Serodiagnosis of infectious mononucleosis by using recombinant Epstein-Barr virus antigens and enzyme-linked immunosorbent assay technology

Antibodies to lytic infection proteins in lymphocryptovirus-infected rhesus macaques: a model for humoral immune responses to epstein-barr virus infection

Humoral immune responses to rhesus lymphocryptovirus (rhLCV) lytic infection proteins were evaluated in the rhesus macaque animal model for Epstein-Barr virus (EBV) infection. We found a hierarchy of humoral responses to 14 rhLCV lytic infection proteins in naturally infected rhesus macaques, with (i) widespread and robust responses to four glycoproteins expressed as late proteins, (ii) frequent but less robust responses to a subset of early proteins, and (iii) low-level responses to immediate-early proteins. This hierarchy of humoral responses was similar to that reported for EBV-infected humans, with the notable exception of the response to rhBARF1. Serum antibodies to rhBARF1 were frequently detected in healthy rhLCV-infected macaques, but in humans, anti-BARF1 antibodies have been reported primarily in patients with EBV-positive nasopharyngeal carcinoma (NPC). The macaque data accurately predicted that serum antibodies against BARF1 are a normal response to EBV infection when human serum samples are analyzed. The rhesus macaque animal provides a unique perspective on humoral responses to EBV infection in humans and can be a valuable model for EBV vaccine development.

Epstein-Barr virus and disease activity in multiple sclerosis

OBJECTIVES

To study in relapsing-remitting (RR) multiple sclerosis (MS) whether exacerbations and brain activity as measured by magnetic resonance imaging (MRI) are associated with plasma levels of anti-Epstein Barr (EBV) antibodies and EBV DNA.

METHODS

This was a prospective study with 73 RR MS patients followed for an average of 1.7 years with frequent neurological examination and blood sampling. Antibodies to various EBV proteins were measured by ELISA and plasma EBV DNA was measured by PCR.

RESULTS

All MS patients had IgG antibodies to EBV (viral capsid antigen (VCA) and/or EBV nuclear antigen (EBNA)), irrespective whether samples were taken at stable disease or exacerbation. A significantly elevated percentage of the patients (48%) had antibodies against EBV antigens (early antigen, EA) that indicate active viral replication, compared with the age matched healthy controls (25%). Antibodies against a control herpesvirus, cytomegalovirus, were similar between the two groups. The percentage of EA positive individuals and EA titres did not differ between stable disease or exacerbation. Anti-VCA IgM was positive in three cases, unrelated to disease activity. Using a highly sensitive PCR on 51 samples taken at exacerbation visits, only three patients were found to have one timepoint with viraemia, and this viraemia was unrelated to disease activity. Of special note was the fact that anti-EA seropositive patients remained seropositive during follow up, with stable titres over time. We hypothesised that these patients may constitute a subgroup with higher disease activity, due to the triggering effect of a chronic attempt of the virus to reactivate. The EA positive group did not differ from the EA negative with respect to clinical disease activity or other characteristics. However, in the EA positive group, analysis with gadolinium enhanced MRI indicated more MRI disease activity.

CONCLUSIONS

There was no evidence for increased clinical disease activity in the subgroup of MS patients with serological signs of EBV reactivation. However, the observation that chronic EBV reactivation may be associated with increased inflammatory activity as assessed by gadolinium enhanced MRI lesions should be reproduced in a larger and independent dataset.

Measurement of EBV-IgG anti-VCA avidity aids the early and reliable diagnosis of primary EBV infection

Current serological methods for the diagnosis of Epstein-Barr virus (EBV) infection still differentiate poorly between primary infection and reactivation. This is particularly true when IgG and IgM antibodies are present simultaneously and only a single serum sample is provided for analysis. The demonstration of the IgG avidity state has the potential to distinguish recent from past or reactivated infection. An analysis of the kinetics of avidity maturation of anti-VCA antibodies in primary EBV infection was undertaken with longitudinally collected sets of sera from 28 well-characterised EBV cases and in sera from 35 cases with previous EBV infection and recent primary infection due to HIV, CMV, or hepatitis A. Antibodies directed against the viral capsid antigen (VCA) and Epstein-Barr nuclear antigen (EBNA-1) were sought, using a commercial enzyme immunoassay (EIA). In parallel with standard IgG anti-VCA detection, serum was incubated with 8 M urea to disrupt low-avidity complexes to allow calculation of the percentage avidity. In cases with primary EBV infection, the mean avidity rose from 54% at 6 weeks to 82% by 28 weeks after the onset of symptoms, but remained lower than that of the control sera (96%). The addition of the avidity measurement improved the sensitivity of IgG and IgM anti-VCA testing in diagnosis of primary EBV infection from 93% to 100%. The specificity of IgM anti-VCA testing alone was poor, with 14 of 35 cases (49%) demonstrating false-positive results, but it improved to 97% by the demonstration of high-avidity IgG anti-VCA. The combination of negative IgG anti-EBNA and low-avidity IgG anti-VCA had a sensitivity and specificity of 100%. The routine addition of IgG anti-VCA avidity estimation to diagnostic EBV serology is recommended.

