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Biomedical subjects

K Hedman

Publications and source records attributed to K Hedman.

At least 37 records · Page 2Linked to original sources
PubMed1999

Prevalence of parvovirus B19 DNA in bone marrow of patients with haematological disorders.

Patients with haematological disorders (n = 100) were examined for prevalence of parvovirus B19 DNA in the bone marrow and serum, irrespective of B19-related symptoms. B19 DNA was studied using 2 nested PCRs and the serum samples were further analysed with B19-specific IgG, IgM and avidity as well as seroreactivity against linear and conformational epitopes of the B19 VP2 antigen. The latter assays specify whether the IgG antibody response represents acute or past B19 infection. B19 DNA was detected in 4 of the 100 bone marrow samples, whereas all the serum samples were B19 DNA negative. None of the 4 B19 DNA positive patients had symptoms typical of B19 infection and serology showed past infection. Furthermore, 2 were still B19 DNA positive in bone marrow more than 1 y after the first sample indicating virus persistence. The seroprevalence for B19 IgG was 59% and 2 patients were B19 IgM positive. Thus, presence of B19 DNA in bone marrow from patients with haematological disorders is not a general finding in seropositive patients. B19 DNA can persist in bone marrow, but in our material this finding showed no clear correlation with symptomatic B19 infection.

Adult↗
PubMed1999

A new method with general diagnostic utility for the calculation of immunoglobulin G avidity.

The reference method for immunoglobulin G (IgG) avidity determination includes reagent-consuming serum titration. Aiming at better IgG avidity diagnostics, we applied a logistic model for the reproduction of antibody titration curves. This method was tested with well-characterized serum panels for cytomegalovirus, Epstein-Barr virus, rubella virus, parvovirus B19, and Toxoplasma gondii. This approach for IgG avidity calculation is generally applicable and attains the diagnostic performance of the reference method while being less laborious and twice as cost-effective.

Antibodies, Protozoan↗
PubMed1999

Acute-phase-specific heptapeptide epitope for diagnosis of parvovirus B19 infection.

The major capsid protein VP2 of human parvovirus B19, when studied in a denatured form exhibiting linear epitopes, is recognized exclusively by immunoglobulin G (IgG) antibodies of patients with acute or recent B19 infection. By contrast, conformational epitopes of VP2 are recognized both by IgG of the acute phase and by IgG of past immunity. In order to localize the VP2 linear epitope(s) specific for acute-phase IgG, the entire B19 capsid protein sequence was mapped by peptide scanning using well-characterized acute-phase and control sera. A unique heptapeptide epitope showing strong and selective reactivity with the acute-phase IgG was detected and characterized. By using this linear epitope (VP2 amino acids 344 to 350) and virus-like particles exhibiting conformational VP2 epitopes, an innovative approach, second-generation epitope-typing enzyme immunoassay, was set up for improved diagnosis of primary infections by human parvovirus B19.

Acute Disease↗
PubMed1998

Etiology of pneumonia and other common childhood infections requiring hospitalization and parenteral antimicrobial therapy. SE-TU Study Group.

The etiology of acute lower respiratory tract infections (mostly pneumonia) in children is well characterized, but these are only some of the community-acquired infections warranting parenteral antimicrobial therapy. We prospectively evaluated all such infections among children aged 3 months to 15 years by use of blood cultures, examination of nasopharyngeal aspirates, and serologies for 15 viral, 7 bacterial, and 1 protozoal agent. Immunocompromised patients and those with urinary tract infection, meningitis, or osteoarticular infection were excluded. In all, 170 children were included. The pathogenic agent was identified in 62% of the cases. Bacteria were detected in 54%, and a pneumococcus was found in 59% of the cases identified. Viruses were found in 15% overall. Sole bacterial or viral infections were detected in 47.1% and 8.1%, respectively. Since thorough screening established the etiology in less than two-thirds of patients ill enough to be hospitalized and treated parenterally, better diagnostics are needed, especially to identify those who would truly benefit from antimicrobial therapy.

Adolescent↗
PubMed1998

Immunoreactivation of Epstein-Barr virus due to cytomegalovirus primary infection.

Serological diagnosis of herpes virus infections is hampered by concurrent expression of IgM for heterologous members of this virus family. To assess the frequency of such multiple diagnostic findings and to understand their etiology, we sought by using IgG, IgM, and IgG avidity test serodiagnoses for Epstein-Barr virus (EBV) among immunocompetent or immune-suppressed patients with well-documented cytomegalovirus (CMV) primary infection. Controls had primary infection by EBV or had acute septic or severe respiratory infection. Among EBV-seropositive patients with CMV primary infection, a large proportion (13/56, 23%) showed antibody profiles of EBV reactivation: seroconversion of VCA IgM and/or > or = fourfold rise of VCA IgG, together with high or intermediate avidity of VCA IgG. Most of the CMV patients with EBV serodiagnosis showed also diagnostic HHV-6 antibody rises. In contrast to the frequently occurring CMV-induced EBV immunoreactivation, EBV primary infections did not appear to induce immunoreactivations of CMV (0/22). Only one (2%) CMV patient had a significant varicella zoster virus (VZV) antibody rise. The studies show that CMV is a particularly active inducer of some, but not all, members of the herpes virus family and suggest that the in vivo interplay between CMV and EBV occurs unidirectionally. The high frequency of heterologous herpes virus immunoreactivations poses demands on laboratory diagnosis.

