequence is present only in the genome of female Schistosoma mansoni at different stages of the life cycle, at a frequency of approximately 75 copies per adult female genome. The sequence is not expressed and probably represents satellite DNA in the heterochromatin region of the W chromosome. It is demonstrated that the DNA clone may be used for the rapid determination of the sex of cercariae without the need for DNA isolation or Southern blotting.

Animals↗
PubMed1989

Differentiation of Schistosoma mansoni from S. rodhaini using cloned DNA probes.

The ribosomal RNA (rRNA) gene units of Schistosoma mansoni and S. rodhaini, of the lateral spined egg group, have been studied. The schistosome rRNA gene unit consists of a regular interspersion of the two genes encoding the large and small rRNA units with two spacers. The large spacer is not transcribed while the small spacer is part of the transcription unit. Variation in the rRNA gene unit between the two species is demonstrated to take the form of loss or gain of restriction sites within the non-transcribed and transcribed spacers. This variation has been demonstrated to enable the differentiation of S. mansoni from S. rodhaini by Southern hybridization analysis. In addition, a DNA clone representing a female specific, tandemly repeated sequence, is demonstrated to enable differentiation of S. mansoni and S. rodhaini using dot blot hybridization analysis.

Animals↗
PubMed1989

Antibody to carbohydrate and polypeptide epitopes on the surface of schistosomula of Schistosoma mansoni in Egyptian patients with acute and chronic schistosomiasis.

125I-Schistosoma mansoni schistosomulum surface antigens were immunoprecipitated with human antibodies from individual Egyptian patients diagnosed as being either acutely or chronically infected with S. mansoni. Both sets of patients were found to have IgG antibodies in their sera capable of immunoprecipitating the major Mr greater than 200, 38 and 32K antigens. However, the immunoprecipitation of the Mr greater than 200K antigen was found to constitute a significantly greater proportion of the total precipitate achieved with acute sera than with chronic sera. The Mr 38 and 32K antigens were more variably precipitated by the acute sera than the chronic sera but the proportion of the total precipitation that these two antigens constituted was not found to be significantly different between the two sets of sera. Immunoprecipitation with pooled antibodies absorbed with egg and adult worm homogenates which had been treated to remove either carbohydrate or polypeptide epitopes demonstrated that the Mr greater than 200K antigen was the principal target of egg-cross-reactive anti-carbohydrate antibody amongst the antigens detected. The Mr 38 and 32K antigens were found to be precipitated by antibodies to protease-sensitive and periodate-insensitive polypeptide epitopes. These results are consistent with egg-cross-reactive anti-carbohydrate IgG antibody making a greater contribution to schistosomulum surface recognition in acute infection than in chronic infection. Indeed the presence of a higher level of egg-cross-reactive and anti-carbohydrate antibody directed against schistosomulum surface epitopes in an acute serum pool than in a chronic serum pool was confirmed by measurement of antibody binding to whole schistosomula.

Acute Disease↗
PubMed1989

Variable species and stage specificity of schistosomulum surface epitopes recognized by mice vaccinated with highly irradiated cercariae.

Antibodies from mice vaccinated with highly irradiated Schistosoma mansoni or S. haematobium cercariae were used to characterize schistosomulum surface epitopes which were found to be diverse in their species and stage specificities. The epitopes recognized on the Mr greater than 200,000 and 15,000 schistosomulum surface antigens of S. mansoni and the Mr greater than 200,000 schistosomulum surface antigen of S. haematobium were found to be cross-specific whereas those on the Mr 38,000, 32,000 and 20,000 schistosomulum surface antigens of S. mansoni and the Mr 35,000, 30,000 and 24,000 schistosomulum surface antigens of S. haematobium were only immunoprecipitated by homologous antibody and are thus possible targets of the protective species-specific immunity stimulated by highly irradiated cercariae. The epitopes recognized on the Mr greater than 200,000 and 38,000 antigens of S. mansoni were shown to cross-react with both the egg and the adult worm whereas those on the Mr 32,000 and 20,000 antigens only cross-reacted with the adult worm, and those on the Mr 15,000 antigen cross-reacted with neither the adult worm nor the egg. In addition the epitopes on the Mr 38,000 and 32,000 antigens were demonstrated to be polypeptide in nature. Those on the Mr greater than 200,000, 20,000 and 15,000 antigens, on the other hand, could not be conclusively defined.

