Differential IgM response to conformational and linear epitopes of parvovirus B19 VP1 and VP2 structural proteins

A DNA sensor based on CbAgo effector protein and on a dual electrochemical signal amplification strategy for B19 parvovirus detection

Human parvovirus B19 is a prevalent childhood infectious virus that poses a great challenge to public health, so the detection of B19V is of great importance. In this study, a DNA sensor based on CbAgo, a Cas effector, and a dual electrochemical signal amplification strategy was developed by using a novel nanocomposite MnO2/CMK-3/g-C3N4/AgNPs for initial signal amplification, with CMK being an ordered mesoporous carbon nanomaterial. Single-walled carbon nanotubes (SWCNTs) were used as electrocatalytic probes for secondary signal amplification to detect B19 DNA. The detection process begins with polymerase chain reaction (PCR) amplification using the B19V infectious clone plasmid (pB19-M20) as a template and NS1-F/R as primers, followed by specific cleavage of B19 DNA based on the programmable cutting sites of CbAgo effector protein. This study enriches the application of Argonaute proteins in sensing and introduces a novel method to detect B19V. Under optimized conditions, the biosensor can detect B19 DNA in the range of 10-15-10-10 M, with a detection limit (LOD) of 0.2 fM. The results indicate that the developed DNA sensor holds promise for reliable and sensitive detection of B19 DNA in human serum.

Comparison of 4 commercial enzyme immunoassays for serology testing of human parvovirus B19 infection

BACKGROUND

Parvovirus B19 is a pathogenic virus often diagnosed by serology, yet little is known about analytical performance of commercial enzyme immunoassays (EIAs).

OBJECTIVE

To investigate performance of 4 EIAs for parvovirus B19 IgM and IgG: Liaison, Euroimmun, Mikrogen and Virion/Serion.

STUDY DESIGN

To compare 4 EIAs to Biotrin's ELISA on 168 samples and determine consensus score for discordant samples using Mikrogen's confirmatory line assay.

RESULTS

Two thirds of results for IgM/IgG were identical for all 4 EIAs and Biotrin. Liaison shows the highest IgM sensitivity, but has low specificity. Euroimmun lacks IgM sensitivity. Mikrogen had a good overall performance, but had the lowest IgG specificity. Virion/Serion had variable performance with a low IgM specificity and the most borderline and cross-reactive results.

CONCLUSIONS

Liaison and Mikrogen have similar performance to Biotrin's ELISA. Euroimmun lacks sensitivity and Virion/Serion produced many borderline and cross-reactive results.

Advances in the Development of Antiviral Strategies against Parvovirus B19

Parvovirus B19 (B19V) is a human pathogenic virus, responsible for an ample range of clinical manifestations. Infections are usually mild, self-limiting, and controlled by the development of a specific immune response, but in many cases clinical situations can be more complex and require therapy. Presently available treatments are only supportive, symptomatic, or unspecific, such as administration of intravenous immunoglobulins, and often of limited efficacy. The development of antiviral strategies against B19V should be considered of highest relevance for increasing the available options for more specific and effective therapeutic treatments. This field of research has been explored in recent years, registering some achievements as well as interesting future perspectives. In addition to immunoglobulins, some compounds have been shown to possess inhibitory activity against B19V. Hydroxyurea is an antiproliferative drug used in the treatment of sickle-cell disease that also possesses inhibitory activity against B19V. The nucleotide analogues Cidofovir and its lipid conjugate Brincidofovir are broad-range antivirals mostly active against dsDNA viruses, which showed an antiviral activity also against B19V. Newly synthesized coumarin derivatives offer possibilities for the development of molecules with antiviral activity. Identification of some flavonoid molecules, with direct inhibitory activity against the viral non-structural (NS) protein, indicates a possible line of development for direct antiviral agents. Continuing research in the field, leading to better knowledge of the viral lifecycle and a precise understanding of virus–cell interactions, will offer novel opportunities for developing more efficient, targeted antiviral agents, which can be translated into available therapeutic options.

