Mapping of B-cell epitopes of hemagglutinin protein of rinderpest virus

Recombinant DNA technology for producing new rinderpest virus vaccines

With few exceptions, vaccination aims to control rather than eliminate or eradicate disease. The eradication of smallpox in the 1970s led to two other human diseases, polio and measles, being targeted for eradication by the World Health Organization. In general, animal diseases are ignored by the public, however, recent targeting of the rinderpest virus, the agent of cattle plague, has put this virus on the verge of global extinction. For centuries, this virus was responsible for major cattle plagues in Europe, Asia and Africa. The success of the Global Rinderpest Eradication Program is an illustration of the power of vaccines to alter people's lives economically and socially when used in an internationally coordinated way. In this review, the history of the development of rinderpest vaccines and the new research being undertaken to produce marker vaccines, using recombinant DNA technology and reverse genetics, are described. In addition, the valuable contribution that marker vaccines can make in the final stages of the rinderpest eradication program is outlined.

Structural basis for the function of anti-idiotypic antibody in immune memory

We had earlier proposed a hypothesis to explain the mechanism of perpetuation of immunological memory based on the operation of idiotypic network in the complete absence of antigen. Experimental evidences were provided for memory maintenance through anti-idiotypic antibody (Ab(2)) carrying the internal image of the antigen. In the present work, we describe a structural basis for such memory perpetuation by molecular modeling and structural analysis studies. A three-dimensional model of Ab(2) was generated and the structure of the antigenic site on the hemagglutinin protein H of Rinderpest virus was modeled using the structural template of hemagglutinin protein of Measles virus. Our results show that a large portion of heavy chain containing the CDR regions of Ab(2) resembles the domain of the hemagglutinin housing the epitope regions. The similarity demonstrates that an internal image of the H antigen is formed in Ab(2), which provides a structural basis for functional mimicry demonstrated earlier. This work brings out the importance of the structural similarity between a domain of hemagglutinin protein to that of its corresponding Ab(2). It provides evidence that Ab(2) is indeed capable of functioning as surrogate antigen and provides support to earlier proposed relay hypothesis which has provided a mechanism for the maintenance of immunological memory.

PEPOP: computational design of immunogenic peptides

Background

Most methods available to predict protein epitopes are sequence based. There is a need for methods using 3D information for prediction of discontinuous epitopes and derived immunogenic peptides.

Results

PEPOP uses the 3D coordinates of a protein both to predict clusters of surface accessible segments that might correspond to epitopes and to design peptides to be used to raise antibodies that target the cognate antigen at specific sites. To verify the ability of PEPOP to identify epitopes, 13 crystallographically defined epitopes were compared with PEPOP clusters: specificity ranged from 0.75 to 1.00, sensitivity from 0.33 to 1.00, and the positive predictive value from 0.19 to 0.89. Comparison of these results with those obtained with two other prediction algorithms showed comparable specificity and slightly better sensitivity and PPV. To prove the capacity of PEPOP to predict immunogenic peptides that induce protein cross-reactive antibodies, several peptides were designed from the 3D structure of model antigens (IA-2, TPO, and IL8) and chemically synthesized. The reactivity of the resulting anti-peptides antibodies with the cognate antigens was measured. In 80% of the cases (four out of five peptides), the flanking protein sequence process (sequence-based) of PEPOP successfully proposed peptides that elicited antibodies cross-reacting with the parent proteins. Polyclonal antibodies raised against peptides designed from amino acids which are spatially close in the protein, but separated in the sequence, could also be obtained, although they were much less reactive. The capacity of PEPOP to design immunogenic peptides that induce antibodies suitable for a sandwich capture assay was also demonstrated.

Conclusion

PEPOP has the potential to guide experimentalists that want to localize an epitope or design immunogenic peptides for raising antibodies which target proteins at specific sites. More successful predictions of immunogenic peptides were obtained when a peptide was continuous as compared with peptides corresponding to discontinuous epitopes. PEPOP is available for use at .

