A new peptide for human parvovirus B19 antibody detection

Human Parvoviruses

Parvovirus B19 (B19V) and human bocavirus 1 (HBoV1), members of the large Parvoviridae family, are human pathogens responsible for a variety of diseases. For B19V in particular, host features determine disease manifestations. These viruses are prevalent worldwide and are culturable in vitro, and serological and molecular assays are available but require careful interpretation of results. Additional human parvoviruses, including HBoV2 to -4, human parvovirus 4 (PARV4), and human bufavirus (BuV) are also reviewed. The full spectrum of parvovirus disease in humans has yet to be established. Candidate recombinant B19V vaccines have been developed but may not be commercially feasible. We review relevant features of the molecular and cellular biology of these viruses, and the human immune response that they elicit, which have allowed a deep understanding of pathophysiology.

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.

Generation of neutralizing human monoclonal antibodies against parvovirus B19 proteins

Infections caused by human parvovirus B19 are known to be controlled mainly by neutralizing antibodies. To analyze the immune reaction against parvovirus B19 proteins, four cell lines secreting human immunoglobulin G monoclonal antibodies (MAbs) were generated from two healthy donors and one human immunodeficiency virus type 1-seropositive individual with high serum titers against parvovirus. One MAb is specific for nonstructural protein NS1 (MAb 1424), two MAbs are specific for the unique region of minor capsid protein VP1 (MAbs 1418-1 and 1418-16), and one MAb is directed to major capsid protein VP2 (MAb 860-55D). Two MAbs, 1418-1 and 1418-16, which were generated from the same individual have identity in the cDNA sequences encoding the variable domains, with the exception of four base pairs resulting in only one amino acid change in the light chain. The NS1- and VP1-specific MAbs interact with linear epitopes, whereas the recognized epitope in VP2 is conformational. The MAbs specific for the structural proteins display strong virus-neutralizing activity. The VP1- and VP2-specific MAbs have the capacity to neutralize 50% of infectious parvovirus B19 in vitro at 0.08 and 0.73 microgram/ml, respectively, demonstrating the importance of such antibodies in the clearance of B19 viremia. The NS1-specific MAb mediated weak neutralizing activity and required 47.7 micrograms/ml for 50% neutralization. The human MAbs with potent neutralizing activity could be used for immunotherapy of chronically B19 virus-infected individuals and acutely infected pregnant women. Furthermore, the knowledge gained regarding epitopes which induce strongly neutralizing antibodies may be important for vaccine development.

Rheumatic manifestations of parvovirus B19 infection

Human parvovirus B19 is an emerging DNA virus. B19 infection is common and widespread. Major manifestations of B19 infection are transient aplastic crisis, erythema infectiosum, hydrops fetalis, acute and chronic rheumatoid-like arthropathy, and, in the immunocompromised host, chronic or recurrent bone marrow suppression. A number of less common manifestations of B19 infection include various rash illnesses, neuropathies, and acute fulminant liver failure. Of rheumatologic interest, B19 infection must be differentiated from early presentation of more classic erosive rheumatoid arthritis and, in some cases, systemic lupus erythematosus. It is unlikely that B19 plays a role in classic erosive rheumatoid arthritis, but understanding pathogenesis of B19 arthropathy may provide insights into the mechanisms by which rheumatoid arthritis develops. Evidence for persistence of B19 infection suggests that human parvovirus B19 infection may serve as a model for the study of virus-host interactions and the role of viruses in the pathogenesis of rheumatic diseases.

Comparative evaluation of three recombinant antigen-based enzyme immunoassays for detection of IgM and IgG antibodies to human parvovirus B19

BACKGROUND

Diagnosis of acute and past infection with parvovirus B19 is based on detection of IgM and IgG antibodies.

OBJECTIVES

To evaluate two commercial recombinant antigen-based enzyme immunoassay (EIA) test kits for detection of IgM and IgG antibodies to parvovirus B19 and to compare the commercial EIAs to in-house EIA test procedures.