Human IgM monoclonal antibodies block HIV-transmission to immune cells in cervico-vaginal tissues and across polarized epithelial cells in vitro

The importance of natural IgM antibodies in protection against infections is still emerging and these antibodies have a potential role in the maintenance of homeostasis through clearance of apoptotic bodies, complement-dependent mechanisms, inflammation and exclusion of misfolded proteins. Natural IgM act as a first line of defence against unknown hazardous factors and are present in most vertebrates. We investigated the functional capacity of anti-HIV-1 IgM monoclonal antibodies, from a combinatorial Fab library derived from healthy individuals, and evaluated their protective role in inhibiting HIV-1 in vitro when passing across the human mucosal epithelial barrier. Primary HIV-1 isolates were efficiently transmitted over the tight polarized epithelial cells when added to their apical surface. Efficient inhibition of HIV-1 transmission was achieved when anti-HIV-1 IgM monoclonal antibodies were added to the basolateral side of the cells. Two of these human IgM MoAbs had the ability to neutralize HIV and reduced infection of dendritic cells in primary cervico-vaginal tissue biopsies in vitro. This indicates a potential role of natural IgM antibodies in the reduction of HIV-1 transmission in mucosal tissues and improve our understanding of how natural IgM antibodies against a neutralizing epitope could interfere with viral transmission.

Parvovirus B19 Achievements and Challenges

Parvovirus B19 is a widespread human pathogenic virus, member of the Erythrovirus genus in the Parvoviridae family. Infection can be associated with an ample range of pathologies and clinical manifestations, whose characteristics and outcomes depend on the interplay between the pathogenetic potential of the virus, its adaptation to different cellular environments, and the physiological and immune status of the infected individuals. The scope of this review is the advances in knowledge on the biological characteristics of the virus and of virus-host relationships; in particular, the interactions of the virus with different cellular environments in terms of tropism and ability to achieve a productive replicative cycle, or, on the contrary, to establish persistence; the consequences of infection in terms of interference with the cell physiology; the process of recognition of the virus by the innate or adaptive immune system, hence the role of the immune system in controlling the infection or in the development of clinical manifestations. Linked to these issues is the continuous effort to develop better diagnostic algorithms and methods and the need for development of prophylactic and therapeutic options for B19V infections.

Diagnosis of in utero Parvovirus B19 infection and maternal immune response - the relevance of linear epitopes and advanced serologic testing

IMPORTANCE OF THE FIELD

Parvovirus B19 (B19V) infection in utero causing fetal anemia and non-immune hydrops fetalis (NIHF) is a potentially life-threatening event for the fetus. Postexpositional non-invasive diagnosis is based on maternal IgG/IgM response and detection of viral genome in maternal blood. Serologic testing directs prenatal follow-up. Fetal infection is confirmed by polymerase chain reaction or in situ hybridization in fetal blood and/or amniotic fluid cells. The performance of serologic tests is significant in order to direct pre- and perinatal care at rational use of resources. Timing of diagnostic procedures and knowledge of the time course of infection in pregnant, asymptomatic women are critical. IgM negative testing in the presence of prolonged viremia may complicate individual risk analysis in pregnancy. Recently, advanced IgG avidity assays and epitope-type specific assays (IgG ETS EIA) have been re-evaluated.

AREAS COVERED IN THIS REVIEW

Epidemiology, clinical relevance and management of B19V infection in pregnancy. A review of the current literature (November 1984 - May 2009) and evaluation of current information on performance and predictive value of molecular and VP1/VP2 antigen-based IgG tests directed at the diagnosis of materno-fetal B19V infection and detection of past immunity. New aspects of B19V-associated fetal disease other than anemia/NIHF are also covered.

WHAT THE READER WILL GAIN

An overview of immunology and clinical relevance of B19V infection in pregnancy, of the potential value of advanced serologic testing and fields of future research.

TAKE HOME MESSAGE

In the absence of a commercially available vaccine, serologic tests remain important tools in individual risk analysis of pregnant women exposed to B19V. Sequential application of IgG avidity and IgG ETS EIAs may improve risk stratification and timing of invasive testing in B19V-exposed pregnancies, in particular with IgM-negativity and/or persistent DNAemia. Prospective evaluation of these test systems correlated to fetal outcome in order to reduce fetal morbidity and mortality as well as the overall burden of disease of B19V with regard to fetal malformation may be subject to future research.