Animals↗
PubMed1989

Protective immunization of mice against Schistosoma mansoni with purified adult worm surface membranes.

Immunity to Schistosoma mansoni in the mouse was induced by vaccination with adult worm surface membrane (mb-S). Of several adjuvants tested, including Freund's, BCG and alum, 50 micrograms of saponin per mouse given subcutaneously with the antigen was the easiest to administer, and gave consistent protection, approaching levels usually seen in our mouse model after exposure to irradiated cercariae. An antibody response to the schistosomular surface was detected in mice immunized with mb-S plus saponin which was predominantly anti-polypeptide, not anti-carbohydrate, and thus similar to the antibody response of mice exposed to irradiated cercariae. The level of antibodies to Mr 90,000 and 38,000 schistosomular surface antigens as well as to Mr 25,000 adult surface membrane antigen was significantly correlated with the presence of protection.

Adjuvants, Immunologic↗
PubMed1989

Topical antibiotic prophylaxis for cataract surgery: a controlled trial of fusidic acid and chloramphenicol.

The effectiveness of topical fusidic acid 1%, in a viscous drop base, to reduce or eliminate ocular microflora in patients undergoing cataract surgery has been studied. Forty-two patients received fusidic acid on a double-blind basis and for comparison 21 patients were similarly assessed with topical chloramphenicol. A further 17 patients received no treatment other than subconjunctival cephazolin administered to all operated eyes at the time of surgery. Quantitative bacterial counts from the conjunctivae and lash lines of each patient were made 24 hours before surgery, on the morning of operation and again 48 hours after surgery. With a regimen of five administrations on the day prior to surgery, neither topical fusidic acid 1.0% nor chloramphenicol 0.5% produced clinically or statistically significant reductions of the ocular microflora. In contrast perioperative subconjunctival cephazolin effectively reduced or eliminated lid and conjunctival microflora following surgery. This study indicates that the effectiveness of a topical antibiotic preparation for overt ocular infection cannot be directly extrapolated to the effect on resident ocular microflora, at least with short-term use for presurgical prophylaxis.

Administration, Topical↗
PubMed1989

Serological differentiation of acute and chronic schistosomiasis mansoni by antibody responses to keyhole limpet hemocyanin.

The existence of a shared epitope between the hemocyanin of the marine mollusk Megathura crenulata, better known as the keyhole limpet, and schistosomula has been reported. This epitope has been shown to be a major immunogen in human infection. In this study, keyhole limpet hemocyanin (KLH) was used to measure antibodies recognizing the cross-reacting epitopes in sera from patients with acute and chronic schistosomiasis using an enzyme-linked immunosorbent assay (ELISA). Marked differences in IgG and IgM antibody response were noted between acutely and chronically infected patients at a reciprocal serum dilution of up to 2,560. The acute sera had a mean +/- SD OD490 nm values for IgG and IgM of 1.0 +/- 0.44 and 1.34 +/- 0.6 compared to mean +/- SD IgG and IgM absorbance for the chronic sera of 0.22 +/- 0.10 and 0.22 +/- 0.11 respectively. Setting our lowest positive limit at greater than 2 SD above the mean of the chronic sera, 28 of the 30 patients previously diagnosed as having acute schistosomiasis were correctly identified by their IgG and IgM response. Of 5 patients studied longitudinally, IgG persisted at the same levels 10-13 weeks after treatment. IgM levels, on the other hand, showed a tendency to decrease but remained above the established cut-off level. This study provides further evidence for the association of schistosomulum surface carbohydrate antibody with acute infection and demonstrates the ability of a simple non-competitive ELISA using microtiter plates coated with minute quantities of KLH to differentiate serologically between cases of acute and chronic schistosomiasis.

Acute Disease↗
PubMed1988

Analysis of the anti-Schistosoma mansoni surface antibody response during murine infection and its potential contribution to protective immunity.

