Peptide based enzyme-linked immunoassays for detection of anti-HSV-2 IgG in human sera

Design and Optimization of a Monkeypox virus Specific Serological Assay

Monkeypox virus (MPXV), a member of the Orthopoxvirus (OPXV) genus, is a zoonotic virus, endemic to central and western Africa that can cause smallpox-like symptoms in humans with fatal outcomes in up to 15% of patients. The incidence of MPXV infections in the Democratic Republic of the Congo, where the majority of cases have occurred historically, has been estimated to have increased as much as 20-fold since the end of smallpox vaccination in 1980. Considering the risk global travel carries for future disease outbreaks, accurate epidemiological surveillance of MPXV is warranted as demonstrated by the recent Mpox outbreak, where the majority of cases were occurring in non-endemic areas. Serological differentiation between childhood vaccination and recent infection with MPXV or other OPXVs is difficult due to the high level of conservation within OPXV proteins. Here, a peptide-based serological assay was developed to specifically detect exposure to MPXV. A comparative analysis of immunogenic proteins across human OPXVs identified a large subset of proteins that could potentially be specifically recognized in response to a MPXV infection. Peptides were chosen based upon MPXV sequence specificity and predicted immunogenicity. Peptides individually and combined were screened in an ELISA against serum from well-characterized Mpox outbreaks, vaccinee sera, and smallpox sera collected prior to eradication. One peptide combination was successful with ~86% sensitivity and ~90% specificity. The performance of the assay was assessed against the OPXV IgG ELISA in the context of a serosurvey by retrospectively screening a set of serum specimens from the region in Ghana believed to have harbored the MPXV-infected rodents involved in the 2003 United States outbreak.

A general approach for predicting protein epitopes targeted by antibody repertoires using whole proteomes

Antibodies are essential to functional immunity, yet the epitopes targeted by antibody repertoires remain largely uncharacterized. To aid in characterization, we developed a generalizable strategy to predict antibody-binding epitopes within individual proteins and entire proteomes. Specifically, we selected antibody-binding peptides for 273 distinct sera out of a random library and identified the peptides using next-generation sequencing. To predict antibody-binding epitopes and the antigens from which these epitopes were derived, we tiled the sequences of candidate antigens into short overlapping subsequences of length k (k-mers). We used the enrichment over background of these k-mers in the antibody-binding peptide dataset to predict antibody-binding epitopes. As a positive control, we used this approach, termed K-mer Tiling of Protein Epitopes (K-TOPE), to predict epitopes targeted by monoclonal and polyclonal antibodies of well-characterized specificity, accurately recovering their known epitopes. K-TOPE characterized a commonly targeted antigen from Rhinovirus A, predicting four epitopes recognized by antibodies present in 87% of sera (n = 250). An analysis of 2,908 proteins from 400 viral taxa that infect humans predicted seven enterovirus epitopes and five Epstein-Barr virus epitopes recognized by >30% of specimens. Analysis of Staphylococcus and Streptococcus proteomes similarly predicted 22 epitopes recognized by >30% of specimens. Twelve of these common viral and bacterial epitopes agreed with previously mapped epitopes with p-values < 0.05. Additionally, we predicted 30 HSV2-specific epitopes that were 100% specific against HSV1 in novel and previously reported antigens. Experimentally validating these candidate epitopes could help identify diagnostic biomarkers, vaccine components, and therapeutic targets. The K-TOPE approach thus provides a powerful new tool to elucidate the organisms, antigens, and epitopes targeted by human antibody repertoires.

Optimization of peptide-based ELISA for serological diagnostics: a retrospective study of human monkeypox infection

