Identification of an immunodominant epitope within the phosphoprotein of rabies virus that is recognized by both class I- and class II-restricted T cells

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

Characterization of Russian rabies virus vaccine strain RV-97

The RV-97 rabies virus vaccine strain is widely used in Russia as a component of the live attenuated oral anti-rabies vaccine "Sinrab". This vaccine has also been used in some other countries, such as Kazakhstan, Belarus, and Ukraine. Entire genome sequencing is an effective tool for studying the genetic properties of virus strains. In this study, a simple technique for obtaining the entire genome sequence of the rabies virus was used. The entire genome sequence and the deduced amino acid sequences of the major viral proteins were compared with those of other rabies vaccine virus strains. The RV-97 strain forms a separate phylogenetic branch and seems to be phylogenetically more related to the group of Japanese vaccine strains. It also contains several unique amino acid changes in known immunodominant sites of G and P proteins.

Cytotoxic T-lymphocyte target proteins and their major histocompatibility complex class I restriction in response to adenovirus vectors delivered to mouse liver

The activation of cytotoxic T lymphocytes (CTLs) to cells infected with adenovirus vectors contributes to problems of inflammation and transient gene expression that attend their use in gene therapy. The goal of this study was to identify in a murine model of liver gene therapy the proteins that provide targets to CTLs and to characterize the major histocompatibility complex (MHC) class I restricting elements. Mice of different MHC haplotypes were infected with an E1-deleted adenovirus expressing human alkaline phosphatase (ALP) or beta-galactosidase as a reporter protein, and splenocytes were harvested for in vitro CTL assays to aid in the characterization of CTL epitopes. A library of vaccinia viruses was created to express individual viral open reading frames, as well as the ALP and lacZ transgenes. The MHC haplotype had a dramatic impact on the distribution of CTL targets: in C57BL/6 mice, the hexon protein presented by both H-2Kb and H2Db was dominant, and in C3H mice, H-2Dk-restricted presentation of ALP was dominant. Adoptive transfer of CTLs specific for various adenovirus proteins or transgene products into either Rag-I or C3H-scid mice infected previously with an E1-deleted adenovirus verified the in vivo relevance of the adenovirus-specific CTL targets identified in vitro. The results of these experiments illustrate the impact of lr gene control on the response to gene therapy with adenovirus vectors and suggest that the efficacy of therapy with adenovirus vectors may exhibit considerable heterogeneity when applied in human populations.

A simple method to test the ability of individual viral proteins to induce immune responses

Immune responses to a mouse fibroblast line, transfected with a plasmid that causes expression of the rabies virus glycoprotein under the control of a simian virus 40 early promoter, were studied. Transfected cells were shown to be recognized in vitro by a panel of monoclonal antibodies directed to conformational epitopes of the different antigenic sites of the glycoprotein. They stimulated rabies virus glycoprotein-specific T helper cells in the presence of antigen-presenting cells and were, furthermore, recognized by rabies virus-induced cytolytic T cells. In vivo, immunization of H-2-compatible mice with the transfected cell line led to a rabies virus glycoprotein-specific antibody response, and to protection against a subsequent challenge with live virus. We propose this procedure, i.e. use of cell lines transfected with plasmids expressing a viral protein under a mammalian promoter, as a simple and inexpensive method to screen individual viral proteins for their ability to elicit immune responses, including T helper cells, cytolytic T cells, antibodies, and protection against viral challenge.

Resistance of mice vaccinated with rabies virus internal structural proteins to lethal infection

Mice were vaccinated with recombinant vaccinia virus (rVac) expressing the glycoprotein (G), nucleoprotein (N), phosphoprotein (NS) or matrix protein (M) of rabies virus and their resistance to peripheral lethal infection with street rabies virus was examined. Mice vaccinated with rVac-G or rVac-N developed strong antibody responses to the corresponding proteins and essentially all mice survived challenge infection. Mice vaccinated with rVac-NS or rVac-M developed only a slight antibody response, however, a significant protection (59%) was observed in the rVac-NS-vaccinated mice, whereas rVac-M-vaccinated mice were not protected. No anti-G antibodies were detected in the sera of mice which has been vaccinated with rVac-N or rVac-NS and survived challenge infection. Passive transfer of anti-N monoclonal antibodies (MAbs) recognizing an epitope located on amino acids 1-224 of the protein prior to challenge resulted in significant protection, although the protection was not complete even with a high amount of antibodies. In contrast, none of the mice given MAbs recognizing an epitope of amino acids 247-415 or F(ab')2 fragments from a protective MAb IgG were protected. Administration of anti-CD 8 MAb to rVac-N-vaccinated mice showed no significant effect on protection. Our observations suggest that a considerable part of the protection achieved by the vaccination with rVac-N can be ascribed to the intact anti-N antibodies recognizing an epitope located on amino acids 1-224 of the protein.

Posttranslational side chain modification of a viral epitope results in diminished recognition by specific T cells

A stretch of 16 amino acid residues within the nominal phosphoprotein of rabies virus was shown to carry an immunodominant epitope for class I- and class II-restricted T cells. The nominal phosphoprotein of rabies virus is thought to be heterogeneously phosphorylated at multiple serine and threonine residues. The synthetic peptide that expressed the T-cell epitope contained a single serine residue corresponding to position 196 of the protein. Phosphorylation of this serine within the synthetic peptide caused a significant decrease of the antigenic potency of the peptide. A similar effect was seen if the serine was replaced by an alanine or if the peptide was glycosylated at its acidic residues. These data suggest that T-cell-mediated recognition of antigen presented by major histocompatibility complex class I- or II-positive cells is impaired not only by point mutations but also by posttranslational side chain modifications of residues within viral epitopes.

Immune response to the nominal phosphoprotein of rabies virus

The immune response to the nominal phosphoprotein (NS protein) of rabies virus was investigated with the use of a vaccinia recombinant virus that expressed the NS protein of a fixed rabies virus strain. Mice of the H-2k haplotype that were injected with either live rabies virus or the vaccinia recombinant virus developed a strong cytolytic T-cell response specific for the NS protein. This response was under immune response (Ir) gene control. The NS protein as presented by the vaccinia recombinant virus was a poor inducer of rabies virus-specific T-helper (Th) cells and B cells in the H-2k background. Furthermore, mice of the H-2k haplotype could not be protected by vaccination with the vaccinia recombinant virus expressing the NS protein, although protection in outbred mice was partial and incomplete. These data indicate that cytolytic T cells to the NS protein of rabies virus are insufficient to protect mice against a challenge with rabies virus.