Antibody response to the rubella virus structural proteins in infants with the congenital rubella syndrome

Prevalence of Rubella Antibodies Among Children in the Democratic Republic of the Congo

BACKGROUND

While generally mild in children, rubella infection in early pregnancy can lead to miscarriage, fetal death or congenital rubella syndrome. Rubella vaccination is not yet available as a part of routine immunization in the Democratic Republic of the Congo (DRC), and the burden of infection is unknown.

METHODS

In collaboration with the 2013-2014 DRC Demographic and Health Survey, a serosurvey was carried out to assess population immunity to vaccine-preventable diseases. Dry blood spot samples collected from children 6-59 months of age were processed using the Dynex Technologies Multiplier FLEX chemiluminescent immunoassay platform (Dynex Technologies, Chantilly, VA).

RESULTS

Among the 7195 6- to 59-month-old children, 33% were positive and <1% indeterminate for rubella antibodies in weighted analyses. Seroprevalence was positively associated with age of the child and province, with seropositivity highest in Bandundu (53%) and lowest in Kasai-Oriental (20%). In multivariate analyses, serologic evidence of infection was associated with age of the mother and child, socioeconomic status and geographic location.

CONCLUSIONS

Rubella infection is prevalent among children in the DRC, and while most seroconversion occurs in young children, a significant proportion of children remain at risk and may enter reproductive age susceptible to rubella infection. While not currently in place, implementation of a surveillance program will provide improved estimates of both rubella virus circulation and the burden of congenital rubella syndrome. Such information will play an important role in future policy decisions, vaccine delivery strategies and may provide a basis upon which the effectiveness of rubella antigen introduction may be assessed.

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.

The role of rubella-immunoblot and rubella-peptide-EIA for the diagnosis of the congenital rubella syndrome during the prenatal and newborn periods

Rubella infection during the first trimester of pregnancy can cause the congenital rubella syndrome (CRS). Patients with CRS were shown to have a decreased humoral and cellular immunity. It is not known whether asymptomatic newborns who had experienced intrauterine infection with rubella virus (RV) differ in their antibody response from newborns with CRS. In this study we compared both groups for a difference which might be a useful diagnostic criterion for CRS during the prenatal and newborn periods. We used the nonreducing Rubella-Immunoblot and the Rubella-IgG-Peptide-Enzyme Immunoassay (EIA) to determine the antibodies directed to rubella proteins E1, E2 and C. The results showed that only newborns with CRS who had experienced RV infection during the first 12 weeks of gestation showed significantly reduced levels of antibodies directed to both the linear RV E1 epitope (SP 15) and the topographic RV E2 epitope. Asymptomatic newborns infected mostly later than week 10 of gestation showed normal levels of antibodies. These data suggest that the lack of antibody response in CRS is linked to the immaturity of the fetal immune system during the first trimester of gestation. Rubella-IgG-Peptide-EIA and Rubella-Immunoblot should be used additionally for CRS diagnosis in the prenatal/newborn periods. These results may have an impact on the early treatment of late-onset symptoms of CRS patients.

Assembly of the reovirus outer capsid requires mu 1/sigma 3 interactions which are prevented by misfolded sigma 3 protein in temperature-sensitive mutant tsG453

A temperature-sensitive reovirus mutant, tsG453, whose defect was mapped to major outer capsid protein sigma 3, makes core particles but fails to assemble the outer capsid around the core at non-permissive temperature. Previous studies that made use of electron cryo-microscopy and image reconstructions showed that mu 1, the other major outer capsid protein, but not sigma 3, interact extensively with the core capsid. Although wild-type sigma 3 and mu 1 interact with each other, immunocoprecipitation studies showed that mutant sigma 3 protein was incapable of interacting with mu 1 at the non-permissive temperature. In addition, restrictively-grown mutant sigma 3 protein could not be precipitated by some sigma 3-specific monoclonal antibodies. These observations suggest that in a wild-type infection, specific sigma 3 and mu 1 interactions result in changes in mu 1 conformation which are required to allow mu 1/sigma 3 complexes to condense onto the core capsid shell during outer capsid assembly, and that sigma 3 in non-permissive tsG453 infections is misfolded such that it cannot interact with mu 1.