Although smallpox has been eradicated, other diseases caused by virulent orthopoxviruses such as monkeypox virus (MPV) remain endemic in remote areas of western and central sub-Saharan Africa, and represent a potential biothreat due to international travel and/or inadvertent exposure. Unfortunately, extensive antigenic cross-reactivity among orthopoxviruses presents a challenge to serological diagnosis. We previously reported a 20mer peptide-based ELISA that identified recent MPV infection with >90% sensitivity and >90% specificity. However, the sensitivity of this approach was not determined with samples obtained at later time points after antibody titers had declined from their peak levels. To improve assay sensitivity for detecting MPV-specific antibodies at later time points, we compared diagnostic 20mer peptides to 30mer peptides. In addition, optimal 30mer peptides were tested in combination or after conjugating selected peptides to a carrier protein (bovine serum albumin) to further improve assay performance. An optimized combination of four unconjugated 30mer peptides provided 100% sensitivity for detecting MPV infection at 2-6 months post-infection, 45% sensitivity for detecting MPV infection at >2 years post-infection, and 99% specificity. However, an optimized combination of two peptide conjugates provided 100% sensitivity for detecting MPV infection at 2-6 months post-infection, 90% sensitivity for detecting MPV infection at >2 years post-infection, and 97% specificity. Peptide-based ELISA tests provide a relatively simple approach for serological detection of MPV infection. Moreover, the systematic approach used here to optimize diagnostic peptide reagents is applicable to developing improved diagnostics to a broad range of other viruses, and may be particularly useful for distinguishing between closely-related viruses within the same genus or family.

Rapid detection and differentiation of antibodies to HIV-1 and HIV-2 using multivalent antigens and magnetic immunochromatography testing

A simplified lateral-flow assay for the detection of antibodies to HIV using magnetic-bead conjugates and multibranched peptides from both HIV-1 and HIV-2 was developed. Magnetic immunochromatography testing (MICT) uses a standard lateral-flow platform that incorporates magnetic-bead conjugates for quantitative measurement of the magnetic field distortion associated with the bound magnetic conjugate (reported as adjusted relative magnetic units [MAR]). The results of the optimized MICT assay were compared to standard enzyme immunoassay (EIA) and Western blotting (WB) results using a blinded 649-member panel of specimens from the United States, Cameroon, and West Africa. The panel was comprised of samples from individuals infected with various HIV-1 subtypes (n = 234) or HIV-2 (n = 65) and HIV-seronegative specimens (n = 350). Additionally, 13 HIV-1 seroconversion panels (total specimens = 85), a worldwide panel containing seven of the major circulating HIV-1 subtypes (n = 18), an HIV-2 panel, an HIV-1/HIV-2 mixed panel, and 100 prospective specimens were tested with completely concordant results. Assay reproducibility (observed MAR) for both intra- and interrun testing was excellent, with coefficients of variation of <12%. MICT can provide a rapid, low-cost method of determining HIV antibody status requiring no subjective interpretations.

Assessment of synthetic chimeric multiple antigenic peptides for diagnosis of GB virus C infection

The use of synthetic peptides of both structural and nonstructural proteins of GB virus C (GBV-C) has been studied for the development of new systems to diagnose infection caused by this virus. In an attempt to increase the antigenicity of linear peptide sequences, chimeric multiple antigenic peptides (MAPs) containing epitopes from E2, NS4, and NS5 GBV-C proteins have been synthesized. The synthetic constructs were evaluated by ELISA to establish whether the epitopes in chimeric branched peptides are more efficiently recognized by the specific antibodies compared to the monomeric linear sequences. Moreover, we have investigated the application of a commercial biosensor instrument for the detection of antibodies against the GBV-C in human serum samples. The results of the immunoassays reported in this work highlight the usefulness of synthetic tetrameric branched peptides containing sequences from envelope and nonstructural GBV-C proteins for the diagnosis of GBV-C infection. The potential clinical value of the MAP(4)(E2-NS5a) for the serodiagnosis of GBV-C infection was demonstrated, thus providing the basis for performing prevalence studies of the infection among the hemodialyzed and hepatitis C virus (HCV)-infected population.

Comparative performance of a novel herpes simplex virus type 2-specific enzyme-linked immunosorbent assay using a targeted chain oligopeptide, peptide 55