Inhibition of macrophage inflammatory protein-1 alpha production by Epstein-Barr virus

Infection with Epstein-Barr virus (EBV) exerts substantially immunomodulating activities in vitro and in vivo. In this context, EBV-induced chemokine production and the influence of EBV on this highly redundant system of inflammatory proteins have hardly been investigated. This study analyzed the production of interleukin-8, RANTES, monocyte chemotactic protein-1, and macrophage inflammatory protein-1 alpha (MIP-1 alpha) on EBV infection of peripheral blood mononuclear cells from immune EBV-seropositive (EBV(+)) and noninfected EBV-seronegative (EBV(-)) individuals. EBV failed to induce the production of MIP-1 alpha in EBV(+) as well as EBV(-) individuals, whereas the other chemokines studied were readily expressed. Moreover, EBV completely down-regulated lipopolysaccharide (LPS)- and phytohemagglutinin-induced MIP-1 alpha production up to 4 hours after induction. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of EBV- and LPS-stimulated cultures revealed that EBV inhibited MIP-1 alpha production on the transcriptional level. This effect was abolished by addition of antiglycoprotein (gp)350/220, a monoclonal antibody against EBV's major envelope glycoprotein, which mediates binding of the virus to the EBV receptor, CD21. However, recombinant gp350/220 protein alone did not inhibit the LPS-induced MIP-1 alpha production, indicating that infection of the target cell is indispensable for this effect. In summary, we demonstrate a new immunomodulating activity of EBV on the chemokine system that probably helps the virus to evade the host's immune system favoring lifelong infection.

Detection of Epstein-Barr virus DNA in peripheral blood of paediatric patients with Hodgkin's disease by real-time polymerase chain reaction

Hodgkin's disease (HD) is commonly associated with latent Epstein-Barr virus (EBV) infection. The aim of our study was a detailed molecular analysis of the EBV status in the peripheral blood of paediatric patients with HD. Blood samples from HD patients were examined before (n=28) and after treatment (n=12). The control group consisted of 20 healthy children and 10 immunosuppressed children with primary EBV infection. EBV load in plasma and peripheral blood mononuclear cells (PBMC) were determined by real time quantitative polymerase chain reaction (RQ-PCR) as recently described. Before treatment, EBV DNA was detected in the plasma of 13/24 EBV-seropositive HD patients, whereas in plasma of healthy controls no EBV DNA was detectable (P<0.001). After treatment, no EBV genomes were found in the plasma of 6 HD patients in stable and complete remission. In contrast, 2/5 HD patients with relapse of disease were positive for EBV DNA in the plasma. In PBMCs, no differences were found in EBV load measured in HD patients before or after treatment and healthy controls. A high EBV load was found in both the plasma and PBMCs of all immunosuppressed patients with primary EBV infection. Thus, EBV DNA detection in the plasma of paediatric HD patients might be of value for non-invasive diagnostic, prognostic and follow-up tests for HD.

Patients at risk for development of posttransplant lymphoproliferative disorder: plasma versus peripheral blood mononuclear cells as material for quantification of Epstein-Barr viral load by using real-time quantitative polymerase chain reaction

BACKGROUND

Early diagnosis of Epstein-Barr virus (EBV)-associated posttransplant lymphoproliferative disorder (PTLD) is required to detect a stage of disease that is more likely to respond to treatment. Elevated levels of EBV DNA were found in peripheral blood of patients at the onset of PTLD.

METHODS

To compare plasma and peripheral blood mononuclear cells (PBMCs) as material for real-time quantitative polymerase chain reaction (RQ-PCR) measurement of Epstein-Barr viral load, we used two sets of primers and probes specific for the BAM HI-K or BAM HI-W region of the EBV genome.

RESULTS

Patients with PTLD had a median viral load of 19,200 EBV genomes/microg DNA (n=9) or 3,225 EBV genomes/100 microl plasma (n=5), being significantly higher compared with immunosuppressed patients with primary (n=9) or reactivated (n=20) EBV infection or immunosuppressed patients without serological signs of active EBV infection (n=67) (P<0.001). Hence, a value of greater than 5,000 EBV genomes/microg PBMC DNA was considered as a diagnostic parameter for PTLD with a sensitivity and specificity of 1.00 or 0.89, respectively. When plasma was analyzed, however, a value of greater than 1,000 EBV genomes/100 microl plasma had both a sensitivity and specificity of 1.00 for the diagnosis of PTLD. During remission of PTLD, viral load was more effectively cleared in plasma compared with PBMCs. In plasma of nonimmunosuppressed individuals, even a qualitative detection of EBV-related sequences was sensitive and specific for the diagnosis of primary EBV infection, whereas for analysis of PBMC DNA a quantitative parameter had to be considered to differentiate healthy individuals (< 100 EBV genomes/microg PBMC DNA) from patients with primary EBV infection (>100 EBV genomes/microg PBMC DNA).

CONCLUSION

Although both PBMCs and plasma were useful as material for EBV-specific RQ-PCR in immunosuppressed patients and nonimmunosuppressed individuals, the specificity of analysis seemed to be higher if plasma was taken for analysis.