Adolescent↗
PubMed1997

Persistence of parvovirus B19 DNA in synovial membranes of young patients with and without chronic arthropathy.

BACKGROUND: Human parvovirus B19 replicates in erythroid precursors of the bone marrow, and several diseases have been attributed to this virus including some cases of juvenile chronic arthropathy. METHODS: Tissue samples from children with juvenile arthritis and from healthy young adults with recent joint trauma were examined for B19 DNA by PCR. We also studied the timing of the parvovirus infection serologically. FINDINGS: All samples of synovial fluid, bone marrow, and blood were negative for B19 DNA. Eight (28%) of the 29 children with chronic arthritis had B19 DNA in synovial tissues. However, an even higher proportion of the non-arthropathy controls were positive for B19 DNA in synovial membranes (13 [48%] of 27). All the individuals with B19 DNA in synovial membrane had serum IgG antibodies to B19. INTERPRETATION: Genomic B19 DNA can persist in the synovial membranes not only in patients with chronic arthropathy but also in healthy immunocompetent individuals. The diagnostic criteria for parvovirus arthropathy must be reevaluated.

Adolescent↗
PubMed1997

Immunoglobulin G avidity in the serodiagnosis of congenital rubella syndrome.

The avidity of specific IgG was investigated in three infants with serologically verified congenital rubella infection. Two sera were taken from each infant: the first soon after birth and the second at the age of 23 to 31 months. Avidity of specific IgG was measured by a protein-denaturing enzyme immunoassay using urea as the elution factor, and avidity then determined by the end-point ratio (derived from antibody titration) and the avidity index methods. Rubella-specific IgM was present in the first sera of all patients, but not in the second sera. However, low avidity of specific IgG persisted in two children until age 23 to 31 months, as determined by the end-point ratio method. These data are in agreement with the findings of previous studies of avidity in congenital rubella, and show the usefulness of the protein-denaturing IgG-avidity assays employing the end-point ratio method for serological diagnosis of congenital rubella even after disappearance of specific IgM.

Antibodies, Viral↗
PubMed1997

False-positive results in immunoglobulin M (IgM) toxoplasma antibody tests and importance of confirmatory testing: the Platelia Toxo IgM test.

Although tests for detection of immunoglobulin M (IgM) toxoplasma antibodies have been reported to have a high degree of accuracy, it is well recognized by investigators in the United States and Europe that false-positive results may occur with many of these tests, at times to an alarming degree. Unfortunately, this information is not well documented in the literature. Studies on various toxoplasma IgM test kits are frequently flawed. The investigators often use reference tests which have not previously been carefully evaluated as well as sera that were not appropriate to answer the question of how often false-positive results might occur. We recently had the unique opportunity to evaluate the accuracy of the Platelia Toxo IgM test in 575 serum samples obtained during an outbreak of toxoplasmosis which occurred in 1995 in the Capital Regional District of British Columbia, Canada. When compared with results obtained in a reference IgM enzyme-linked immunosorbent assay (ELISA), the Platelia Toxo IgM test had a sensitivity of 99.4%, specificity of 49.2%, positive predictive value of 51.9%, negative predictive value of 99.3%, and an overall agreement of 67.0%. In an attempt to resolve discrepancies between these two tests, a serological profile (Sabin-Feldman dye test, IgA and IgE antibody tests, differential agglutination [AC/HS] test, and IgG avidity method) was performed. Of 153 serum samples that were positive in the Platelia Toxo IgM test and negative in the IgM ELISA, 71 (46.4%) were negative in the Sabin-Feldman dye test. Of the serum samples that were positive in the dye test, 77 (93.9%) had a serological profile most compatible with an infection acquired in the distant past. These results reveal high numbers of false-positive results in the Platelia Toxo IgM test and highlight the importance of appropriate evaluation of commercial tests that are currently being marked. Our results also emphasize the importance of confirmatory testing to determine whether the results of an IgM antibody test reflect the likelihood of a recently acquired infection.

Animals↗
PubMed1997

Primary and secondary infections by human parvovirus B19 following bone marrow transplantation: characterization by PCR and B-cell molecular immunology.

