Localization of the virus neutralizing and hemagglutinin epitopes of E1 glycoprotein of rubella virus

Rational design and evaluation of the recombinant multiepitope protein for serodiagnosis of rubella

BACKGROUND

Rubella is an infection caused by rubella virus (RV) and is generally regarded as a mild childhood disease. The disease continues to be of public health importance mainly because when the infection is acquired during early pregnancy it often results in fetal abnormalities, which are classified as congenital rubella syndrome (CRS). An accurate diagnosis for rubella is thus of pivotal importance for proper treatment.

OBJECTIVE

To produce a recombinant multiepitope protein (rMERUB) for the diagnosis of rubella, based on conserved immunodominant epitopes of glycoprotein E1 and E2.

METHODS

A synthetic gene was designed and cloned into vector pET21a with a 6xHis tag at the C-terminal for affinity purification and overexpressed in Escherichia coli cells. Biophysical analysis of rMERUB was performed by circular dichroism. Biological activity was assessed using an in-house ELISA assay.

RESULTS

Expression in Escherichia coli showed a ~22 kDa protein that was purified and used to perform structural assays and an IgG ELISA. Structural analyses reveal rMERUB has a β leaf pattern that promotes the exposure of epitopes, thus allowing antibody recognition. Evaluation of 33 samples (22=positive; 11=negative) was performed using in-house ELISA and this was compared with a commercial kit. The sensitivity was 100% (95% CI: 85-100) and specificity 90.91% (95% CI: 62-99). Excellent agreement (Kappa index = 0.9) was obtained between ELISA assays.

CONCLUSIONS

The careful choice of epitopes and the high epitope density, coupled with simple-step purification, pinpoints rMERUB as a promising alternative for rubella diagnosis, with potential for the development of a diagnostic kit.

Preliminary multiplex microarray IgG immunoassay for the diagnosis of toxoplasmosis and rubella

BACKGROUND

During pregnancy, toxoplasmosis and rubella can cause serious damage to the mother and the foetus through vertical transmission. Early diagnosis enables implementation of health measures aimed at preventing vertical transmission and minimising damage caused by these diseases.

OBJECTIVE

Here, we report the development of a multiplex assay for simultaneous detection of IgG antibodies produced during toxoplasmosis and rubella infection.

METHODS

This assay is based on xMap technology. Initially, by singleplex assays, we evaluated the following antigens: one Toxoplasma gondii lysate; two antigenic extracts of T. gondii (TOX8131 and TOX8122); fragments of T. gondii antigens [SAG-1 (amino acids 45-198), GRA-7 (24-100), GRA-1 (57-149), ROP-4, and MIC-3 (234-306)]; two chimeric antigens composed of fragments of SAG-1, GRA-7, and P35 (CTOX and CTOXH); and fragments of Rubella virus antigens [E-1 (157-176, 213-239, 374-390), E-2 (31-105), and C (1-123)].

FINDINGS

A multiplex assay to simultaneously diagnose toxoplasmosis and rubella was designed with the best-performing antigens in singleplex and multiplex assays, which included CTOXH, T. gondii lysate, TOX8131, E-1, and E-2. The multiplex assay showed 100% sensitivity and specificity for anti-T. gondii IgG detection and 95.6% sensitivity and 100% specificity for anti-R. virus IgG detection.

MAIN CONCLUSIONS

We found that, despite the difficulties related to developing multiplex systems, different types of antigens (extracts and recombinant proteins) can be used to develop high-performance diagnostic tests. The assay developed is suitable to screen for prior T. gondii and R. virus infections, because it is a rapid, high-throughput, low-cost alternative to the current standard diagnostic tools, which require multiple individual tests.

Study of rubella candidate vaccine based on a structurally modified plant virus

A novel rubella candidate vaccine based on a structurally modified plant virus - spherical particles (SPs) - was developed. SPs generated by the thermal remodelling of the tobacco mosaic virus are promising platforms for the development of vaccines. SPs combine unique properties: biosafety, stability, high immunogenicity and the effective adsorption of antigens. We assembled in vitro and characterised complexes (candidate vaccine) based on SPs and the rubella virus recombinant antigen. The candidate vaccine induced a strong humoral immune response against rubella. The IgG isotypes ratio indicated the predominance of IgG1 which plays a key role in immunity to natural rubella infection. The immune response was generally directed against the rubella antigen within the complexes. We suggest that SPs can act as a platform (depot) for the rubella antigen, enhancing specific immune response. Our results demonstrate that SPs-antigen complexes can be an effective and safe candidate vaccine against rubella.

The key role of rubella virus glycoproteins in the formation of immune response, and perspectives on their use in the development of new recombinant vaccines

Rubella is a highly contagious viral disease which is mostly threatens to women of reproductive age. Existent live attenuated vaccines are effective enough, but have some drawbacks and are unusable for a certain group of people, including pregnant women and people with AIDS and other immunodeficiency. Thereby the development of alternative non-replicating, recombinant vaccines undoubtedly is needed. This review discusses the protein E1 and E2 role in formation of immune response and perspectives in development of new generation recombinant vaccines using them.