Use of rubella virus E1 fusion proteins for detection of rubella virus antibodies

Two glutathione S-transferase fusion proteins containing 44 (p1503) and 75 (p1509) amino acid residues of the rubella virus E1 glycoprotein were expressed in Escherichia coli with the aim of producing a recombinant rubella virus antigen for use in serological assays. p1503 contained three neutralizing and hemagglutinating epitopes (G. M. Terry, L. M. Ho-Terry, P. Londesborough, and K. R. Rees, Arch. Virol. 98:189-197, 1988); p1509 contained the putative neutralization domain described by Mitchell et al. (L. A. Mitchell, T. Zhang, M. Ho, D. Decarie, A. Tingle, M. Zrein, and M. Lacroix, J. Clin. Microbiol. 30:1841-1847, 1992) in addition to the three epitopes present in p1503. Both fusion proteins were soluble and affinity purified on glutathione-Sepharose 4B. In Western blots (immunoblots), p1503 and p1509 reacted with human sera containing rubella virus-specific immunoglobulin G. When used as antigens in indirect enzyme immunoassays to detect rubella virus-specific immunoglobulin G, p1503 correctly identified the rubella virus antibody status of 43 (76.8%) and p1509 correctly identified that of 48 (85.7%) of 56 serum samples received for routine rubella virus antibody screening. The results obtained with p1509 compare well with those obtained with a latex agglutination assay.

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.

Reactivity of a recombinant rubella E1 antigen expressed in E. coli

The E1 nucleic acid sequence of rubella virus strain Judith (RJ) has been cloned into an E. coli expression vector LB03. The reactivity of the expressed unglycosylated antigen (E1J) was compared with its glycosylated counterpart in native virus (RJ) using rabbit and human sera. Rabbit antisera raised against RJ and E1J reacted differently with wild type, RJ (laboratory strain) and RA27/3 (vaccine virus) strains in a kinetic neutralisation test. Reciprocally, human post RA27/3 vaccination sera were also found to differ from post infection or post re-infection sera in their reactivity with RJ and E1J antigens. Our observations suggest that E1, in the conformation adopted in the RA27/3 virion may have unique antigenic properties.

Cellular and humoral immune responses to rubella virus structural proteins E1, E2, and C

Better understanding of cell-mediated immune responses to rubella virus would provide the basis for the development of safe and effective vaccines against rubella and would aid in analysis of the pathophysiology of congenital rubella syndrome. We have expressed individual rubella virus structural proteins, E1, E2 and C, via vaccinia virus recombinants. Using the expressed recombinant proteins as antigens, we were able to demonstrate antigen-specific lymphocyte proliferative responses in control individuals and individuals with congenital rubella syndrome. Among the two human groups studied, E1 glycoprotein proved to be a better immunogen than E2 or C. For the control individuals, significant differences in proliferative responses to the structural proteins E1, E2, and C were observed. These differences were not significant in individuals with congenital rubella syndrome. In parallel to the lymphoproliferative responses, immunoglobulin G responses were also found directed mainly to the E1 glycoprotein. These results suggest that E1 may be the most important rubella virus antigen to study in determining the domains required for constructing subunit vaccines against rubella.

Characterization of rubella virus-specific antibody responses by using a new synthetic peptide-based enzyme-linked immunosorbent assay