Due to the preparative regimen necessary, bone marrow transplantation (BMT) consistently results in severe immunodeficiency, often associated with anaemia, leukopenia and thrombocytopenia. Parvovirus B19 replicates in red blood cell precursors in the bone marrow and causes erythema infectiosum ('fifth disease'), anaemia, arthritis and foetal death. We assessed the significance of B19 infections as a cause of post-BMT complications. Over 900 serial serum samples from 201 allogeneic bone marrow recipients were studied by polymerase chain reaction (PCR) and by modern serodiagnostic methods. During the first 6 months after transplantation all BMT recipients remained B19 PCR-negative. Antibody screening for B19 infections was performed up to 36 months post-transplantation. Three cases of acute B19 infection were diagnosed during the second year post-BMT. To characterize the adoptively transferred immune system we measured subclasses and avidity of anti-VP1 IgG and epitope-type specificity (ETS) of anti-VP2 IgG, which allowed functional differentiation of primary and secondary B-cell responses long after BMT. The profile of the immune response was that of a primary infection in 1 and of reinfection in 2 of the 3 acute cases. Both types were clinically mild. Infection by human parvovirus B19 is not a frequent cause of post-BMT cytopenias. The findings with the new B19 antibody markers support the concept that the donated marrow determines the type of antiviral B-cell responses.

Adult↗
PubMed1996

IgG subclass response to human parvovirus B19 infection.

BACKGROUND: IgG antibodies are essential to immunity against human parvovirus B19 and can neutralize infection both in bone marrow cell cultures infected in vitro and in chronically infected immunosuppressed individuals. OBJECTIVES: To assess the levels and response kinetics of IgG subclasses towards individual structural proteins of human parvovirus B19. STUDY DESIGN: Subclasses of IgG for capsid proteins VP1 or VP2 were quantified by EIA using monoclonal antibodies in 30 acutely infected and 30 convalescent patients, as well as in 32 remotely infected and 20 non-infected controls. RESULTS: In all groups of seropositive individuals the predominant subclass for either structural protein was IgG1. Subclass IgG3 was associated with acute infection. By contrast, IgG4 appeared months after infection, and occurred specifically towards VP1. The ratio of VP1-specific subclasses IgG3 and IgG4 provided a diagnostic test for recent infection with a specificity of 98% and a sensitivity of 97%. CONCLUSIONS: Comparative measurement of VP1-specific IgG3 and IgG4 is useful in diagnosis. The IgG4 results point to long-term expression of immunologically active VP1 and to T-cell help of T(h)2 type for B-cells recognizing VP1.

Journal Article↗
PubMed1996

Latent transforming growth factor-beta 1 and its binding protein are components of extracellular matrix microfibrils.

We studied the localization of latent transforming growth factor-beta 1 (TGF-beta 1) and its binding protein (LTBP-1) in the extracellular matrix of cultured human fibroblasts by immunofluorescence and immunoelectron microscopy. Immunofluorescence of confluent fibroblast cultures indicated that LTBP-1 localizes to extracellular fibrillar structures resembling fibronectin-collagen matrix. Similar fibrillar structures were detected in cells stained with antibodies specific for TGF-beta 1 propeptide (beta 1-LAP). Both LTBP-1 and beta 1-LAP colocalized with fibronectin in double immunofluorescence analysis. These fibrillar structures were resistant to extraction with sodium deoxycholate, which is further evidence that LTBP-1 and large latent TGF-beta 1 complexes are integral components of the extracellular matrix. SV-40-transformed human fibroblasts lacked extracellular LTBP-1 fibers. EM analysis revealed approximately 10-nm-thick microfibrils that were labeled by anti-LTBP at 90-140-nm intervals. In addition, LTBP-1 was found in structures that were heavily labeled for fibronectin. The accumulation of LTBP-1 in the fibronectin matrix could be reconstituted in vitro. When isolated matrix components were immobilized on nitrocellulose and incubated with fibroblast conditioned medium, LTBP-1 from the medium associated with cellular fibronectin but not with heparan or chondroitin sulfate, vitronectin, tenascin, laminin, or collagen I or IV. The association of LTBP-1 with cellular fibronectin was abolished by treatment of the medium with plasmin, which cleaves LTBP-1 and inhibits its assembly to matrix. The present results indicate that latent TGF-beta 1 complexes are components of the extracellular matrix and suggest that alterations of the pericellular matrix could result in aberrant TGF-beta signaling.

Carrier Proteins↗
PubMed1995

Accurate serodiagnosis of B19 parvovirus infections by measurement of IgG avidity.