Rubella and pregnancy: diagnosis, management and outcomes

Rubella is a mild viral disease that typically occurs in childhood. Rubella infection during pregnancy causes congenital rubella syndrome, including the classic triad of cataracts, cardiac abnormalities and sensorineural deafness. Highly effective vaccines have been developed since 1969, and vaccination campaigns have been established in many countries. Although there has been progress, the prevention and diagnosis of rubella remain problematic. This article reviews the implications and management of rubella during pregnancy.

Characterization of rubella virus genotypes among pregnant women in northern Vietnam, 2011-2013

Rubella virus (RV) infection is an unresolved clinical complication that affects children in developing countries including Vietnam. RV infection during the first trimester of pregnancy causes severe birth defects known as congenital rubella syndrome. This study reports on the genomic characterization of RV strains circulating in northern Vietnam during 2011-2013. RV-IgM positive amniotic fluid specimens were collected from 38 women from northern Vietnam who presented with clinical rubella at the National Hospital of Obstetrics and Gynecology in Hanoi, Vietnam. The RV genes were determined by nested PCR with primers amplifying the 739-nucleotide coding region of the E1 gene. The sequences from the amplified DNA fragments were phylogenetically analyzed and compared to reference RV strains. Seventeen out of 38 samples are positive for RV detecting. All new RV isolates are clustered to genotype 2B. Eighteen amino acid mutations were found in the T and B cell epitopes. These results suggest that genotype 2B RV strains frequently circulate in northern Vietnam. These data describe the RV genotype in Vietnam with the aim of improving maternal and child health in this country.

Genomic analysis of the Chinese genotype 1F rubella virus that disappeared after 2002 in China

Genotype 1F was likely localized geographically to China as it has not been reported elsewhere. In this study, whole genome sequences of two rubella 1F virus isolates were completed. Both viruses contained 9,761 nt with a single nucleotide deletion in the intergenic region, compared to the NCBI rubella reference sequence (NC 001545). No evidence of recombination was found between 1F and other rubella viruses. The genetic distance between 1F viruses and 10 other rubella virus genotypes (1a, 1B, 1C, 1D, 1E, 1G, 1J 2A, 2B, and 2C) ranged from 3.9% to 8.6% by pairwise comparison. A region known to be hypervariable in other rubella genotypes was also the most variable region in the 1F genomes. Comparisons to all available rubella virus sequences from GenBank identified 22 nucleotide variations exclusively in 1F viruses. Among these unique variations, C9306U is located within the recommended molecular window for rubella virus genotyping assignment, could be useful to confirm 1F viruses. Using the Bayesian Markov Chain Monte Carlo (MCMC) method, the time of the most recent common ancestor for the genotype 1F was estimated between 1976 and 1995. Recent rubella molecular surveillance suggests that this indigenous strain may have circulated for less than three decades, as it has not been detected since 2002.

Chimeric derivatives of hepatitis B virus core particles carrying major epitopes of the rubella virus E1 glycoprotein

Three variants of the major rubella virus (RV) E1 protein virus-neutralizing epitope from position 214 to 285 were exposed on the hepatitis B virus (HBV) C-terminally truncated core (HBcΔ) in a virus-like particle (VLP) vector and were produced in Escherichia coli. All three chimeras demonstrated VLPs in bacterial cell lysates, but only HBcΔ-E1(245-285) demonstrated the correct VLP structure after purification. The other chimeras, HBcΔ-E1(214-285) and HBcΔ-E1(214-240), appeared after purification as non-VLP aggregates of 100 to 900 nm in diameter according to dynamic light scattering data. All three variants possessed the intrinsic antigenic activity of RV E1, since they were recognized by natural human anti-RV E1 antibodies and induced an anti-RV E1 response in mice. HBcΔ-E1(214-240) and HBcΔ-E1(245-285) can be regarded as prototypes for a putative RV vaccine because they were able to induce antibodies recognizing natural RV E1 protein in RV diagnostic kits.

Rubella epidemic in Vietnam: characteristic of rubella virus genes from pregnant women and their fetuses/newborns with congenital rubella syndrome

BACKGROUND

Rubella remains poorly controlled in Southeast Asia, including Vietnam.

OBJECTIVES

The aim of this study was to characterize rubella virus spread in Vietnam during 2011-2012.

STUDY DESIGN

Amniotic fluid, throat swab and placenta samples were collected from 130 patients (110 cases from pregnant women with suspected rubella and 20 cases from fetuses/newborns). Viral RNA was obtained directly from clinical specimens, amplified by PCR, and then the E1 gene containing 739 nucleotides recommended by the WHO to identify the viral genotypes was sequenced.

RESULTS

By screening with real-time PCR, viral RNA was detectable in amniotic fluids from 103 out of 110 (93.6%) pregnant women with suspected rubella and in the throat swabs from all of 20 (100%) fetuses/newborns. In addition, viral RNA was also detected in the placenta from all cases of fetuses/newborns. All of 20 fetuses/newborns presented with congenital cataract. Twenty-four strains with the E1 gene were obtained by PCR. Using phylogenetic analysis with rubella reference sequences, all of the strains were found to be genotype 2B. Interestingly, 94% (30/32) of Vietnamese strains, including 9 strains from the database, formed an independent cluster within the genotype 2B suggesting that indigenous viruses are prevalent in this region.

CONCLUSIONS

Rubella virus identified in Vietnam belonged to the genotype 2B. Importantly, the infection rate of rubella virus in fetuses/newborns was 100% and all of them had congenital cataract. Our results indicate an establishment of rubella prevention in this area is an urgent task in order to improve maternal and child health.

