Epitope-mapping on the Epstein-Barr virus major capsid protein using systematic synthesis of overlapping oligopeptides

Molecular diversity of IgG responses to Epstein-Barr virus proteins in asymptomatic Epstein-Barr virus carriers

The Epstein-Barr virus (EBV) is a ubiquitous pathogen that infects over 90 % of adults. EBV is the primary etiological agent of infectious mononucleosis and is closely associated with nasopharyngeal carcinoma, gastric carcinoma, Hodgkin lymphoma and Burkitt lymphoma. Clinical serological assays for EBV diagnosis only survey a small portion of the viral proteome, which does not represent the total antigenic breadth presented to the immune system during viral infection. In this study, we have generated an expression library containing the majority of EBV ORFs, and have systematically evaluated IgG responses to those EBV proteins in sera from EBV carriers. In addition to confirming previously recognized dominant EBV antigens, this study has identified additional immunodominant antigens, and has revealed a more expansive antigenic profile of the humoral responses to EBV in asymptomatic carriers. This EBV expression library will be deposited in a public repository with the goal of disseminating this new research tool for the application of identifying potential new biomarkers for EBV-associated diseases.

Reduced Transplacental Transfer of a Subset of Epstein-Barr Virus-Specific Antibodies to Neonates of Mothers Infected with Plasmodium falciparum Malaria during Pregnancy

Over 35% of children in a region of malaria endemicity are infected with Epstein-Barr virus (EBV) by 6 months of age. This susceptibility may be linked to impaired transplacental transfer of antibodies. In this study, we determined the effect of malaria exposure during pregnancy on the transfer of EBV-specific maternal antibodies in a region of western Kenya that experiences endemic malaria. Pregnant mothers were recruited and followed up until delivery to determine levels of neonatal malaria exposure. Levels of EBV lytic (viral capsid antigen [VCA], Z transcriptional activator [Zta], and early diffuse antigen complex [EAd]) and EBV latent (EBV nuclear antigen-1 (EBNA1]) and tetanus-specific IgG antibodies were measured in 70 paired maternal and cord blood samples using a Luminex-bead-based assay. A high proportion (63%) of the infants were exposed to malaria in utero. Levels of EBV- and tetanus-specific antibodies were similar in malaria-infected mothers and in mothers who had no detectable malaria infection. Malaria-exposed neonates had significantly lower levels of anti-EBNA1, anti-Zta, and anti-EAd antibodies than were seen in their mothers. In utero malaria exposure resulted in significant reductions in transplacental transfer of anti-VCA-p18 and anti-EBNA1 antibodies of 13% and 22%, respectively. Neonates received significantly low levels of anti-Zta and anti-EAd antibodies irrespective of malaria exposure levels. In multivariate analysis, in utero malaria exposure was associated with a significant reduction in the transfer of anti-VCA-p18 and anti-EBNA1 antibodies to the neonates (P = 0.0234 and P = 0.0017, respectively). Malaria during pregnancy results in differential levels of transfer of EBV-specific antibodies from the mother to the fetus. The impaired transplacental transfer of some antibodies may lead to the malaria-exposed neonates being susceptible to early EBV infection.

Epstein-Barr Virus-Specific Humoral Immune Responses in Health and Disease

Epstein-Barr virus (EBV) is widely distributed in the world and associated with a still increasing number of acute, chronic, malignant and autoimmune disease syndromes. Humoral immune responses to EBV have been studied for diagnostic, pathogenic and protective (vaccine) purposes. These studies use a range of methodologies, from cell-based immunofluorescence testing to antibody-diversity analysis using immunoblot and epitope analysis using recombinant or synthetic peptide-scanning. First, the individual EBV antigen complexes (VCA , MA, EA(D), EA(R) and EBNA) are defined at cellular and molecular levels, providing a historic overview. The characteristic antibody responses to these complexes in health and disease are described, and differences are highlighted by clinical examples. Options for EBV vaccination are briefly addressed. For a selected number of immunodominant proteins, in particular EBNA1, the interaction with human antibodies is further detailed at the epitope level, revealing interesting insights for structure, function and immunological aspects, not considered previously. Humoral immune responses against EBV-encoded tumour antigens LMP1, LMP2 and BARF1 are addressed, which provide novel options for targeted immunotherapy. Finally, some considerations on EBV-linked autoimmune diseases are given, and mechanisms of antigen mimicry are briefly discussed. Further analysis of humoral immune responses against EBV in health and disease in carefully selected patient cohorts will open new options for understanding pathogenesis of individual EBV-linked diseases and developing targeted diagnostic and therapeutic approaches.

Early age at time of primary Epstein-Barr virus infection results in poorly controlled viral infection in infants from Western Kenya: clues to the etiology of endemic Burkitt lymphoma

BACKGROUND

Infection with Epstein-Barr virus (EBV) early in life and repeated malaria exposure have been proposed as risk factors for endemic Burkitt lymphoma (eBL).

