Equine immunity to viruses. |
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| Authors: | J Slater D Hannant |
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| Institution: | Department of Clinical Veterinary Medicine, University of Cambridge, United Kingdom. jds1001@cam.ac.uk |
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| Abstract: | The identification of some of the adaptive immune responses to infection with equine viruses has been the first step toward rational immunoprophylactic design. Sufficient knowledge of infection-induced immunity and informed estimates of the requirements for long-term immunity for EIV have now been obtained. Thus, the future for inactivated EIV vaccines is promising now that new adjuvants have been applied to induce cellular immunity and safe methods have been designed to stimulate virus-neutralizing (VN) antibody at mucosal surfaces. Adenoviruses induce circulating VN antibody, the presence of which appears to correlate with protection from reinfection. Therefore, the potential of vaccines to induce VN antibody and protect from challenge is an important next step with this virus. With persistent viruses such as EHV-1, antibody-mediated protection from infection can be achieved only at the site of initial infection, that is, the nasopharynx and upper respiratory tract. Systemic dissemination is very rapid and consequently VN antibody is unlikely to play a major role in prevention of disease once the initial infection event has occurred. Cellular immune responses, particularly CTLs, play a dominant role in protection and recovery and are important in immune surveillance and determination of the outcome of reactivation of latent virus. Therefore, the key to future EHV-1 vaccine design is to focus on stimulation of CTL responses, and this requires the successful presentation of vaccine-derived antigenic peptides to MHC class I molecules that are recognized by specific receptors on CTL. There is some evidence that stimulation of EHV-1-specific CTL precursors may correlate with immunity to this virus. By analogy with gamma herpesviruses in humans, CTL precursor frequency may also function as an immune correlate for EHV-2. Although EAV infection induces strong immunity in females and geldings, persistent infection of the genital tract is an important route of dissemination from stallions. Although inactivated vaccines induce strong immunity (which depends upon VN activity of serum antibody) to first infection, the immunologic control of persistent infection is currently poorly understood; however, analogy with other persistent viruses suggests that CTLs are also likely to play an important role in the control of persistent EAV infections. |
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