Phylogenetic analysis of rubella viruses in Vietnam during 2009-2010

Rubella virus (RV) usually causes a mild disease. However, infection during the first trimester of pregnancy often leads to severe birth defects known as congenital rubella syndrome (CRS). Although wild-type RVs exist and circulate worldwide, their genotypes remain unknown in many countries. The aim of this study was to identify the molecular characteristics of RVs found in Vietnam during the years 2009-2010 and to provide the first data concerning RV genotypes in this country. Throat swab samples were collected between 2009 and 2010 from four CRS cases and nine rubella infection cases visiting one Children's Hospital and one outpatient clinic in Ho Chi Minh City. The 739-nucleotide coding region of the RV E1 gene recommended by the World Health Organization was amplified by reverse transcriptase PCR, and the resulting DNA fragments were then sequenced. Sequences were assigned to genotypes by phylogenetic analysis with RV reference strains. RV RNA was detected in 11 clinical specimens. Phylogenetic analysis of the sequences showed that all 11 strains belonged to 2B genotype. Several variations in amino acids were found, among which five changes were involved in the B and T cell epitopes. These data indicate that viruses of genotype 2B were circulating in Vietnam. The increasing information about RV genotype in Vietnam should aid in the control of rubella infection and CRS in this country.

Quantitative and qualitative assay of rubella IgA antibody in breast milk

Breast milk contains immunological factors, such as IgA antibody, which help to prevent infectious diseases. A total of 197 paired samples of colostrum and breast milk was collected from postpartum mothers in Gunma City, Japan, and examined for anti-rubella IgA antibody by enzyme-linked immunosorbent assay (ELISA) and Western blotting (WB). The anti-rubella virus IgA ranged from 0.5 to 78.5 U/ml with a mean of 6.05 U/ml and a median of 3.6 U/ml in colostrum, and from 0.5 to 32.7 U/ml with a mean of 2.74 U/ml and a median of 2 U/ml in milk. The differences between the means of titers of total IgA and anti-rubella virus IgA in colostrum and in milk were significant statistically. The levels of anti-rubella virus IgA in both colostrum and breast milk correlated positively with the anti-rubella virus hemagglutination inhibition (HI) titers in the sera of mother, indicating that the levels of these different classes of antibodies correlated. Based on WB, anti-rubella virus IgA in both colostrum and breast milk reacted with the rubella viral protein E1 and C, but not with the E2 protein.

Phylogenetic analysis of rubella virus strains from an outbreak in Madrid, Spain, from 2004 to 2005

An outbreak of rubella affected 460 individuals in 2004 and 2005 in the community of Madrid, Spain. Most of the patients were nonvaccinated Latin American immigrants or Spanish males. This study presents the first data on rubella virus genotypes in Spain. Forty selected clinical samples (2 urine, 5 serum, 3 blood, 2 saliva, and 28 pharyngeal exudate samples) from 40 cases were collected. The 739-nucleotide sequence recommended by the World Health Organization obtained from viral RNA in these samples was analyzed by using the MEGA v4.0 software. Seventeen isolates were obtained from 40 clinical samples from the outbreak, including two isolated from congenital rubella syndrome cases. Only viral RNA of genotype 1j was detected in both isolates and clinical specimens. Two variations in amino acids, G253C and T394S, which are involved in neutralization epitopes arose during the outbreak, but apparently there was no positive selection of either of them. The origin of the outbreak remains unknown because of poor virologic surveillance in Latin America and the African countries neighboring Spain. On the other hand, this is the first report of this genotype in Europe. The few published sequences of genotype 1j indicate that it comes from Japan and the Philippines, but there are no epidemiological data supporting this as the origin of the Madrid outbreak.

Expression and characterization of rubella virus glycoprotein E1 in yeast cells

OBJECTIVES

To express E1 glycoprotein of rubella virus (RuV) strain JR23 in yeast and develop a diagnostic assay using expressed E1 protein as coating antigen in comparison with other diagnostic assays.

METHODS

cDNA of E1 open reading frame of RuV was PCR amplified using plasmid pMD18-T-E1 as template and cloned into plasmid pBluscriptII SK+. After being confirmed by PCR, restriction endonuclease digestion and sequencing, pBluscriptII SK(+)-E1 plasmid DNA was digested by restriction endonuclease EcoR I and Xba I, and a fragment of 1.5 kb was isolated and cloned into a yeast expression pGAPZ(alpha)A, resulting in pGAPZ(alpha)A-E1. After confirmation by sequencing, pGAPZ(alpha)A- E1 was transformed into yeast GS115 cells with LiCl method. E1 protein expression in GS115 was analyzed by SDS-PAGE and Western blot. An indirect ELISA was developed using the recombinant E1 protein as coating antigen for detecting RuV E1 antibodies in 90 serum samples. To compare the specificity, sensitivity and reproducibility of the assay with other methods, the same serum samples were also assayed by RuV culture medium as coating antigen (Jingmei kit and German RECI kit). Statistical analyses were performed to compare the differences among these methods and to determine which coating antigen source, the recombinant E1 protein or RuV-infected culture medium, is more suitable for the assay.