In silico screened Mycobacterium avium subsp. paratuberculosis (MAP) recombinant proteins upregulated under stress conditions are immunogenic in sheep

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne's disease (JD) in ruminants. MAP is known to enter a dormant phase outside the host, typically on soil. In vitro experiments have reported regulation of certain MAP genes when exposed to stressors similar to what is thought to produce dormancy. It is believed that in vivo regulation of dormancy genes and associated proteins by MAP may play a role in evading the host defence mechanisms and induce the host immune response against these dormancy-related proteins. Five proteins encoded by dormancy-related genes that were previously found to be upregulated under stress conditions and predicted through in silico analysis to possess immune epitopes (three hypothetical proteins and two proteins involved in fatty acid metabolism) were selected. Recombinant proteins were produced, purified and evaluated by indirect enzyme-linked immunosorbent assay (ELISA) for immunogenicity using a panel of sera obtained from sheep unexposed and exposed to MAP. The antibody levels of the exposed group were significantly higher than the unexposed group (P<0.001). Individually, the five proteins were found to discriminate between sera from sheep exposed to MAP compared to unexposed sheep. At 91% diagnostic specificity, the diagnostic sensitivity of the recombinant antigen ELISA ranged from 24% to 42% and AUC(ROC) from 0.7015 to 0.8405.

Risk of fetal hydrops and non-hydropic late intrauterine fetal death after gestational parvovirus B19 infection

BACKGROUND

Risk assessment of parvovirus B19 (B19)-associated fetal complications following gestational B19 infection remains controversial.

OBJECTIVES

To determine the risk of fetal hydrops or non-hydropic late intrauterine fetal death following acute maternal B19 infection at defined gestational weeks.

STUDY DESIGN

Observational cohort study of pregnant women with serologic evidence of acute B19 infection. If available, fetal or neonatal tissue samples from cases complicated by fetal loss or hydrops were investigated for the presence of B19 DNA by polymerase chain reaction (PCR) and/or in situ hybridization (ISH).

RESULTS

Of 236 women with known pregnancy outcome, 228 had a live birth and 8 a fetal loss. The observed rate of fetal hydrops for all pregnant women was 4.2% (10/236) (95% confidence interval [CI], 2.1-7.7) and 10.6% (10/94) (95% CI, 5.2-18.7) for those infected between 9 and 20 weeks gestation. Tissue samples from 8 hydrops cases were investigated by PCR or ISH and all were B19 DNA positive. Fetal death occurring during or after gestational week 22 was only observed in one case which was associated with B19-derived fetal hydrops.

CONCLUSIONS

Our findings demonstrate that although adverse fetal outcome is a rare complication of gestational B19 infection, a relevant risk of fetal hydrops exists particularly for women infected between 9 and 20 weeks' gestation. Cases of B19-derived non-hydropic late intrauterine fetal death were not observed in the present study.

Serodiagnosis of human bocavirus infection

Background. A new human-pathogenic parvovirus, human bocavirus (HBoV), has recently been discovered and associated with respiratory disease in small children. However, many patients have presented with low viral DNA loads, suggesting HBoV persistence and rendering polymerase chain reaction-based diagnosis problematic. Moreover, nothing is known of HBoV immunity. We examined HBoV-specific systemic B cell responses and assessed their diagnostic use in young children with respiratory disease.

Patients and methods. Paired serum samples from 117 children with acute wheezing, previously studied for 16 respiratory viruses, were tested by immunoblot assays using 2 recombinant HBoV capsid antigens: the unique part of virus protein 1 and virus protein 2.