STUDY DESIGN

A panel of 121 sera was used to compare the three IgM EIAs. The panel included 84 sera submitted for parvovirus B19 testing and 37 sera that were IgM positive for other viral pathogens. The same serum panel plus an additional 14 sera submitted for B19 testing was used to compare the three IgG EIAs. The commercial EIAs were performed according to manufacturers' instructions. Using the in-house EIA test procedures as the reference, sensitivity and specificity for each of the commercial EIAs was determined.

RESULTS

The commercial B19 IgM EIAs showed agreements of 95.0 and 93.4% to the in-house IgM EIA. Compared to the in-house B19 IgM EIA, the commercial B19 IgM EIAs were 97.4 and 97.5% sensitive, respectively. Specificities were 93.5 and 91.4%, respectively. Sensitivities for the commercial IgG EIAs, compared to in-house IgG EIA, were 88.0 and 85.2%, respectively, and specificities were 94.1 and 98.0%.

CONCLUSION

We found that the commercial parvovirus B19 IgM and IgG EIAs are comparable to standard in-house EIAs and are suitable for testing for B19 antibodies in human sera.

Comparison of seven commercial tests for the detection of parvovirus B19-specific IgM

Several enzyme immunoassays (EIA) for the detection of parvovirus B19 IgM (anti-B19 IgM) are now commercially available. In this study, seven commercial EIAs (Biotrin, DAKO, Viramed, Viratech, R-Biopharm, Mast) were compared with an in-house EIA (MvP-EIA) using native viral B19 particles and the reference IgM radioimmunoassay (MACRIA). A total of 88 sera were tested. Results agreed in 39/88 (44.3%) sera, whereas 47/88 (53.4%) were discrepant and 2/88 (2.3%) gave an equivocal result. Assay sensitivity ranged from 70.3 to 100% and specificity, from 75.9 to 100%. The best results were obtained with two EIAs (Biotrin, DAKO) using baculovirus-expressed B19 proteins as antigen. This study has shown that baculovirus-expressed B19 antibody tests are suitable tools for detecting anti-B19 IgM.

Evaluation of four commercial enzyme immunoassays for detection of immunoglobulin M antibodies to human parvovirus B19

Four commercial enzyme immunoassays (EIAs) for the detection of parvovirus B19-specific immunoglobulin M (IgM) antibodies [Biotrin Parvovirus B19 IgM (Biotrin International, Ireland); Parvoscan B19 IgM (Euro-Diagnostica, Sweden); Parvovirus IgM (Immunobiological Laboratories [IBL], Germany); and human parvovirus B19 IgM (Hillcrest Biologicals, USA)] were compared to indirect immunofluorescence assay (IFA) and polymerase chain reaction (PCR). Using IFA as the reference test, high sensitivities (> or = 97%) were observed with all four EIAs, though the specificities of the Biotrin and IBL EIAs (99% and 96% respectively) were significantly higher than those of the Hillcrest and Euro-Diagnostica EIAs (81% and 79% respectively).

Evaluation of 4 commercial test kits for parvovirus B19-specific IgM

Four commercial test kits for parvovirus B19 IgM were evaluated by testing 491 sera assembled into 7 panels. The serum panels were designed to assess sensitivity and specificity of the commercial assays and to reflect the various clinical settings in which acute B19 infection forms part of the differential diagnosis. A mu-capture radioimmunoassay (MACRIA) was used as the reference test. With respect to MACRIA, the commercial B19 IgM assays showed an overall sensitivity of 70.1-84.1% and specificity of 92.2 to 97.4%. Assay performance varied in different clinical situations. In sera from adults with acute B19 arthropathy, all 4 assays were 100% sensitive, but in children with fifth disease, the sensitivity ranged from 44.1 to 88.6%. The sensitivity of all 4 assays was also low when testing samples collected more than 6 weeks after onset of symptoms and in women with B19-associated embryopathy. Specificity was greater than 97% in healthy blood donors, but varied from 70.9 to 83.3% in patients acutely infected with other viruses, including rubella. Although the IgM test kits here evaluated may be usefully introduced for B19 diagnosis in certain settings, knowledge of their limitations will be important when results have been interpreted.