Herpes simplex virus (HSV) glycoprotein G (gG2) has been used as the basis of many serological assays for the detection of HSV type 2 (HSV-2)-specific antibodies. In the present study, an enzyme-linked immunosorbent assay (ELISA), the Pathozyme Viro HSV-2 immunoglobulin G (IgG) ELISA (Omega Diagnostics, Alva, United Kingdom), based on an immunodominant epitope of gG2 presented in a branched-chain format (peptide 55), was compared with two commercially available gG2-specific assays, the Bioelisa HSV-2 IgG assay (Biokit, S.A., Barcelona, Spain) and the HerpesSelect HSV-2 IgG assay (Focus Diagnostics, Cypress, CA). A panel of 218 well-characterized serum samples was tested. Thirty-one samples were determined to be HSV-2 IgG antibody positive and 164 samples were determined to be negative with all three kits. The levels of concordance between the tests were 95.9% between the Omega and HerpeSelect assays, 90.8% between the Omega and Bioelisa assays, and 94.5% between the HerpeSelect and Bioelisa assays. Twenty-three samples gave discordant results. Western blot results showed that of these, the results for 77% were correctly identified by the Omega assay, the results for 68% were correctly identified by the HerpeSelect assay, and the results for 13.6% were correctly identified by the Bioelisa assay. Although there was a high level of agreement between the results obtained by the three assays and no false-positive results were detected by any of the three kits, confirmation of the results for samples with discordant results by Western blotting suggested that the peptide 55-based Omega assay is the most sensitive and specific assay among the assays evaluated.

Amplification and cloning of herpes simplex virus type 2 glycoprotein G from an Iranian isolate

Herpes Simplex Virus type-2 (HSV-2) is the main cause of genital herpes infection. Its prevalence is increasing worldwide and varies widely with generally higher rate in developing than developed countries and urban than rural areas. HSV-2 Iranian isolate was propagated in HeLa cell line. The viral genome was extracted by phenol-chloroform and used as template in nested polymerase chain reactions (n-PCR) to amplify gG-2 gene. The amplified gene was cloned into a cloning vector (pTZ57R/T) and transformed into competent E. coli DH5a. The recombinant vector encoding the gene of interest was confirmed by restriction enzyme analysis and sequencing.

HIV-1, HSV-2 and syphilis among pregnant women in a rural area of Tanzania: prevalence and risk factors

BACKGROUND

Evidence suggests that a substantial proportion of new HIV infections in African countries are associated with herpes simplex virus type 2 (HSV-2). Thus, the magnitude of HSV-2 infection in an area may suggest the expected course of the HIV epidemic. We determined prevalence of genital herpes, syphilis and associated factors among pregnant women from a remote rural Tanzanian community that has a low but increasing HIV prevalence.

METHODS

We analysed 1296 sera and responses to a standard structured questionnaire collected from pregnant women aged between 15-49 years, attending six different antenatal clinics within rural Manyara and Singida regions in Tanzania. Linked anonymous testing (with informed consent) of the serum for specific antibodies against HSV-2 was done using a non-commercial peptide- 55 ELISA. Antibodies against syphilis were screened by using rapid plasma reagin (RPR) and reactive samples confirmed by Treponema pallidum haemagglutination assay (TPHA).

RESULTS

Previous analysis of the collected sera had shown the prevalence of HIV antibodies to be 2%. In the present study the prevalence of genital herpes and syphilis was 20.7% (95% CI: 18.53-23.00) and 1.6% (95% CI: 1.03-2.51), respectively. The presence of HSV-2 antibodies was associated with polygamy (OR 2.2, 95% CI: 1.62 - 3.01) and the use of contraceptives other than condoms (OR 1.7, 95% CI: 1.21 - 2.41). Syphilis was associated with reporting more than one lifetime sexual partner (OR 5.4, 95% CI: 1.88 - 15.76) and previous spontaneous abortion (OR 4.3, 95% CI: 1.52-12.02).

CONCLUSION

The low prevalence of HIV infection offers a unique opportunity for strengthening HIV prevention in a cost-effective manner. The identification and control of other prevalent curable STIs other than syphilis and specific intervention of HSV-2 in specific populations like pregnant women would be one among approaches towards preventing incident HIV infections.

Prevalence of antibodies against herpes simplex virus types 1 and 2 in children and young people in an urban region in Tanzania