Cross-reactivity of Epstein-Barr virus-specific immunoglobulin M antibodies with cytomegalovirus antigens containing glycine homopolymers

Timely and reliable detection of acute primary human cytomegalovirus (HCMV) infection is important in prenatal screening programs and for differential diagnosis of infectious mononucleosis-like disease. Enzyme-linked immunosorbent assays (ELISAs) based on HCMV proteins enable the sensitive detection of immunoglobulin M (IgM) antibodies during primary infection. However, concerns have been raised about possible cross-reactivities of the HCMV antigens used for the design of such ELISAs with IgM antibodies induced by Epstein-Barr Virus (EBV). In this study we investigated whether IgM antibodies generated during acute EBV infection reacted with recombinant HCMV antigens. Serum samples from patients with primary EBV infection frequently scored positive when tested in different HCMV IgM ELISAs, irrespective of whether conventional or recombinant antigens were used for the design of the HCMV IgM assays. Such cross-reactive IgM antibodies were found to be directed against short glycine-rich motifs contained within the nonstructural HCMV proteins pUL44 and pUL57. Further analyses revealed that these glycine-rich motifs were major antigenic domains for IgM antibodies induced during HCMV infection. Their deletion from recombinant proteins abrogated reactivity with IgM synthesized during HCMV infection. EBV-induced IgM antibodies that reacted with HCMV antigens showed similar kinetics of reactivity in HCMV- or EBV-specific assays in the course of primary EBV infection, indicating that the two populations of antibodies were highly overlapping. The results demonstrate that primary EBV infection leads to the induction of IgM antibodies that specifically bind to widely used diagnostic antigens of HCMV. This has to be considered in the interpretation of HCMV-specific IgM assays.

Serological diagnosis of Epstein-Barr virus infection by novel ELISAs based on recombinant capsid antigens p23 and p18

A new pair of Epstein-Barr virus ELISAs (Biotest Anti-EBV VCA IgG and VCA IgM ELISA) was evaluated for usefulness for routine diagnosis of acute EBV infections. The ELISAs are based on two viral capsid antigens (VCA), p23 (BLRF2, full-length) and p18 (BFRF3, carboxy-half), that are combined by autologous gene fusion. In total, 179 sera were tested in direct comparison with classical VCA immunofluorescence assays (IFA). With the help of clinical data and additional reference serology, i.e., heterophile antibodies, anti-EA IgG (IFA) and anti-EBNA-1 IgG (ELISA), the patients were divided into the following categories: seronegatives (46), acute primary infections (67), previous infections (39), suspected reactivations (20) and constellations with intermediate serological patterns (7). The VCA IgG and VCA IgM ELISAs showed overall agreement to IFA of 95.0% and 94.4%, respectively. The calculated analytical performance (sensitivity; specificity) of VCA IgG and VCA IgM was 94.0%; 97.8% and 97.1%; 96.5%, respectively. A certain delay in seroconversion of anti-p23-p18 IgG may account for a significant difference in sensitivity of the VCA IgG ELISA between primary (88.4%) and previous infections (100%). In summary, the new recombinant VCA ELISAs yielded good correlation to VCA IFA and in combination with EBNA-1 IgG allow rapid, sensitive, and specific diagnosis of infectious mononucleosis or EBV immune status in general.

Altered prevalence and reactivity of anti-Epstein-Barr virus antibodies in patients with multiple sclerosis

In this study, the prevalence and reactivity of anti-Epstein-Barr virus (EBV) antibodies were investigated in 107 patients with multiple sclerosis (MS) in comparison to age- and gender-matched healthy controls from a north German state. We found a significant 100% EBV-seropositivity and a significant lack of primary EBV infections in the MS group, indicating that all MS patients are infected with EBV before the development of MS. Although there were no differences in reactivities of EBV-specific anti-early antigen (EA)-immunoglobulin G (IgG), -IgM, and -IgA antibodies between each group, MS patients had significant lower anti-Epstein-Barr nuclear antigen (EBNA)1-IgG antibody titers as a possible serological sign for a defective control of the persistent latent EBV carrier state and EBV reactivations. Longitudinal studies of MS patients are necessary to further determine the implications of EBV reactivations on the course and disease activity of MS.

Evaluation of two slide agglutination tests and a novel immunochromatographic assay for rapid diagnosis of infectious mononucleosis

The results of three tests used for the rapid diagnosis of infectious mononucleosis (IM) were compared with those of Epstein-Barr virus-specific serology. The sensitivities ranged from 15 to 33% in children under 13 years of age and from 59 to 81% in patients over 13 years. The specificities ranged from 86 to 100% in both age groups. These tests have a poor sensitivity for the diagnosis of IM, particularly in children.

Generation of monoclonal antibodies directed against the immunogenic glycoprotein K8.1 of human herpesvirus 8

Human Herpesvirus 8 (HHV-8) is clearly associated with Kaposi's sarcoma (KS), body cavity-based lymphomas (BCBL), and certain forms of multifocal Castleman's disease (MCD). It appears to be the sexually transmissible agent involved in the development of AIDS-associated KS. HHV-8 genomes are invariably present in BCBL-derived cell lines where lytic replication of the virus can be induced by phorbol esters (PE). First-generation HHV-8 serological assays were based on these cell lines. More recently, several genes encoding HHV-8 antigens have been identified. One of the most reactive antigens is encoded by HHV-8 open reading frame K8.1. Although K8.1 does not exhibit overt sequence homology to any other known gene, it is likely to be analogous to gp220/350 of Epstein-Barr or gp150 of murine herpesvirus-68, virion-envelope glycoproteins involved in target cell recognition. Mice were immunized with purified GST-K8.1 fusion protein expressed in E. coli. After fusion of murine plasma cells with the myeloma cell line P3-X63-Ag8. monoclonal antibodies (MAbs) were generated, which are specifically directed against K8.1 protein. The binding site for each MAb was identified by deletion mutant analysis using recombinant GST-K8.1 mutants and K8.1-specific peptides. Without exception, the epitopes recognized by these MAbs were located within the N-terminal part of the protein [amino acids (aa) 29 to 80], thus identifying a highly immunogenic region. These antibodies will not only be useful tools for HHV-8 diagnostics, but will also facilitate the analysis of K8.1 function.