A synthetic parvovirus B19 capsid protein can replace viral antigen in antibody-capture enzyme immunoassays

To establish a renewable source of parvovirus B19 antigens for diagnostic tests, gene sequences for the viral capsid proteins, VP1 and VP2, were cloned into baculovirus expression vectors and the recombinant viruses used to infect Sf9 insect cells. Cell lysates examined by immunoblotting demonstrated reactive proteins corresponding to the expected sizes of native VP1 (83 kDa) and VP2 (58 kDa). The VP2 protein was produced efficiently in quantity and self-assembled into empty capsids as shown by density equilibration in a CsCl step gradient. The VP2 protein was purified and used as an antigen in antibody-capture enzyme immunoassays for the detection of B19 IgG and IgM antibodies. Compared to a standard antibody-capture EIA based on whole viral antigen, the VP2-EIA gave a sensitivity of 100% and specificity of 97% in detection of B19 IgM in 138 patients suspected of B19 infection. No IgM-positive specimens were missed. IgG detection yielded a sensitivity of 100% and specificity of 96% in the same population. Recombinant VP2 capsid proteins expressed in baculovirus-infected insect cells can substitute for serum-derived B19 virus in standard antibody-capture EIA for the detection of B19 IgG and IgM with comparable results.

Evaluation of five commercial tests for detection of immunoglobulin M antibodies to human parvovirus B19

The following commercial tests for detection of immunoglobulin M antibodies to human parvovirus B19 were evaluated: Ideia Parvovirus B19-IgM, MRL Diagnostics Human Parvovirus B19 IgM ELISA, Parvoscan-B19, and Biotrin Parvo B19 IgM EIA and IF. A total of 203 serum specimens from patients who probably have current B19 infections or have other viral infections and sera with rheumatoid factor were investigated. Between 75 and 79 of 102 serum samples from patients thought to have current B19 infections yielded positive results with the different tests. Ideia had the highest specificity (94.8%), while Parvoscan showed a specificity of only 70.1%. Our evaluation results show that Ideia, MRL, and Biotrin EIA and IF can be recommended for diagnostic purposes.

A recombinant immunoblot and ELISA for detection of acute parvovirus B19 infection

Laboratory diagnosis of parvovirus B19 (B19) infection has been hampered by the limited availability of B19 virus. Recombinant viral proteins are now available for use as antigen in serological assays. We compared detection of anti-B19 IgM by "mu-capture assay" using viral B19 particles to a recombinant (rec.) immunoblot and a rec. enzyme-immunoassay (ELISA) using viral structural proteins as antigens expressed in E. coli. The rec. immunoblot was 94.3% sensitive and 96.4% specific for anti-B19 IgM, and the sensitivity of the rec. ELISA was 94.3% and the specificity, only 72.7%. There was an agreement between the "mu-capture assay" and the rec. immunoblot in 87.8% and the rec. ELISA in only 74.4%. For detection of anti-B19 IgG in patients with acute B19 infection, the rec. immunoblot was 94.3% and the rec. ELISA 85.7% sensitive. The rec. immunoblot is more reliable for detection of acute B19 infection than the rec. ELISA.

Human parvovirus B19 infections: routine diagnosis by a new nested polymerase chain reaction assay

A nested primer PCR assay was developed to detect human parvovirus B19 in various clinical specimens in a routine diagnostic laboratory. Under optimized conditions the highly specific assay had a sensitivity of less than 10 genome units. For practical reasons, however, this sensitivity was adjusted to 10-100 virus genomes in diagnostic applications. Using clinical specimens from 200 patients with suspected B19 infection, nested PCR was shown to have important diagnostic advantages over the detection of B19 specific antibodies. The data suggest that on the basis of serological data as obtained with currently available test systems a considerable proportion of B19 infections would be misdiagnosed. Examples for the usefulness of the PCR assay in routine diagnosis are given.