METHODS

Infants were enrolled from 2 rural sites in Kenya: the Kisumu District, where malaria transmission is holoendemic and risk for eBL is high, and the Nandi District, where malaria transmission is limited and the risk for eBL is low. Blood samples were taken from infants through 2 years of age to measure EBV viral load, EBV antibodies, and malaria parasitemia.

RESULTS

We observed a significantly younger age at time of primary EBV infection in children from Kisumu compared with children from Nandi (mean age, 7.28 months [±0.33 SEM] in Kisumu vs 8.39 months [±0.26 SEM] in Nandi), with 35.3% of children in Kisumu infected before 6 months of age. To analyze how different predictors affected EBV viral load over time, we performed multilevel mixed modeling. This modeling revealed that residence in Kisumu and younger age at first EBV infection were significant predictors for having a higher EBV viral load throughout the period of observation.

CONCLUSIONS

Children from a region at high risk for eBL were infected very early in life with EBV, resulting in higher viral loads throughout infancy.

Purified hexameric Epstein-Barr virus-encoded BARF1 protein for measuring anti-BARF1 antibody responses in nasopharyngeal carcinoma patients

WHO type III nasopharyngeal carcinoma (NPC) is highly prevalent in Indonesia and 100% associated with Epstein-Barr virus (EBV). NPC tumor cells express viral proteins, including BARF1, which is secreted and is considered to have oncogenic and immune-modulating properties. Recently, we found conserved mutations in the BARF1 gene in NPC isolates. This study describes the expression and purification of NPC-derived BARF1 and analyzes humoral immune responses against prototype BARF1 (B95-8) and purified native hexameric BARF1 in sera of Indonesian NPC patients (n = 155) compared to healthy EBV-positive (n = 56) and EBV-negative (n = 16) individuals. BARF1 (B95-8) expressed in Escherichia coli and baculovirus, as well as BARF1-derived peptides, did not react with IgG or IgA antibodies in NPC. Purified native hexameric BARF1 protein isolated from culture medium was used in enzyme-linked immunosorbent assay (ELISA) and revealed relatively weak IgG and IgA responses in human sera, although it had strong antibody responses to other EBV proteins. Higher IgG reactivity was found in NPC patients (P = 0.015) than in regional Indonesian controls or EBV-negative individuals (P < 0.001). IgA responses to native BARF1 were marginal. NPC sera with the highest IgG responses to hexameric BARF1 in ELISA showed detectable reactivity with denatured BARF1 by immunoblotting. In conclusion, BARF1 has low immunogenicity for humoral responses and requires native conformation for antibody binding. The presence of antibodies against native BARF1 in the blood of NPC patients provides evidence that the protein is expressed and secreted as a hexameric protein in NPC patients.

No evidence for intrathecal IgG synthesis to Epstein Barr virus nuclear antigen-1 in multiple sclerosis

BACKGROUND

Recent studies suggest an intrathecal IgG response against Epstein Barr virus (EBV) in multiple sclerosis (MS), implicating a pathogenic role for the virus in MS.

OBJECTIVES

To determine the spectrum of anti-EBV antibodies and B-cell epitopes within EBV nuclear antigen-1 (EBNA-1). Furthermore, to determine whether EBNA-1-specific IgG is produced intrathecally.

STUDY DESIGN

Immunoblot analysis was used to study the anti-EBV IgG response in serum and cerebral spinal fluid (CSF) in MS and controls. EBNA-1 B-cell epitopes were identified by immunoscreening of 12 residue long peptides, with 11 residue overlap, spanning EBNA-1. Thirteen peptides containing all immunoreactive regions were constructed and used in paired serum and CSF of MS patients (n=17) and controls (n=18). Subsequently, reactivity to the identified immunodominant peptide was analysed in a large cohort of serum and CSF of MS patients (n=114) and disease controls (n=62).

RESULTS

No difference was observed in the overall anti-EBV antibody diversity, but EBNA-1 reactivity was increased in MS patients versus controls for immunoblot and ELISA (p<0.0001). Epitope analysis on EBNA-1 revealed one immunodominant region covering residues 394-451: EBNA-1(394-451). Anti-EBNA-1(394-451) IgG levels in serum and CSF were significantly higher in MS patients compared to controls. However, normalization for total IgG content of paired serum and CSF samples abrogated this disease association.

CONCLUSIONS

MS patients have normal overall anti-EBV antibody responses with increased reactivity to EBNA-1(394-451). No evidence was found for intrathecal EBNA-1-specific IgG synthesis in MS.

