Showing papers by "Swedish Institute published in 1999"

Small, Clonally Variant Antigens Expressed on the Surface of the Plasmodium falciparum–Infected Erythrocyte Are Encoded by the rif Gene Family and Are the Target of Human Immune Responses

Abstract: Disease severity in Plasmodium falciparum infections is a direct consequence of the parasite's efficient evasion of the defense mechanisms of the human host. To date, one parasite-derived molecule, the antigenically variant adhesin P. falciparum erythrocyte membrane protein 1 (PfEMP1), is known to be transported to the infected erythrocyte (pRBC) surface, where it mediates binding to different host receptors. Here we report that multiple additional proteins are expressed by the parasite at the pRBC surface, including a large cluster of clonally variant antigens of 30–45 kD. We have found these antigens to be identical to the rifins, predicted polypeptides encoded by the rif multigene family. These parasite products, formerly called rosettins after their identification in rosetting parasites, are prominently expressed by fresh isolates of P . falciparum . Rifins are immunogenic in natural infections and strain-specifically recognized by human immune sera in immunoprecipitation of surface-labeled pRBC extracts. Furthermore, human immune sera agglutinate pRBCs digested with trypsin at conditions such that radioiodinated PfEMP1 polypeptides are not detected but rifins are detected, suggesting the presence of epitopes in rifins targeted by agglutinating antibodies. When analyzed by two-dimensional electrophoresis, the rifins resolved into several isoforms in the pI range of 5.5–6.5, indicating molecular microheterogeneity, an additional potential novel source of antigenic diversity in P . falciparum . Prominent polypeptides of 20, 22, 76–80, 140, and 170 kD were also detected on the surfaces of pRBCs bearing in vitro–propagated or field-isolated parasites. In this report, we describe the rifins, the second family of clonally variant antigens known to be displayed by P . falciparum on the surface of the infected erythrocyte.

Effect of Ag particle size on electrical conductivity of isotropically conductive adhesives

Abstract: The present work is to introduce nanoparticles in micro-sized metal particles to study particle distribution in polymer matrix. Previous examinations of the silver-filled particles reveal that the micro-sized particle fillers appear as full density silver flakes, while nanoparticle fillers appear as highly porous agglomerates, similar to open-cell foams. Actually little work has been carried out to study the cross-sectional area of a particle-particle-contact in isotropically conductive adhesives (ICA). In this study, transmission electron microscope is chosen as a main measure to analyze the distribution of different-sized particles. The percentage of the nanoparticles varies from 20 wt% and 50 wt% to full percentage within micro-sized particles, and the total metal content in epoxy resin is 70 wt%. So the change of contact area and contact behavior with various volume ratio of nano-sized and micro-sized particles was investigated. At the same time, the electrical resistivity was measured, which is compared with the different level of the filler loading.

Deformation microstructures and textures in steels

Abstract: Experimental evidence concerning the evolution of textures and substructures during cold rolling of low–carbon steel is presented and reviewed with some reference to the importance of these during subsequent annealing. Attention is paid to the orientation dependence of microstructure and stored energy of deformation. These are considered in relation to the Taylor factors for grains of different orientations in homogeneous deformation, and to the occurrence of different types of heterogeneity. Certain grain–scale heterogeneities appear to be important in defining the textures, which can now be predicted with some success using so–called relaxed constraint models. Intragranular heterogeneities also play a role and these especially affect the variation in substructure between grains. The strain–rate sensitivity of flow stress is an important parameter, which, depending on its sign and magnitude, may cause either severe strain localization in shear bands or lead to very homogeneous deformation structures where the influence of crystal orientation almost disappears.