Detection of parvovirus B19 in donated blood: a model system for screening by polymerase chain reaction

A highly sensitive and rapid method for routinely screening large numbers of donated blood units for parvovirus B19 by the polymerase chain reaction (PCR) was developed. Over a 3-month trial period in Edinburgh, B19 DNA was detected in 6 of 20,000 consecutive units of blood (0.03%), in concentrations ranging from 2.4 x 10(4) to 5 x 10(10) copies of viral DNA per ml. Seroconversion for B19-specific immunoglobulin M and immunoglobulin G and disappearance of circulating B19 DNA occurred in the interval between donation and recall in four of the five implicated donors who could be recalled. B19 DNA was detected in 18 of 27 separate batches of non-heat-treated factor VIII and IX concentrate manufactured from donated plasma unscreened for B19 DNA. Dry-heat treatment at 80 degrees C for 72 h reduced but did not always eliminate detectable B19 from factor VIII concentrates, consistent with recent observations that current methods for virus inactivation during blood product manufacture are insufficient to entirely eliminate B19 infectivity. The methods developed in this study for PCR screening could be applied routinely to prevent transfusion of B19 in blood and blood products and could play an important role in the prevention of iatrogenic transmission of infection. PCR screening could also be used for detection and exclusion of a range of other transmission-associated viruses for which current serological detection methods are only partially effective.

Recombinant parvovirus B19 capsids as a new substrate for detection of B19-specific IgG and IgM antibodies by an enzyme-linked immunosorbent assay

A new enzyme-linked immunosorbent assay for the detection of B19-specific IgG and IgM antibodies was established using B19 capsids synthesized in a baculovirus expression system. These B19 capsids, consisting of either coat protein VP2 alone or of both VP1 and VP2, have been shown to be similar to native virus in size and appearance. The results obtained for the detection of B19-specific antibodies showed good correlations with a radioimmunoassay which uses native B19 virus and an immunofluorescence assay based on insect cells expressing coat protein VP1. The course of the antibody response could be followed by determining the titers of sequential serum samples taken after a recent B19 infection. Both types of recombinant capsids form an excellent source of antigen for the detection of both B19 IgG and IgM antibodies and are a very promising substitute for native virus.

Prokaryotic expression of a VP1 polypeptide antigen for diagnosis by a human parvovirus B19 antibody enzyme immunoassay

To produce parvovirus B19 antigen for diagnostic purposes, partially overlapping segments covering the genes encoding the viral structural proteins VP1 and VP2 were cloned into expression vectors. The constructs were induced in Escherichia coli, resulting in the expression of beta-galactosidase fusion proteins. In immunoblotting experiments with sera from patients with erythema infectiosum, immunoglobulin G (IgG) and IgM antibodies bound to a single polypeptide of 235 amino acids at the N terminus of VP1. The DNA fragment encoding this polypeptide was amplified by the polymerase chain reaction and cloned into an expression vector. The viral capsid antigen expressed in E. coli was purified by preparative agarose gel electrophoresis and used in IgG and IgM solid-phase enzyme immunoassays. Comparison with reference gamma- and mu-capture radioimmunoassays using whole virus antigen showed that these antibody tests are suitable for the serodiagnosis of human infections caused by parvovirus B19.

Prevalence of antibodies to parvovirus B19 in selected groups of patients and healthy individuals

The prevalence of antibodies to parvovirus B19 in sera (n = 745) of various groups of patients and healthy individuals was determined by the enzyme immunoassay, using viral particles as antigen. Among healthy individuals, anti-B19 IgG prevalence was highest in nurses (65.4% (17/26)); in medical students it was 34.1% (47/138) and in pregnant females, 24.4% (48/197). 37.0% (44/119) of HIV-negative haemophiliac patients and 91.7% (33/36) of haemophilic patients with HIV infection were anti-B19 IgG-positive. 45.8% (55/120) of dialysis patients and 27.5% (30/109) of patients with asymptomatic HIV infection were positive for anti-B19 IgG. With the exception of HIV-infected haemophiliac patients, no specific "risk group" for B19 infection could be identified.

