Equine herpesvirus 1 glycoprotein D expressed in E. coli provides partial protection against equine herpesvirus infection in mice and elicits virus-neutralizing antibodies in the horse

Expressão e caracterização da glicoproteína D do herpesvírus equídeo 1 em Pichia pastoris

RESUMO O herpesvírus equídeo 1 (EHV-1) apresenta distribuição mundial e causa graves prejuízos à equideocultura. É agente de surtos de doença respiratória, reprodutiva e neurológica, em equídeos jovens e adultos. A glicoproteína D (gD) do envelope viral é essencial para ligação e penetração em células permissivas e direcionamento do sistema imunológico do hospedeiro, induz respostas imunes humorais e celulares, sendo um antígeno apropriado para ser utilizado em vacinas e imunodiagnóstico. O objetivo deste trabalho foi expressar e caracterizar a gD do EHV-1 em Pichia pastoris para posterior utilização como antígeno em técnicas de imunodiagnóstico e formulação de vacinas recombinantes. Uma sequência de DNA que codifica uma forma truncada da gDEHV-1 foi clonada no vetor pPICZαA de expressão em P. pastoris. Obteve-se uma proteína de ~41 kDa, como esperado. A proteína apresentou glicosilação entre 4 kDa e 16 kDa, demonstrada por deglicosilação enzimática. A proteína recombinante foi caracterizada antigenicamente e imunogenicamente por Western blot, utilizando-se anticorpos policlonais equinos anti-EHV-1, e por ELISA indireto em modelo murino, demonstrando que a gD recombinante manteve epítopos similares aos da proteína nativa. Esses resultados sugerem que a gDEHV-1 é um antígeno promissor para uso como imunobiológico no controle do EHV-1.

TLR-5 agonist Salmonella abortus equi flagellin FliC enhances FliC-gD-based DNA vaccination against equine herpesvirus 1 infection

Equine herpesvirus 1 (EHV-1) induces serious respiratory infections, viral abortion, neurological signs, and neonatal mortality in horses. Despite the use of vaccines, EHV-1 infection also causes a high annual economic burden to the equine industry. The poor immunogenicity of and protection conferred by EHV-1 vaccines are the major factors responsible for the spread of EHV-1 infection. The present study examined the immunogenicity of a novel DNA vaccine co-expressing FliC, a flagellin protein, in Salmonella abortus equi and the gD protein of EHV-1. Mice and horses were immunized intramuscularly with the vaccine, and mice were challenged with EHV-1. Immunofluorescence and western blotting revealed that FliC and gD can be efficiently expressed in cells. This novel vaccine significantly increased gD-specific antibody and interferon gamma (IFN-γ) levels in immunized mice and horses. Compared with controls, the viral load and morbidity were markedly reduced in FliC-gD-immunized mice after they were challenged with EHV-1. Furthermore, the immunogenicity of FliC-gD in a natural host was tested. Our results indicate that vaccinated mice and horses exhibit increased humoral and improved cellular immune responses.

Immunoprotective response induced by recombinant glycoprotein D in the BALB/c respiratory mouse model of Equid alphaherpesvirus 1 infection

Equid alphaherpesvirus 1 (EHV-1) infection causes abortion, respiratory disease, perinatal deaths and neurological disorders in horses. The natural infection and available vaccines provide only partial and short-lived protection against reinfections. In the present study, we analyzed the ability of purified baculovirus-expressed glycoprotein D (gD) administered by different routes to induce protective immunity in BALB/c mice after challenge with the EHV-1 AR8 strain. Clinical signs varied among the different groups of mice immunized by parenteral routes, and, although gD induced a specific serum IgG response, it did not prevent the virus from reaching the lungs. Intranasally immunized mice showed no clinical signs, and virus isolation from lungs, histological lesions and antigen detection by immunohistochemistry were negative. In addition, by this route, gD did not stimulate the production of serum IgG and IgA. However, a specific IgA response in the respiratory tract was confirmed in intranasally immunized mice. Thus, we conclude that the mucosal immune response could reduce the initial viral attachment and prevent the virus from reaching the lungs. Our findings provide additional data to further study new immunization strategies in the natural host.

Intramuscular Immunization of Mice with the Live-Attenuated Herpes Simplex Virus 1 Vaccine Strain VC2 Expressing Equine Herpesvirus 1 (EHV-1) Glycoprotein D Generates Anti-EHV-1 Immune Responses in Mice

Vaccination remains the best option to combat equine herpesvirus 1 (EHV-1) infection, and several different strategies of vaccination have been investigated and developed over the past few decades. Herein, we report that the live-attenuated herpes simplex virus 1 (HSV-1) VC2 vaccine strain, which has been shown to be unable to enter into neurons and establish latency in mice, can be utilized as a vector for the heterologous expression of EHV-1 glycoprotein D (gD) and that the intramuscular immunization of mice results in strong antiviral humoral and cellular immune responses. The VC2-EHV-1-gD recombinant virus was constructed by inserting an EHV-1 gD expression cassette under the control of the cytomegalovirus immediate early promoter into the VC2 vector in place of the HSV-1 thymidine kinase (UL23) gene. The vaccines were introduced into mice through intramuscular injection. Vaccination with both the VC2-EHV-1-gD vaccine and the commercially available vaccine Vetera EHV^XP 1/4 (Vetera; Boehringer Ingelheim Vetmedica) resulted in the production of neutralizing antibodies, the levels of which were significantly higher in comparison to those in VC2- and mock-vaccinated animals (P < 0.01 or P < 0.001). Analysis of EHV-1-reactive IgG subtypes demonstrated that vaccination with the VC2-EHV-1-gD vaccine stimulated robust IgG1 and IgG2a antibodies after three vaccinations (P < 0.001). Interestingly, Vetera-vaccinated mice produced significantly higher levels of IgM than mice in the other groups before and after challenge (P < 0.01 or P < 0.05). Vaccination with VC2-EHV-1-gD stimulated strong cellular immune responses, characterized by the upregulation of both interferon- and tumor necrosis factor-positive CD4⁺ T cells and CD8⁺ T cells. Overall, the data suggest that the HSV-1 VC2 vaccine strain may be used as a viral vector for the vaccination of horses as well as, potentially, for the vaccination of other economically important animals.IMPORTANCE A novel virus-vectored VC2-EHV-1-gD vaccine was constructed using the live-attenuated HSV-1 VC2 vaccine strain. This vaccine stimulated strong humoral and cellular immune responses in mice, suggesting that it could protect horses against EHV-1 infection.