Absorption of serum from chronically infected mice with homogenized schistosome eggs reduced antibody binding to the schistosomulum surface by 94%, indicating that almost all schistosomulum surface recognition during chronic infection is due to epitopes shared with the egg. Absorption of the serum with egg homogenate from which protein antigens had been removed by boiling and digestion with proteinase K resulted in a similar reduction of antisurface antibody demonstrating that all the shared epitopes that are recognized are carbohydrate in nature. Analysis of the time course of anticarbohydrate antibody production and the levels of antibody in mice infected with a single sex of schistosome indicated that eggs directly stimulated this response. Mouse mAb were identified that bound at very high levels to the schistosomulum surface and that recognized carbohydrate epitopes shared with the egg. Three of these had previously been demonstrated to passively transfer resistance, indicating that these surface carbohydrates are potential targets of protective immunity in the mouse. All the anticarbohydrate mAb also bound to the surface of schistosomula of other schistosome species. Thus, the strong immune response against these epitopes in chronic infection could account for the cross-specific immunity observed. Mice vaccinated with irradiated cercariae lacked high levels of anticarbohydrate antibodies and their recognition of the surface was largely due to antibody to species-specific polypeptide epitopes. With respect to the Mr greater than 200,000 and 38,000 antigens, it was demonstrated that these epitopes were present on the same antigens that bear the carbohydrate moieties recognized by antibodies from chronically infected mice. This specific polypeptide recognition is also reflected in the immunity generated by exposure to irradiated cercariae.

Animals↗
PubMed1988

Plasminogen activator inhibitor (PAI-1) in plasma and platelets.

The distribution of PAI-1 in the plasma and platelets of normal individuals and of patients with platelet abnormalities was studied. An ELISA, capable of measuring PAI-1 in plasma at 1.5 ng/ml, and a functional assay of t-PA inhibition were used to assay platelet-free plasma (PFP), platelet-rich plasma in which the platelets were lysed (PRP) and serum. The PAI-1 concentration of normal PFP was 21.0 +/- 7.2 ng/ml (mean +/- SD) and those of PRP and serum were 282.6 +/- 68.0 and 270.3 +/- 71.9 ng/ml. The concentration of PAI-1 in PRP was proportional to the platelet count with 0.67 +/- 0.18 ng/10(6) platelets. Patients with thrombocytopenia had approximately normal PAI-1 concentrations in PFP; the extremely low concentrations in serum or PRP reflected the platelet count. A patient with grey platelet syndrome showed a comparable pattern, confirming that PAI-1 occurs in the platelet alpha-granules and indicating that the plasma concentration of PAI-1 is independent of the platelet pool of PAI-1. The median inhibitory activities towards t-PA were 1.6, 8.7 and 8.3 units/ml in normal PFP, PRP and serum respectively. PAI-1 in PFP had a median specific activity (units/mg PAI-1) about 5-fold higher than platelet PAI-1. Plasma and platelets represent two distinct pools of PAI-1, both of which should be considered in studies on the relationship between circulating PAI-1 and thrombotic disease.

Adult↗
PubMed1987

Characterisation of the structure and expression of the gene encoding a major female specific polypeptide of Schistosoma mansoni.

A previously described cDNA clone, pSF10, of Schistosoma mansoni encoding the very dominant female specific polypeptide (FSP) has been used to characterize the gene and its expression. The gene is detectable in different isolates of S. mansoni and is estimated to be present in 3 copies per haploid genome. The gene is not sex linked and exhibits neither amplification nor rearrangement concomitant with expression. Expression of the gene by parasites maturing in hamsters is first detected after 5 weeks when the RNA is present at 1/10 the level of that of 6 week worms. Although the FSP gene is specifically and highly expressed by egg laying female worms a corresponding polypeptide produced by the cell-free translation of RNA is not detectable. It was confirmed, however, that pSF10 does indeed encode a mRNA by DNA sequence analysis. The sequence demonstrated a mRNA containing a poly(A) tail and two open reading frames. One reading contains no methionine but is very high (47%) in glycine. This amino acid composition could account for the inability to detect the gene product by cell-free translation in the presence of [35S]methionine.

Animals↗
PubMed1987

Resistance to reinfection with Schistosoma haematobium in Gambian children: analysis of their immune responses.