Polymerase chain reaction with double primer pairs for detection of human parvovirus B19 induced aplastic crises in family outbreaks

Parvovirus B19 DNA can be detected by polymerase chain reaction with double primer pairs (nested PCR). Recent infection was documented by a retrospective serological study using Parvoscan-B19 enzyme linked immunosorbent assay (EIA) for detection of B19 human parvovirus IgM and IgG antibodies in serum or plasma specimens. In 3 families B19 outbreaks caused aplastic crises necessitating blood transfusion in 5 children and 1 adult with hereditary sphaerocytosis. Four members from 2 of the families had clinically overt haemolytic anaemia prior to the event. Two members in another family presented with an aplastic crisis disclosing the underlying chronic haemolytic disease. All 7 patients were identified as PCR positive in serum samples taken 3-14 days after the onset of symptoms. Comparison with dot blot hybridization revealed detectable DNA in only 2/3 PCR positive patients. Thus, nested PCR is more sensitive than the dot blot hybridization method and is therefore a suitable complement to the antibody assay for identifying recent B19 infection.

Antigenic and immunogenic epitopes shared by human papillomavirus type 16 and bovine, canine, and avian papillomaviruses

All types of papillomaviruses (PV) share common, so-called group-specific epitopes. To identify the major group-specific epitopes, we immunized 26 guinea pigs or rabbits with purified bovine PV type 1 (BPV), canine PV, or avian PV from the common chaffinch. The resulting hyperimmune sera, as well as a commercially available rabbit antiserum to BPV and seven monoclonal antibodies to BPV, were tested in an enzyme-linked immunosorbent assay with a set of 66 overlapping 20-amino-acid peptides representing the complete sequence of the major capsid proteins (L1 and L2) of human PV type 16 (HPV 16). Sera from the same animals before immunization were used as controls. The minimal reactive epitopes within each peptide were further characterized by testing of truncated peptides. The cross-reactive epitopes were clustered in two regions of L1, an internal region (at positions 171 to 235), which contained three epitopes, and the more reactive region at the carboxy terminus (at positions 411 to 475), which contained six epitopes. The most reactive of the HPV 16 broadly cross-reactive epitopes was a carboxy-terminal epitope which had the sequence DTYRF and which reacted with nine of the antisera to BPV, canine PV, or avian PV, with the commercially available rabbit antiserum to BPV, and also with a mouse monoclonal antibody to BPV. Antipeptide antisera to all of the HPV 16 L1 peptides and to the most antigenically reactive of their truncated analogs were made in guinea pigs. Antipeptide antisera reactive with BPV were obtained for three of the cross-reactive epitopes, and one of these antisera allowed highly sensitive detection of group-specific PV antigen by immunoperoxidase staining.

Evaluation of commercial enzyme linked immunosorbent assay for detection of B19 parvovirus IgM and IgG

An indirect enzyme linked immunosorbent assay (ELISA) (Parvoscan-B19; Sweden) was compared with an in-house MACRIA for the detection of B19 specific IgM. A Parvoscan-B19 IgG test was also evaluated for its ability to detect a recent B19 infection in paired sera. Two hundred and twenty sera submitted to the laboratory for B19 serology and four MACRIA positive control sera were assayed for B19 IgM. Confirmation of the response of sera giving discordant results in the two assays was sought by the use of a "nested" polymerase chain reaction (PCR) for the detection of B19 DNA. The Parvoscan-B19 IgM test was 79% sensitive and 96% specific. Parvoscan-B19 was poor at detecting parvovirus infection in sera collected two to three months after the onset of symptoms. When sera collected more than seven weeks after the onset of symptoms were excluded from the analysis, Parvoscan-B19 IgM was 84% sensitive and 96% specific. Rubella specific IgM positive sera, rheumatoid factor positive sera, and heterophil antibody positive sera were also assayed for B19 IgM. No false positive results were encountered with these problematic sera. By using the cut off criteria for the Parvoscan-IgM test previously advocated by the manufacturers, 90% sensitivity and 87% specificity could be achieved. False positive results, however, occurred with six of the 17 rubella IgM positive sera, four of the 10 rheumatoid factor positive sera, and two of the 11 heterophil antibody positive sera tested. It is concluded that the Parvoscan-B19 was specific but insensitive when compared with in-house assays.