Reliability of four methods for the diagnosis of acute infection by Epstein-Barr virus

We studied the reliability of new indirect tests in the diagnosis of acute infection by Epstein-Barr virus (EBV). Studied for all samples were method 1, the heterophil antibodies (Abs) (Monolatex, Biokit, Germany); method 2, the IgM Abs to EBV with ELISA tests (antigen pools, Enzygnost, Behring-werke, Germany); method 3, EA (Biotest Diagnostics, Germany); and method 4, the IgG avidity test. The reliability of the four tests for the detection of primary infection by EBV was: sensitivity (method 1: 89.1%; method 2: 100%; method 3: 79.7%; method 4: 99%); specificity (method 1: 98%; method 2: 100%; method 3: 84%; method 4: 100%); positive predictive value (method 1: 97.6%; method 2: 100%; method 3: 73.6%; method 4: 100%), and negative predictive value (method 1: 90.7%; method 2: 100%; method 3: 84%; method 4: 99%). The IgG avidity test (method 4) is simple and automated in the laboratory and is very useful for ascertaining, from a single sample, the time since infection. It is criteria of recent primoinfection higher levels than 55% of IgG with low avidity for the antigen. The investigation of the Abs to antigen pools (method 2) by ELISA of virus had a high reliability, but the investigation of heterophil Abs by latex (method 1) and the Abs IgM to EA (method 2) were lacking in sensibility regarding their use in the diagnosis of the primoinfection.

Serodiagnosis of Epstein-Barr virus infection by using recombinant viral capsid antigen fragments and autologous gene fusion

Using recombinant 15- to 30-kDa fragments and fusion with glutathione S-transferase (GST), we investigated the seroreactivity of three large structural proteins of Epstein-Barr virus (EBV), p150 (BcLF1, capsid), p143 (BNRF1, tegument), and gp125 (BALF4, membrane) in Western blots. None of 13 fragments tested, however, was qualified for diagnostic application. In contrast, the two small viral capsid antigens (VCA), p18 (BFRF3) and p23 (BLRF2), demonstrated sensitive (100%) EBV-specific immunoglobulin G (IgG) reactivities. While p18 additionally showed maximum sensitivity for IgM detection, the IgM sensitivity of p23 was restricted (44%). An autologous fusion protein, p23-p18, which consists N-terminally of full-length p23, followed by the carboxy half of p18, was constructed. This antigen was subjected to indirect VCA enzyme-linked immunosorbent assays (ELISAs), for IgG and IgM, as well as to a micro-capture (microc) IgM ELISA. All assays were found to be 100% specific when EBV-negative sera were tested. Using sera from previously infected individuals, the p23-p18 fusion revealed an improved IgG sensitivity of 99% compared to sensitivities of 97 and 93% for the single antigens p18 and p23, respectively. The sensitivity and specificity of the indirect IgM ELISA with samples of primary and past infections, respectively, were 100%. The microc principle for IgM overcame completely the interference by rheumatoid factors. Compared to the specificity of the indirect IgM version, the specificity with sera collected from rheumatoid arthritis patients increased from 48 to 100%. In summary, the p23-p18 IgG and microc IgM ELISAs showed excellent performances and are promising new diagnostic tests for the detection of EBV-specific antiviral capsid antibodies.

Novel immunoblot assay using four recombinant antigens for diagnosis of Epstein-Barr virus primary infection and reactivation

A new immunoblot assay, composed of four Epstein-Barr virus (EBV)-encoded recombinant proteins (virus capsid antigen [VCA] p23, early antigen [EA] p138, EA p54, and EBNA-1 p72), was compared with an immunofluorescence assay on a total of 291 sera. The test was accurate in 94.5% of cases of primary EBV infection, while an immunoglobulin G anti-VCA p23 band with strong intensity correlated with reactivation.

Comparison of the immunoglobulin-G-specific seroreactivity of different recombinant antigens of the human herpesvirus 8

The open reading frames ORF 52, ORF 65, K12, and K8.1 of the human herpesvirus 8 (HHV8) were expressed as glutathione-S-transferase (GST) fusion proteins and analysed by Western blotting (WB) and enzyme-linked immunosorbent assay (ELISA). The open reading frame (ORF) 65 and K8.1 antigens gave the highest reactivity (71%) in sera from HIV-dependent Kaposi's sarcoma (KS) patients. Therefore both antigens appear to be essential for HHV8 diagnostics, whereas ORF K12 and ORF 52 were of minor importance. Using polymerase chain reaction (PCR) out of the peripheral blood of these KS patients, 48% were detected as positive. By testing an N-terminal-deleted construct (amino acid 80-171) of ORF 65, we could show that the N-terminal region of this protein is essential to mediate full immunogenic reactivity. By analysing different deletion mutants of ORF K8.1, the major epitope was found to be located between aa 29 and 101. The prevalence of antibodies directed against the different antigens was determined for healthy blood donors to be 3-6%. The different antibody patterns obtained in HIV-patients with and without KS support the hypothesis that different antibody profiles develop during the course of KS.