Results. Virus protein 2 was superior to the unique part of virus protein 1 with respect to immunoreactivity. According to the virus protein 2 assay, 24 (49%) of 49 children who were positive for HBoV according to polymerase chain reaction had immunoglobulin (Ig) M antibodies, 36 (73%) had IgG antibodies, and 29 (59%) exhibited IgM antibodies and/or an increase in IgG antibody level. Of 22 patients with an increase in antibody levels, 20 (91%) had a high load of HBoV DNA in the nasopharynx, supporting the hypothesis that a high HBoV DNA load indicates acute primary infection, whereas a low load seems to be of less clinical significance. In a subgroup of patients who were previously determined to have acute HBoV infection (defined as a high virus load in the nasopharynx, viremia, and absence of other viral infections), 9 (100%) of 9 patients had serological evidence of primary infection. In the control group of 68 children with wheezing who had polymerase chain reaction results negative for HBoV in the nasopharynx, 9 (13%) had IgM antibodies, including 5 who displayed an increase in IgG antibody levels and were viremic. No cross-reactivity with human parvovirus B19 was detected.

Conclusions. Respiratory infections due to HBoV are systemic, elicit B cell immune responses, and can be diagnosed serologically. Serological diagnoses correlate with high virus loads in the nasopharynx and with viremia. Serological testing is an accurate tool for disclosing the association of HBoV infection with disease.

Positive reactions on Western blots do not necessarily indicate the epitopes on antigens are continuous

Epitope mapping (identification of an antigenic site recognized by an antibody) is an important component of vaccine development and immunological assays. It is widely accepted that in Western blots, antibodies react exclusively with continuous epitopes: discontinuous epitopes are assumed to be irreversibly destroyed by electrophoresis under the denaturing conditions used for sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Here, we demonstrate that the epitopes recognized by four different monoclonal antibodies were identified as discontinuous epitopes when characterized by radioimmunoprecipitation assays and enzyme-linked immunosorbent assays, yet each of these antibodies reacted with the corresponding antigen on Western blots. Reaction on Western blots may be due to epitope renaturation during or after the transfer of the protein to a membrane. Therefore, positive reactions on Western blots do not necessarily indicate that epitopes are continuous and this caveat should be kept in mind while characterizing them.

Reactivity of genotype-specific recombinant proteins of human erythrovirus B19 with plasmas from areas where genotype 1 or 3 is endemic

Human erythrovirus (parvovirus) B19 (B19) is a common human pathogen. The recent discovery of three genotypes, 1 to 3, raised issues related to the ability of genotype-specific antigens to cross-react with antibodies elicited by other genotypes. This study assessed antibody capture and immunoglobulin G (IgG) cross-reactivity between genotype 1 and genotype 3 recombinant antigens and analyzed the potential gain of adding VP1 protein to VP2 capsid antigen. Plasma samples from genotype 1- or genotype 3-infected populations were blindly tested with blindly prepared reagents. The IgG reactivity was assessed with baculovirus-expressed VP2 or VP1 and VP2 recombinant genotype 1 or genotype 3 proteins in a standardized enzyme immunoassay (EIA). A high degree of agreement (>95%) between EIA results was observed, with Spearman correlation coefficient and kappa reliability coefficient results of >/=0.95 for samples from the United Kingdom and >/=0.77 for samples from Ghanaian children, respectively. Most discrepant results were related to equivocal reactivity. The addition of VP1 to VP2 capsids did not significantly impact antibody detection. These data suggest that the currently available genotype-1-based IgG EIA is suitable to detect antibody to B19 genotype 3 in Ghanaian children. However, samples from the Ghanaian adult population exhibited atypical results in the assay, possibly due to the high levels of nonspecific IgG antibodies found in adults living in this region. Within these limitations, the study demonstrates that genotype 1 and genotype 3 antigens are equally effective in detecting either antibody species.

Serologic and molecular detection of human Parvovirus B19 infection

Following its identification by Yvonne Cossart in 1975, human Parvovirus B19 has been recognized as the causative agent of a wide range of diseases. In childhood, the most common disease is a typical exanthema called "fifth disease". In adults, viral infection may be responsible for fetal loss and for aplastic anaemia in immuno-compromised patients. Because persistent viral infection may induce an autoimmune response, Parvovirus B19 is emerging as an environmental factor linked to the pathogenesis of autoimmunity. As a result of its expanding disease spectrum, Parvovirus B19 is the subject of intense efforts to clarify the pathogenesis of virus-related disorders as well as improve diagnostic laboratory testing including standardization of serological and nucleic acid-based detection assays. Enzymatic immunoassays based on conformational antigens have proven to be the most important tools for accurate diagnosis in the majority of cases. In other selected clinical cases, the detection of Parvovirus B19 infection can be complemented by PCR and, more recently, by the real-time PCR.