Development of 2 types of competitive enzyme-linked immunosorbent assay for detecting antibodies to the rinderpest virus using a monoclonal antibody for a specific region of the hemagglutinin protein

A competitive enzyme-linked immunosorbent assay (C-ELISA) has been developed and standardized for the detection of antibodies to the rinderpest virus (RPV) in sera from cattle, sheep, and goats. The test is specific for rinderpest because it does not detect antibodies to peste-des-petits-ruminants virus (PPRV). The test depends on the ability of the monoclonal antibody (MAb) directed against the hemagglutinin (H) protein of RPV to compete with the binding of RPV antibodies in the positive serum to the H protein of this virus. This MAb recognized a region from amino acids 575 to 583 on the H protein of RPV that is unique to the RPV H protein and is not present on the hemagglutinin-neuraminidase protein of PPRV. Another C-ELISA (peptide C-ELISA) was set up using this specific region as an antigen. A threshold value of 64.4% inhibition was established for the RPV C-ELISA, with 90 known RPV-negative and 30 RPV-positive serum samples. Using common serum samples, a cutoff value of 43.0% inhibition for the peptide C-ELISA was established. Based on statistical analysis, the overall sensitivity and specificity of the RPV C-ELISA, relative to those of a commercial kit, were found to be 90.00% and 103.33%, respectively. However, the sensitivity and specificity of the peptide C-ELISA were found to be 180.00% and 73.33%, respectively. Although a common MAb in 2 new C-ELISA systems was used, variation in their percent inhibition, due to the use of different antigens, was observed. Taking into consideration the difference in percent inhibition of the 2 described assays and the commercial kit (50%), it was found that the RPV C-ELISA and the peptide C-ELISA are more specific and sensitive tools than the commercial kit for assessing herd immune status and for epidemiologic surveillance.

Maintenance of antigen-specific immunological memory through variable regions of heavy and light chains of anti-idiotypic antibody

Immunological memory is characterized by a quick and enhanced immune response after re-exposure to the same antigen. To explain the mechanism involved in generation and maintenance of immunological memory, we had earlier proposed a hypothesis involving the relay of memory by idiotypic and anti-idiotypic B cells. The peptidomimic present in the hypervariable region of anti-idiotypic antibody was hypothesized to carry forward immunological memory. In the present work, we provide evidence supporting a role for the anti-idiotypic antibody in eliciting antigen-specific B-cell and T-cell responses. Employing the idiotypic monoclonal antibody (Ab(1)) specific for haemagglutinin (H) protein of rinderpest virus, Ab(2beta) was generated, which possesses an internal image of the H protein in the region between amino acids 527 and 556. We demonstrate that antigen-specific memory is perpetuated by immunization with Ab(2), as shown by maintenance of antigen-specific T-cell responses upon restimulation in vitro of Ab(2) immune splenocytes by antigen-presenting cells expressing H protein or pulsed with H-protein-derived peptides. We have also shown that boosting with antigen-specific anti-idiotypic B cells generates a memory response in antigen-primed mice. Evidence has been provided for the existence of an antigen-specific B-cell idiotypic network in the body that supports the perpetuation of immunological memory as proposed in the relay hypothesis.

Systemic and oral immunogenicity of hemagglutinin protein of rinderpest virus expressed by transgenic peanut plants in a mouse model

Rinderpest causes a devastating disease, often fatal, in wild and domestic ruminants. It has been eradicated successfully using a live, attenuated vaccine from most part of the world leaving a few foci of disease in parts of Africa, the Middle East, and South Asia. We have developed transgenic peanut (Arachis hypogaea L.) plants expressing hemagglutinin (H) protein of rinderpest virus (RPV), which is antigenically authentic. In this work, we have evaluated the immunogenicity of peanut-expressed H protein using mouse model, administered parenterally as well as orally. Intraperitoneal immunization of mice with the transgenic peanut extract elicited antibody response specific to H. These antibodies neutralized virus infectivity in vitro. Oral immunization of mice with transgenic peanut induced H-specific serum IgG and IgA antibodies. The systemic and oral immunogenicity of plant-derived H in absence of any adjuvant indicates the potential of edible vaccine for rinderpest.