Clinical reliability of IgG, IgA, and IgM antibodies in detecting Epstein-Barr virus at different stages of infection with a commercial nonrecombinant polyantigenic ELISA

We studied the diagnostic reliability of a modification of the Enzygnost EBV test (Behringwerke, Germany) for the detection of IgG, IgA, and IgM antibodies (Abs) in the diagnosis of Epstein-Barr virus (EBV) disease. One hundred and twenty-three serum samples were studied: 14 asymptomatic subjects without EBV infection, 48 patients with primary infection, 46 subjects with past EBV infection (11 patients with other acute infections), 8 patients without EBV infection but with other viral infection, and 7 patients with probable acute clonal stimulation of B lymphocytes caused by different microorganisms. Enzygnost EBV is based on an ELISA test with a pool of viral antigens. In our series the reliability of IgM for the diagnosis of recent primary EBV infection was: sensitivity 100%, specificity 95%, positive predictive value 90.5%, and negative predictive value 100%. The IgG detection with Enzygnost was: sensitivity 98%, specificity 100%, positive predictive value 100%, and negative predictive value 91.7%. Only two subjects had positive IgA. The Enzygnost test is an efficient method for the diagnosis of EBV infection although a few IgM false positives can occur.

Comparative evaluation of the use of immunoblots and of IgG avidity assays as confirmatory tests for the diagnosis of acute EBV infections

BACKGROUND

Despite the availability of several different markers for Epstein--Barr virus (EBV) serology, the EBV status of some patients cannot be resolved from a single serum sample with routine testing. To avoid the requirement of follow-up samples, supplementary tests have to be used in these cases.

OBJECTIVE

To evaluate the usefulness of avidity and immunoblot assays as supplementary tests for the diagnosis of acute EBV infections.

STUDY DESIGN

Three groups of samples for which a definite diagnosis on the EBV status could not be obtained with the routine serological tests were further examined by an EBV IgG avidity assay, by an immunoblot based on a lysate of EBV infected cells, and by a second immunoblot based on recombinant EBV antigens. The three groups consisted of 38 samples with negative/borderline EB nuclear antigen 1 (EBNA-1) antibodies, negative/borderline EBV IgM and positive EBV IgG; 10 samples with indeterminate EBNA-1 and/or EBV IgM assays because of control antigen reactions; and 4 samples with positive EBV IgM results that were not plausible.

RESULTS

The avidity assay differentiated between acute and past infections for all samples. In contrast, some cases remained unresolved with both the recombinant and the lysate immunoblot. Two samples were incorrectly classified with the lysate immunoblot. Interpretation of the lysate immunoblot banding patterns was complicated when anticellular antibodies were present.

CONCLUSION

Avidity testing appears to be the confirmatory method of choice to differentiate between acute and past EBV infections.

Serodiagnosis of infectious mononucleosis in children

BACKGROUND

Although anti-viral capsid antigen (VCA)-immunoglobin M (IgM) is the most reliable serological marker of primary Epstein-Barr virus (EBV) infection, it could only be detected in limited cases of infectious mononucleosis in children. We analyzed anti-EBV antibodies by an enzyme-linked immunosorbent assay (ELISA), a sensitive method for detecting IgM antibody and compared these results with those obtained by a conventional indirect immunofluorescence (IF) method.

METHODS

Anti-Epstein-Barr virus early antigen (EA)-IgM and nuclear antigen 1 (EBNA1)-IgG were examined by an ELISA assay in 180 sera from 70 infants and children with infectious mononucleosis, diagnosed serologically by standard IF methods.

RESULTS

Although by IF, VCA-IgM was detected in only 37 of 70 (52.9%) of the sera from the acute phase of the disease, by ELISA, EA-IgM was detected in 65/70 (92.9%) of these sera. Among infants less than 12 months of age. EA-IgM was positive in 11/13 cases (84.6%) while VCA-IgM was detected in only 3/13 cases (23.1%). Anti-Epstein-Barr virus nuclear antigen 1-IgG was not detected by ELISA in the sera from the acute phase of infectious mononucleosis. Anti-EBNA was not detected by IF in about one-third of the sera during 6-8 months after onset of the disease, whereas by ELISA, EBNA1-IgG was detected in 93.0%. Sera that were positive or negative for both EA-IgM and EBNA1-IgG by ELISA were observed in several cases after the patients recovered from the disease.

CONCLUSIONS

Although serodiagnosis by the combination of ELISA for EA-IgM and EBNAI-IgG was more sensitive than IF methods, especially in the case of infants and young children, several patients during convalescence and recovery might be judged as seronegative or as being in highly reactivated states.

The significance of Epstein-Barr virus seropositivity in multiple sclerosis patients?

The objective of this study was to evaluate and investigate the significance of the previously found 100% seropositivity toward Epstein-Barr virus (EBV) found in multiple sclerosis (MS) patients in contrast to healthy controls. Using a commercially available ELISA-test (Biotest), which differentiates infections with EBV into previous infections, primary infections, reactivated infections and no previous infection, we found 137 of 138 MS patients and 124 of 138 healthy controls seropositive. A primary infection in 4 of the 124 EBV seropositive healthy controls in contrast to no primary infections in the MS EBV seropositive group was significant (P=0.049652, Fishers exact test). This may be suggestive of a lack of primary infections in MS patients, and thus strengthens the idea that MS patients are infected with EBV before development of MS. Further studies are in progress to analyse whether EBV infection is a prerequisite for the development of this disease.