RESULTS

A fragment of 1.5 kb, corresponding to the full open reading frame of E1, was PCR amplified and cloned in yeast expression vector. The clone was confirmed by restriction digestion, PCR and sequencing. E1 as a secretive protein was successfully expressed by GS115. Its molecular weight was about 58 kDa. SDS-PAGE showed that the recombinant protein was expressed efficiently and constantly in Pichia pastoris GS115 cells. The expression level reached a peak 48 h after culturing and stabilized thereafter. E1 protein was detected in both supernatant and cells. Western blot showed that the secretive E1 protein in the supernatants could react with both the anti-RuV-positive serum and a monoclonal antibody against E1. However, E1 protein derived from cells could only react with the anti-RuV-positive serum, polyclonal antibody, but not the monoclonal antibody. Compared with the German RECI kit, the sensitivity, specificity, and accordance rate of the assay using recombinant E1 protein as coating antigen were 67.11, 71.43 and 67.78%, respectively, while those of the assay using RuV-infected culture medium as coating antigen were 50, 78.57 and 54.44%, respectively. Compared with the German RECI kit, the sensitivity, specificity, and accordance rate of the ELISA assay using the Jingmei kit were 84.71, 71.43 and 82.22%, respectively. The data indicated that recombinant E1 protein derived from the yeast expression system can serve as a better source than RuV-infected cell medium as coating antigen for detecting antibodies against RuV in the indirect ELISA assay. Statistical analysis of the data generated from two independent experiments using recombinant E1 protein as coating antigen indicated that the assay was very consistent with no statistically significant difference between the two experiments (p > 0.05). 76 out of 90 serum samples were detected positive using the German RECI kit, while 68, 55 and 41 samples were positive using the Jingmei kit, recombinant E1 and RuV-infected cell medium, respectively. Statistical analyses indicated that the positive rates were significantly different among all four assays (p < 0.05) except for one pair (German RECI kit and the Jingmei kit: p > 0.05). Comparing the positive rates obtained from the assay using recombinant E1 and that using RuV-infected cell medium, it seems that the recombinant E1 protein is a better source than RuV culture medium as coating antigen in the indirect ELISA assay for detection of RuV antibody.

CONCLUSIONS

The recombinant yeast expression vector of RuV E1 glycoprotein was constructed successfully. The E1 protein as a secretive protein was successfully expressed by GS115 and maintained its antigenicity very well. As coating antigen, the recombinant E1 protein served a better source than RuV culture medium in the indirect ELISA method for the detection of RuV antibody.

Rubella

Maternal rubella is now rare in many developed countries that have rubella vaccination programmes. However, in many developing countries congenital rubella syndrome (CRS) remains a major cause of developmental anomalies, particularly blindness and deafness. WHO have provided recommendations for prevention of CRS, and, encouragingly, the number of countries introducing rubella vaccination programmes has risen. However, declining uptake rates due to concerns about the measles-mumps-rubella vaccine in the UK, and increasing numbers of cases in some European countries coupled with poor uptake rates might jeopardise this progress. Surveillance of postnatally and congenitally acquired infection is an essential component of CRS prevention since rubella is difficult to diagnose on clinical grounds alone. Laboratory differentiation of rubella from other rash-causing infections, such as measles, parvovirus B19, human herpesvirus 6, and enteroviruses in developed countries, and various endemic arboviruses is essential. Reverse transcriptase PCR and sequencing for diagnosis and molecular epidemiological investigation and detection of rubella-specific IgG and IgM salivary antibody responses in oral fluid are now available.

A synthetic peptide ELISA for the screening of rubella virus neutralizing antibodies in order to ascertain immunity

One hundred and fifty-one human sera from patients exposed to rubella virus (RV) and shown to be negative for IgM antibodies were tested for total RV-IgG, hemagglutination inhibition (HAI) and for virus neutralizing (VN) antibodies using a peptide enzyme-linked immunosorbent assay (ELISA) based on BCH-178, a peptide representing one of several known neutralizing epitopes on RV hemagglutinin (E1). The data showed that, among 39 and 51 sera with HAI and RV-IgG titres of 1/128 and >150 IU/ml, respectively, neutralizing antibody readings using the BCH-178 ELISA were above cut-off values. However, 13% of HAI positive sera (titre > or =1/16) and 16% of RV-IgG ELISA positive sera (> or =20 IU/ml) were below the cut-off value of the BCH-178 ELISA. This may explain why several cases of congenital rubella syndrome (CRS) have been observed in spite of positive titres. We suggest that a diagnosis of sufficient immunity against RV infection or reinfection may be safer if an additional test detecting antibodies against VN RV epitopes is positive as well.

Rubella virus replication and links to teratogenicity

Rubella virus (RV) is the causative agent of the disease known more popularly as German measles. Rubella is predominantly a childhood disease and is endemic throughout the world. Natural infections of rubella occur only in humans and are generally mild. Complications of rubella infection, most commonly polyarthralgia in adult women, do exist; occasionally more serious sequelae occur. However, the primary public health concern of RV infection is its teratogenicity. RV infection of women during the first trimester of pregnancy can induce a spectrum of congenital defects in the newborn, known as congenital rubella syndrome (CRS). The development of vaccines and implementation of vaccination strategies have substantially reduced the incidence of disease and in turn of CRS in developed countries. The pathway whereby RV infection leads to teratogenesis has not been elucidated, but the cytopathology in infected fetal tissues suggests necrosis and/or apoptosis as well as inhibition of cell division of critical precursor cells involved in organogenesis. In cell culture, a number of unusual features of RV replication have been observed, including mitochondrial abnormalities, and disruption of the cytoskeleton; these manifestations are most probably linked and play some role in RV teratogenesis. Further understanding of the mechanism of RV teratogenesis will be brought about by the investigation of RV replication and virus-host interactions.