Evaluation of a synthetic-peptide enzyme-linked immunosorbent assay for immunoglobulin M to human parvovirus B19

A synthetic peptide corresponding to a part of the virus protein 1-virus protein 2 overlapping region of human parvovirus B19 was used in an indirect enzyme-linked immunosorbent assay. Antibodies of the immunoglobulin (Ig) M class were measured in serum samples from patients with erythema infectiosum and controls. In comparison with an IgM assay using native B19 viral antigen, the peptide antigen assay was 92% sensitive and 87% specific. B19 IgM reactivities were seen in a limited number of children with other viral diseases. Specific IgM reactivities to short synthetic viral peptides have previously been reported only with Epstein-Barr virus. Since other sources of viral antigen are limited, the peptide antigen assay may be a useful alternative for the diagnosis of B19-associated disease in human beings.

Self-assembled B19 parvovirus capsids, produced in a baculovirus system, are antigenically and immunogenically similar to native virions

B19 parvovirus is pathogenic in humans, causing fifth disease, transient aplastic crisis, some cases of hydrops fetalis, and acquired pure red cell aplasia. Efforts to develop serologic assays and vaccine development have been hampered by the virus's extreme tropism for human bone marrow and the absence of a convenient culture system. We constructed recombinants containing either the major (VP2) or minor (VP1) structural proteins of B19 in a baculovirus-based plasmid, from which the polyhedrin gene had been deleted; these recombinant plasmids were used to generate recombinant infectious baculovirus. Subsequent infection of insect cells in vitro resulted in high-level expression of either B19VP1 or VP2. Parvovirus capsids were obtained by self-assembly in cell cultures coinfected with either VP1- and VP2-containing baculoviruses or, surprisingly, VP2-containing baculoviruses alone. Empty B19 capsids composed of VP1 and VP2 could replace serum virus as a source of antigen in a conventional immunoassay for detection of either IgG or IgM antiparvovirus antibodies in human serum. Immunization of rabbits with capsids composed of VP1 and VP2 resulted in production of antisera that recognized serum parvovirus on immunoblot and neutralized parvovirus infectivity for human erythroid progenitor cells. Baculovirus-derived parvovirus antigen can substitute for scarce viral antigen in immunoassays and should be suitable as a human vaccine.

A cyclized peptide for studies of human parvovirus B19 infection

Synthetic peptides corresponding to human parvovirus B19 sequences were evaluated for immunoreactivity with the sera of infected persons. A cyclized peptide deduced from the N terminus of viral protein VP2 and containing the amino acids 284-307 showed a high reactivity with IgM class antibodies when comparing seropositive and seronegative sera.

New oligopeptide immunoglobulin G test for human parvovirus B19 antibodies

A new, highly sensitive and specific enzyme immunoassay using oligopeptides as antigen (enzyme-linked immunosorbent assay [ELISA] B19-OP) for detecting parvovirus B19-specific immunoglobulin G (IgG) was established. As antigens, B19-specific oligopeptides of 24 and 30 kDa derived from a 196-kDa fusion protein of beta-galactosidase and viral capsid protein (VPI) of B19 after CNBr cleavage and separation by high-pressure liquid chromatography were used. Of 139 serum specimens tested in parallel for anti-B19 IgG by standard ELISA using B19 particles as antigen and by ELISA B19-OP, 73 (52.5%) were positive and 63 (45.3%) were negative in both tests, and 3 (2.2%) were negative by standard ELISA but positive by ELISA B19-OP and by immunoblot. By using ELISA B19-OP, it was possible to detect anti-B19 IgG in an asymptomatic blood donor 4 weeks after acute infection, and anti-B19 IgG titers of 10(-5) could be measured in convalescent-phase sera.