Molecular and structural characterization of fluorescent human parvovirus B19 virus-like particles

Although sharing a T=1 icosahedral symmetry with other members of the Parvoviridae family, it has been suggested that the fivefold channel of the human parvovirus B19 VP2 capsids is closed at its outside end. To investigate the possibility of placing a relatively large protein moiety at this site of B19, fluorescent virus-like particles (fVLPs) of B19 were developed. The enhanced green fluorescent protein (EGFP) was inserted at the N-terminus of the structural protein VP2 and assembly of fVLPs from this fusion protein was obtained. Electron microscopy revealed that these fluorescent protein complexes were very similar in size when compared to wild-type B19 virus. Further, fluorescence correlation spectroscopy showed that an average of nine EGFP domains were associated with these virus-like structures. Atomic force microscopy and immunoprecipitation studies showed that EGFP was displayed on the surface of these fVLPs. Confocal imaging indicated that these chimeric complexes were targeted to late endosomes when expressed in insect cells. The fVLPs were able to efficiently enter cancer cells and traffic to the nucleus via the microtubulus network. Finally, immunoglobulins present in human parvovirus B19 acute and past-immunity serum samples were able to detect antigenic epitopes present in these fVLPs. In summary, we have developed fluorescent virus-like nanoparticles displaying a large heterologous entity that should be of help to elucidate the mechanisms of infection and pathogenesis of human parvovirus B19. In addition, these B19 nanoparticles serve as a model in the development of targetable vehicles designed for delivery of biomolecules.

Identification and characterization of persistent human erythrovirus infection in blood donor samples

The presence of human erythrovirus DNA in 2,440 blood donations from the United Kingdom and sub-Saharan Africa (Ghana, Malawi, and South Africa) was screened. Sensitive qualitative and real-time quantitative PCR assays revealed a higher prevalence of persistent infection with the simultaneous presence of immunoglobulin G (IgG) and viral DNA (0.55 to 1.3%) than previously reported. This condition was characterized by a low viral load (median, 558 IU/ml; range, 42 to 135,000 IU/ml), antibody-complexed virus, free specific IgG, and potentially infectious free virus. Human erythrovirus genotype 1 (formerly parvovirus B19) was prevalent in the United Kingdom, Malawi, and South Africa. In contrast, only human erythrovirus genotype 3 (erythrovirus variant V9) was prevalent in Ghana. Genotype 3 had considerable genetic diversity, clustering in two probable subtypes. Genotype 1-based antibody assays failed to detect 38.5% of Ghanaian samples containing antibodies to genotype 3 virus but did not fail to detect cases of persistent infection. This study indicates a potential African origin of genotype 3 human erythrovirus and considerable shortcomings in the tools currently used to diagnose erythrovirus infection.

Advances in the biology, diagnosis and host-pathogen interactions of parvovirus B19

Increased recognition of parvovirus B19 (B19), an erythrovirus, as a significant human pathogen that causes fetal loss and severe disease in immunocompromised patients has resulted in intensive efforts to understand the pathogenesis of B19-related disease, to improve diagnostic strategy that is deployed to detect B19 infection and blood-product contamination and, finally, to elucidate the nature of the cellular immune response that is elicited by the virus in diverse patient cohorts. It is becoming clear that at least three related erythrovirus strains (B19, A6/K71 and V9) are circulating in the general population and that viral entry into target cells is mediated by an expanding range of cellular receptors, including P antigen and beta-integrins. Persistent infection by B19 is emerging as a contributory factor in autoimmune disease, a hypothesis that is constrained by the detection of B19 in the skin of apparently healthy individuals. B19 infection during pregnancy may account for thousands of incidences of fetal loss per annum in Europe, North America and beyond, yet there is currently only minimal screening of pregnant women to assess serological status, and thereby risk of infection, upon becoming pregnant. Whilst major advances in diagnosis of B19 infection have taken place, including standardization of serological and DNA-based detection methodologies, blood donations that are targeted at high-risk groups are only beginning to be screened for B19 IgG and DNA as a means of minimizing exposure of at-risk patients to the virus. It is now firmly established that a Th1-mediated cellular immune response is mounted in immunocompetent individuals, a finding that should contribute to the development of an effective vaccine to prevent B19 infection in selected high-risk groups, including sickle-cell anaemics.

