The Harry M. Zweig Memorial Fund for Equine Research

Analysis of the Innate Immune Response to EHV-1 Infection

Dr. Bettina Wagner

WagnerEquine herpesvirus type 1 (EHV-1) negatively impacts the equine industry, both economically and medically. Existing vaccines are of low efficacy or offer only partial protection from infection. Therefore, improved strategies to protect horses from EHV-1 are needed. A protective vaccine of high efficacy would induce an immune response that resembles the natural host response required to cure infection and develop immunity. Studies on the protective immune response to EHV-1 infection will provide this information and allow the development of more effective vaccines. In the proposed study we will identify key protective responses to EHV-1 infection.

Innate immune response mechanisms provide a first line of host defense after infection with viral pathogens. The innate immune system is composed of cells expressing receptors that are at the ready to respond to the first sign of infection. The response is mainly through direct killing mechanisms to eliminate the invader and through the production of inflammatory mediators that both control the growth of the invader and call other cells of the immune system to the site of infection where they are recuited into the fight to eliminate the invader. The response is initiated by specific receptors expressed on cells of the innate immune system.

The most important of these receptors is the family of Toll-like receptors (TLRs). TLRs are transmembrane proteins that directly bind to pathogens and induce the activation of innate immune cells that express them. Stimulation of TLRs induces the production of interferons (IFNs) and chemokines that direct the ensuing immune response. Two TLR family members have been demonstrated to play an important role in host defense agains other herpesviruses, TLR2 and TLR9 (Figure 1). In Aim 1 of this proposal we will define the role of equine TLR2 and TLR9 in the immune respones to EHV-1.

Immune modulators that produced during viral infection and control the immune response include IFN-α and chemokines. IFN-α inhibits viral replication, activates cells of the immune system and regulates the immune response. Chemokines are critical for the recruitment of immune cells to the site of infection and for their activation. Activation of cells through TLRs induces the production of both IFN-α?and chemokines. In Aim 2 of this proposal we will identify and characterize the IFNs and chemokines that are produced in response to EHV-1 infection, and provide details about the cells critical for this production.

In order to improve research of the immune response in veterinary species including the horse, a network of investigators has been assembled whose main goal is the development of reagents for immunological studies. Dr. Wagner’s group at Cornell is one of the three core facilities of this US Veterinary Immune Reagent Network. This ongoing US wide collaborative effort started in 2006. For the horse, our network plans to develop 12 monoclonal antibodies, four of which are to cytokines and eight to cell surface markers. Several reagents, including novel antibodies to equine cytokines and interferon have already been produced by our group (Wagner et al. 2006, 2008 and in press). In Aim 3 of this proposal we seek complementary funding for the development of additional key reagents to investigate the immune response to EHV-1 in horses. We propose to generate two antibodies to the most interesting equine chemokine candidates in EHV-1 infection. The potential candidates are not yet part of the reagent initiative mentioned above. Our main focus will be on molecules that have recently become of high interest and are at the cutting edge of immunological research in herpesvirus pathogenesis. The approach will provide new tools for the identification of the early immunological events that lead to protection against EHV-1 infections and neurological disease.

Overall the goal of this project is the identification of innate immune response cascades and their consequences for disease succeptibility in EHV-1 infection in horses. This foundational approach is essential for the rational design and development of more efficient vaccines and novel treatment strategies to improve equine health and well-being.

It is important to note that due to the ability of TLRs to activate innate immune responses, ligands for TLRs have been used to improve experimental vaccines in horses. For example, the TLR9 ligand CpG DNA mixed with Emulsigen improved the serological response of horses vaccinated with killed equine influenza virus vaccine (Lopez et al 2006). Therefore, understanding the role that TLRs play in the induction of IFN-α and chemokines may provide usefull targets for the improvement of vaccines and for development of novel therapies designed to enhance and complement the normal immune response to EHV-1.