Rubella virus (RV)-specific immunoglobulin G antibodies were studied by enzyme-linked immunosorbent assay (ELISA) techniques in sera from RV (RA 27/3)-vaccinated individuals, patients experiencing natural RV infection, congenital rubella syndrome patients, and individuals failing to respond to repeated RV immunization. Results obtained by using whole-RV ELISAs (detergent-solubilized M33 strain or intact Gilchrist strain) and hemagglutination inhibition (HAI) and neutralization (NT) assays were compared with results obtained with the same sera by using ELISAs employing a synthetic peptide, BCH-178, representing a putative neutralization domain on the RV E1 protein. Murine RV E1-specific monoclonal antibodies with HAI and NT activities exhibited strong reactivity in ELISAs with BCH-178 peptide. In sera from RA 27/3-vaccinated individuals collected at 0 (prevaccine), 1, 2, 3, 4, 5, 6, 12, and 24 to 52 weeks postvaccine, the development of E1-peptide-reactive antibodies closely paralleled increases in RV-specific antibodies measured by whole-RV ELISAs and HAI and NT assays. Similarly, sequential serum samples obtained from patients during acute and convalescent phases of natural RV infection showed a coordinate increase in RV-specific antibodies as measured by whole-RV and peptide ELISAs. Conversely, congenital rubella syndrome patient sera, although exhibiting high levels of antibody in whole-RV ELISAs, had little or no antibody directed to the neutralization domain peptide. Sera from patients failing to respond to repeated RV immunization contained very low levels of RV-specific antibody in all ELISAs. Our results that the sequence represented by BCH-178 peptide may be a previously unidentified neutralization epitope for human antibodies on the RV E1 protein and may prove useful in determining effective RV immunity.

Detection of rubella virus-specific immunoglobulin G (IgG), IgM, and IgA antibodies by immunoblot assays

Immunoblot (IB) assays were developed for detection of rubella virus (RV)-specific immunoglobulin G (IgG), IgM, and IgA antibodies in human serum following natural infection or immunization. IB assays performed under nonreducing conditions were compared with those performed under reducing conditions and with immunoprecipitation assays. Significant loss of antigenicity (greater than 90%) of RV E1 and E2 proteins was observed when IB assays were performed in the presence of 2-mercaptoethanol as compared with assays under nonreducing conditions. In contrast, the antigenicity of RV capsid protein was not influenced by reducing agents. Sensitivity of IB for RV-specific IgG antibodies was determined to be 0.01 IU/ml under nonreducing conditions. In the determination of RV-specific IgM and IgA antibodies by IB, pretreatment of serum with protein G to remove competing high-affinity RV-specific IgG or rheumatoid factor significantly improved assay sensitivity. IB assays were observed to be superior to immunoprecipitation assays in their ability to better define the specificities of RV-specific antibodies and to detect antibodies of all immunoglobulin classes. However, the conformational sensitivity of RV protein antigenicity should be an important consideration in the interpretation of RV-specific antibodies by IB assays.

Analysis of T- and B-cell epitopes of capsid protein of rubella virus by using synthetic peptides

A nested set of 11 overlapping synthetic peptides covering the entire sequence of rubella virus capsid protein was synthesized, purified, and tested against human rubella virus-specific T-cell lines and rubella virus-seropositive sera. T-cell lines derived from four donors responded strongly to four synthetic peptides containing residues 96 to 123, 119 to 152, 205 to 233, and 255 to 280. Only one peptide (residues 255 to 280) was recognized by all four T-cell lines. Two human immunodominant linear B-cell epitopes were mapped to residues 1 to 30 and 96 to 123 by using peptide-specific enzyme-linked immunosorbent assay. All 11 synthetic peptides were highly immunogenic and induced strong antibody responses in rabbits against the respective immunized peptides. Seven of the 11 rabbit antipeptide antisera (anti-1-30, -74-100, -96-123, -119-152, -205-233, -231-257, and -255-280) specifically recognized the capsid protein on immunoblots. Identification of these T- and B-cell epitopes represents the first step toward rational design of synthetic vaccines against rubella.

Recognition of synthetic peptides with sequences of rubella virus E1 polypeptide by antibodies and T lymphocytes

Antigenicity of rubella virus E1 polypeptide was analyzed using synthetic peptides with predicted amino acid sequences. Overlapping solid-phase bound peptides were used to define antibody binding domains and a panel of free peptides to study T-cell responsiveness. Several antibody-binding areas including those earlier described to contain major neutralizing epitopes were recognized by human sera positive for rubella antibodies. T-cell lines specific for rubella virus were established from 14 rubella immune subjects. All cell lines responded to rubella virion-derived antigen but only eight (57%) responded to one or more of the synthetic peptides. Individual patterns of peptide recognition were found but peptide 8 representing amino acids 402-422 was most often stimulatory to T-cells lines, either alone (3 subjects) or in combination with peptide 3 (amino acids 245-269) or 3 and 4 (amino acids 269-287). The response was HLA restricted but no single DR specificity for this restriction was identified.