Comparison of three commercially available serologic assays used to detect human parvovirus B19-specific immunoglobulin M (IgM) and IgG antibodies in sera of pregnant women

A split-sample study was conducted to evaluate the performances of three enzyme immunoassays (EIAs) utilizing one or more conformational antigens to detect human parvovirus B19 (B19V)-specific immunoglobulin M (IgM) or IgG in the sera of 198 pregnant women. We compared EIAs available from Biotrin International, Inc. (Dublin, Ireland), Medac Diagnostika (Wedel, Germany), and Mikrogen (Martinsried, Germany). Specimens with discordant results were analyzed further using an immunofluorescence assay (Biotrin). Equivocal data accounted for close to half of all the discrepant results for both IgM and IgG, with 7 of 15 discrepant results from the Medac and Mikrogen kits involving equivocal data and the Biotrin kit giving a single equivocal result. For each specimen, a consensus was established from the four test results if agreement occurred among at least three of four results. Overall, the highest percentage of agreement with the consensus results was seen when Biotrin kits were used; 194 (100%) of 194 and 194 (99.5%) of 195 results for IgM and IgG, respectively, agreed with the consensus results. When Medac kits were used, 189 (97.4%) of 194 and 191 (97.9%) of 195 results for IgM and IgG, respectively, agreed with the consensus, and when Mikrogen kits were used, 179 (92.3%) of 194 and 193 (99%) of 195 results for IgM and IgG, respectively, agreed with the consensus. Given the consensus results, the Medac EIA appeared to generate presumed false-positive results for IgM and the Mikrogen EIA appeared to generate presumed false-positive results for IgG and IgM. In summary, the Biotrin EIAs produced far fewer equivocal results than the other assays and results of the Biotrin EIAs agreed more often with the consensus results than did those of the other commercially available EIAs for detecting B19V-specific IgM and IgG antibodies.

Detection of parvovirus B19 IgG: choice of antigens and serological tests

Serum samples were analysed for the presence of (a) IgG against VP1+VP2 using recombinant native conformational antigens by ELISA test (b) IgG against VP2 using recombinant native conformational antigens by ELISA test and (c) IgG against VP1 and against VP2 using denatured linear antigens by Western blot. Out of the 446 samples examined, 353 were positive for specific B19 IgG and out of these, 98.6 % proved positive in the ELISA assay using conformational VP1+VP2 antigens, 94.6% proved positive in the ELISA assay using conformational VP2 antigens, 89.5% were positive at the Western blot assay using denatured linear VP1 and VP2 antigens, with all proving positive for linear VP1 and only 29.5% out of the positive samples proving positive for linear VP2. Since all samples positive by Western blot proved positive by ELISA, our data show that recombinant capsids obtained either with VP1+VP2 or with VP2 alone, used in ELISA, are very useful for detecting the immune response against both conformational and native linear epitopes of B19 structural proteins although some sera may have antibodies directed exclusively against VP1+VP2 antigens and few may have antibodies directed exclusively against VP2 antigens alone.