Dried-blood sampling for epstein-barr virus immunoglobulin G (IgG) and IgA serology in nasopharyngeal carcinoma screening

Dried-blood (DB) samples on filter paper are considered clinical specimens for diagnostic use because of the ease of collection, storage, and transport. We recently developed a synthetic-peptide-based immunoglobulin A (IgA) (EBNA1 plus viral capsid antigen [VCA]-p18) enzyme-linked immunosorbent assay (ELISA) for nasopharyngeal carcinoma (NPC) screening. Here, we evaluate the use of two filter papers for DB sampling, i.e., Schleicher & Schuell (S&S) no. 903 and Whatman no. 3; the DB samples were either taken directly from a finger prick or spotted from a Vacutainer blood collector. The elution of DB samples on filter paper was optimized and tested for IgG and IgA reactivity by ELISA (EBNA1 plus VCA-p18) and compared to simultaneously collected plasma samples. The results showed that both types of filter paper can be used for sample collection in NPC diagnosis by using either finger prick or blood spot sampling. Both DB sampling methods produced comparable ELISA (EBNA1 plus VCA-p18) results for IgG and IgA reactivity in 1:100-diluted plasma samples. DB samples of whole blood or finger prick blood show correlation coefficients (r(2)) of 0.825 to 0.954 for IgA on S&S no. 903 filter paper, 0.9133 to 0.946 for IgA on Whatman no. 3 filter paper, 0.807 to 0.886 for IgG on S&S no. 903 filter paper, and 0.819 to 0.934 for IgG on Whatman no. 3 filter paper. Using plasma IgA as a reference, DB sampling showed sensitivities and specificities of 75.0 to 96.0% and 93.5 to 100%, respectively. DB samples could be stored at 37 degrees C for 1 to 4 weeks on S&S no. 903 filter paper and 1 to 6 weeks on Whatman no. 3 filter paper without a significant loss of reactivity, with provision of transport options for tropical conditions. IgA proved to be more stable than IgG. Whatman no. 3 filter paper is a more economical yet diagnostically comparable alternative to S&S no. 903 filter paper. Finger prick DB sampling is proposed for NPC diagnosis, particularly for remote hospitals and field screening studies.

Single-assay combination of Epstein-Barr Virus (EBV) EBNA1- and viral capsid antigen-p18-derived synthetic peptides for measuring anti-EBV immunoglobulin G (IgG) and IgA antibody levels in sera from nasopharyngeal carcinoma patients: options for field screening

Assessment of immunoglobulin A (IgA) antibody responses to various Epstein-Barr virus (EBV) antigen complexes, usually involving multiple serological assays, is important for the early diagnosis of nasopharyngeal carcinoma (NPC). Through combination of two synthetic peptides representing immunodominant epitopes of EBNA1 and viral capsid antigen (VCA)-p18 we developed a one-step sandwich enzyme-linked immunosorbent assay (ELISA) for the specific detection of EBV reactive IgG and IgA antibodies in NPC patients (EBV IgG/IgA ELISA). Sera were obtained from healthy donors (n = 367), non-NPC head and neck cancer patients (n = 43), and biopsy-proven NPC patients (n = 296) of Indonesian and Chinese origin. Higher values of optical density at 450 nm for EBV IgG were observed in NPC patients compared to the healthy EBV carriers, but the large overlap limits its use for NPC diagnosis. Using either EBNA1 or VCA-p18 peptides alone IgA ELISA correctly identified 88.5% and 79.8% of Indonesian NPC patients, with specificities of 80.1% and 70.9%, whereas combined single-well coating with both peptides yielded sensitivity and specificity values of 90.1 and 85.4%, respectively. The positive and negative predictive values (PPV and NPV, respectively) for the combined EBNA1 plus VCA EBV IgA ELISA were 78.7% and 93.9%, respectively. In the Indonesia panel, the level of EBV IgA reactivity was not associated with NPC tumor size, lymph node involvement, and metastasis stage, sex, and age group. In the China panel the sensitivity/specificity values were 86.2/92.0% (EBNA1 IgA) and 84.1/90.3% (VCA-p18 IgA) for single-peptide assays and 95.1/90.6% for the combined VCA plus EBNA1 IgA ELISA, with a PPV and an NPV for the combined EBV IgA ELISA of 95.6 and 89.3%, respectively. Virtually all NPC patients had abnormal anti-EBV IgG diversity patterns as determined by immunoblot analysis. On the other hand, healthy EBV carriers with positive EBV IgA ELISA result showed normal IgG diversity patterns. By using EBV IgG immunoblot diversity as confirmation assay for EBV IgA ELISA-positive samples, the sensitivity and specificity for NPC diagnosis increased to 98% and 99.2%, respectively, in the Indonesian NPC samples. The use of these combined methods for seroepidemiological screening studies is proposed.

Continuous B-epitope maps of cytochrome P450cam (CYP101) obtained by peptide scanning: correlation to spatial structure

Protein continuous B-epitopes can be revealed using short synthetic peptides that overlap a known protein sequence. Since the whole protein surface is considered to possess antigenic properties, a question that arises is whether a set of linear B-epitopes determined by peptide scanning correlates with a protein spatial structure. We have chosen cytochrome P450cam (CYP101) of Pseudomonas putida, with known 3D structure, as a template. Sera of two rabbits and antibody egg yolk preparations from three chickens were produced against the P450cam molecule. These polyclonals were analyzed separately in ELISA with 409 overlapping P450cam hexapeptides. The whole set of continuous antigenic sites of P450cam covered about 45% of the P450cam sequence. However, immunodominant sites (those revealed with more than 50% antibody preparations), the so-called "antigenic core," represent only 9% of the protein sequence. While the amount of water-accessible residues in the total antigenic map (42%) was close to that in the whole native P450cam molecule (39%), the amount of water-accessible residues in the antigenic core was significantly higher (64%). These results led to the conclusion that antigenic core epitopes can be associated to the molecular surface, whereas epitopes with low detection frequency may partly correspond to unfolded regions of the protein molecule.