Herpes simplex virus type 1 (HSV-1) is transmitted by close contact, both sexual and nonsexual, and infections are acquired during childhood and adolescence. Herpes simplex virus type 2 (HSV-2), however, is thought to be transmitted mainly by sexual contact. Most HSV-2 infections are consequently expected to occur after the onset of sexual activity. Recent reports indicate an increasing prevalence of HSV-2 on the African continent, but most studies have been performed on adult cohorts. In the present study, we collected sera from Tanzanian children and young persons from 1 to 20 years old, with at least 100 individuals in each age group. Antibodies against HSV-1 and HSV-2 were detected by an in-house Western blot method which was shown to perform well in comparison with a commercial Western blot assay. Type-specific antibodies were also analyzed by two noncommercial enzyme-linked immunosorbent assay methods based upon the antigenicities of branched synthetic oligopeptides corresponding to epitopes in glycoprotein G of HSV-1 or HSV-2. The prevalence of HSV-1 antibodies increased gradually from 73% for the age group of 1 to 4 years to 92% for the age group of 17 to 20 years. The prevalence of HSV-2 antibodies was unexpectedly high, as 15% of the children were infected by the age of 8 years, with the incidence increasing gradually to 40% in the age group of 17 to 20 years. The reason for this unexpectedly high frequency is not clear but could suggest that nonsexual transmission of HSV-2 is more common than previously thought. There was no statistically significant association between seropositivities for HSV-2 and human immunodeficiency virus.

A branched, synthetic oligopeptide corresponding to a region of glycoprotein G of HSV-1 reacts sensitively and specifically with HSV-1 antibodies in an ELISA

Herpes simplex viruses types 1 and 2 (HSV-1 and HSV-2), which are common worldwide, are so similar that antibodies directed against one serotype may crossreact with antigens from the other one. Methods for specific detection of antibodies against HSV-1 or HSV-2 are based upon the antigenicities of glycoproteins G. However, due to the cost, the available commercial methods may not readily be used in developing countries. A different enzyme-linked immunosorbent assay (ELISA) method, based upon a synthetic oligopeptide corresponding to an immunogenic region in glycoprotein G of HSV-2, has been used recently and successfully for detection of HSV-2 antibodies. In the present study, the sequences of a newly identified immunogenic and type-specific region in glycoprotein G of HSV-1 was used to synthesize three different, branched oligopeptides. The performances of these peptides in an ELISA were investigated by testing Scandinavian and African sera which were characterized by commercial ELISA and Western blotting methods and divided into four groups either lacking HSV antibodies, containing antibodies against one or the other virus, or against both types. The peptide which corresponded in sequence to the immunodominant region was as specific and sensitive by an ELISA as were the commercial methods. The method is inexpensive and reliable.

Peptide dendrimers

Dendrimers are branched structures and represent a fast growing field covering many areas of chemistry. Various types of dendrimers differing in composition and structure are mentioned, together with their practical use spanning from catalysis, transport vehicles to synthetic vaccines. The main stress is given to peptide dendrimers, namely, multiple antigenic peptides (MAPs). Their synthesis, physicochemical properties, biological activities, etc. have been described with many examples. MAPs can be used as diagnostics, mimetics, for complexation of different cations, as vaccines against parasites, bacteria, viruses, etc.

Performance and use of a ribonucleotide reductase herpes simplex virus type-specific serological assay

In response to the increasingly evident need for herpes simplex virus (HSV) serotype-specific serologic assays that rely on proteins other than glycoprotein-G (gG), we developed a rapid serologic assay that is based on type-specific epitopes within the large subunit of HSV ribonucleotide reductase (R1). The assay (Au-2 enzyme-linked immunosorbent assay [ELISA]) uses an HSV type 2 (HSV-2) R1 peptide antigen. It provides a reliable method for detecting serotype-specific antibody to a protein other than gG-2. The Au-2 ELISA has high sensitivity and specificity as determined by direct comparison to Western blotting, a widely accepted "gold standard," and to ELISA with an HSV-1 R1 peptide (Au-1). The use of the Au-2 ELISA in conjunction with the gG-2-based assays will improve the sensitivity and specificity of serologic diagnosis and patient management.

Herpes simplex 2 risk among women in a polygynous setting in rural West Africa

OBJECTIVES

To determine risk factors for herpes simplex 2 (HSV2) infection in women in a polygynous rural Gambian population.

METHODS

Data from women who participated in a cross-sectional survey of reproductive health were matched to their own and, for women who had been or were married (ever-married), their spouses' data collected in a cross-sectional survey of fertility interests, including information on marital histories.