Rubella virus replication and links to teratogenicity

Rubella virus (RV) is the causative agent of the disease known more popularly as German measles. Rubella is predominantly a childhood disease and is endemic throughout the world. Natural infections of rubella occur only in humans and are generally mild. Complications of rubella infection, most commonly polyarthralgia in adult women, do exist; occasionally more serious sequelae occur. However, the primary public health concern of RV infection is its teratogenicity. RV infection of women during the first trimester of pregnancy can induce a spectrum of congenital defects in the newborn, known as congenital rubella syndrome (CRS). The development of vaccines and implementation of vaccination strategies have substantially reduced the incidence of disease and in turn of CRS in developed countries. The pathway whereby RV infection leads to teratogenesis has not been elucidated, but the cytopathology in infected fetal tissues suggests necrosis and/or apoptosis as well as inhibition of cell division of critical precursor cells involved in organogenesis. In cell culture, a number of unusual features of RV replication have been observed, including mitochondrial abnormalities, and disruption of the cytoskeleton; these manifestations are most probably linked and play some role in RV teratogenesis. Further understanding of the mechanism of RV teratogenesis will be brought about by the investigation of RV replication and virus-host interactions.

Effects of mutations in the rubella virus E1 glycoprotein on E1-E2 interaction and membrane fusion activity

Rubella virus (RV) virions contain two glycosylated membrane proteins, E1 and E2, that exist as a heterodimer and form the viral spike complexes on the virion surface. Formation of an E1-E2 heterodimer is required for transport of E1 out of the endoplasmic reticulum lumen to the Golgi apparatus and plasma membrane. To investigate the nature of the E1-E2 interaction, we have introduced mutations in the internal hydrophobic region (residues 81 to 109) of E1. Substitution of serine at Cys82 (mutant C82S) or deletion of this hydrophobic domain (mutant dt) of E1 resulted in a disruption of the E1 conformation that ultimately affected E1-E2 heterodimer formation and cell surface expression of both E1 and E2. Substitution of either aspartic acid at Gly93 (G93D) or glycine at Pro104 (P104G) was found to impair neither E1-E2 heterodimer formation nor the transport of E1 and E2 to the cell surface. Fusion of RV-infected cells is induced by a brief treatment at a pH below 6. 0. To test whether this internal hydrophobic domain is involved in the membrane fusion activity of RV, transformed BHK cell lines expressing either wild-type or mutant spike proteins were exposed to an acidic pH and polykaryon formation was measured. No fusion activity was observed in the C82S, dt, and G93D mutants; however, the wild type and the P104G mutant exhibited fusogenic activities, with greater than 60% and 20 to 40% of the cells being fused, respectively, at pH 4.8. These results suggest that it is likely that the region of E1 between amino acids 81 and 109 is involved in the membrane fusion activity of RV and that it may be important for the interaction of that protein with E2 to form the E1-E2 heterodimer.

Characterization of an overlapping CD8+ and CD4+ T-cell epitope on rubella capsid protein

A synthetic peptide corresponding to rubella virus capsid protein residues 263 to 275 which contains an epitope recognized by a cloned CD4+ cytotoxic T-lymphocyte (CTL) line was used to induce CD8+ T-cell lines specific to this peptide. A peptide-specific CD8+ CTL clone was derived and characterized. This peptide-specific CD8+ CTL clone exhibited cytotoxicity against target cells infected by a vaccinia recombinant virus expressing rubella virus capsid protein, but not by target cells infected by vaccinia recombinant virus expressing rubella virus E1 or E2 envelope proteins. Analysis of HLA class I restriction of the CD8+ CTL clone revealed that A11 and A3 were restrictive elements. Fine mapping with truncated and overlapping peptide analogs revealed a nonamer sequence, C(264-272), as the T-cell epitope eliciting stronger cytotoxicity. Two anchor residues for binding to HLA A11 and A3 were identified at position 2 (isoleucine) and at position 9 (histidine) or at position 8 (arginine) of the epitope sequence. The identification of overlapping CD4+ and CD8+ T-cell epitopes within the capsid protein sequence C(263-275) implicates a strategy for using such epitopes in a candidate peptide-based rubella vaccine.