Production monitoring and purification of EBV encoded latent membrane protein 1 expressed and secreted by recombinant baculovirus infected insect cells

Epstein-Barr virus (EBV) encoded latent membrane protein 1 (LMP1) is expressed in malignancies with latency type II and III and is an important transforming protein. To further study this protein LMP1 was expressed by and purified from recombinant baculovirus infected Sf9 cells. Expression levels of LMP1 in EBV transformed B cell lines and Sf9 cells were analyzed using a newly developed quantitative LMP1-capture ELISA. Highest expression was found in the cell line X50/7 (6.2 ng/10(7) cells), whereas expression levels of recombinant LMP1 (bLMP1) in Sf9 cells reached 506 ng/10(7) cells. Surprisingly bLMP1 could also be detected in the culture medium as a stable full-length protein. Highest expression in Sf9 cells (506 ng/10(7) cells) was observed at 48 h post infection and in the culture medium (1590 ng/ml) at 96 h post infection. Before purification bLMP1 was solubilised using 0.22 m octyl-beta-glucoside at pH 6.0. Purification of bLMP1 using Q-Sepharose FF yielded 10-80 times enriched bLMP1 fractions, indicating that Q-Sepharose can be used for pre-purification. A one-step monoclonal antibody based immunoaffinity chromatography yielded highly purified bLMP1. Although the overall yields (20 microg purified LMP1 from 100 ml culture supernatant) and protein concentrations were low, higher concentrations of >95% purified BLMP1 could be reached after freeze drying.

Bioreactor-scale production and one-step purification of Epstein-Barr nuclear antigen 1 expressed in baculovirus-infected insect cells

Epstein-Barr virus (EBV)-encoded nuclear antigen 1 (EBNA1) is expressed in all EBV-associated malignancies and is essential for EBV-genome maintenance. Antibodies to EBNA1 are abundantly detected in serum of most EBV carriers but EBNA1 escapes recognition by effector T-lymphocytes. To further study the functional and immunological characteristics of EBNA1 it is important to have sufficient quantities of purified EBNA1 available. This paper describes a simple, reproducible method for the production and purification of EBV-encoded EBNA1 expressed in insect cells (bEBNA1). For quantification of EBNA1 expression levels in cell lines and for monitoring bEBNA1 purification and overall yields we developed a quantitative and EBNA1-specific capture ELISA. We observed that EBV-positive cell lines express EBNA1 at different levels, with the B cell lymphoblastoid cell line X50/7 having the highest production. However, much larger quantities (380-fold) were obtained by expressing bEBNA1 in recombinant-baculovirus-infected Sf9 insect cells. Scaling-up experiments revealed that bEBNA1 expression kinetics and protein stability are identical in 1-liter stirred bioreactors when compared to expression in stationary culture flasks. Optimal expression was reached after 72 h following inoculation at 1 pfu/cell, when insect cell viability was about 50%. For purification the nuclear fraction containing most of the bEBNA1 (>95%) was isolated. Solubilized bEBNA1 was purified by a one-step oriP DNA-Sepharose affinity purification procedure, using biotinylated PCR-amplified family of repeats (FR)-domain products immobilized onto streptavidin agarose. A >200-fold specific enrichment was reached and yields of bEBNA1 with an estimated purity of >95%.

Molecular fine-specificity analysis of antibody responses to human cytomegalovirus and design of novel synthetic-peptide-based serodiagnostic assays

To identify single immunodominant marker proteins which can replace complex virion antigen in serodiagnostic assays, we investigated in detail the molecular fine specificity of antibody responses in different individuals with latent or active human cytomegalovirus (HCMV) infection. An overview of the HCMV proteins recognized by human antibodies was obtained by immunoblotting. For selected immunodominant proteins the epitope fine specificity of the antibody response was determined by a peptide-scanning enzyme-linked immunosorbent assay (ELISA). Epitope clusters were synthesized as combination peptides and were used for further serologic analysis of immunoglobulin M (IgM) and IgG reactivities with panels of sera from different groups of patients in comparison to those with cytomegalovirus (CMV) virion antigen. Several serum samples had significantly higher reactivities with peptides than with the CMV virion antigen. However, individual serum samples occasionally recognized diverse peptide epitopes, stressing the importance of using combinations of peptides in serologic assays. From these studies we were able to define a specific combination of peptides derived from pp52 (UL44) and pp150 (UL32) for the specific and highly sensitive early detection of HCMV IgM, whereas a combination of peptides from pp150 (UL32), gB (UL55), and pp28 (UL99) was selected to give optimal and specific reactivity with HCMV IgG. On the basis of the results obtained with these peptide combinations, new, highly specific serodiagnostic assays were constructed. These assays had sensitivities of 98.9 and 96.4% for IgG and IgM, respectively, in comparison with the results obtained with the "gold standard," the virion antigen-based ELISA. From the results of this study we conclude that specific combinations of highly defined synthetic peptides can replace complex HCMV virion extracts used in current serodiagnostics and may add to further standardization of HCMV serology.