Baculovirus display of fusion protein of Peste des petits ruminants virus and hemagglutination protein of Rinderpest virus and immunogenicity of the displayed proteins in mouse model

Recombinant Bombyx mori nucleopolyhedroviruses (BmNPV) displaying the immunodominant ectodomains of fusion glycoprotein (F) of Peste des petitis ruminants virus (PPRV) and the hemagglutinin protein (H) of Rinderpest virus (RPV), on the budded virions as well as the surface of the infected host cells have been constructed. The F and H protein sequences were inserted in-frame within the amino-terminal region of BmNPV envelope glycoprotein GP64 expressing under the strong viral polyhedrin (polh) promoter. We improved the recombinant virus selection in BmNPV by incorporating the green fluorescent protein gene (gfp) as selection marker under a separate promoter within the transfer cassette harboring the desired genes. Following infection of the insect larvae or the host-derived BmN cells with these recombinant BmNPVs, the expressed GP64 fusion proteins were displayed on the host cell surface and the budded virions. The antigenic epitopes of the recombinant proteins were properly displayed and the recombinant virus particles induced immune response in mice against PPRV or RPV.

Oral immunization of cattle with hemagglutinin protein of rinderpest virus expressed in transgenic peanut induces specific immune responses

Rinderpest is an acute, highly contagious often fatal disease of large and small ruminants, both domestic and wild. Global eradication of rinderpest needs a robust, safe and cost-effective vaccine. The causative agent, rinderpest virus (RPV) is an important member of the genus Morbillivirus in the Paramyxoviridae family. We have generated transgenic peanut (Arachis hypogea L.) plants expressing hemagglutinin protein of RPV and report here, the induction of immune responses in cattle following oral feeding with transgenic leaves expressing hemagglutinin protein without oral adjuvant. Hemagglutinin-specific antibody was detected in the serum as confirmed by immunohistochemical staining of virus-infected cells, and in vitro neutralization of virus infectivity. Oral delivery also resulted in cell-mediated immune responses.

Expression of hemagglutinin protein of rinderpest virus in transgenic tobacco and immunogenicity of plant-derived protein in a mouse model

The use of transgenic plants as a production system for recombinant subunit vaccines has been considered safe and economical compared to cell culture methods. We have exploited this approach to produce rinderpest virus hemagglutinin (H) protein in transgenic tobacco as a model plant for testing the immunogenicity of plant-derived hemagglutinin protein. The transgenic nature of the plants was confirmed by molecular analysis such as gene specific PCR and Southern hybridization using full-length H gene as a probe. The Mendelian pattern of inheritance of the transgene has been demonstrated in T(1) generation. The transgenic plants express the H protein of molecular weight 72 kDa. The plant derived H protein is antigenically authentic as revealed by reactivity with H-specific antibodies as well as convalescent sera. The induction of immune response was tested in mice after intraperitoneal immunization with plant-derived H. High titers of antibodies were induced which were H-specific and they neutralized the infectivity of rinderpest virus.

Competitive enzyme-linked immunosorbent assay based on monoclonal antibody and recombinant hemagglutinin for serosurveillance of rinderpest virus

A competitive enzyme-linked immunosorbent assay (C-ELISA) which detects antibodies unique to rinderpest virus (RPV) has been developed. This test can differentiate antibodies against RPV and those against peste des petits ruminants virus. The recombinant RPV hemagglutinin (H)-protein C-ELISA (recH C-ELISA) is based on the ability of a well-characterized monoclonal antibody (MAb) produced with the soluble, secreted form of the H protein (Sec H protein) of RPV made in a baculovirus expression system to compete with the binding of RPV antibodies in the serum of vaccinated or infected, recovered animals to the Sec H protein. The B-cell epitope recognized by the MAb corresponds to amino acids 575 to 583 on the H protein, which is not present on the antigenically closely related peste des petits ruminants virus hemagglutinin-neuraminidase protein. Initially, a positive-negative threshold cutoff value for percent inhibition of 34 was established with 500 known RPV-negative serum samples. The recH C-ELISA was developed with the enzyme immunoassay software of a commercial RPV C-ELISA kit. Comparative analysis of the test results for 700 serum samples obtained with the commercial kit gave a sensitivity of 112.4% and a specificity of 72.4%. Variations in percent inhibition values were observed for the two assay systems. These variations may have been due to the undefined amount of antigen present in the commercial kit as well as the use of a different MAb. The recH C-ELISA detected more positive serum samples compared to the number detected by the commercial kit, with the results confirmed by a virus neutralization test. Thus, recH C-ELISA is a sensitive tool for RPV serosurveillance in disease eradication programs.