Rubella reimmunization: comparative analysis of the immunoglobulin G response to rubella virus vaccine in previously seronegative and seropositive individuals

Rubella virus (RV)-specific immunoglobulin G (IgG) antibodies were studied in military recruits undergoing unselected immunization with live attenuated measles, mumps, and rubella virus (MMR) vaccine. Three different whole-RV enzyme immunoassays (EIAs) and an epitope-specific EIA with a synthetic peptide (BCH-178c) representing a heutralization domain on the RV E1 envelope protein were used. Before vaccination, 84.2, 87.7, and 84.5% of the subjects tested (n = 399) were found to be seropositive (> 10 IU/ml or assay equivalent) by the three whole-RV EIAs, respectively, while only 82.5% were seropositive by the BCH-178c EIA. Although prevaccination seropositivity rates were similar for the whole-RV EIAs (sensitivity, 94 to 100%), many sera considered seropositive by the whole-RV EIAs had E1 peptide EIA antibody levels of < 10 IU/ml (sensitivity, 77.4 to 80.7%). One month after vaccination, 97.8, 97.2, and 93.5% of the subjects who were followed (n = 356) were seropositive by the three whole-RV EIAs, respectively, while 89% had BCH-178c peptide-specific IgG titers of > 10 IU/ml. After vaccination, depending on the assay used, up to 20.6% of initially seropositive individuals exhibited a greater than fourfold increase in RV-specific IgG, while up to 47.3% showed a greater than twofold increase. Increased antibody titers after vaccination (seroboosting) were most frequently associated with low levels of BCH-178c peptide-specific IgG before vaccination. RV protein-specific IgG was also studied by immunoblot assays in a subset (n = 56) of individuals receiving the MMR vaccine. Of these, 89.4 and 91.1% exhibited RV protein (E1, E2, and C protein)-specific IgG before and after vaccination, respectively. Seroboosting (two- to fourfold increase in EIA titers of individuals seropositive by the whole-RV EIA before vaccination) was usually accompanied by a shift in the IgG immunoblot pattern from a single (E1) to multiple (E1-E1, E1-C, or E1-E2-C) specificities, suggesting exposure of new epitopes as a result of viral replication.

Cell surface expression of a functional rubella virus E1 glycoprotein by addition of a GPI anchor

Rubella virus (RV) envelope glycoproteins E1 and E2 are targeted to the Golgi as heterodimers. While E2 contains a transmembrane Golgi retention signal, E1 is arrested in a pre-Golgi compartment in the absence of E2, and appears to require heterodimerization in order to reach the Golgi. Various forms of E1 with deletions in the ectodomain or lacking the cytoplasmic (CT) and transmembrane (TM) domains, as well as the 29 C-terminal amino acid residues of the ectodomain were also retained intracellularly. We therefore investigated the possibility of targetting E1 to the plasma membrane by addition of a glycosylphosphatidylinositol (GPI) anchor. We found that E1GPI was transported to the cell surface where it retained the hemadsorption activity characteristic of the wild-type E1/E2 heterodimer. Furthermore, coexpression of a mammalian GPI-specific phospholipase D (GPI-PLD) resulted in the release of E1GPI and in constitutive expression of a soluble form of E1. This study thus demonstrates that the GPI anchor has a dominant effect over the E1 pre-Golgi retention signal and that E1 is sufficient for hemadsorption.

Evaluation of rubella virus E2 and C proteins in protection against rubella virus in a mouse model

An animal model is described that can provide further information for evaluating novel vaccines against rubella virus (RV). A group of mice was immunized with the lysate of insect cells infected by a recombinant baculovirus expressing E2 and C proteins of RV. Another group of mice was immunized with the RA27/3 rubella vaccine. After 2 weeks, both groups of mice were challenged intramuscularly with live RV and the blood was drawn after 8, 24, 48 and 72 h. The presence of rubella challenge virus in an unnatural host, such as the mouse, was monitored by RT-PCR. The mice immunized with the RA27/3 rubella vaccine were the only ones able to inhibit the challenge virus replication, E2 and C proteins, which alone are not sufficient to protect animals against RV, served as a negative control for a protective vaccine against RV that expresses E1 protein of RV.

Generation of rubella virus-neutralising antibodies by vaccination with synthetic peptides

Four short peptides from rubella virus proteins E1 and E2, predicted to contain B cell epitopes, were used to vaccinate BALB/c mice. Sera from peptide-vaccinated animals reacted with viral antigens in ELISA and three of the four induced virus-neutralising antibody (nAb) responses. Peptide PY4, in contrast to the others, induced IgG2a responses upon vaccination and stimulated spleen cells in vitro produced IFN gamma in the absence of IL-5. It was reasoned that vaccination with PY4 caused Th1 subset activation, the appropriate type of response for anti-viral immunity and hence the efficient neutralising antibody response. Presentation of peptide for vaccination proved to be as important as the sequence. Similar profiles of IgG1 and IgG2a were detected in the sera of mice vaccinated with PY4 in Freund's complete adjuvant or alum; however nAb responses were not found when alum was used.

Expression and characterization of a soluble rubella virus E1 envelope protein

Individual specific antigenic rubella virus (RV) structural proteins are required for accurate serological diagnosis of acute and congenital rubella infections as well as rubella immune status. The RV envelope glycoprotein E1 is the major target antigen and plays an important role in viral-specific immune responses. The native virion is difficult to produce in large quantities and the protein subunits are also difficult to isolate without loss of antigenicity. The production of a soluble RV E1 (designated E1 delta Tm) using the baculovirus-insect cell expression system is described. In contrast to wild-type RV E1, the genetically engineered E1 delta Tm protein lacks a transmembrane anchor. It behaved as a secretory protein and was secreted abundantly from insect cells. Pulse-chase studies were used to examine the synthesis, glycosylation, and secretion of E1 delta Tm by the insect cells. The secreted E1 delta Tm protein was purified from serum-free medium by one-step immunochromatography. The purified E1 delta Tm protein retained full antigenicity and may be a convenient source of E1 protein for use in diagnostic assay and rubella vaccine development.