The relationship between reinfection with Schistosoma haematobium and immunological parameters was studied in a group of Gambian children aged from 8 to 13 years. Each individual's exposure to infection was assessed from observations of water contact, cercarial densities and infected snail densities at water contact sites. Eosinophil counts were made and responses to egg antigen (SEA) and adult worm antigen (WWH) measured by ELISA. Low levels of reinfection were associated with a high eosinophil count, high levels of antibodies against WWH and SEA, increased age and low exposure. In a multiple regression analysis of the association of reinfection with eosinophil count, antibody levels, exposure, age and sex, the effects of eosinophil count and exposure were still very significant after allowing for all the other variables. The effects of the antibody levels were close to significance after allowance for exposure and eosinophil count (for WWH: P = 0.09; for SEA: P = 0.07), although the evidence was less clear after additional allowance was made for age and sex. The ability of sera from the children to recognize different parasite antigens was also examined by immunoprecipitation of labelled schistosomulum surface, WWH, SEA and S. haematobium adult worm mRNA in vitro translation products. Schistosomulum surface antigens were recognized by all the sera and there was little variation in this response. There was more variation in their responses to SEA and WWH and a marked heterogeneity in the response to in vitro translation products. However, the pattern of antigen recognition appeared unrelated to susceptibility to reinfection.

Adolescent↗
PubMed1987

Progress towards a defined vaccine for schistosomiasis.

During the last five years considerable progress has been made in studies o f schistosome immunology. Convergent views have emerged from the study of human and animal immunity which agree on the mechanisms required and the antigens involved. The reproducible induction of protective immunity with attenuated parasites and with antigenic preparations has now led to agreement that vaccination against schistosomiosis is on achievable goal. The evidence that led to this optimistic view was reviewed at a scientific working group on 'Prospects for Immunological Intervention in Human Schistosomiosis' held in Geneva in May 1986, under the auspices of the UNDP/World Bonk/WHO Special Programme.

Journal Article↗
PubMed1987

Surface antigens of and cross-protection between two geographical isolates of Schistosoma mansoni.

Two isolates of Schistosoma mansoni from Puerto Rico and Egypt were examined to determine if there were differences in surface antigens of the schistosomulum and to assess the ability of the two isolates to induce protection against one another in vivo. Immune mouse and human patient antisera recognized the same antigens on the schistosomulum surface of both isolates. However, mice immunized with schistosomula-released products from the Egyptian isolate recognized an additional antigen of Mr 13K on the Egyptian schistosomulum surface which was not present in the Puerto Rican isolate. In quantitative radioimmunoassay, sera from mice vaccinated with irradiated Egyptian cercariae bound more strongly to Egyptian schistosomula than to Puerto Rican parasites. Both isolates cross-protected against each other, but mice were less immune to challenge with Egyptian cercariae after being immunized with Puerto Rican irradiated cercariae. There was no difference in immunity to challenge when Egyptian irradiated cercariae were used to immunize. Although this evidence suggested some heterogeneity within the Egyptian isolate, cloned cercariae of the Egyptian isolate did not vary in their ability to cross-protect against each other. Furthermore, antisera from mice immunized with clones of Egyptian cercariae recognized the same schistosomulum surface antigens. The results reported here indicate that although there were small differences between the two isolates the major surface antigens are conserved.

Animals↗
PubMed1987

Surface and species-specific antigens of Schistosoma haematobium.

Of the surface antigens identified by radio-iodination, two-dimensional gel analyses showed no similarities between those of Schistosoma haematobium and Schistosoma mansoni, thus providing a basis for the species specificity of these antigens described previously (Simpson, Knight, Hagan, Hodgson, Wilkins & Smithers (1985) Parasitology 90, 499-508). The surface antigens of S. haematobium were glycosylated and comprised an acidic polypeptide of Mr 17,000 as well as a complex set of polypeptides of approximate pI 6-7, which resolved in the Mr range 20,000-30,000. At least one of the lower Mr forms of this complex is also present in the adult worm. Limited cross-reaction was observed with S. mansoni infection sera and this may be due to a shared carbohydrate epitope. In contrast, extensive cross-reaction was observed using sera from mice immunized with S. bovis. This pattern parallels the species-specificity of vaccine-induced immunity. Extensive cross-reaction was also observed within cell-free translation products of m-RNA from adult worms of S. haematobium and S. mansoni by use of heterologous human infection sera. The few antigens which were species-specific may represent surface antigens.

Animals↗