Monoclonal antibody-defined epitope map of expressed rubella virus protein domains

An expanded library of murine monoclonal antibodies (MAbs) was generated by infecting BALB/C mice with the Therien strain of rubella virus (RV) and selecting secreting hybrids by enzyme-linked immunosorbent assay (ELISA) using purified virion targets. A panel of plasmids containing specified RV cDNA fragments was also constructed by using a variety of strategies with pGE374- and pGE374-derived expression vectors. Hybrid RecA-RV-beta-galactosidase (LacZ)- or RecA-RV-truncated LacZ-containing proteins collectively representing the entire open reading frame of the structural proteins of RV were overexpressed in Escherichia coli. Bacterial lysates were then probed by ELISA with selected MAbs and by immunoblot following separation by electrophoresis under denaturing conditions. With this approach, MAbs that appeared to react with linear determinants defined epitopes localized within the following domains: MAbs C-1, C-2, and C-8 bind epitopes within the predicted amino-terminal 21 amino acids of the capsid region C9 to C29; MAb C-9 binds to a domain bounded by C64 and C97; MAbs E2-1 through E2-6 bind to the E2 glycoprotein backbone region from E2(1) to E2(115); MAbs E1-18 and E1-20 bind to the E1 glycoprotein region from E1(202) to E1(283). MAb E1-18 neutralizes RV infectivity; MAb E1-20 neutralizes infectivity and modestly inhibits hemagglutination. Analyses with selected synthetic peptides have confirmed several of the molecular domains deduced with the expressed proteins. These plasmid constructions and peptides have proven useful in beginning to unravel the molecular organization of several antigenic sites of this human pathogen.

Antibody response to rubella virus structural proteins in multiple sclerosis

The antibody response to the structural proteins of rubella virus was studied in patients with multiple sclerosis (MS). Irrespective of the antibody titer to whole rubella virus, the relative proportion of the IgG response to the surface glycoprotein E1 was diminished, and that to the surface glycoprotein E2 was elevated in MS patients when compared to a matched control population of normal health individuals or a group of patients with systemic lupus erythematosus and other collagen vascular diseases. No difference was observed in the response to the core protein of rubella virus on comparing the MS and normal control groups. This divergence in the relative antibody response to the viral surface proteins suggests that the vigorous antibody response to rubella virus reported in MS is not simply an expression of a nonspecific polyvalent B-cell response.

Development of automated immunoassays for immune status screening and serodiagnosis of rubella virus infection

The fully automated IMx immunoassay analyzer was used to develop a system for the detection of IgG and IgM antibodies to rubella virus for immune status screening and diagnosis of primary infections. Reagents and assay protocol software were developed using rubella virus sensitized microparticles as the solid phase to capture specific antibodies from serum samples. Anti-human IgG or IgM antibody coupled to alkaline phosphatase enzyme followed by methylumbelliferyl phosphate substrate was used to detect the presence or absence of antibodies specific to the antigens on the solid phase. To evaluate the efficacy of the IMx rubella IgG assay, immune status screening was performed with a clinical patient population of 501 sera. When compared to an IgG specific enzyme immunoassay and passive hemagglutination assay the agreement was greater than 99%. The IMx rubella IgM assay was utilized to determine the presence of rubella specific IgM antibodies in 462 sera. These results were compared to IgM specific enzyme immunoassay results and also demonstrated greater than 99% agreement. Seroconversion following rubella vaccination of susceptible individuals was demonstrated by IgG and IgM antibody responses as early as two weeks postvaccination. In addition to automation, the IMx system offers rapid assay times and calibration curve storage without sacrificing clinical efficacy.

A bio-engineered rubella E1 antigen

The major rubella envelope protein, E1, and a segment of it, comprising amino acids 207-353, have been separately expressed as fusion proteins with the IgG binding region of Staphylococcus aureus protein A in Escherichia coli. The proteins carry E1-specific antigenicity recognized by monoclonal antibodies raised against whole virus confirming that correct glycosylation is not required for antigenicity. The use of these bioengineered antigens in immunoassays for diagnosis of rubella infection and for immunization in experimental animals is described.