In an attempt to improve diagnosis of illnesses caused by parvovirus B19 and to discriminate primary from secondary infections, a protein-denaturing assay for avidity of parvovirus-specific IgG antibodies was developed. The assay used three types of purified recombinant antigens: a fusion protein containing the unique portion of the structural protein VP1, entire capsids made up of the major structural protein VP2 alone, or VP2 plus VP1. The avidity assays were evaluated by testing sequential acute-phase serum samples from 61 well-characterized patients (34 were followed > or = 6 months), sera from 38 controls with evidence of past infection, and sera from 388 seropositive patients studied for evidence of B19 infection during an epidemic. Parvovirus capsids consisting of VP2 alone yielded unusual IgG avidity and IgG antibody responses. Three different IgG avidity assays based on VP1 protein antigens were highly sensitive and specific and were considered suitable for identification of recent primary infections by human parvovirus B19.

Antibodies, Viral↗
PubMed1995

Epitope type-specific IgG responses to capsid proteins VP1 and VP2 of human parvovirus B19.

Temporal reactivities of IgG towards native and linear antigenic determinants in assembled capsids or isolated structural proteins of human parvovirus B19 were measured by an epitope type-specific IgG EIA and by immunoblots. Antigens used were baculovirus-expressed B19 capsids composed of the proteins VP1 and VP2 in their native proportion, VP2 alone, or a prokaryotic VP1 fusion protein. Follow-up sera after primary infection were compared with samples from previously infected persons. The IgG responses during acute and early convalescence phases were directed towards both conformational and linear epitopes of VP2. The antibodies against the linear VP2 epitopes disappeared abruptly within 6 months; however, the conformational VP2 antibodies persisted. The epitope type-specific IgG reactivity of VP1 was strikingly different from that of VP2. On the basis of these results, two novel tests were developed for patient diagnosis. Both tests are suitable for verifying the time of human parvovirus infection.

Antibodies, Viral↗
PubMed1995

Outcome of children after maternal primary Toxoplasma infection during pregnancy with emphasis on avidity of specific IgG. The Study Group.

Congenital toxoplasmosis results from maternal primary infection during pregnancy. In our serologic screening study 42 of 16,733 pregnant women had findings suggestive of primary infection. Here we document the outcome of their offspring, 37 of 39 liveborn children. After 12 months postnatally, serologically verified congenital toxoplasmosis appeared in 4 children. All these children had persisting IgG at the age of 12 months by both the dye test and the IgG enzyme-linked immunosorbent assay. All the congenitally infected infants had also specific IgM and IgA and showed significant increases in avidity of specific IgG during the 12-month follow-up. One of them had a unilateral retinal scar and intracranial calcifications. An additional 3 infants of the mothers with primary infection during early pregnancy presented with unilateral retinal scars but without seroresponses during the first 12 months of life. Maternal high avidity of IgG during the first trimester is a strong indicator against primary infection during pregnancy; the fetuses of such mothers are at low risk for congenital toxoplasmosis.

Base Sequence↗
PubMed1995

Cost-benefit analysis of screening for toxoplasmosis during pregnancy.

Congenital toxoplasmosis is a risk for fetus both in 'low' and 'high risk' areas. A cost-benefit analysis based on data from a Finnish prospective study (20.3% seropositivity of pregnant mothers and incidence of 2.4/1,000 seronegative pregnancies) and on Finnish cost data was performed to compare the no-screening and screening alternatives for primary toxoplasma infections during pregnancy. A maternal-feto transmission risk of 40%, effectiveness of treatment of 50%, and discount rate of 4% were used as other baseline probabilities. The calculations were carried out by decision analysis combined with sensitivity analysis. The total annual costs of congenital toxoplasmosis without screening amount to US$ 128/pregnancy/year, and with systematic serological screening, US$ 95/pregnancy. Thus screening reduces the costs by 25%. The present value of net savings in Finland would be US$ 2.1 million every year. A one-way sensitivity analysis showed that screening together with health education is preferable to health education without screening if the incidence of maternal primary infections exceeds 1.1/1,000 and effectiveness of treatment is better than 22.1%. Screening for toxoplasma infections during pregnancy is economically worthwhile even in a country with a low incidence. A scheme of systematic screening for maternal primary toxoplasma infections combined with health education should be considered.

Cost-Benefit Analysis↗
PubMed1994

Evaluation of protein-denaturing immunoassays for avidity of immunoglobulin G to rubella virus.

Immunoassays have been recently developed that measure the avidity of IgG antibodies to complex microbial antigens and are suitable for serologic diagnosis of infectious diseases. In these avidity ELISAs, protein-denaturing agents are applied either as diluents of patient sera to prevent the immune complexing of IgG (diluting principle), or the preformed complexes are treated with the protein denaturants (eluting principle). We compared four protein denaturants previously used in such assays, in a diagnostic avidity ELISA for rubella IgG. Diethylamine, guanidine, thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate at an optimum pH. Patient sera obtained recently after primary infection were distinguished from sera representing past rubella immunity by any protein denaturant tested by the eluting principle, which was superior to the diluting principle.

Antibody Affinity↗