Novel ribosomal mutations affecting translational accuracy, antibiotic resistance and virulence of Salmonella typhimurium

Abstract: Many mutations in rpsL cause resistance to, or dependence on, streptomycin and are restrictive (hyperaccurate) in translation. Dependence on streptomycin and hyperaccuracy can each be reversed phenotypically by mutations in either rpsD or rpsE. Such compensatory mutations have been shown to have a ram phenotype (ribosomal ambiguity), increasing the level of translational errors. We have shown recently that restrictive rpsL alleles are also associated with a loss of virulence in Salmonella typhimurium. To test whether ram mutants could reverse this loss of virulence, we have isolated a set of rpsD alleles in Salmonella typhimurium. We found that the rpsD alleles restore the virulence of strains carrying restrictive rpsL alleles to a level close to that of the wild type. Unexpectedly, three out of seven mutant rpsD alleles tested have phenotypes typical of restrictive alleles of rpsL, being resistant to streptomycin and restrictive (hyperaccurate) in translation. These phenotypes have not been previously associated with the ribosomal protein S4. Furthermore, all seven rpsD alleles (four ram and three restrictive) can phenotypically reverse the hyperaccuracy associated with restrictive alleles of rpsL. This is the first demonstration that such compensations do not require that the compensating rpsD allele has a ribosomal ambiguity (ram) phenotype.

The morphological transition of Helicobacter pylori cells from spiral to coccoid is preceded by a substantial modification of the cell wall.

Abstract: The morphological transition of Helicobacter pylori cells from spiral to preceded by a substantial modification of the cell wall.

Case-case comparisons to study causation of common infectious diseases.

Abstract: Background Analytical studies of reportable infectious diseases often use the small minority of cases detected through surveillance systems. For many diseases, notification of cases represents a non-random selection process. Apparent differences in exposure histories may be due to biases involved in the surveillance system selection of cases compared to randomly selected controls. In addition, differential recall between cases and controls may occur. One way to avoid these problems is to compare cases with another group of cases with a different disorder selected by a similar surveillance system, although this can introduce new biases. Methods In infectious diseases cases with the same disease can be divided into aetiologically meaningful subgroups by subtyping the pathogen. Exposure history can then be compared between these subgroups. Results Several biases are removed. The control group composed of other cases does not represent the exposure history of the study base but differs from it in a predictable and useful way. People considered as controls will have a higher incidence of general predisposing factors than the general population. Analysis is limited to factors associated with exposure to the infecting agent. Conclusions Case-case comparison is a development of case-control methodology made possible by laboratory typing techniques. These comparisons allow a more restricted but more refined analysis of the association of some exposures with infection. Determination of how exposure to the infectious agent occurred is more efficient and unbiased than in standard case-control studies but general factors determining whether disease occurs after an infectious exposure can not be studied.

Identification of an anti-mycobacterial domain in NK-lysin and granulysin.

Abstract: NK-lysin and granulysin are homologous cationic anti-bacterial peptides produced by pig and human cytolytic lymphocytes, respectively. The solution structure of NK-lysin comprises five amphipathic alpha-helices. To investigate the properties of a helix-loop-helix region postulated to be a membrane-docking part of NK-lysin, we synthesized 22- and 29-residue peptides reproducing this region for both NK-lysin and granulysin. CD spectroscopy of the synthetic peptides in a liposomal solution showed spectra typical of alpha-helical peptides. The peptides were active against Gram-positive and Gram-negative bacteria, with the two NK-lysin peptides showing higher anti-bacterial activities than the two from granulysin. One NK-lysin peptide was active against Pseudomonas aeruginosa and Staphylococcus aureus, two organisms against which NK-lysin is inactive. Granulysin peptides were inactive against these bacteria, in contrast with granulysin, which is known to be active against them. Both NK-lysin and all synthetic analogues killed Mycobacterium tuberculosis and K562 tumour cells, but did not display haemolytic activity. These results identify a potent anti-mycobacterial domain in NK-lysin and granulysin consisting of a 22-residue (helix 3) sequence plus a disulphide-constrained loop.