Mapping the antigenic structure of porcine parvovirus at the level of peptides

The antigenic structure of the capsid proteins of porcine parvovirus (PPV) was investigated. A total of nine linear epitopes were identified by Pepscan using porcine or rabbit anti-PPV antisera. No sites were identified with a panel of neutralising monoclonal antibodies (MAbs). All epitopes were located in the region corresponding to the major capsid protein VP2. Based on this information, and on analogy to other autonomous parvoviruses, 24 different peptides were synthesised, coupled to keyhole limpet haemocyanin (KLH) and used to immunise rabbits. Most antisera were able to bind viral protein. Only peptides from the N-terminal part of VP2 were able to induce virus-neutralising antibodies, although at low levels. A similar neutralising activity could be obtained in pigs. The exposure of the N-terminus was shown in full virions, both by immunoelectron microscopy and absorption experiments. It is concluded that in PPV, the VP2 N-terminus is involved in virus neutralisation (VN) and peptides from this region are therefore primary targets for developing peptide-based vaccines against this virus.

Identification of peptides mimicking the antigenicity and immunogenicity of conformational epitopes on Japanese encephalitis virus protein using synthetic peptide libraries

Monoclonal antibodies (mAbs) N.03 and N.08 that recognize conformational epitopes on the prM protein of Japanese encephalitis virus (JEV) were analyzed to identify their peptide ligands by using a novel approach that combined two different synthetic peptide libraries. Immunoscreening of a library containing 20(5) sequences of pentapeptides revealed that the ligands for N.03 and N.08 had motif sequences, (Y/W/F)GG(I/L/M) and (N/Q)WY(D/E), respectively. To select higher-affinity ligands, we synthesized and screened another type of library with 20 peptide mixtures that were based on the identified motif, where only one amino acid position was defined; and the process was reiterated for the remaining undefined positions. Consequently, the peptides YGGIYMNG and QWYDDR were identified as peptide ligands of N.03 and N.08, respectively. These peptides bound specifically to the antigen-combining sites of the mAbs as confirmed by competitive binding assays. Mouse antisera directed against the peptide YGGIYMNG specifically recognized JEV, while those against QWYDDR did not. These data demonstrated that peptide ligands which reproduce or mimic the immunogenicity as well as the antigenicity of conformational epitopes can be at least partly identified using this approach. This approach may be useful for analyzing conformational epitopes, which are generally difficult to characterize, and might provide a step toward vaccine development when applied to protective mAbs.

Antibody responses to defined epitopes in the Epstein-Barr virus BZLF1-encoded transactivator protein among human immunodeficiency virus-infected patients

The Epstein-Barr virus BZLF1-encoded replication activator (ZEBRA) is a key mediator of reactivation from latency to the viral productive cycle. In the present study, the serum antibody responses against three defined ZEBRA epitopes (designated ZEBRA-1, -19, and -22) were determined for 50 human immunodeficiency virus (HIV)-seropositive patients and 100 matched healthy control subjects. The anti-ZEBRA responses were more commonly found among HIV-seropositive patients than among healthy controls for all the three ZEBRA epitopes tested (P < 0.0003, P < 0.003, and P < 0.001, respectively). Comparison of ZEBRA antibody levels with the degree of immunodeficiency (CD4 cell counts), CDC grouping, and HIV p24 antigen positivity showed little association, suggesting that induction of ZEBRA antibodies is an early event after HIV infection.

Design of synthetic peptides for oral vaccination

The rational design of effective oral vaccines based on synthetic peptides is a very ambitious undertaking, and involves the solution of huge problems related to protection of the antigens against degradation in the alimentary tract, efficient uptake of the antigens by the relevant cells, and efficient induction of long lasting systemic immunity, local immunity, or both. This paper summarises the steps, necessary to develop such synthetic oral vaccines. These steps involve: (1) the definition of B-cell epitopes; (2) the definition of T-cell epitopes; (3) definition of the carrier or backbone molecule; (4) definition of an immunomodulating element; (5) definition of an adjuvant element; and (6) definition of a targeting element. Good progress is being made with respect to the first three steps, the other steps still provide major challenges, notably the definition of targeting elements. Nevertheless, the first synthetic oral vaccines may become reality in the near future, depending on the speed by which new technology in the area of molecular recognition will develop, i.e. the appropriate chemistry, organic chemistry, molecular modelling, resolution of the molecular interaction of key molecules in microbiology and immunology.