Expression and characterization of virus-like particles containing rubella virus structural proteins

Rubella virus (RV) virions contain two envelope glycoproteins (E1 and E2) and a capsid protein (C). Noninfectious RV-like particles (VLPs) containing three structural proteins were expressed in a BHK cell line (BHK-24S) by using an inducible promoter. These VLPs were found to resemble RV virons in terms of their size, their morphology, and some biological activities. In immunoblotting studies, VLPs were found to bind similarly to native RV virions with 10 of a panel of 12 RV-specific murine monoclonal antibodies. Immunization of mice with VLPs induced specific antibody responses against RV structural proteins as well as virus-neutralizing and hemagglutination-inhibiting antibodies. After immunization of mice with VLPs, in vitro challenge of isolated lymphocytes with inactivated RV and individual RV structural proteins stimulated proliferation. Our data suggest the possibility of using VLPs as immunogens for serodiagnostic assays and RV vaccines.

Recombinant rubella E1 fusion proteins for antibody screening and diagnosis

BACKGROUND

Until rubella is eradicated there will be a continuing need for rubella antibody surveillance. Antigen production using recombinant DNA technology may be a viable alternative to traditional techniques of producing antigens for enzyme immunoassays (EIAs).

OBJECTIVES

To investigate the potential of bacterial fusion proteins containing rubella E1 protein sequences for use in EIAs to detect rubella antibodies.

STUDY DESIGN

Purified bacterial fusion proteins containing rubella E1 sequences to be used as antigens in EIAs and compared to 'traditional' assays using virus derived antigens for rubella antibody screening.

RESULTS

cDNA clones coding for the complete rubella E1 protein sequence and subfragments of E1 were modified for expression as carboxy terminal fusions with either beta-galactosidase or glutathione-S-transferase. beta-galactosidase fusions with the complete E1 coding sequence or amino acids 201 to 307, which contain known epitopes, resulted in the production of predominantly insoluble fusion proteins unsuitable for use in EIA. Nine glutathione-S-transferase-E1 fusion proteins were produced with individual fusion proteins exhibiting varying properties with regard to the levels of protein produced, apparent stability, solubility and the potential for affinity purification using glutathione agarose. Reduction of the E1 component to only 44 amino acids containing three B-cell epitopes (Terry et al., 1988) produced an abundant soluble GST-E1 fusion protein (3.5 mug/ml), which could be affinity purified using glutathione agarose. This fusion protein has been successfully used in EIA to detect rubella antibodies.

CONCLUSIONS

We have shown that GST-E1 fusions have potential as antigens in tests for rubella antibodies.

Analysis of overlapping T- and B-cell antigenic sites on rubella virus E1 envelope protein. Influence of HLA-DR4 polymorphism on T-cell clonal recognition

A CTL antigenic site located between residues 273 and 291 of the E1 envelope protein of RV was identified by 51Cr-release assays employing SPs. Two E1-specific CTL clones were examined for immune recognition of RV wild-type and attenuated vaccine strains and recombinant E1 protein. The exact sequence (273-284) recognized by both clones was delineated by using truncated and overlapping SPs covering these residues. The defined T-cell site overlapped almost completely with a virus neutralizing antibody-binding site previously identified with mouse monoclonal and human antibodies. A series of single aa-substituted SP analogues of E1(273-284) was used to define residues critical for T-cell recognition. Using EBV-BL displaying different HLA-DR haplotypes and -DR4 subtypes as targets to determine MHC class II restriction elements, immune recognition by both T-cell clones was shown to be associated with HLA-DR4. Three HLA-DR4 subtypes (DR4Dw13A, DR4Dw13B, and DR4KT2) sharing a common residue, glutamic acid at position 74 in their beta 1 chains, were able to present SP E1(273-284) to the T-cell clones.

Molecular biology of rubella virus

This chapter summarizes the present medical significance of rubella virus. Rubella virus infection is systemic in nature and the accompanying symptoms are generally benign, the most pronounced being a mild rash of short duration. The most common complication of rubella virus infection is transient joint involvement such as polyarthralgia and arthritis. The primary health impact of rubella virus is that it is a teratogenic agent. The vaccination strategy is aimed at elimination of rubella and includes both universal vaccination of infants at 15 months of age with the trivalent measles, mumps, rubella (MMR) vaccine and specific targeting with the rubella vaccine of seronegative women planning pregnancy and seronegative adults who could come in contact with women of childbearing age, although it is recommended that any individual over the age of 12 months without evidence of natural infection or vaccination be vaccinated. Medically, the current challenge posed by rubella virus is to achieve complete vaccination coverage to prevent resurgences.