Evaluation of three commercial enzyme-linked immunosorbent assays and two latex agglutination assays for diagnosis of primary Epstein-Barr virus infection

Three commercially available enzyme-linked immunosorbent assays (ELISAs) from Gull, Biotest, and Behring (Enzygnost) and two latex agglutination tests for heterophile antibodies (Monolatex [Biotest] and Mono-Lex [Trinity Laboratories]) were evaluated for the diagnosis of primary Epstein-Barr virus (EBV) infection and EBV seropositivity. Two hundred fourteen consecutive samples from 197 patients with symptoms of primary EBV infection were analyzed by the five assays at a clinical microbiology laboratory. The samples were also analyzed independently by immunofluorescence methods at a reference laboratory. According to the reference methods, 37 patients (40 serum samples) had primary EBV infections, 120 patients (127 serum samples) had had past EBV infections, 33 patients (36 serum samples) were seronegative, and 7 patients (11 serum samples) exhibited atypical reactions. The respective sensitivities and specificities for the diagnosis of primary EBV infection were 95 and 100% for the Gull assays, 100 and 94% for the Biotest assays, and 100 and 89%, for the Enzygnost assays. The Monolatex and Mono-Lex methods showed similar sensitivities and specificities (78 to 85% and 100 to 99%, respectively) for the diagnosis of primary EBV infection. This study demonstrates the usefulness of commercially available assays for the rapid diagnosis of primary EBV infection, but also the importance of large-scale testing of routine samples before choosing an assay.

Comparative evaluation of three ELISA techniques and an indirect immunofluorescence assay for the serological diagnosis of Epstein-Barr virus infection

BACKGROUND

The reference method for detecting specific Epstein-Barr virus (EBV) antibodies is indirect immunofluorescence (IF) with EBV-infected cells. The availability of protein purified from infected cells and more recently of recombinant polypeptides designed to contain immunodominant epitopes, has enabled the development of commercial enzyme-linked immunosorbent assays (ELISA) for the specific serodiagnosis of EBV infection.

OBJECTIVE

Evaluation of ELISA-based EBV serodiagnosis in comparison with indirect immunofluorescence.

STUDY DESIGN

We have first compared three commercial ELISA test systems with our in house indirect immunofluorescence assay for classifying correctly a set of serum samples into clinical categories (acute infection, past infection, interfering non-EBV infection, persistent infection). Additionally a prospective analysis with the best performing ELISA test (Enzygnost) was then carried out by running the ELISA test in parallel with the indirect immunofluorescence assay on 324 consecutive clinical samples sent to our laboratory for EBV serodiagnosis.

RESULTS

For the serodiagnosis of past EBV infection and acute EBV infection all three commercial ELISAs performed well in comparison with indirect immunofluorescence. When testing samples positive for cytomegalovirus (CMV), Toxoplasma or herpes simplex IgM, interference in the IgM tests was observed with the three ELISAs. In some instances we could demonstrate that the positive IgM results were due to EBV reactivation. The observed discrepancies between ELISA and IF for the serodiagnosis of chronic EBV infection or EBV reactivation, point to the difficulty for the serodiagnosis of persistent EBV infection on single serum samples. According to our prospective study the EBV IgG determination was accurate. A positive IgM result was not always indicative of an acute infection. Positive IgM results due to EBV reactivation were observed. A positive EBV nuclear antigen (EBNA) IgG result in those samples precluded acute infection.

CONCLUSIONS

90-95% of samples could be classified correctly into clinical categories by a two parameter ELISA system detecting IgG and IgM against a standardized mixture of EBV antigens, allowing standardization and automation of EBV-specific serology. The absence of EBNA IgG was useful as a second line confirmatory assay for acute EBV infection.

Detection of Epstein-Barr viral DNA in serum using rapid-cycle PCR

Our study describes the comparison of a rapid nested PCR assay to standard serology techniques for the detection of Epstein-Barr virus (EBV) in serum. The sera of 81 patients with suspected EBV infection were analyzed; 54 were positive for one or more of the standard serology markers, i.e., IgM viral capsid antigen (VCA), IgG-VCA, Epstein-Barr nuclear antigen 1 (EBNA-1), and early antigen (EA), and 27 were negative for all serology markers. The sera from 15 normal healthy blood donors were also included. No EBV DNA was detected in any of the 15 blood donor samples or in any of the 27 samples with negative serology results. Eleven samples (20%) of the 54 with positive EBV serology results were positive for EBV DNA. Of these samples, 9 were EBV IgM-VCA positive and anti-EBNA negative, suggesting acute infection. One of the 11 samples had high titers of IgM-VCA, IgG-VCA, anti-EBNA, and anti-EA. The last of the 11 samples was from a patient with acute infectious mononucleosis without sufficient sample volume for EBV serology testing. Seventeen of the total 96 samples from the study were IgM-VCA positive and anti-EBNA negative and 9 of these 17 samples (53%) tested positive for EBV DNA. These data suggest that the detection of EBV DNA by PCR in serum may be a useful indicator of active infection rather than latent virus.

Acute encephalopathy with bilateral striatal necrosis: favourable response to corticosteroid therapy

A case of acute encephalopathy with selective bilateral symmetrical striatal lesions is reported. The patient was a previously healthy 4-year-old boy who became obtunded after a febrile illness and fell into a state of delirium with severe pain in the feet. He showed abnormal postures: hyperextension of the neck and upper limbs and extreme flexion of both lower limbs, and abnormal involuntary movements of the limbs: tremor, athetotic movement and right hemiballismus. Analysis of serum antibody titres suggested recent primary infection of herpes simplex type 1 (HSV-1). Cranial T2-weighted magnetic resonance imaging (MRI) demonstrated areas of high-signal intensity involving the whole basal ganglia bilaterally. He showed rapid clinical improvement after the initiation of corticosteroid therapy; complete clinical recovery was noted 3 months after the onset. Serial MRI studies demonstrated a rapid reduction of the lesions, resulting in only slight T2-hyperintense areas in both caudate nuclei. The pathogenesis of the disorder remains unknown, though an autoimmune mechanism has been speculated. The clinical and laboratory findings in this case suggested a possible role of HSV-1 in the pathomechanism of the disorder and a beneficial effect of early corticosteroid therapy.