Relevance of B19 markers in serum samples for a diagnosis of parvovirus B19-correlated diseases

In order to evaluate the optimal and essential diagnostic test(s) for a correct diagnosis of B19 diseases, 344 consecutive serum samples were tested from 344 patients with clinical suspicion of B19 infection during an epidemic period (early Spring-Autumn 2000). Sera were tested for B19 DNA by a standardized competitive polymerase chain reaction-enzyme-linked immunosorbent assay (PCR-ELISA) and dot-blot hybridization and for specific IgM and IgG by ELISA. Of 344 patients examined, 125 were positive for markers of B19-associated disease: 49 had both B19 DNA and IgM, 50 had B19 DNA without IgM, and 26 had IgM without B19 DNA. After examination of the different patterns of B19 markers as diagnostic tools for B19 infection, IgM determination detected only 60% of B19-documented infections. IgM tests were nevertheless fundamental, as they were the unique diagnostic marker in 20.8% of documented infections (26 of 125 patients), in the diagnosis of recent, but still symptomatic infections when B19 DNA was no longer detectable. The determination of B19 DNA with PCR permitted detection of 79.2% of infections and therefore represented an essential test. PCR was fundamental for the diagnosis of B19 disease, as the unique diagnostic marker in 32% of documented infections (50 of 125 patients), both in acute infections at the onset of symptoms before the appearance of immunological response, and during the course of persistent B19 infections in which IgM had cleared. The contemporaneous determination of B19 DNA by PCR and specific IgM appears to be the most appropriate diagnostic protocol for the correct laboratory diagnosis of B19 infection.

Detection of parvovirus B19 NS1-specific antibodies by ELISA and western blotting employing recombinant NS1 protein as antigen

Human parvovirus B19 (B19) encodes a number of nonstructural proteins, including the major protein, NS1, and two structural proteins, VP1 and VP2. The use of denatured NS1 in enzyme-linked immunosorbent assay (ELISA) and Western blot (WB) assay has provided an opportunity to study some of the immunologic properties of NS1, but the results have been equivocal and the diagnostic sensitivity poor, probably because of the absence of conformational epitopes. Various viral isolates and baculovirus vectors were employed to produce recombinant B19 NS1 under nondenaturing conditions for the first time. To assess the antigenicity of purified B19 NS1, the reaction patterns of 252 samples were compared by B19 NS1 and VP2 ELISA. In sera from individuals with past infection (VP2 IgG-positive), the use of this new antigen increased significantly the sensitivity of ELISA compared with WB (78% vs. 33%, P = 0.001), contradicting perpetuated claims that B19 NS1 IgG is detected primarily in patients with arthralgia or chronic infection. Previous reports of the absence of NS1 IgG during the initial phase of infection (< 6 weeks) were proved incorrect by the detection of NS1 IgG in 60% of samples from patients recently infected by B19. Including conformational epitopes in the ELISA increases the diagnostic sensitivity, although immunologically, a temporal (years) attenuation of NS1 antibodies appears to take place. This novel diagnostic tool may be useful as a supplement in case of borderline results by VP2 ELISA and for monitoring the efficacy of future capsid-based B19 vaccines.

Diagnostic procedures in B19 infection

In immunologic normal hosts, both children and adults, B19 can cause acute, generally self-limiting diseases. The infection leads to a viremia that can be present, at high titre, for about one week, then the onset of a specific immune response controls the infection. B19 infection in pregnancy can be associated with non-immunologic foetal hydrops or foetal death. In immunocompromised hosts, B19 can persist over several months and sometimes years. Persistent or recurrent B19 infections can be associated with chronic clinical manifestations or with transient clinical syndromes, generally related to the recrudescence of viral replication. Since the infection has been associated with a wide variety of clinical manifestations and some clinical features of B19 infection, such as anemia, artropathy and rash, can be common to other pathogens, a laboratory diagnosis of B19 infection is required. A diagnostic protocol must consider both the type of pathology and the type of patient. In immunocompetent individuals serological and virological testing is complementary, while in immunocompromised patients viral detection is the diagnosis of choice. Viral detection methods are generally based, nowadays, on the direct detection of B19 genome in clinical specimens. B19 DNA is mainly detected by hybridizations assays and by the most sensitive PCR assays. Serological diagnosis of B19 infection is generally achieved by detection of IgM and IgG antibodies to the B19 structural proteins VP1 and VP2. IgM detection is most often performed by capture assays, both in EIA and RIA formats, IgG are mainly detected by indirect EIA and immunofluorescence tests.