RESULTS

Data were available on 150 never-married and 525 ever-married women. HSV2 prevalence was 16% amongst never-married women and 36% amongst ever-married women. For ever-married women, their own personal characteristics (age, ethnicity and genital cutting status) and events from their husbands' marriage history were important determinants of HSV2 infection. Women whose husbands married for the first time over age 35 were at greater risk than women whose husbands married by age 24 [odds ratio (OR) 2.72, 95% confidence interval (CI) 1.20-6.10]. Women whose husband reported interest in a new marriage were more likely to be HSV2 positive (OR 1.91, 95% CI 1.18-3.09). Women whose husbands were currently monogamous but had had previous marriages (OR 2.76, 95% CI 1.30-5.88) and women in currently polygynous marriages (OR 2.88, 95% CI 1.66-5.01) were three times as likely to be HSV2 positive as women who were their husband's only wife ever.

CONCLUSION

Much transmission of HSV2 in this setting occurs within marriage where opportunity for personal protection is limited. High levels of transmission within marriage may undermine the impact of sexual behaviour change programmes aiming to reduce HSV2 and HIV incidence and complicate their evaluation.

Performance characteristics of a glycoprotein G based oligopeptide (peptide 55) and two different methods using the complete glycoprotein as assays for detection of anti-HSV-2 antibodies in human sera

Assays for serological diagnosis of HSV-2 infection in clinical settings have been generally available only recently. We wanted to investigate and compare the diagnostic utility of three different ELISAs for detection of anti-HSV-2 IgG antibodies, using intact glycoprotein G or an oligopeptide from a portion of the protein as antigens. HSV-1 negative/HSV-2 negative sera (n = 32), HSV-1 positive/HSV-2 negative sera (n = 30) and sera from HSV-2 culture positive individuals (n = 36), collected at least 6 months after culture verified HSV-2 genital infection were examined. Cut-off values were determined according to the manufacturer's instructions, and also by establishing new cut-off values at the level of highest diagnostic efficiency. Sensitivities and specificities were compared for each assay. In addition, test accuracies were compared using receiver-operating characteristics (ROC) methodology. Establishment of new cut-off values increased the performance characteristics for all three tests. At similarly set cut-off values, the peptide 55 assay showed the highest diagnostic sensitivity (100%) and specificity (98%). All three assays displayed high efficiency and also high agreement between the tests (kappa > 0.85 for all comparisons). The performance of all three assays were satisfactory although the highest efficiency and accuracy was obtained with the peptide 55 assay.

Use of a fragment of glycoprotein G-2 produced in the baculovirus expression system for detecting herpes simplex virus type 2-specific antibodies

Fragments of glycoprotein G (gG-2(281-594His)), comprising residues 281 to 594 of herpes simplex virus type 2 (HSV-2), glycoprotein G of HSV-1 (gG-1(t26-189His)), and glycoprotein D of HSV-1 (gD-1(1-313)), were expressed in the baculovirus expression system to develop an assay for the detection of HSV-1 and HSV-2 type-specific antibodies. The expression of the gG-1(t26-189His) and gG-2(281-594His) fragments was analyzed by Western blotting using monoclonal antibodies LP10 and AP1, respectively. The molecular masses of the major products of gG-1(t26-189His) and the fragment of gG-2(281-594His) were 36 to 39 kDa and 64 to 72 kDa, respectively. Human sera positive for HSV-1 reacted with gG-1(t26-189His), sera positive for HSV-2 reacted with the gG-2(281-594His) fragment, and sera positive for both types reacted with gG-1(t26-189His) and gG-2(281-594His) in Western blotting. The human sera recognized polypeptides of gG-2(281-594His) with molecular masses of 57 to 67 and 120 to 150 kDa and additional faint bands of 21, 29, and 45 kDa. The recombinant gG-1(t26-189His) and the recombinant gG-2(281-594His) fragment were used as type-specific antigens for the detection of HSV-1- and HSV-2-specific antibody responses in human sera, respectively. As type-common antigens, an extract of HSV-1-infected Vero cells and recombinant gD-1(1-313) were used. An enzyme-linked immunosorbent assay to detect type-specific antibodies was developed, and the sensitivity and specificity were evaluated by comparison with commercial tests by using sera obtained from different sources. The sensitivity and specificity were 91.5 and 95.5%, respectively, compared to the Gull assay. The gG-2(281-594His) fragment can be obtained in relatively large quantities at low cost.