Basic aspects of immunomodulation through active immunization

This paper reviews how immunomodulation through active vaccination has evolved in the past 25 years. Although initially it progressed isolated from the main stream of immunological research and vaccine development, lately it merged with this main stream and is taking full advantage of the newest developments in vaccinology. The first immunomodulation vaccine is already on the market, while various others are close to it. Not in the least because one of the major stumbling blocks of immunomodulation through active vaccination, the inherent low immunogenicity of 'self' antigens, has in a number of other cases been solved. Most progress has been made in veterinary applications and has helped to formulate practical rules, necessary to break immunotolerance. It is not unlikely that these rules will be used to design better immunomodulation vaccines to be used in humans; notably to control fertility or combat tumours.

Linear epitopes of the replication-activator protein of Epstein-Barr virus recognised by specific serum IgG in nasopharyngeal carcinoma

The linear antigenic epitopes of the Epstein-Barr virus replication activator protein (ZEBRA), recognised by specific serum IgG in nasopharyngeal carcinoma (NPC), were determined. This was achieved by synthesizing the entire amino acid sequence of ZEBRA as a set of 29, 22-residue peptides with an overlap of 14 amino acids. The ZEBRA peptides were tested in enzyme-linked immunosorbent assay (ELISA) for IgG binding in sera from 37 selected NPC patients who had IgG antibodies to the native ZEBRA protein. The most immunogenic epitope was peptide 1 at the amino-terminal end with 36 of the sera reactive against it. Further analysis of peptide 1, using the multipin peptide-scanning technique, defined a 10-amino-acid sequence FTPDPYQVPF, which was strongly bound by IgG. Two other regions of ZEBRA were also identified as immunodominant IgG epitopes, namely peptide 11 (amino acids 82-103) and peptide 19/20 (amino acids 146-175) with 8-13 of the NPC sera reactive against the peptides. The number of peptides reactive with individual NPC serum varies from 1 to 6 or more and there is some correlation between a greater number of peptide (at least 4) bound and a higher (at least 1:40) titre of serum IgA to viral capsid antigen. The immunodominant ZEBRA peptide 1 could be utilised in IgG ELISA for the detection of NPC.

Epitope mapping: synthetic approaches to the understanding of molecular recognition in the immune system

Progress in the field of immunochemistry is rapidly increasing due to very efficient methods of epitope mapping. Experimental results on the allele-specific sequence motifs of MHC-binding peptides allow the exact forecast of T-cell epitopes and, in combination with B-cell prediction methods and synthetic adjuvant systems, fully synthetic vaccines may be constructed. Methods of multiple peptide synthesis are of particular use for such constructs and for the fine mapping of monoclonal antibodies or sera of patients. Peptide libraries, containing hundred thousands of different oligopeptides are made available for novel screening procedures. These techniques and their applications in various fields are summarized and discussed with respect to efficiency and productivity.

Gene mapping and expression of two immunodominant Epstein-Barr virus capsid proteins

The genomic localization of two immunodominant genes encoding two proteins of the Epstein-Barr virus capsid antigen (VCA) complex, VCA-p18 and VCA-p40, has been identified. For that purpose, lambda gt11-based cDNA libraries were constructed from HH514.c16 cells induced for virus production. The libraries were screened with a monoclonal antibody, EBV.OT41A, directed against VCA-p40 or with affinity-purified human antibodies against VCA-p18. Sequencing of the inserts of positive plaques showed that VCA-p18 and VCA-p40 are encoded within open reading frames (ORFs) BFRF3 and BdRF1, respectively. Peptide scanning analysis of the predicted protein of ORF BdRF1 resulted in defining the epitope of monoclonal antibody EBV.OT41A at the C-terminal region. The dominant VCA-p18 reactivity of human sera can be completely inhibited by preadsorption with Escherichia coli-expressed BFRF3-beta-galactosidase. Serum of a rabbit immunized with BFRF3-beta galactosidase reacts with a VCA-specific protein of 18 kDa. In addition, BFRF3-beta-galactosidase affinity-purified antibodies react with VCA-p18 of virus-producing cells (HH514.c16). Complete inhibition of viral DNA polymerase activity by phosphonoacetic acid is associated with the absence of RNAs and protein products of both ORFs, indicating that VCA-p18 and VCA-p40 are true late antigens.

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.

Identification of group-common linear epitopes in structural and nonstructural proteins of enteroviruses by using synthetic peptides

Synthetic peptides were employed in enzyme-linked immunosorbent assays to identify group-common linear epitopes in the structural and nonstructural proteins of enteroviruses. Nine linear epitopes were recognized by using sera from patients with heterotypic immunoglobulin G antibody responses to enterovirus infections. The most-reactive peptides were derived from conserved regions of the amino-terminal part of VP1, whereas peptides representing sequences from other conserved regions of VP1, as well as VP2, VP3, and VP4, and from a nonstructural region showed no or poor reactivity. These findings may be useful in the development of serological tests for the diagnosis of infections caused by a broad range of enteroviruses.