Epstein-Barr Viral Antigens Used in the Diagnosis of Nasopharyngeal Carcinoma

The major antigen complexes of Epstein-Barr virus (EBV) include the latent infectious proteins, early antigens, membrane antigens and viral capsid antigens. The various polypeptides within each antigen complex have been identified and isolated through gene-cloning technology. These polypeptides are exploited to be used as serological markers for the diagnosis of nasopharyngeal carcinoma (NPC) through enzyme-linked immunosorbent assay. This paper reviews the recent studies on the profile of antibodies in patients with NPC towards these EBV polypeptides of each antigen complex. The sensitivity and specificity of each polypeptide when used as serological markers to NPC patients' sera are summarized. Copyright 1996 S. Karger AG, Basel

Expression and purification of an Epstein-Barr virus encoded 23-kDa protein and characterization of its immunological properties

Serodiagnosis of Epstein-Barr virus (EBV) infection is currently based on the detection of antibodies to distinct EBV antigens by immunofluorescence and enzyme-linked immunosorbent assay-based tests, or in part on the detection of heterophile antibodies by the Paul-Bunnell-Davidson heterophile assay. In the past few years, the specificity and the sensitivity of serodiagnostic assay systems has been improved considerably by the use of purified recombinant EBV antigens. Screening of EBV-positive sera for antigenic reactivities by immunoprecipitation with extracts of EBV-positive cells revealed a 23-kDa protein (p23) that was recognized by antibodies from all EBV carriers tested. Open reading frame BLRF2 was identified as the coding region for this protein. After cloning and high-level expression of the BLRF2 open reading frame as DHFR fusion protein in Escherichia coli, the recombinant protein was purified to near homogeneity with the help of continuous elution electrophoresis. Sera from both EBV-positive and -negative donors were screened by immunoblot analysis and enzyme-linked immunosorbent assay for IgM and IgG antibodies against the EBV-encoded protein p23. Since anti-p23 antibodies were not detectable in 30 of 30 EBV-negative sera, and 294 of 302 EBV-positive sera had either IgM and/or IgG antibody responses to this protein, recombinant p23 seems to be a useful diagnostic marker for EBV-infection.

The DNA-binding protein pUL57 of human cytomegalovirus is a major target antigen for the immunoglobulin M antibody response during acute infection

A small polypeptide from pUL57 of human cytomegalovirus was identified as a major target for the immunoglobulin M antibody response. This antigen seems to be superior to antigenic fragments from pp150 and p52 in the identification of sera from acutely infected patients. It may therefore represent an essential antigen for recombinant immunoglobulin M antibody tests for human cytomegalovirus.

Detection of Epstein-Barr virus-specific antibodies by means of baculovirus-expressed EBV gp125

A major antigenic component of the Epstein-Barr virus viral capsid antigen (VCA) complex is the glycoprotein, gp125. Baculovirus-expressed gp125 reacted with Epstein-Barr virus IgG antibodies in a panel of 44 serum specimens using an immunoblot assay with over 97% sensitivity, and 100% specificity as compared to anti-VCA reactivity in an immunofluorescence assay. In addition, no evidence for cross-reactivity was seen in reactions with members of a panel of human serum specimens of known reactivity with each of the other known human herpesviruses. Thus, baculovirus-expressed gp125 should prove a stable platform on which new Epstein-Barr virus-specific serodiagnostic tests can be built.

Avidities of IgG directed against viral capsid antigen or early antigen: useful markers for significant Epstein-Barr virus serology

Classical Epstein-Barr virus (EBV) serology can be misleading in some cases due to the variability of the viral capsid antigen (VCA)-IgM response, persistent or reactivated VCA-IgM, or loss of anti-EBNA-1 during suppression of the cellular immune system. Therefore, we studied the usefulness and significance of avidity determinations of VCA-IgG and EA-IgG to achieve unequivocal interpretation of serological results. Avidities of EBV capsid antigen-specific IgG (VCA-IgG) and early antigen-specific IgG (EA-IgG) were determined by indirect immunofluorescence during and after acute EBV infection. Low-avidity antibodies were removed from antigen-antibody complexes by incubation with 6 M urea for 3 minutes. The analysis of 105 sera taken at defined time spans with regard to the onset of clinical symptoms allowed us to determine the kinetics of maturation of avidity of VCA-IgG. All sera had low-avidity antibodies at the onset of disease. More than 90% of the sera showed an avidity index below 0.25 during the first 10 days after the onset of disease. Fifty percent of the sera exhibited an avidity index of 0.25 or above 20-30 days after the onset of clinical symptoms. Sera from past infections uniformly exhibited avidity indices of 0.5 or 1. Avidity of EA-IgG may still be low when avidity of VCA-IgG is already borderline or high, thus allowing further differentiation of acute and recent infections. Avidity determination represents an important additional marker of serology in classical cases and allows diagnosis in aberrant cases, such as acute infections with low or undetectable VCA-IgM.(ABSTRACT TRUNCATED AT 250 WORDS)

Early serodiagnosis of acute human cytomegalovirus infection by enzyme-linked immunosorbent assay using recombinant antigens

DNA fragments from eight different reading frames of human cytomegalovirus (HCMV) were generated by PCR and subsequently cloned and expressed in Escherichia coli in fusion with glutathione S-transferase. The recombinant viral antigens were evaluated in immunoblot analyses. The most reactive antigens were purified and further evaluated in ELISAs. For this, sera from healthy blood donors and immunocompetent individuals with acute HCMV infection, and follow-up sera from transplant recipients with acute primary HCMV infection were used. The results of our experiments indicate that only three particular recombinant polypeptides from two viral proteins are necessary for serodiagnosis. While a fragment covering amino acids (aa) 495 to 691 of pp150 (150/1) was the most suitable antigen for the identification of infected individuals in general, immunoglobulin M antibodies against the C-terminal parts of pp150 (aa 862 to 1048; 150/7) and p52 (aa 297 to 433; 52/3) proved to be excellent serological markers to monitor acute HCMV infection. The selected recombinant antigens enable the improvement of serodiagnosis of HCMV-related diseases, especially during the early stages of infection.