Microbiological and Serological Diagnosis of Pertussis

Abstract: Swedish vaccine trials have been used to examine sensitivity and specificity of diagnostic procedures for Bordetella pertussis infection. The proportions of cases diagnosed by culture and serology were 55% and 45%, respectively, when both methods were optimized. The culture method included nasopharyngeal aspiration, direct inoculation on plates, enrichment, and repeated collection of samples. An enzyme-linked immunosorbent assay for IgG antibodies to pertussis toxin (PT) and to filamentous hemagglutinin, with paired sera, was used for serology. Preexposure sera other than the acute serum increased the sensitivity of serology by 10%. A serology quality-assurance program to control imprecision and allow comparability over time and between laboratories is described. The direct fluorescent antibody technique had a sensitivity of 38% and a specificity of 99.6% in comparison with culture. A nested polymerase chain reaction (PCR) with the PT promoter region as target was 95% sensitive in comparison with culture if a cation-exchange resin was used to reduce inhibition. PCR enabled us to identify 83 positive samples in addition to 215 culture-positive ones-an increase of 38%--all with other indicators of pertussis infection.

The weighting exercise for the Swedish version of the EuroQol.

Abstract: The EuroQol weighting exercise consists of three parts. In the first, the respondents state their own health using five dimensions with three levels in each, and then they rate their own health state on a visual analogue scale. In the second part, respondents attach weights to some of the possible health states. The last part contains questions about background information. The present article presents such weights derived from a sample of the Swedish population. The sample of 1000 Swedish citizens was drawn randomly from a national address register. The overall response rate was 54.2%, though 315 (31.5%) of the responses were ultimately deemed usable. Most of the health states included in the weighting exercise were well-chosen. Most of them were represented by at least one of the respondents. The respondent characteristics that had any influence on the valuation of health states in the weighting exercise was rating of own health, age and level of education, where a higher rating of own health, higher age and lower level of education resulted in higher valuations. Copyright © 1999 John Wiley & Sons, Ltd.

Bordetella pertussis, Bordetella parapertussis, Mycoplasma pneumoniae, Chlamydia pneumoniae and persistent cough in children.

Abstract: Material collected during a prospective pertussis vaccine trial in 1992-95 was examined for Bordetella pertussis (culture and serology), Bordetella parapertussis (culture), Mycoplasma pneumoniae and Chlamydia pneumoniae (PCR). From 64% (99/155) of episodes with cough for less than 100 d, 115 aetiological agents were identified in one southern and one northern subset of DT-recipients. The most common single agent was B. pertussis, representing 56%(64/115), with a median cough period of 51 d, followed by M. pneumoniae 26%(30/115), 23 d, C. pneumoniae 17% (19/115), 26 d, and B. parapertussis 2% (2/115). For co-infections, the median duration of cough was about 60 d. Spasmodic cough for 21 d or more (clinical WHO criteria for pertussis) was present in 82% (41/50) of infections with B. pertussis as single agent, 38% (17/45) with B. parapertussis, 38% (5/13) with C. pneumoniae, 26% (5/19) with M. pneumoniae and 30%(17/56) in cases where no aetiology was found. In children with cough for more than 100 d (n = 78) using all vaccine arms, B. pertussis was responsible in 83% (65/78), in 21%(16/78) together with other agents. Acellular vaccines were more efficient against serious disease than whole cell vaccine. Antibiotic treatment was more common at the southern (34%) study site than at the northern one (12%). The findings indicate that diagnosis should rely on laboratory confirmation, both for rational treatment of an individual case and for monitoring outbreaks.

Identification of Mycobacterium kansasii by using a DNA probe (AccuProbe) and molecular techniques.

Abstract: The newly formulated Mycobacterium kansasii AccuProbe was evaluated, and the results obtained with the new version were compared to the results obtained with the old version of this test by using 116 M kansasii strains, 1 Mycobacterium gastri strain, and 19 strains of several mycobacterial species The sensitivity of this new formulation was 974% and the specificity was 100% Still, three M kansasii strains were missed by this probe To evaluate the variability within the species, genetic analyses of the hsp65 gene, the spacer sequence between the 16S and 23S rRNA genes, and the 16S rRNA gene of several M kansasii AccuProbe-positive strains as well as all AccuProbe-negative strains were performed Genetic analyses of the one M gastri strain from the comparative assay and of two further M gastri strains were included because of the identity of the 16S rRNA gene in M gastri to that in M kansasii The data confirmed the genetic heterogeneity of M kansasii Furthermore, a subspecies with an unpublished hsp65 restriction pattern and spacer sequence was described The genetic data indicate that all M kansasii strains missed by the AccuProbe test belong to one subspecies, the newly described subspecies VI, as determined by the hsp65 restriction pattern and the spacer sequence Since the M kansasii strains that are missed are rare and all M gastri strains are correctly negative, the new formulated AccuProbe provides a useful tool for the identification of M kansasii

The economics of preventing revisions in total hip replacement.