Mapping antibody binding sites on cytochrome c with synthetic peptides: are results representative of the antigenic structure of proteins?

Crystallographic work on antigen-antibody complexes has revealed that extensive surface areas of proteins may interact with antibodies. On the other hand, most experimental approaches to locate and define antigenic determinants of protein antigens rely on the linear sequence of the polypeptide chain. Hence the question arises whether mapping of antibody binding sites by analysis of the reactivity of anti-protein antibodies with synthetic peptides can provide a representative picture of the antigenic structure of a protein antigen. We have addressed this question using yeast iso-1 cytochrome c as a protein antigen against which antisera were raised in rabbits. The reaction of the antisera with 103 synthetic hexapeptides covering the entire sequence of cytochrome c was tested by the pepscan procedure in which peptides are coupled to polyethylene rods and tested by ELISA. For the assay, anti-cytochrome c antibodies were fractionated by affinity chromatography on native yeast iso-1 cytochrome c and on apo-cytochrome c; the latter is a random coil. It was found that only antibodies retained by the apo-cytochrome c affinity column react with synthetic peptides. These antibodies comprise a small fraction, probably less than 2%, of all cytochrome c-specific antibodies. The majority of antigenic determinants, which seem to consist of strongly conformation-dependent topographic epitopes, could not be uncovered by the peptide approach. Epitope mapping with short peptides seems of limited usefulness in the case of small, globular, and conformationally stable proteins like cytochrome c.

Identification of a novel EBV-induced membrane glycoprotein of 43 kDa with H667 MAb

Using purified B95-8 Epstein-Barr virus (EBV), a MAb designated H667 was produced. We demonstrated by indirect membrane immunofluorescence (IF) on six EBV producer cell lines and by immunoelectron microscopy that H667 reacted with a membrane antigen. H667 recognized a 43-kDa EBV protein (p43) as determined by immunoblotting using purified EBV from the six producer cell lines. Phosphonoacetic acid treatment of B95-8 cells was associated with the disappearance of p43, indicating that it was a late antigen. This antigen was shown to be a glycoprotein by incorporation of [14C]glucosamine and was shown to contain an N-asparagine-linked glycosyl group by its sensitivity to tunicamycin. It was named gp43. The H667 MAb inhibited B95-8 EBV cord blood lymphocyte transformation only when a low inoculum was used but failed to inhibit EA induction in Raji cells by P3HR1 EBV. Human sera reactivity against the gp43 antigen was studied. By the immunoblotting method, using H667 immunoaffinity chromatography-purified gp43, we showed that 70.9% of the human sera tested had antibodies directed against gp43. By IF blocking tests, we found that only 12.5% of the sera tested were reactive, indicating that the epitope corresponding to the H667 MAb was not the most immunogenic gp43 epitope.

Distribution of linear antigenic sites on glycoprotein gp55 of human cytomegalovirus

Human convalescent serum and bacterial fusion proteins constructed from overlapping open reading frames of the nucleotide sequence encoding the human cytomegalovirus gp55 component of the major envelope glycoprotein complex, gp55-116 (gB), were used to localize antigenic regions recognized by human antibodies. All donor serum analyzed contained antibody reactivity for an antigenic site(s) located between amino acids (AA) 589 and 645, a region containing a previously defined linear site recognized by neutralizing monoclonal antibodies (U. Utz, B. Britt, L. Vugler, and M. Mach, J. Virol. 63:1995-2001, 1989). Furthermore, in-frame insertion of two different synthetic oligonucleotides encoding four amino acids into the sequence at nucleotide 1847 (AA 616) eliminated antibody recognition of the fusion protein. A second antibody binding site was located within the carboxyl terminus of the protein (AA 703 through 906). A competitive binding inhibition assay in which monoclonal antibodies were used to inhibit human antibody reactivity with recombinant gp55-116 (gB) suggested that the majority of human anti-gp55-116 (gB) antibodies were directed against a single antigenic region located between AA 589 and 645. Furthermore, inoculation of mice with fusion proteins containing this antigenic site led to a boostable antibody response. These results indicated that the antigenic site(s) located between AA 589 and 645 was an immunodominant antibody recognition site on gp55 and likely the whole gp55-116 (gB) molecule. The enhanced immunogenicity of this region in vivo may account for its immunodominance.

Immunoaccessible peptide sequences of the major outer membrane protein from Chlamydia trachomatis serovar C

The antigenicity of the major outer membrane protein of Chlamydia trachomatis serovar C was assessed by using overlapping hexapeptide homologs of serovar C major outer membrane protein and rabbit antisera in a peptide enzyme-linked immunosorbent assay. Five immunogenic sites were found distributed within variable sequences of the protein: four were immunodominant and three were surface exposed on native elementary bodies of serovar C. None was surface exposed on serovars H, I, and J.