Development of a recombinant enzyme-linked immunosorbent assay for detection of antibodies against Epstein-Barr virus nuclear antigens 2A and 2B

The baculovirus expression system was used to produce full-length Epstein-Barr virus nuclear antigens (EBNAs) 2A and 2B. Recombinant baculoviruses that contained the EBNA-2A- and EBNA-2B-encoding sequences were constructed. The proteins were expressed in Spodoptera frugiperda SF-9 cells infected with the recombinant viruses and were characterized by using monoclonal and human polyclonal antibodies by immunoblotting and immunofluorescence techniques. Partially purified extracts of the EBNA-2A- and EBNA-2B-infected insect cells were used to establish a new enzyme-linked immunosorbent assay for the detection of antibodies against EBNA-2A and EBNA-2B. Preferential reactivity toward the type A or type B EBNA-2 protein was observed in 36% of serum specimens from Swiss patients with acute infectious mononucleosis and in 81% of Swiss patients with latent Epstein-Barr virus infection. Of the patients in the latter group, sera from 76% reacted preferentially with EBNA-2A, sera from 5% reacted preferentially with EBNA-2B, sera from 12% showed similar reactivities against both antigens, and sera from 7% were nonreactive.

Epstein-Barr virus infection in HIV-positive patients

The relationship between Epstein-Barr virus (EBV) viral load in peripheral blood and HIV infection was determined in 103 HIV-infected patients. Epstein-Barr virus was detected by polymerase chain reaction in 75% of the patients, 21% of whom had the more uncommon EBV subtype 2. The highest levels of EBV were found in patients with 100-400 CD4+ cells/mm3 and not in those with more profound immunosuppression. An association was identified between EBV load and HIV proviral levels (p < 0.001), an IgM response to EBV early antigens (p < or = 0.01) and p24 antigenemia (p < 0.01 in patients with > 100 CD4+ cells), but not with other clinical or laboratory parameters. Combinations of different EBV and HIV parameters identified a subgroup of patients with a 2.2- to 4.8-fold risk of > or = 35% decline in CD4+ counts over six months. The association between EBV and HIV markers may reflect a significant pathogenic interaction between the two viruses.

Identification and molecular characterization of two diagnostically relevant marker proteins of the Epstein-Barr virus capsid antigen complex

The molecular specificity of the IgG response against Epstein-Barr virus (EBV) was studied in 345 randomly collected sera of normal healthy individuals. The sera were tested on immunoblots containing antigens of the cell line HH514.c16 (a superinducible derivate of P3HR1), noninduced or induced for the expression of early antigens (EA) or viral capsid antigens (VCA), and from the EBV-negative cell line Ramos-Nut. This study reveals a remarkable similar antigen recognition pattern of IgG class antibodies in sera of healthy EBV carriers. The protein bands recognized predominantly have molecular weights of 18 kD, 36/38 kD, 40 kD, 72 kD, and 160 kD. The 72 kD and 36/38 kD bands were identified as EBNA1 and "Zebra," respectively, using reading frame-specific antisera. The bands at 160 kD (major capsid protein), 40 kD, and 18 kD were identified as VCA-class proteins. Of all EBV-seropositive sera tested, 98% reacted with either p18 or p40 or both. The synthesis of the antigens p18 and p40 was inhibited by phosphonoacetic acid, indicating that these were true late proteins. The detection of p18 and p40 in purified virion and capsid preparations confirms that these proteins are structural components of viral capsid antigen complex.

Serological diagnosis of infectious mononucleosis using three anti-Epstein-Barr virus recombinant ELISAs

A new Epstein-Barr virus (EBV) ELISA system (Biotest Anti-EBV recombinant) was evaluated for usefulness for routine diagnosis of EBV primary infection. The assay system is composed of three different microtest plates coated with three highly purified recombinant EBV antigens. The early antigens p138 (BALF2, truncated) and p54 (BMRF1, whole sequence) are used as a mixture for testing IgM (assay 1) and IgG (assay 2) antibodies. In addition, the EBNA-1 antigen p72 (BKRF1, carboxy-half) is used for detecting IgG antibodies (assay 3). Three panels of sera were examined in direct comparison with standard immunofluorescence (IF): Specimens of (i) 120 infectious mononucleosis (IM) patients, (ii) 60 patients with acute CMV infection, toxoplasmosis or rheumatic disease, respectively, and (iii) 185 healthy blood donors as a control group. 119 IM patients were clearly recognized as having acute primary infection (sensitivity 99.2% compared to VCA-IgM by IF). Three apparently false-positive results were obtained with patients of other diseases and none within the control group (specificity 98.8%). The data suggest that the recombinant ELISA can be used advantageously for standardized rapid diagnosis of acute EBV primary infection.