Abstract: We showed that the selection of a cost-effective type of cement and method of prophylaxis against deep infections for patients undergoing total hip replacement depended on the number of arthroplasties performed each year at individual hospitals. When 100 arthroplasties were performed each year, the use of Palacos cement and systemic antibiotics reduced the total costs to the department, i.e., the cost of cement, infection prophylaxis and revisions. The use of gentamicin-impregnated cement in combination with systemic antibiotics will further reduce the risk of revision and is another cost-effective strategy. The most effective infection prophylaxis would be achieved with a combination of gentamicin-impregnated cement, systemic antibiotics and surgical enclosure. However, the additional cost of the surgical enclosure would not be offset by cost savings due to reduced risk of revisions.

Autoantibodies against the tumour-associated antigen GA733-2 in patients with colorectal carcinoma

Abstract: The tumour-associated antigen (TAA) GA733-2 is expressed as a non-secreted surface molecule on the majority of human colorectal carcinoma cells. The antigen has been used as a target for passive and active immunotherapy during the last decade. To determine the incidence of autoantibodies against this antigen, sera from 1068 patients with colorectal carcinoma were analysed for naturally occurring IgG antibodies against the baculovirus-produced GA733-2E protein. A total of 14.5% of the patients had IgG antibodies against the antigen. In 519 patients, sera were collected at the time of diagnosis and 15% of those patients had anti-GA733-2E IgG antibodies. There was a tendency to a higher frequency of patients with antibodies among those in the advanced Dukes stages: 11% in stage A and 32% in stage D respectively (P = 0.06). Antibodies could be detected for up to 10 years after the diagnosis. Patients with Crohn's disease or colitis ulcerosa (n = 20) did not elicit anti-GA733-2E antibodies. No healthy control donor (n = 45) had detectable antibodies against the antigen. The specificity of GA733-2E-reactive serum IgG was indicated by significant inhibition of mAb17-1A (originally used to define GA733-2) binding to the GA733-2E antigen. Sera of positive patients bound to the GA733-2-expressing human colorectal carcinoma cell line, SW948. No significant correlation was found between the presence of antibodies and survival in the present patient population. However, the high incidence of autoantibodies against this tumour antigen in colorectal carcinoma patients confirms its antigenicity in humans and supports the use of the GA733-2 antigen as a target for immunotherapy.

T-cell-epitope mapping of the idiotypic monoclonal IgG heavy and light chains in multiple myeloma.

Abstract: The idiotypic structures of the myeloma protein might be regarded as tumor-specific antigens. The present study was designed to map T-cell epitopes of the idiotypic myeloma protein to prove the existence of naturally occurring major-histocompatibility-complex-dependent idiotype (peptide)-specific T cells in multiple myeloma. The fine specificity of idiotype-reactive, interferon-γ-producing blood T cells of a patient with multiple myeloma stage I was characterized by identification of idiotype (heavy and light chains)-derived MHC-restricted T-cell epitopes. T cells specifically reacting with peptides corresponding to each of the 3 complementarity-determining regions (CDRs) of the heavy-chain variable part (VH) of the autologous idiotype were found. In contrast, none of the peptides corresponding to the 3 CDRs of the light chain (VL) induced a specific T-cell response. The idiotype amino-acid sequence corresponding to the junction of the VH, diversity (D), and joining (J) gene segments of the VH appeared to be an important target for T cells, since the sequence expressed MHC-class-I- as well as MHC-class-II-restricted epitopes. The study provides further support for the existence of MHC-restricted idiotype-specific T cells, which may target immunogenic CDR peptides in multiple myeloma. Such T cells could be an important part of the specific anti-tumor immune responses induced in idiotype vaccination protocols. Int. J. Cancer 80:671–680, 1999. © 1999 Wiley-Liss, Inc.