Rubella virus-specific cytotoxic T-lymphocyte responses: identification of the capsid as a target of major histocompatibility complex class I-restricted lysis and definition of two epitopes

The role of major histocompatibility complex (MHC) class I-restricted CD8+ cytotoxic T lymphocytes in immunity to rubella virus (RV) infection is unknown. Lymphocytes of RV-immune individuals were prestimulated on an RV-infected MHC class I-matched (or partially matched) fibroblast monolayer which generated CD8+ lymphoblasts capable of lysing RV-infected fibroblast targets in a class I-restricted manner. Using an infectious Sindbis virus (SV) vector which expressed the RV capsid protein (SV/RubC), lymphocytes from 17 of 22 RV-immune individuals prestimulated on RV-infected fibroblast monolayers lysed SV/RubC-infected fibroblast targets. A sequence within the amino terminus of the capsid protein that was previously shown to contain immunodominant class II-restricted T-cell epitopes was evaluated for class I-restricted epitopes. Fibroblast targets pulsed with synthetic peptides representing subsequences within C1 to C29 (subscripts indicate amino acid positions) were lysed effectively when the targets and effectors matched at multiple class I alleles. By limiting the number of matching class I alleles, an A2-restricted epitope was identified within C9 to C22 and an epitope that could be presented by multiple class I molecules was identified within C11 to C29. A sequence such as C1 to C29 which contains both MHC class I- and MHC class II-restricted epitopes recognized by a heterologous human population may serve as a component of an effective synthetic vaccine.

Identification of immunoreactive regions of rubella virus E1 and E2 envelope proteins by using synthetic peptides

Relatively large (16-33 aa) synthetic peptides (SPs) representing defined sequences of rubella virus (RV) E1 and E2 envelope proteins were used in lymphocyte stimulation and enzyme immunoassays to map immunoreactive regions recognized by peripheral blood mononuclear cells (PBMNC) and serum antibodies from healthy RV-seropositive, RV-seronegative, and RV-vaccinated adults. Five distinct immunoreactive regions were identified in RV E1 protein, spanning residues (11-39), (154-179), (199-239), (226-277), and (389-412), which stimulated cellular responses in 29-83% of the subjects tested. Two SPs, E1(213-239) and E1(258-277) containing previously-identified virus neutralizing antibody domains, reacted with serum antibodies and also stimulated lymphoproliferation suggesting that these E1 sequences contain linked or overlapping B-and T-cell antigenic sites. The frequency and magnitude of cellular responses to E2 SPs were somewhat lower. SPs encompassing E2 residues (50-72), (140-199), and (244-263) stimulated lymphocyte responses in 28-64% of the subjects tested, while to a lesser degree, SPs within residues (1-36) were also stimulatory. E2 SPs within the regions (1-36), (151-170), and (244-263) also showed low levels of antibody reactivity with sera from RV-seropositive subjects. E2(244-263) which induced the highest level of response among the E2 SPs tested, was of interest due to previous reports of sequence homology of this RV region with human myelin and its potential immunopathogenic role in demyelinating autoimmune diseases. Identification of these potentially immunodominant regions of RV envelope proteins is an important first step in the rational design of new RV vaccines.

Human T- and B-cell epitopes of E1 glycoprotein of rubella virus

The identification of T- and B-cell sites recognized frequently by human populations could provide the basis for selecting the candidate T- and B-cell epitopes for the development of an effective synthetic vaccine against rubella. Rubella virus E1 glycoprotein has been shown to be the predominant antigen to which the majority of human populations develop lymphocyte proliferative and antibody responses. To define the T- and B-cell epitopes of E1 glycoprotein of rubella virus, 23 overlapping synthetic peptides corresponding to more than 90% of the amino acid sequence of E1 were synthesized and tested for their capacities to induce proliferative and antibody responses of 10 seropositive individuals. The most frequently recognized T-cell epitopes were EP19 (residues 324-343), with 7 of 10 responders, and both EP12 (residues 207-226) and EP17 (residues 289-308), with 6 of 10 responders, respectively. Two immunodominant linear B-cell epitopes were mapped to residues 157 to 176 (EP9, 8/10) and 374 to 390 (EP22, 6/10) by using peptide-specific enzyme linked immunosorbent assay.

An antibody- and synthetic peptide-defined rubella virus E1 glycoprotein neutralization domain

We previously described a monoclonal antibody (MAb) library generated by infecting BALB/c mice with rubella virus (RV) and selected by an enzyme-linked immunosorbent assay (ELISA) using purified virion targets. Plasmid pARV02-01, which expresses the fusion protein RecA1-35-GIGDLGSP-E1(202)-E1(283)-GDP-LacZ9-1015 in Escherichia coli, was shown to be a ligand for MAbs E1-18 and E1-20 (J. S. Wolinsky, M. McCarthy, O. Allen-Cannady, W. T. Moore, R. Jin, S. N. Cao, A. Lovett, and D. Simmons, J. Virol. 65:3986-3994, 1991). Both of these MAbs neutralize RV infectivity. A series of five overlapping synthetic peptides was made to further explore the requirements of this MAb binding domain. One of these peptides (SP15; E1(208) to E1(239)) proved an effective ligand for both MAbs in the ELISA. Stepwise synthesis of SP15 defined the minimal amino-terminal requirement for binding MAb E1-18 as E1(221) and that of MAb E1-20 as E1(223); the minimal carboxyl-terminal requirement is uncertain but does not exceed E1(239). Immunization of mice and rabbits with SP15 induced polyvalent antibody reactive with SP15, with other overlapped and related but not unrelated synthetic peptides, and with RV. The rabbit anti-SP15 antibody showed neutralization activity to RV similar to that of MAbs E1-18 and E1-20 but lacked hemagglutination inhibition activity. These data define a neutralization domain on E1 and suggest that the RV epitopes conserved by SP15 may be critical for protective host humoral immune responses.