Detection of HSV-2 in genital ulcers from STD patients in Dar es Salaam, Tanzania

BACKGROUND

Genital ulcer disease (GUD) is common in many developing countries. Several reports indicate that there is an association with HIV infection. Analysis by polymerase chain reaction (PCR) has demonstrated that the ulcers are frequently caused by herpes simplex type 2 (HSV-2), although HSV-1 is becoming increasingly important in many parts of the world. Comparable studies have not been performed in Tanzania.

OBJECTIVES

To determine the prevalence of HSV-2 and HSV-1 in genital ulcers in Dar es Salaam, Tanzania and determine their possible association with HIV infection.

STUDY DESIGN

Samples were collected from 70 consecutive patients with GUD attending a clinic for sexually transmitted diseases. Specimens from ulcers were analysed by PCR for the presence of HSV-2 and HSV-1, and sera were examined for antibodies against HSV-2 and HIV.

RESULTS AND DISCUSSION

HSV-2 DNA was detected in 64% of the specimens from ulcers while HSV-1 DNA was not found in any of them. Antibodies to HSV-2 and HIV were detected in 79.7 and 42% of the patients' sera, respectively. Although there was a significant positive association between HIV and HSV-2 seropositivity, HSV-2 DNA in genital ulcers was not more prevalent among HIV seropositive than among HIV seronegative individuals.

CONCLUSION

The prevalence of HSV-2 antibodies among Tanzanian patients with genital ulcers is very high, and HSV-2 is detected in most of the ulcers. There is an association between infections with HIV and HSV-2, but the relationship is not clear.

Monoclonal antibodies and human sera directed to the secreted glycoprotein G of herpes simplex virus type 2 recognize type-specific antigenic determinants

Glycoprotein G-2 (gG-2) of herpes simplex virus type 2 (HSV-2) is cleaved to a secreted amino-terminal portion (sgG-2) and to a cell-associated carboxy-terminal portion which is further O-glycosylated to constitute the mature gG-2 (mgG-2). In contrast to mgG-2, which is known to elicit a type-specific antibody response in the human host, information on the immunogenic properties of sgG-2 is lacking. Here the sgG-2 protein was purified on a heparin column and used for production of monoclonal antibodies (mAbs). Four anti-sgG-2 mAbs were mapped using a Pepscan technique and identified linear epitopes which localized to the carboxy-terminal part of the protein. One additional anti-sgG-2 mAb, recognizing a non-linear epitope, was reactive to three discrete peptide stretches where the most carboxy-terminally located stretch was constituted by the amino acids (320)RRAL(323). Although sgG-2 is rapidly secreted into the cell-culture medium after infection, the anti-sgG-2 mAbs identified substantial amounts of sgG-2 in the cytoplasm of HSV-2-infected cells. All of the anti-sgG-2 mAbs were HSV-2 specific showing no cross-reactivity to HSV-1 antigen or to HSV-1-infected cells. Similarly, sera from 50 HSV-2 isolation positive patients were all reactive to sgG-2 in an enzyme immunoassay whilst no reactivity was seen in 25 sera from HSV-1 isolation positive patients or in 25 serum samples from HSV-negative patients suggesting that sgG-2 is a novel antigen potentially suitable for type-discriminating serodiagnosis.

In situ deprotection: a method for covalent immobilization of peptides with well-defined orientation for use in solid phase immunoassays such as enzyme-linked immunosorbent assay

The orientation of an immobilized antigen is important for recognition by, e.g., an antibody. When noncovalent passive adsorption is used for immobilization, the number of ways that the antigen can attach to the surface is numerous and control of how the antigen orientates on the surface is limited. Covalent immobilization restricts the number of the ways that the antigen can be immobilized to the number of reactive groups on the antigen and, hence, the orientation of the immobilized antigen is more predictable. Peptide antigens were synthesized and purified with protection groups on the lysine and cysteine side chains. These peptides, which have only one good nucleophilic group (the N-terminal alpha-amino group), were immobilized covalently in microtiter plates supplied with tresyl groups on the surface and the protection groups were cleaved off in situ after immobilization. The controlled orientation of these peptides resulted in enhanced recognition by antibodies in general. An enzyme-linked immunosorbent assay for detection of antibodies against a peptide derived from outer surface protein C from Borrelia burgdorferi, found in Lyme borreliosis patients, was established using this strategy. Lyme borreliosis suspect patient sera showed up to a 10-fold increase in the signal when the orientation of the peptide antigen was controlled by the in situ deprotection strategy.