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

Four recombinant, diagnostically useful Epstein-Barr virus (EBV) proteins representative of the viral capsid antigen (p150), diffuse early antigen (p54), the major DNA-binding protein (p138), and the EBV nuclear antigen (p72) (W. Hinderer, H. Nebel-Schickel, H.H. Sonneborn, M. Motz, R. Kühbeck, and H. Wolf, J. Exp. Clin. Cancer Res. 7[Suppl.]:132, 1988) were used to set up individual enzyme-linked immunosorbent assays (ELISAs) for the qualitative and quantitative detection of immunoglobulin M (IgM) and IgG antibodies. In direct comparison with results obtained by standard immunofluorescence or immunoperoxidase assays, it was then shown that the recombinant EBV ELISAs provide the means for specific and sensitive serodiagnosis of infectious mononucleosis (IM) caused by EBV. The most useful markers in sera from such patients proved to be IgM antibodies against p54, p138, and p150. Additional positive markers for recent or ongoing IM apparently were IgG antibodies against p54 and p138. In contrast, anti-p72 IgG had a high preference for sera from healthy blood donors and, therefore, can be considered indicative of past exposure to the virus. Altogether, the individual ELISAs proved to be as specific and at least as sensitive for the diagnosis of IM as the currently available standard techniques are. Moreover, our findings suggest that, by combining individual test antigens, a workable ELISA system consisting of three assays (IgM against p54, p138, and p150; IgG against p54 and p138; and IgG against p72) can be established for the standardized rapid diagnosis of acute EBV infections.

Structure of viral B-cell epitopes

Four categories of viral epitopes can be distinguished that have been designated cryptotopes, neotopes, metatopes and neutralization epitopes. Specific examples of each epitope type are presented and the methods used for locating their positions in viral proteins are described. The epitopes of four well-characterized viruses, namely poliovirus, foot-and-mouth disease virus, influenza virus and tobacco mosaic virus are briefly described.

Recent advances in solid-phase peptide synthesis and preparation of antibodies to synthetic peptides

Peptides prepared by the solid-phase peptide synthesis (SPPS) approach are used increasingly in biological research, for instance to elicit anti-peptide antibodies that will recognize the intact, cognate protein. Recent advances in SPPS are reviewed, including the use of new coupling reagents, new methods for evaluating peptide purity and new techniques of automated and multiple peptide synthesis. Methods for enhancing peptide immunogenicity are discussed such as the use of adjuvants and liposomes, and of synthetic branched polypeptides as carriers.

Immunoblotting reactivity of human sera from various sources against purified Epstein-Barr virus

The immunoblotting technique was used to analyse polypeptides of purified Epstein-Barr virus reacting with antibodies present in sera from clinically healthy individuals, from patients with infectious mononucleosis (IM) or AIDS, and from renal transplant recipients. Polypeptides with molecular sizes in the range of 40-290 kDa were detected. The 47- and 160-kDa nucleocapsid polypeptides, as well as the 72-, 74-, 140-, 220- and 290-kDa membrane polypeptides were the major viral proteins detected in the sera. Sera from clinically healthy individuals contained antibodies directed against all EBV membrane and nucleocapsid antigens. Sera from renal transplant recipients, from patients with IM and from patients with AIDS failed to react with certain nucleocapsid and membrane antigens; in particular, sera from AIDS patients and renal transplant recipients did not react with the 220-kDa polypeptide, one of the major membrane antigens, while sera from subjects with IM and from healthy individuals did. A high proportion of sera from patients with IM (38% vs 5% of clinically healthy individuals and 0-5% of the AIDS patients and renal transplant recipients) reacted with a 42-kDa polypeptide, suggesting its possible role in acute EBV infection.

Epstein-Barr virus specific marker molecules for early diagnosis of infectious mononucleosis

The molecular specificity of the antibody response against Epstein-Barr Virus (EBV) is studied in patients with acute primary EBV-infection, i.e. infectious mononucleosis syndrome. Using the immunoblot technique both IgM and IgG antibody responses are studied in sera obtained serially until week 20 after onset of symptoms. Healthy seropositive blood donors are used as control. Antigens are prepared from virus producer cell lines B95-8, P3HR1 and HH514-c16 (a superinducible derivative of P3HR1), induced for the expression of early antigens (EA) or viral capsid antigens (VCA) and from the EBV-negative cell lines BJAB and RAMOS. The 'WC'-serum, described by Edson et al. (J. Immunol. 130, 1983) is used to characterize EA- and VCA-specific polypeptides and to define their subcellular location. The immunoblot studies reveal an enormous diversity in EBV-specific polypeptides recognised by different individual patients, both for IgM and IgG. In addition, these patterns were markedly different from those found with control blood donor sera. The latter predominantly recognised bands at 72 kDa (EBNA) and 41 and 18 kDa respectively (both VCA components). Despite the great individual variation observed, EA-specific polypeptides at 138 kDa and at 45-52 kDa were recognised by both IgM and IgG antibodies in first serum samples of all patients tested.