In vitro aging of Helicobacter pylori: changes in morphology, intracellular composition and surface properties.

Abstract: Background. During the conversion from the bacillary into the coccoid form, Helicobacter pylori organisms are known to change extensively. The aim of this study was to determine some of the changes that occur regarding morphology, intracellular composition and surface properties during the aging of bacteria in vitro. Materials and Methods. H. pylori from agar plate cultures of different ages was used in this study. The intracellular composition of the two morphological forms of the bacteria was tested by density centrifugation, DNA extraction and quantitative OD, mRNA and ATP measurements. Immunoblotting was used to observe changes in secreted/superficial protein patterns, and hydrophobicity measurements were used to observe changes in surface properties. Results. All bacillary H. pylori organisms changed morphology gradually over 10 days of culture. Rods had a higher density than cocci; bacteria stored in PBS had the highest density and bacteria stored in water had the lowest. The quantitative DNA, RNA and ATP content were reduced in the aging bacteria. Fewer immunogenic proteins were expressed, and an increased surface hydrophobicity was observed in the older cultures. Conclusion. This study highlights several aspects of H. pylori aging in vitro and shows some of the differences that exist between bacillary and coccoid forms. This information is important for understanding the transmission and survival of H. pylori outside the human host, as the degradative changes in the intracellular composition and the surface properties shown here point to dead bacteria, and not to a viable but nonculturable form.

An international outbreak of Vero cytotoxin-producing Escherichia coli O157 infection amongst tourists; a challenge for the European infectious disease surveillance network

Abstract: In March 1997, an outbreak of Vero cytotoxin-producing Escherichia coli O157 (VTEC) infection occurred amongst holidaymakers returning from Fuerteventura, Canary Islands. For the investigation, a confirmed case was an individual staying in Fuerteventura during March 1997, with either E. coli O157 VTEC isolated in stool, HUS or serological evidence of recent infection; a probable case was an individual with bloody diarrhoea without laboratory confirmation. Local and Europe-wide active case finding was undertaken through national centres, Salm-Net and the European Programme of Intervention Epidemiology, followed by a case-control study. Fourteen confirmed and one probable case were identified from England (7), Finland (5), Wales (1), Sweden (1) and Denmark (1) staying in four hotels. Three of the four hotels were supplied with water from a private well which appeared to be the probable vehicle of transmission. The case-control study showed illness was associated with consumption of raw vegetables (OR 8.4, 95% CI 1-5-48.2) which may have been washed in well water. This investigation shows the importance of international collaboration in the detection and investigation of clusters of enteric infection.

The trophoblastic epithelial barrier is not infected in full-term placentae of human immunodeficiency virus-seropositive mothers undergoing antiretroviral therapy.

Abstract: To study the mechanism of the placental barrier function, we examined 10 matched samples of term placentae, cord blood, and maternal blood obtained at delivery from human immunodeficiency virus (HIV)-infected mothers with children diagnosed as HIV negative in Sweden. All placentae were histologically normal, and immunochemistry for HIV type 1 p24 and gp120 antigens was negative. Highly purified trophoblasts (93 to 99% purity) were negative for HIV DNA and RNA, indicating that the trophoblasts were uninfected. Although HIV DNA was detected in placenta-derived T lymphocytes and monocytes, microsatellite analysis showed that these cells were a mixture of maternal and fetal cells. Our study indicates that the placental barrier, i.e., the trophoblastic layer, is not HIV infected and, consequently, HIV infection of the fetus is likely to occur through other routes, such as breaks in the placental barrier.

European Antimicrobial Resistance Surveillance System (EARSS): objectives and organisation.

Abstract: ‘Effective European surveillance must have the agreement and active involvement of all participants’, concluded a European Union (EU) conference on the need for surveillance of resistant microorganisms (the microbial threat), held in September 1998 in De

Adherent surface mucus gel restricts diffusion of macromolecules in rat duodenum in vivo.

Abstract: The aim of this study was to investigate the permeability of the adherent mucus gel layer in rat duodenum in vivo to macromolecules applied in the lumen. Rats were anesthetized with thiobarbiturate...